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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-48019	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23493#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://www.algolia.com/department/product-management	Product management teams Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. 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https://www.algolia.com/products/intelligent-data-kit	Intelligent Data Kit Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. 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Solutions Industries SEE ALL Ecommerce Ecommerce B2B Commerce B2B Commerce Fashion Fashion Grocery Grocery Media Media Marketplaces Marketplaces SaaS SaaS Higher Education Higher Education Use Cases SEE ALL Documentation search Documentation search Enterprise search Enterprise search Headless commerce Headless commerce Image search Image search Mobile & App search Mobile & App search Retail Media Network Retail Media Network Site search Site search Visual search Visual search Voice search Voice search Departments Digital Experience Digital Experience Ecommerce Ecommerce Engineering Engineering Merchandising Merchandising Product Management Product Management Pricing Developers Get started Developer Hub Developer Hub Documentation Documentation Integrations Integrations UI Components UI Components Autocomplete Autocomplete Resources Code Exchange Code Exchange Engineering Blog Engineering Blog MCP MCP Discord Discord Webinars & Events Webinars & Events Quick Links Quick Start Guide Quick Start Guide For Open Source For Open Source API Status API Status Support Support Resources Discover Algolia Blog Algolia Blog Resource Center Resource Center Customer Stories Customer Stories Webinars & Events Webinars & Events Newsroom Newsroom Customers Customer Hub Customer Hub What's New What's New Knowledge Base Knowledge Base Documentation Documentation Algolia Academy Algolia Academy Professional Services Professional Services Quick Access Company Partners Support Login Logout Request demo Get started Search Algolia Close Request demo Get started Other Types Filter --> Clear All Filters Filters Looking for our logo? We got you covered! Brand guidelines Download logo pack Intelligent Data Kit Smarter data. Simpler process. More possibilities. Transform, enrich, and prepare data, simply, with our built-in toolkit. Introducing the Intelligent Data Kit Messy, siloed data is one of the biggest blockers to great search and personalization. The Intelligent Data Kit solves that by putting intuitive tools and AI guidance in the hands of every team—not just data engineers.  Data transformation Reshape your data — clean out irrelevant fields, create dynamic attributes, compute custom rankings, and more. Technical users can work directly in code, and non-technical users can use the no-code UI.  Learn more Enrich your data Algolia Fetch allows you to connect external sources via API and pull data automatically to have an always up-to-date index.  Learn more Seamless integrations Connect with your existing stack using no-code connectors. Pull in real-time data from APIs like DeepL, Stripe, and Google Maps to enrich search results. Learn more Some things you can do with the Intelligent Data Kit Highlight promotions automatically Tag products for seasonal campaigns Exclude junk/test data from search Create size categories from raw data Derive missing discount values Enrich records using live external data --> Benefits at a glance Whether you're a merchandiser, content manager, or developer, you can now clean, enrich, and activate your data—faster than ever. Boost search relevance and personalization Clean, enriched data improves relevance scoring, powering more accurate results and tailored experiences across search, recommendations and merchandising. Speed up time to value The Intelligent Data Kit eliminates repetitive cleaning tasks, minimizes index bloat, and streamlines integration with external APIs. Increase transparency and trust Gain visibility into how data is transformed, enriched, and used, fostering trust across teams and helping ensure compliance with internal standards. Reduce development bottlenecks With intuitive no-code tools and AI-guided transformations, business users can take action—speeding up experimentation, campaign launches, and product iteration. Intelligent Data Kit FAQs What is the Intelligent Data Kit? 0 It’s a suite of tools from Algolia that helps you clean, enrich, and connect your data—so you can unlock better search, insights, and digital experiences without heavy dev work. Who is the Intelligent Data Kit for? 0 The Kit is designed for both technical and non-technical users. Business teams can make data changes via a visual interface, while developers benefit from robust integrations and reduced maintenance overhead. Do I need to know how to code to use it? 0 No coding is required. You can use plain-English prompts or drag-and-drop controls to perform complex data transformations. Developers can also plug into APIs or advanced pipelines as needed. What kinds of data can I clean or transform? 0 Anything from product catalogs and content metadata to user behavior logs. Common use cases include tagging seasonal products, removing junk/test data, computing rankings, and structuring filters like price tiers or size buckets. How does this improve my Algolia search experience? 0 Cleaner, enriched data leads to more relevant search results and personalized experiences. You can also reduce noise in your index, improve performance, and gain more control over how items are ranked and filtered. Can I connect it to external APIs or tools? 0 Yes. The Fetch capability allows you to enrich records with real-time data from third-party sources like DeepL, Google Maps, or Stripe, all within your Algolia transformation pipeline. Is this included in my current plan? 0 The Intelligent Data Kit is available today. Contact your Algolia representative to check compatibility with your current plan and pricing tier. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23608	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23608#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23511#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://www.algolia.com/products/features/data-transformation	Transforming your search experience starts with transforming your data Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark blue Algolia logo blue Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. 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We got you covered! Brand guidelines Download logo pack Data transformation Transforming your search experience starts with transforming your data Streamline data preparation and enhance data quality Get a demo Start building for free Code editor 0 A code editor with autocomplete, sampling and debugging capabilities. AI-assisted data transformations 0 Describe what you need in plain language, and AI will automatically generate the transformation logic in the UI for you to review and apply. No-code transformations 0 Non-technical users can also work with a no-code editor to configure data transformations.  Connect to any source 0 Transform data from any source, using our API Client or no-code connectors.  Pre & post-indexing power 0 Refine data before or after indexing for optimal search performance and flexibility. See it in action Use cases and strategies using Data Transformation Any transformation can be done at a record level – no code required Add attributes (tags, categories, labels, etc.), remove attributes, filter records, change data types and more. Calculate attributes Compute discount percentages, normalize attributes, employ gravity / decay scoring models, add weighting values, or convert a flat list of categories into hierarchical structure.  Data Transformation FAQs What is Data Transformation in Algolia? 0 Data Transformation lets you clean, enrich, and standardize your records before they’re indexed in Algolia. It ensures your data is consistent, searchable, and optimized for the best end-user experience without needing to preprocess it elsewhere. Why should I use Algolia’s Data Transformation instead of preprocessing my data? 0 With Data Transformation, you centralize transformations directly within Algolia, reducing the need for external scripts or ETL pipelines. This saves engineering time, ensures consistency, and makes it easier to adapt quickly when your data model changes. What kinds of transformations can I apply? 0 You can normalize text (e.g., casing, trimming whitespace), combine or split fields, generate computed attributes, remove unwanted fields, or enrich records with metadata. The system is flexible and supports a wide range of use cases. Learn more about code and no-code transformations in our documentation .  Do I need to write code to use Data Transformation? 0 No coding is required for many common transformations. Algolia provides a configuration-based interface, though developers can also define custom logic when needed. Learn more about code and no-code transformations in our  documentation .  Can I preview or test transformations before applying them? 0 Transformations run at indexing time, so your search queries remain fast. Performance is optimized so you can handle large datasets without slowing down user search experiences. How does Data Transformation impact indexing speed and performance? 0 Yes, you can preview transformations on sample records before pushing changes live, ensuring accuracy and preventing errors from reaching production. Is Data Transformation secure? 0 Yes. All transformations happen within Algolia’s secure infrastructure. Your data never leaves the platform, and access controls follow your existing Algolia permissions. Learn more about Algolia security and compliance .  How does Data Transformation fit with my existing ETL or pipeline tools? 0 Algolia Data Transformation can complement existing ETL workflows. You can continue using your data pipelines for heavy processing, while leveraging Algolia to handle last-mile, search-specific transformations. Who benefits most from using Data Transformation? 0 Engineering teams save development time, merchandisers can enrich product data without waiting on dev cycles, and end-users enjoy more consistent, relevant search and discovery experiences. Enable anyone to build great Search & Discovery Get a demo Start free Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://www.algolia.com/use-cases	Build Search & Discovery across use cases \| Algolia Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark blue Algolia logo blue Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. Integrations Connect to your existing stack via pre-built libraries and APIs. Infrastructure Overview Data Centers Choose from 70+ data centers across 17 regions. Data Centers Choose from 70+ data centers across 17 regions. Security & Compliance Built for peace of mind. Security & Compliance Built for peace of mind. Solutions Industries SEE ALL Ecommerce Ecommerce B2B Commerce B2B Commerce Fashion Fashion Grocery Grocery Media Media Marketplaces Marketplaces SaaS SaaS Higher Education Higher Education Use Cases SEE ALL Documentation search Documentation search Enterprise search Enterprise search Headless commerce Headless commerce Image search Image search Mobile & App search Mobile & App search Retail Media Network Retail Media Network Site search Site search Visual search Visual search Voice search Voice search Departments Digital Experience Digital Experience Ecommerce Ecommerce Engineering Engineering Merchandising Merchandising Product Management Product Management Pricing Developers Get started Developer Hub Developer Hub Documentation Documentation Integrations Integrations UI Components UI Components Autocomplete Autocomplete Resources Code Exchange Code Exchange Engineering Blog Engineering Blog MCP MCP Discord Discord Webinars & Events Webinars & Events Quick Links Quick Start Guide Quick Start Guide For Open Source For Open Source API Status API Status Support Support Resources Discover Algolia Blog Algolia Blog Resource Center Resource Center Customer Stories Customer Stories Webinars & Events Webinars & Events Newsroom Newsroom Customers Customer Hub Customer Hub What's New What's New Knowledge Base Knowledge Base Documentation Documentation Algolia Academy Algolia Academy Professional Services Professional Services Quick Access Company Partners Support Login Logout Request demo Get started Search Algolia Close Request demo Get started Other Types Filter --> Clear All Filters Filters Looking for our logo? We got you covered! Brand guidelines Download logo pack Use cases overview Algolia powers Search & Discovery across use cases Get a demo Start building for free --> Documentation search Get lightning-fast, typo-tolerant, and language-aware search across your documentation. Learn more Enterprise search Connects your customers to the right content, and your employees to the right information. Empower your organization at scale with AI-driven enterprise search. Learn more Headless commerce Future-proof your storefront with headless commerce and Algolia search. Deliver fast, flexible product experiences across channels with any ecommerce stack. Learn more Image search Let users search with images—not just words. Unlock visual discovery and reverse image search capabilities with Algolia’s image-search solution. Learn more Mobile & App Search Build mobile search that users love. Integrate fast, intelligent search & discovery into apps for better engagement and conversions. Learn more Retail Media Networks Drive incremental revenue by turning your search results into premium ad inventory, without compromising the customer experience.  Learn more Site search Add AI-powered search to your site, instantly, and connect your customers to the content and answers they need. Learn more Visual search Help shoppers go from “I saw it online” to “I found it on your site.” Visual Search makes product discovery effortless — even when your customers don’t know what words to use. Learn more Voice search Enable voice search experiences your users expect. From mobile to assistants, deliver fast, relevant results via natural language. Learn more --> Try the AI search that understands Get a demo Start Free Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23554#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23563	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23520	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Post navigation Previous Previous post: Raspberry Pi for Out of Band Linux PC management Next Next post: Exploiting the Futex Bug and uncovering Towelroot Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress	2026-01-13T08:48:55
https://dev.to/sunny7899/documenting-the-journey-preparing-for-a-senior-ui-engineer-role-at-servicenow-81a	Documenting the Journey: Preparing for a Senior UI Engineer Role at ServiceNow - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Neweraofcoding Posted on Dec 29, 2025 Documenting the Journey: Preparing for a Senior UI Engineer Role at ServiceNow # devjournal # interview # career # ui There’s a moment in every engineering career where you pause—not because you’re stuck, but because you’re leveling up . This blog is about one of those moments for me. Recently, I started preparing for a Senior Software Engineer – UI role at ServiceNow . Instead of rushing through prep, I decided to slow down and document the journey —the prompts, the reflections, and the story behind my work. This post is both a record for myself and a guide for anyone preparing for a similar transition. Why I Decided to Document This Interview prep can feel transactional: Memorize answers Practice talking points Hope it clicks But this role made me realize something: This wasn’t just interview prep. This was a reflection of my career so far. ServiceNow’s focus on AI-powered UX, observability, scale, and craftsmanship forced me to connect dots across my experience—from building dashboards and APIs to integrating ML and designing for trust. So instead of just “preparing answers,” I framed everything as a story . The Prompts That Shaped the Story These were the prompts I worked through—and honestly, they map really well to how senior engineers think. 1. Short Introduction (2 minutes) This wasn’t about listing tools. It was about answering: What problems do I enjoy solving? How does my work create impact? Why does my experience make sense now ? I focused on: Building customer-facing UI Turning complex systems into simple experiences Using AI not as a buzzword , but as a practical tool The goal wasn’t to sound impressive—it was to sound clear . 2. What Do I Know About ServiceNow? (30 seconds) This forced me to zoom out. Not just: “They do workflow automation.” But: They connect people, systems, and processes They’re investing deeply in AI-native experiences Observability isn’t just metrics—it’s insight and action This helped me align my past work with where the platform is going. 3. Why This Role, Why Now? This was one of the most important reflections. I realized I wasn’t leaving my current role because of dissatisfaction. I was leaving because I wanted: More product-driven engineering More scale A place where UI, AI, and platform thinking intersect That clarity alone boosted my confidence. 4. What I Want in My Next Opportunity This wasn’t about perks or titles. I wrote down three things: Ownership from idea to delivery Strong engineering culture (reviews, quality, reliability) Space to grow—technically and as a mentor Simple. Honest. Grounded. 5. A Real Challenge (Not a Perfect Story) Instead of a “hero story,” I picked a messy one: Inconsistent data Tight timelines Evolving requirements Cross-team friction I talked about: Trade-offs Decisions What broke What I learned That reflection reminded me: Senior engineering isn’t about avoiding problems—it’s about navigating them calmly. 6. Questions I Ask Them This flipped the dynamic. Instead of trying to impress, I got curious: What problems matter most right now? How does AI actually show up in the product? How do teams collaborate end-to-end? It made the conversation feel mutual—not one-sided. What This Process Taught Me A few things really stood out: Good interviews are storytelling exercises AI experience matters most when tied to user trust UI engineering at scale is about empathy, not pixels Preparation is confidence—not memorization Most importantly, I realized I already had the experience. I just needed to frame it clearly. Why I’m Keeping This Documented Careers are long. It’s easy to forget: Why you chose certain paths How much you’ve learned What kind of engineer you’re becoming This blog is a checkpoint. Whether or not this specific role works out, the process itself already paid off. I’m sharper, clearer, and more intentional than I was before. And that’s a win. Final Thought If you’re preparing for a senior role: Don’t just study the job description Study your own journey There’s more alignment there than you think. End of entry. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23490	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://dev.to/loiconlyone/jai-galere-pendant-3-semaines-pour-monter-un-cluster-kubernetes-et-voila-ce-que-jai-appris-30l6#r%C3%B4le-k8sworker-le-suiveur-patient	J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. 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Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse BeardDemon Posted on Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # kubernetes # devops # learning Le contexte Bon, soyons honnêtes. Au début, j'avais un gros bordel de scripts bash éparpillés partout. Genre 5-6 fichiers avec des noms comme install-docker.sh , setup-k8s-FINAL-v3.sh (oui, le v3...). À chaque fois que je devais recréer mon infra, c'était 45 minutes de galère + 10 minutes à me demander pourquoi ça marchait pas. J'avais besoin de quelque chose de plus propre pour mon projet SAE e-commerce. Ce que je voulais vraiment Pas un truc de démo avec minikube. Non. Je voulais: 3 VMs qui tournent vraiment (1 master + 2 workers) Tout automatisé - je tape une commande et ça se déploie ArgoCD pour faire du GitOps (parce que push to deploy c'est quand même cool) Des logs centralisés (Loki + Grafana) Et surtout : pouvoir tout péter et tout recréer en 10 minutes L'architecture (spoiler: ça marche maintenant) ┌─────────────────────────────────────────┐ │ Mon PC (Debian) │ │ ┌──────────┐ ┌──────────┐ ┌─────────┐ │ │ Master │ │ Worker 1 │ │ Worker 2│ │ │ .56.10 │ │ .56.11 │ │ .56.12 │ │ └──────────┘ └──────────┘ └─────────┘ └─────────────────────────────────────────┘ Enter fullscreen mode Exit fullscreen mode Chaque VM a 4Go de RAM et 4 CPUs. Oui, ça bouffe des ressources. Non, ça passe pas sur un laptop pourri. Comment c'est organisé J'ai tout mis dans un repo bien rangé (pour une fois): ansible-provisioning/ ├── Vagrantfile # Les 3 VMs ├── playbook.yml # Le chef d'orchestre ├── manifests/ # Mes applis K8s │ ├── apiclients/ │ ├── apicatalogue/ │ ├── databases/ │ └── ... (toutes mes APIs) └── roles/ # Les briques Ansible ├── docker/ ├── kubernetes/ ├── k8s-master/ └── argocd/ Enter fullscreen mode Exit fullscreen mode Chaque rôle fait UN truc. C'est ça qui a changé ma vie. Shell scripts → Ansible : pourquoi j'ai migré Avant (la galère) J'avais un script prepare-system.sh qui ressemblait à ça: #!/bin/bash swapoff -a sed -i '/swap/d' /etc/fstab modprobe br_netfilter # ... 50 lignes de commandes # Aucune gestion d'erreur # Si ça plante au milieu, bonne chance Enter fullscreen mode Exit fullscreen mode Le pire ? Si je relançais le script après un fail, tout pétait. Genre le sed essayait de supprimer une ligne qui existait plus. Classique. Après (je respire enfin) Maintenant j'ai un rôle Ansible system-prepare : - name : Virer le swap shell : swapoff -a ignore_errors : yes - name : Enlever le swap du fstab lineinfile : path : /etc/fstab regexp : ' .swap.' state : absent - name : Charger br_netfilter modprobe : name : br_netfilter state : present Enter fullscreen mode Exit fullscreen mode La différence ? Je peux relancer 10 fois, ça fait pas de conneries C'est lisible par un humain Si ça plante, je sais exactement où Le Vagrantfile (ou comment lancer 3 VMs d'un coup) Vagrant . configure ( "2" ) do \| config \| config . vm . box = "debian/bullseye64" # Config libvirt (KVM/QEMU) config . vm . provider "libvirt" do \| libvirt \| libvirt . memory = 4096 libvirt . cpus = 4 libvirt . management_network_address = "192.168.56.0/24" end # NFS pour partager les manifests config . vm . synced_folder "." , "/vagrant" , type: "nfs" , nfs_version: 4 # Le master config . vm . define "vm-master" do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.10" vm . vm . hostname = "master" end # Les 2 workers ( 1 .. 2 ). each do \| i \| config . vm . define "vm-slave- #{ i } " do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.1 #{ i } " vm . vm . hostname = "slave- #{ i } " end end # Ansible se lance automatiquement config . vm . provision "ansible" do \| ansible \| ansible . playbook = "playbook.yml" ansible . groups = { "master" => [ "vm-master" ], "workers" => [ "vm-slave-1" , "vm-slave-2" ] } end end Enter fullscreen mode Exit fullscreen mode Un vagrant up et boom, tout se monte tout seul. Le playbook : l'ordre c'est important --- # 1. Tous les nœuds en même temps - name : Setup de base hosts : k8s_cluster roles : - system-prepare # Swap off, modules kernel - docker # Docker + containerd - kubernetes # kubelet, kubeadm, kubectl # 2. Le master d'abord - name : Init master hosts : master roles : - k8s-master # kubeadm init + Flannel # 3. Les workers ensuite, un par un - name : Join workers hosts : workers serial : 1 # IMPORTANT: un à la fois roles : - k8s-worker # 4. Les trucs bonus sur le master - name : Dashboard + ArgoCD + Monitoring hosts : master roles : - k8s-dashboard - argocd - logging - metrics-server Enter fullscreen mode Exit fullscreen mode Le serial: 1 c'est crucial. J'avais essayé sans, les deux workers essayaient de join en même temps et ça partait en cacahuète. Les rôles en détail Rôle: k8s-master (le chef d'orchestre) C'est lui qui initialise le cluster. Voici les parties importantes: - name : Init cluster k8s command : kubeadm init --apiserver-advertise-address=192.168.56.10 --pod-network-cidr=10.244.0.0/16 when : not k8s_initialise.stat.exists - name : Copier config kubectl copy : src : /etc/kubernetes/admin.conf dest : /home/vagrant/.kube/config owner : vagrant group : vagrant - name : Installer Flannel (réseau pod) shell : \| kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml environment : KUBECONFIG : /home/vagrant/.kube/config - name : Générer commande join pour les workers copy : content : " kubeadm join 192.168.56.10:6443 --token {{ k8s_token.stdout }} --discovery-token-ca-cert-hash sha256:{{ k8s_ca_hash.stdout }}" dest : /vagrant/join.sh mode : ' 0755' - name : Créer fichier .master-ready copy : content : " Master initialized" dest : /vagrant/.master-ready Enter fullscreen mode Exit fullscreen mode Le fichier .master-ready c'est un flag pour dire aux workers "go, vous pouvez join maintenant". Rôle: k8s-worker (le suiveur patient) - name : Attendre que le fichier .master-ready existe wait_for : path : /vagrant/.master-ready timeout : 600 - name : Joindre le cluster shell : bash /vagrant/join.sh args : creates : /etc/kubernetes/kubelet.conf register : join_result failed_when : - join_result.rc != 0 - " 'already exists in the cluster' not in join_result.stderr" - name : Attendre que le node soit Ready shell : \| for i in {1..60}; do STATUS=$(kubectl get node $(hostname) -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}') if [ "$STATUS" = "True" ]; then exit 0 fi sleep 5 done exit 1 Enter fullscreen mode Exit fullscreen mode Le worker attend gentiment que le master soit prêt avant de faire quoi que ce soit. Les galères que j'ai rencontrées Galère #1: NFS qui marche pas Au début, le partage NFS entre l'hôte et les VMs plantait. Symptôme: mount.nfs: Connection timed out Enter fullscreen mode Exit fullscreen mode Solution: # Sur l'hôte sudo apt install nfs-kernel-server sudo systemctl start nfs-server sudo ufw allow from 192.168.56.0/24 Enter fullscreen mode Exit fullscreen mode Le firewall bloquait les connexions NFS. Classique. Galère #2: Kubeadm qui timeout Le kubeadm init prenait 10 minutes et finissait par timeout. Cause: Pas assez de RAM sur les VMs (j'avais mis 2Go). Solution: Passer à 4Go par VM. Ça bouffe mais c'est nécessaire. Galère #3: Les workers qui join pas Les workers restaient en NotReady même après le join. Cause: Flannel (le CNI) était pas encore installé sur le master. Solution: Attendre que Flannel soit complètement déployé avant de faire join les workers: - name : Attendre Flannel command : kubectl wait --for=condition=ready pod -l app=flannel -n kube-flannel --timeout=300s environment : KUBECONFIG : /etc/kubernetes/admin.conf Enter fullscreen mode Exit fullscreen mode Galère #4: Ansible qui relance tout à chaque fois Au début, chaque vagrant provision refaisait TOUT depuis zéro. Solution: Ajouter des conditions when partout: - name : Init cluster k8s command : kubeadm init ... when : not k8s_initialise.stat.exists # ← Ça sauve des vies Enter fullscreen mode Exit fullscreen mode L'idempotence c'est vraiment la base avec Ansible. Les commandes utiles au quotidien # Lancer tout cd ansible-provisioning && vagrant up # Vérifier l'état du cluster vagrant ssh vm-master -c 'kubectl get nodes' # Voir les pods vagrant ssh vm-master -c 'kubectl get pods -A' # Refaire le provisioning (sans détruire les VMs) vagrant provision # Tout péter et recommencer vagrant destroy -f && vagrant up # SSH sur le master vagrant ssh vm-master # Logs d'un pod vagrant ssh vm-master -c 'kubectl logs -n apps apicatalogue-xyz' Enter fullscreen mode Exit fullscreen mode ArgoCD et les applications Une fois le cluster monté, ArgoCD déploie automatiquement mes apps. Voici comment je déclare l'API Catalogue: apiVersion : argoproj.io/v1alpha1 kind : Application metadata : name : catalogue-manager-application namespace : argocd spec : destination : namespace : apps server : https://kubernetes.default.svc source : path : ansible-provisioning/manifests/apicatalogue repoURL : https://github.com/uha-sae53/Vagrant.git targetRevision : main project : default syncPolicy : automated : prune : true selfHeal : true Enter fullscreen mode Exit fullscreen mode ArgoCD surveille mon repo GitHub. Dès que je change un manifest, ça se déploie automatiquement. Metrics Server et HPA J'ai aussi ajouté le Metrics Server pour l'auto-scaling: - name : Installer Metrics Server shell : \| kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml environment : KUBECONFIG : /etc/kubernetes/admin.conf - name : Patcher pour ignorer TLS (dev seulement) shell : \| kubectl patch deployment metrics-server -n kube-system --type='json' \ -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/-", "value": "--kubelet-insecure-tls"}]' Enter fullscreen mode Exit fullscreen mode Avec ça, mes pods peuvent scaler automatiquement en fonction de la charge CPU/RAM. Le résultat final Après tout ça, voici ce que je peux faire: # Démarrer tout de zéro vagrant up # ⏱️ 8 minutes plus tard... # Vérifier que tout tourne vagrant ssh vm-master -c 'kubectl get pods -A' # Résultat: # NAMESPACE NAME READY STATUS # apps apicatalogue-xyz 1/1 Running # apps apiclients-abc 1/1 Running # apps apicommandes-def 1/1 Running # apps api-panier-ghi 1/1 Running # apps frontend-jkl 1/1 Running # argocd argocd-server-xxx 1/1 Running # logging grafana-yyy 1/1 Running # logging loki-0 1/1 Running # kube-system metrics-server-zzz 1/1 Running Enter fullscreen mode Exit fullscreen mode Tout fonctionne, tout est automatisé. Conclusion Ce que j'ai appris: Ansible > scripts shell (vraiment, vraiment) L'idempotence c'est pas un luxe Tester chaque rôle séparément avant de tout brancher Les workers doivent attendre le master (le serial: 1 sauve des vies) 4Go de RAM minimum par VM pour K8s Le code complet est sur GitHub: https://github.com/uha-sae53/Vagrant Des questions ? Ping moi sur Twitter ou ouvre une issue sur le repo. Et si vous galérez avec Kubernetes, vous êtes pas seuls. J'ai passé 3 semaines là-dessus, c'est normal que ce soit compliqué au début. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse BeardDemon Follow Nananère je suis très sérieux... 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Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/loiconlyone/jai-galere-pendant-3-semaines-pour-monter-un-cluster-kubernetes-et-voila-ce-que-jai-appris-30l6#gal%C3%A8re-3-les-workers-qui-join-pas	J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse BeardDemon Posted on Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # kubernetes # devops # learning Le contexte Bon, soyons honnêtes. Au début, j'avais un gros bordel de scripts bash éparpillés partout. Genre 5-6 fichiers avec des noms comme install-docker.sh , setup-k8s-FINAL-v3.sh (oui, le v3...). À chaque fois que je devais recréer mon infra, c'était 45 minutes de galère + 10 minutes à me demander pourquoi ça marchait pas. J'avais besoin de quelque chose de plus propre pour mon projet SAE e-commerce. Ce que je voulais vraiment Pas un truc de démo avec minikube. Non. Je voulais: 3 VMs qui tournent vraiment (1 master + 2 workers) Tout automatisé - je tape une commande et ça se déploie ArgoCD pour faire du GitOps (parce que push to deploy c'est quand même cool) Des logs centralisés (Loki + Grafana) Et surtout : pouvoir tout péter et tout recréer en 10 minutes L'architecture (spoiler: ça marche maintenant) ┌─────────────────────────────────────────┐ │ Mon PC (Debian) │ │ ┌──────────┐ ┌──────────┐ ┌─────────┐ │ │ Master │ │ Worker 1 │ │ Worker 2│ │ │ .56.10 │ │ .56.11 │ │ .56.12 │ │ └──────────┘ └──────────┘ └─────────┘ └─────────────────────────────────────────┘ Enter fullscreen mode Exit fullscreen mode Chaque VM a 4Go de RAM et 4 CPUs. Oui, ça bouffe des ressources. Non, ça passe pas sur un laptop pourri. Comment c'est organisé J'ai tout mis dans un repo bien rangé (pour une fois): ansible-provisioning/ ├── Vagrantfile # Les 3 VMs ├── playbook.yml # Le chef d'orchestre ├── manifests/ # Mes applis K8s │ ├── apiclients/ │ ├── apicatalogue/ │ ├── databases/ │ └── ... (toutes mes APIs) └── roles/ # Les briques Ansible ├── docker/ ├── kubernetes/ ├── k8s-master/ └── argocd/ Enter fullscreen mode Exit fullscreen mode Chaque rôle fait UN truc. C'est ça qui a changé ma vie. Shell scripts → Ansible : pourquoi j'ai migré Avant (la galère) J'avais un script prepare-system.sh qui ressemblait à ça: #!/bin/bash swapoff -a sed -i '/swap/d' /etc/fstab modprobe br_netfilter # ... 50 lignes de commandes # Aucune gestion d'erreur # Si ça plante au milieu, bonne chance Enter fullscreen mode Exit fullscreen mode Le pire ? Si je relançais le script après un fail, tout pétait. Genre le sed essayait de supprimer une ligne qui existait plus. Classique. Après (je respire enfin) Maintenant j'ai un rôle Ansible system-prepare : - name : Virer le swap shell : swapoff -a ignore_errors : yes - name : Enlever le swap du fstab lineinfile : path : /etc/fstab regexp : ' .swap.' state : absent - name : Charger br_netfilter modprobe : name : br_netfilter state : present Enter fullscreen mode Exit fullscreen mode La différence ? Je peux relancer 10 fois, ça fait pas de conneries C'est lisible par un humain Si ça plante, je sais exactement où Le Vagrantfile (ou comment lancer 3 VMs d'un coup) Vagrant . configure ( "2" ) do \| config \| config . vm . box = "debian/bullseye64" # Config libvirt (KVM/QEMU) config . vm . provider "libvirt" do \| libvirt \| libvirt . memory = 4096 libvirt . cpus = 4 libvirt . management_network_address = "192.168.56.0/24" end # NFS pour partager les manifests config . vm . synced_folder "." , "/vagrant" , type: "nfs" , nfs_version: 4 # Le master config . vm . define "vm-master" do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.10" vm . vm . hostname = "master" end # Les 2 workers ( 1 .. 2 ). each do \| i \| config . vm . define "vm-slave- #{ i } " do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.1 #{ i } " vm . vm . hostname = "slave- #{ i } " end end # Ansible se lance automatiquement config . vm . provision "ansible" do \| ansible \| ansible . playbook = "playbook.yml" ansible . groups = { "master" => [ "vm-master" ], "workers" => [ "vm-slave-1" , "vm-slave-2" ] } end end Enter fullscreen mode Exit fullscreen mode Un vagrant up et boom, tout se monte tout seul. Le playbook : l'ordre c'est important --- # 1. Tous les nœuds en même temps - name : Setup de base hosts : k8s_cluster roles : - system-prepare # Swap off, modules kernel - docker # Docker + containerd - kubernetes # kubelet, kubeadm, kubectl # 2. Le master d'abord - name : Init master hosts : master roles : - k8s-master # kubeadm init + Flannel # 3. Les workers ensuite, un par un - name : Join workers hosts : workers serial : 1 # IMPORTANT: un à la fois roles : - k8s-worker # 4. Les trucs bonus sur le master - name : Dashboard + ArgoCD + Monitoring hosts : master roles : - k8s-dashboard - argocd - logging - metrics-server Enter fullscreen mode Exit fullscreen mode Le serial: 1 c'est crucial. J'avais essayé sans, les deux workers essayaient de join en même temps et ça partait en cacahuète. Les rôles en détail Rôle: k8s-master (le chef d'orchestre) C'est lui qui initialise le cluster. Voici les parties importantes: - name : Init cluster k8s command : kubeadm init --apiserver-advertise-address=192.168.56.10 --pod-network-cidr=10.244.0.0/16 when : not k8s_initialise.stat.exists - name : Copier config kubectl copy : src : /etc/kubernetes/admin.conf dest : /home/vagrant/.kube/config owner : vagrant group : vagrant - name : Installer Flannel (réseau pod) shell : \| kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml environment : KUBECONFIG : /home/vagrant/.kube/config - name : Générer commande join pour les workers copy : content : " kubeadm join 192.168.56.10:6443 --token {{ k8s_token.stdout }} --discovery-token-ca-cert-hash sha256:{{ k8s_ca_hash.stdout }}" dest : /vagrant/join.sh mode : ' 0755' - name : Créer fichier .master-ready copy : content : " Master initialized" dest : /vagrant/.master-ready Enter fullscreen mode Exit fullscreen mode Le fichier .master-ready c'est un flag pour dire aux workers "go, vous pouvez join maintenant". Rôle: k8s-worker (le suiveur patient) - name : Attendre que le fichier .master-ready existe wait_for : path : /vagrant/.master-ready timeout : 600 - name : Joindre le cluster shell : bash /vagrant/join.sh args : creates : /etc/kubernetes/kubelet.conf register : join_result failed_when : - join_result.rc != 0 - " 'already exists in the cluster' not in join_result.stderr" - name : Attendre que le node soit Ready shell : \| for i in {1..60}; do STATUS=$(kubectl get node $(hostname) -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}') if [ "$STATUS" = "True" ]; then exit 0 fi sleep 5 done exit 1 Enter fullscreen mode Exit fullscreen mode Le worker attend gentiment que le master soit prêt avant de faire quoi que ce soit. Les galères que j'ai rencontrées Galère #1: NFS qui marche pas Au début, le partage NFS entre l'hôte et les VMs plantait. Symptôme: mount.nfs: Connection timed out Enter fullscreen mode Exit fullscreen mode Solution: # Sur l'hôte sudo apt install nfs-kernel-server sudo systemctl start nfs-server sudo ufw allow from 192.168.56.0/24 Enter fullscreen mode Exit fullscreen mode Le firewall bloquait les connexions NFS. Classique. Galère #2: Kubeadm qui timeout Le kubeadm init prenait 10 minutes et finissait par timeout. Cause: Pas assez de RAM sur les VMs (j'avais mis 2Go). Solution: Passer à 4Go par VM. Ça bouffe mais c'est nécessaire. Galère #3: Les workers qui join pas Les workers restaient en NotReady même après le join. Cause: Flannel (le CNI) était pas encore installé sur le master. Solution: Attendre que Flannel soit complètement déployé avant de faire join les workers: - name : Attendre Flannel command : kubectl wait --for=condition=ready pod -l app=flannel -n kube-flannel --timeout=300s environment : KUBECONFIG : /etc/kubernetes/admin.conf Enter fullscreen mode Exit fullscreen mode Galère #4: Ansible qui relance tout à chaque fois Au début, chaque vagrant provision refaisait TOUT depuis zéro. Solution: Ajouter des conditions when partout: - name : Init cluster k8s command : kubeadm init ... when : not k8s_initialise.stat.exists # ← Ça sauve des vies Enter fullscreen mode Exit fullscreen mode L'idempotence c'est vraiment la base avec Ansible. Les commandes utiles au quotidien # Lancer tout cd ansible-provisioning && vagrant up # Vérifier l'état du cluster vagrant ssh vm-master -c 'kubectl get nodes' # Voir les pods vagrant ssh vm-master -c 'kubectl get pods -A' # Refaire le provisioning (sans détruire les VMs) vagrant provision # Tout péter et recommencer vagrant destroy -f && vagrant up # SSH sur le master vagrant ssh vm-master # Logs d'un pod vagrant ssh vm-master -c 'kubectl logs -n apps apicatalogue-xyz' Enter fullscreen mode Exit fullscreen mode ArgoCD et les applications Une fois le cluster monté, ArgoCD déploie automatiquement mes apps. Voici comment je déclare l'API Catalogue: apiVersion : argoproj.io/v1alpha1 kind : Application metadata : name : catalogue-manager-application namespace : argocd spec : destination : namespace : apps server : https://kubernetes.default.svc source : path : ansible-provisioning/manifests/apicatalogue repoURL : https://github.com/uha-sae53/Vagrant.git targetRevision : main project : default syncPolicy : automated : prune : true selfHeal : true Enter fullscreen mode Exit fullscreen mode ArgoCD surveille mon repo GitHub. Dès que je change un manifest, ça se déploie automatiquement. Metrics Server et HPA J'ai aussi ajouté le Metrics Server pour l'auto-scaling: - name : Installer Metrics Server shell : \| kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml environment : KUBECONFIG : /etc/kubernetes/admin.conf - name : Patcher pour ignorer TLS (dev seulement) shell : \| kubectl patch deployment metrics-server -n kube-system --type='json' \ -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/-", "value": "--kubelet-insecure-tls"}]' Enter fullscreen mode Exit fullscreen mode Avec ça, mes pods peuvent scaler automatiquement en fonction de la charge CPU/RAM. Le résultat final Après tout ça, voici ce que je peux faire: # Démarrer tout de zéro vagrant up # ⏱️ 8 minutes plus tard... # Vérifier que tout tourne vagrant ssh vm-master -c 'kubectl get pods -A' # Résultat: # NAMESPACE NAME READY STATUS # apps apicatalogue-xyz 1/1 Running # apps apiclients-abc 1/1 Running # apps apicommandes-def 1/1 Running # apps api-panier-ghi 1/1 Running # apps frontend-jkl 1/1 Running # argocd argocd-server-xxx 1/1 Running # logging grafana-yyy 1/1 Running # logging loki-0 1/1 Running # kube-system metrics-server-zzz 1/1 Running Enter fullscreen mode Exit fullscreen mode Tout fonctionne, tout est automatisé. Conclusion Ce que j'ai appris: Ansible > scripts shell (vraiment, vraiment) L'idempotence c'est pas un luxe Tester chaque rôle séparément avant de tout brancher Les workers doivent attendre le master (le serial: 1 sauve des vies) 4Go de RAM minimum par VM pour K8s Le code complet est sur GitHub: https://github.com/uha-sae53/Vagrant Des questions ? Ping moi sur Twitter ou ouvre une issue sur le repo. Et si vous galérez avec Kubernetes, vous êtes pas seuls. J'ai passé 3 semaines là-dessus, c'est normal que ce soit compliqué au début. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse BeardDemon Follow Nananère je suis très sérieux... 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Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
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Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Getting Started / Server / File File Set up log ingestion using an OpenTelemetry collector with the filelog receiver. 1 Define your OpenTelemetry configuration. Setup the following OpenTelemetry collector. Check out our example here . receivers: filelog: include: [/watch.log] start_at: beginning exporters: otlp/highlight: endpoint: 'https://otel.highlight.io:4317' processors: attributes/highlight-project: actions: - key: highlight.project_id value: '<YOUR_PROJECT_ID>' action: insert batch: service: pipelines: logs: receivers: [filelog] processors: [attributes/highlight-project, batch] exporters: [otlp/highlight] 2 Run the collector Run the OpenTelemetry collector to start streaming the file to highlight. docker run -v /my/file/to/watch.log:/watch.log -v $(pwd)/config.yaml:/etc/otelcol-contrib/config.yaml otel/opentelemetry-collector-contrib 3 Verify your backend logs are being recorded. Visit the highlight logs portal and check that backend logs are coming in. Docker / Docker Compose Fluent Forward [object Object]	2026-01-13T08:48:55
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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/#comment-23492	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://www.highlight.io/docs/getting-started/browser/angular	Angular Star us on GitHub Star Docs Sign in Sign up Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. 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Menu Highlight Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Getting Started / Browser / Angular Using highlight.io with Angular Learn how to set up highlight.io with your Angular application. 1 Install the npm package & SDK. Install the npm package highlight.run in your terminal. # with yarn yarn add highlight.run # with pnpm pnpm add highlight.run # with npm npm install highlight.run 2 Initialize the SDK in your frontend. Grab your project ID from app.highlight.io/setup , and pass it as the first parameter of the H.init() method. To get started, we recommend setting tracingOrigins and networkRecording so that we can pass a header to pair frontend and backend errors. Refer to our docs on SDK configuration and Fullstack Mapping to read more about these options. // app.module.ts import { NgModule } from '@angular/core'; ... import { H } from 'highlight.run'; H.init('<YOUR_PROJECT_ID>', { environment: 'production', version: 'commit:abcdefg12345', networkRecording: { enabled: true, recordHeadersAndBody: true, urlBlocklist: [ // insert full or partial urls that you don't want to record here // Out of the box, Highlight will not record these URLs (they can be safely removed): "https://www.googleapis.com/identitytoolkit", "https://securetoken.googleapis.com", ], }, }); @NgModule({ ... }) export class AppModule { } 3 Identify users. Identify users after the authentication flow of your web app. We recommend doing this in any asynchronous, client-side context. The first argument of identify will be searchable via the property identifier , and the second property is searchable by the key of each item in the object. For more details, read about session search or how to identify users . import { H } from 'highlight.run'; function Login(username: string, password: string) { // login logic here... // pass the user details from your auth provider to the H.identify call H.identify('jay@highlight.io', { id: 'very-secure-id', phone: '867-5309', bestFriend: 'jenny' }); } 4 Verify installation Check your dashboard for a new session. Make sure to remove the Status is Completed filter to see ongoing sessions. Don't see anything? Send us a message in our community and we can help debug. 5 Configure sourcemaps in CI. (optional) To get properly enhanced stacktraces of your javascript app, we recommend instrumenting sourcemaps. If you deploy public sourcemaps, you can skip this step. Refer to our docs on sourcemaps to read more about this option. # Upload sourcemaps to Highlight ... npx --yes @highlight-run/sourcemap-uploader upload --apiKey ${YOUR_ORG_API_KEY} --path ./build ... 6 Instrument your backend. The next step is instrumenting your backend to tie logs/errors to your frontend sessions. Read more about this in our backend instrumentation section. Vue.js Gatsby.js [object Object]	2026-01-13T08:48:55
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We got you covered! Brand guidelines Download logo pack Headless ecommerce Search Create Search & Discovery for your headless ecommerce Provide rich product- and content-based customer experiences in a headless ecommerce framework across all your devices and channels. Get a demo Start building for free ]:border-l md:[&>:nth-child(1)]:border-none md:[&>*:nth-child(4n+1)]:border-none"> 1.7+ Trillion searches every year 99.999% uptime SLA available 382% ROI according to Forrester Research 18,000+ customers across 150+ countries Start your headless journey with an improved search experience Headless ecommerce across all channels You can put our search-as-a-service platform to work with your traditional ecommerce website application, single-page app (SPA), progressive web app (PWA), mobile app, in-store kiosk, business app, and more, all from a single unified platform. Our API-first platform comes with front-end libraries for many popular frameworks. Dump your data silos Index all your product information, plus any editorial and help-desk content. Our search platform comes with an advanced crawler, integration with leading ecommerce platforms, and API clients in 11 languages. No matter which back-end system is housing your product data and content for your ecommerce store, we can index and release in any front-end experience. See our integrations Power true personalized, omnichannel experiences Create a unified personalization strategy across your customer touchpoints. One omnichannel search platform and AI personalization engine means a consistently personalized user experience. As visitors interact with your brand across your touchpoints, Algolia learns about their preferences and personalizes accordingly, making their every experience more rewarding. Develop and iterate 10X faster Algolia’s API first approach allows you easily to experiment with new experiences and front ends without the need for back end engineering Front-end flexibility for an optimal user experience Our front-end implementation is totally flexible, allowing you to build the experience that best meets your needs and promotes your brand. We provide transparent, fully customizable ranking and personalization algorithms. Try it Now Improve business agility with centralized merchandising Powering all user experiences from a single platform empowers your business teams to leverage search management tools for efficient optimization of the storefront. Discover the Merchandising Studio Go API first with your headless architecture Algolia is part of an ecosystem of best-of-breed ecommerce solutions. So whether you call your platform headless commerce, composable commerce, a microservices architecture, Jamstack, MACH, or serverless, our API-first approach marries well with it. Recommended content Merchandising in the era of artificial intelligence (AI) The advent of AI heralds a revolutionary opportunity that will change how merchandisers operate & strategize, but ecommerce businesses will face new challenges as they integrate AI-powered technology. Read more An introduction to data-driven AI merchandising Your homepage is the window into your store. But how do merchandisers maximize the power of their online real estate to drive sales, brand experiences, and other critical outcomes? Read more Zeeman improves Search performance & gives customers a 'remarkably simple' experience Zeeman deployed Algolia in record time and hasn’t looked back, iterating, and improving on Search to the benefit of its customers, its e-commerce and merchandising teams — and its revenue. Read more See more Headless ecommerce solution FAQs Which headless ecommerce platforms is Algolia compatible with? 0 Algolia's API-first solution is compatible with all headless ecommerce platforms. We also offer native integration with  Salesforce Commerce Cloud ,  Magento , and  Shopify . If I integrate Algolia with my headless ecommerce, do you provide front-end components? 0 Yes, you can build your own front end by leveraging our  InstantSearch  components, and you can use our  guides  if you want to build more-advanced versions. You can also start from a  prebuilt packaged  ecommerce search and discovery template. How much does Algolia for a headless ecommerce platform cost? 0 You can start with a  free trial  and find out how it works for you. Then, our competitive general  pricing  would apply. Do you provide services for transitioning to a headless approach for ecommerce? 0 No, but we work with partners who help retailers move to headless ecommerce.  Find out more .Another popular mobile app pattern for maximizing small-screen real estate during a mobile search is faceted search, which lets the searcher narrow their results by applying filters, typically by selecting options provided in a "tray"-style overlay. Faceted search is often utilized by retailers in ecommerce (and the mobile equivalent, m-commerce) and by travel service providers, as well as in online search tools on media websites. One relatively new application for searching on mobile devices is voice search. According to eMarketer, in 2019, 40% of all U.S. Internet users were using voice search, which has grown more popular, albeit slowly. 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https://dev.to/alifunk/llms-are-like-humans-they-make-mistakes-here-is-how-we-limit-them-with-guardrails-24dj	LLMs are like Humans - They make mistakes. Here is how we limit them with Guardrails - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Ali-Funk Posted on Jan 8 LLMs are like Humans - They make mistakes. Here is how we limit them with Guardrails # aws # ai # guardrails # architecture Taming the Probabilistic Engine: Why we can't "fix" AI Hallucinations, but we can Shield them. Introduction It happened again today. While discussing the AWS BeSA program, my LLM started daydreaming. It insisted there was a local IT event in my city that simply doesn’t exist. It was so convincing that I had to correct it three times. As Marko Sluga recently put it in a chat: LLMs are probabilistic engines that prioritize coherence over facts. Just like (his words) "Karen from accounting," they sometimes try to justify a point even when they lack the data. That core nature will never go away. However, while we can't prevent hallucinations 100%, we can highly limit their impact. In this post, I’ll dive into how Grounding and Amazon Bedrock Guardrails act as the essential quality control layer to keep AI outputs within professional boundaries. It took multiple corrections to get the model back on track. While funny in a private chat, this is a massive risk for businesses. Here is how we solve this using Amazon Bedrock. The Logic of Hallucinations LLMs are "next-token predictors." They don't have a concept of "truth"; they have a concept of "probability." If a model is tuned to be highly creative, it will often prefer an invented answer over no answer at all. Step 1: Grounding through RAG To fix this, we implement Retrieval-Augmented Generation (RAG). We provide the model with a specific set of documents. The model is then instructed to answer only based on that provided context. Step 2: Implementing Amazon Bedrock Guardrails Based on my discussion with Marko Sluga today. I learned that "Guardrails" act as the ultimate "quality control" layer. They offer: Contextual Grounding Checks: The system runs a real-time analysis. If the "Relevancy Score" (how much the answer matches the source data) falls below a certain threshold, the output is blocked. Defined Fallbacks: Instead of letting the model "wander off," you configure a standard response: "I cannot answer this based on the available data." Safety & Compliance: Guardrails also handle PII (Personally Identifiable Information) redaction and toxic content filtering, ensuring the AI stays within professional boundaries. Conclusion The difference between a "chatbot" and an "Enterprise AI Agent" is Control. By using Amazon Bedrock Guardrails, we move from a probabilistic guessing game to a reliable system that prioritizes accuracy over creativity. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Ali-Funk Follow Learning in Public. Transitioning into Cloud Security. Currently wrestling with AWS CCP and the Imposter Syndrome. I am here sharing what I learn so you don't have to make the same mistakes as I did. Location Germany Work Aspiring Cloud Security Architect Joined Jan 7, 2026 More from Ali-Funk Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend # aws # community # career # cloud Why I rescheduled my AWS exam today # aws # beginners # cloud # career 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. 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https://jsfiddle.net/6he52mnr/1/	test 3 - JSFiddle - Code Playground over 6 years ago">AN Run --> Vote for features --> Embed fiddle on websites/blogs --> Go PRO JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle. AI Code Completion AI Code Completion is a BYOK implementation. Get your API Key → The model we use is Codestral by Mistral . We won't save your API Key in our database, it's only stored in the browser for your convinience. Your recent fiddles Collections PRO Select collections: New collection Resources URL cdnjs 2 mootools-core.min.js Remove mootools-more-compressed.js Remove Paste a direct CSS/JS URL Type a library name to fetch from CDNJS Async requests Simulating async requests: JSON /echo/json/ JSONP /echo/jsonp/ HTML /echo/html/ XML /echo/xml/ See docs for more info. Changelog JSFiddle Apps Coder Fonts Color Palette Generator CSS Flexbox Generator Sign in Code panel options Change code languages, preprocessors and plugins HTML JavaScript CSS Language HTML HAML Doctype XHTML 1.0 Strict XHTML 1.0 Transitional HTML 5 HTML 4.01 Strict HTML 4.01 Transitional HTML 4.01 Frameset Body tag Language JavaScript CoffeeScript JavaScript 1.7 Babel + JSX TypeScript CoffeeScript 2 Vue React Preact Extensions Alpine.js 2.1.2 AngularJS 1.1.1 AngularJS 1.2.1 AngularJS 1.4.8 AngularJS 2.0.0-alpha.47 Bonsai 0.4.1 Brick edge CreateJS 2013.09.25 CreateJS 2015.05.21 D3 3.x D3 4.13.0 D3 5.9.2 Dojo (nightly) Dojo 1.4.8 Dojo 1.5.6 Dojo 1.6.5 Dojo 1.7.12 Dojo 1.8.14 Dojo 1.9.11 Dojo 1.10.8 Dojo 1.11.4 Dojo 1.12.2 Ember (latest) Enyo (nightly) Enyo 2.0.1 Enyo 2.1 Enyo 2.2.0 Enyo 2.4.0 Enyo 2.5.1 Enyo 2.7.0 ExtJS 3.1.0 ExtJS 3.4.0 ExtJS 4.1.0 ExtJS 4.1.1 ExtJS 4.2.0 ExtJS 5.0.0 ExtJS 5.1.0 ExtJS 6.2.0 FabricJS 1.5.0 FabricJS 1.7.7 FabricJS 1.7.15 FabricJS 1.7.20 Inferno 1.0.0-beta9 JSBlocks (edge) KineticJS 4.0.5 KineticJS 4.3.1 Knockout.js 2.0.0 Knockout.js 2.1.0 Knockout.js 2.2.1 Knockout.js 2.3.0 Knockout.js 3.0.0 Knockout.js 3.4.2 Lo-Dash 2.2.1 Minified 1.0 beta1 MithrilJS 0.2.0 MithrilJS 1.1.6 Mootools (nightly) Mootools 1.3.2 Mootools 1.3.2 (compat) Mootools 1.4.5 Mootools 1.4.5 (compat) Mootools 1.5.1 Mootools 1.5.2 Mootools 1.5.2 (compat) Mootools 1.6.0 Mootools 1.6.0 (compat) No-Library (pure JS) OpenUI5 (latest, mobile) Paper.js 0.22 Pixi 3.0.11 Pixi 4.0.0 Processing.js 1.2.3 Processing.js 1.3.6 Processing.js 1.4.1 Processing.js 1.4.7 Prototype 1.6.1.0 Prototype 1.7.3 RactiveJS 0.7.3 Raphael 1.4 Raphael 1.5.2 Raphael 2.1.0 React 0.3.2 React 0.4.0 React 0.8.0 React 0.9.0 React 0.14.3 RightJS 2.1.1 RightJS 2.3.1 Riot 3.7.4 Shipyard (nightly) Shipyard 0.2 Thorax 2.0.0rc3 Thorax 2.0.0rc6 Three.js r54 Three.js 105 Underscore 1.3.3 Underscore 1.4.3 Underscore 1.4.4 Underscore 1.8.3 Vue (edge) Vue 1.0.12 Vue 2.2.1 WebApp Install 0.1 XTK edge YUI 2.8.0r4 YUI 3.5.0 YUI 3.6.0 YUI 3.7.3 YUI 3.8.0 YUI 3.10.1 YUI 3.14.0 YUI 3.16.0 YUI 3.17.2 Zepto 1.0rc1 jQuery (edge) jQuery 1.9.1 jQuery 2.1.3 jQuery 2.2.4 jQuery 3.2.1 jQuery 3.3.1 jQuery 3.4.1 jQuery Slim 3.2.1 jQuery Slim 3.3.1 jQuery Slim 3.4.1 jTypes 2.1.0 qooxdoo 2.0.3 qooxdoo 2.1 svg.js 2.6.5 svg.js 2.7.1 svg.js 3.0.5 script attribute Language CSS SCSS SASS PostCSS (Stage 0+) PostCSS (Stage 3+) Tailwind CSS Options --> Reset CSS <h3>HTML:</h3> <p id="result"></p> p { padding: 10px; } p { margin: 5px; border: 1px dotted #999; } fetch("/echo/html/", { method: "POST", headers: { "Content-Type": "application/x-www-form-urlencoded; charset=utf-8" }, body: "html=<a href='#'>hello world</a>" }) .then((response) => response.text()) .then((responseText) => { document.querySelector("#result").innerHTML = responseText }) .catch((error) => { console.error(error) }) This fiddle has previously unsaved changes. Apply changes Discard Color Palette Generator Generate a cool color palette with a few clicks CSS Flexbox Generator Generate your CSS Flexbox layout in the simplest of ways Coder Fonts Curated list of quality monospace fonts for coders Share or embed fiddle Customize the embeddable experience for websites Tabs: JavaScript HTML CSS Result Visual: Light Dark Embed snippet Prefer iframe? : ' readonly> No autoresizing to fit the code Render blocking of the parent page Editor settings Customize the behavior and feel of the editor Behavior Auto-run code Only auto-run code that validates Auto-save code Live code validation Hot reload CSS Hot reload HTML General Line numbers Wrap lines Indent With Spaces Code Autocomplete Indent size: 2 spaces 4 spaces Font size: 10px 11px 12px 13px 14px 15px 16px 17px 18px 19px 20px Font family: Console Console in the editor Clear console on run Your recent fiddles Recently created fiddles, including ones created while logged out JSFiddle changelog A log of all the changes made to JSFiddle – big and small. Curated list of monospace coder fonts You can now use different monospace fonts in the editor − we now have a curated list of pretty awesome fonts available including premium ones. Just open the Coder Fonts mini-app from the sidebar or from Editor settings . My current favorites are Input and Commit Mono . CSS Flexbox generator as a JSFiddle app Our CSS Flexbox generator lets you create a layout, and skip knowing the confusing properties and value names (let's be honest the W3C did not make a good job here). Not gonna lie, this was heavily inspired by flexer.dev but coded completely from scratch. Behavior change for External Resources Adding External Resources will no longer create a list of resources in the sidebar but will be injected as a LINK or SCRIPT tag inside of the HTML panel. Code Completion with additional context The Code Completion will now also have the context of all panels before suggesting code to you - so if for example you have some CSS or JS, the HTML panel will suggest code based on the other two panels. 🦄 AI Code Completion (beta) Introducing some AI sprinkle in the editor - Code Completion based on the Codestral model (by Mistral ). For now it's a BYOK implmentation which means you need to provide your own API Key − you can get it for free . Editor switch from CodeMirror to Monaco (same as VSCode) After much deliberation I've decided to make the switch from CodeMirror to Monaco . There's a few reasons for this. CodeMirror 5 is no longer being developed, and the switch to 6 would be a huge rewrite since there's not much compatibility between the two versions. Monaco itself has lots of features already built-in, things that took quite a few external plugins to get into the CodeMirror implementation. I'm incredibly thankful to Marijn for his work on CodeMirror , it has served well for many years. JSFiddle will load faster Technical debt is a drag man. Remember the time when MooTools was state-of-art JS framework? We do and so much of JSFiddle was still dependant on it till this day, but since almost all MooTools features are now available in native JS it was high-time to strip it out of the codebase. This took around a week of work, lots of testing, but it's now done. And the final package of our JS bundle is ~30% smaller . Add a new collection Collect your fiddles in collections Get a Mistral API Key A short guide to getting a free Mistral API Key. Sign up for a Mistral account, and pick the free Experiment subscription plan. Log in, and go to your organization's API Keys section. Click Create new key , fill "JSFiddle" as the name for the API key, and save. Copy the key, and paste it into JSFiddle − under the AI Code Completion in the Sidebar. Done ! AI Code Completion should now be working. Classic Columns Bottom results Right results Tabs (columns) Tabs (rows) System Light Dark Set fiddle expiration 1 day 10 days 1 month 6 months 1 year Keep forever Please Whitelist JSFiddle in your content blocker. Help keep JSFiddle free for always by one of two ways: Whitelist JSFiddle in your content blocker (two clicks) Go PRO and get access to additional PRO features → Ad-free All ads in the editor and listing pages are turned completely off. Use pre-released features You get to try and use features (like the Palette Color Generator) months before everyone else. Fiddle collections Sort and categorize your Fiddles into multiple collections. Private collections and fiddles You can make as many Private Fiddles, and Private Collections as you wish! Console Debug your Fiddle with a minimal built-in JavaScript console. Early AI features Try the AI features we're rolling out. --> Join the 4+ million users, and keep the JSFiddle dream alive. Ad-free All ads in the editor and listing pages are turned completely off. Use pre-released features You get to try and use features (like the Palette Color Generator) months before everyone else. Fiddle collections Sort and categorize your Fiddles into multiple collections. Private collections and fiddles You can make as many Private Fiddles, and Private Collections as you wish! Console Debug your Fiddle with a minimal built-in JavaScript console. JSFiddle is used by you and 4+ million other developers, in many companies ... ... and top educational institutions: Join as PRO	2026-01-13T08:48:55
https://www.highlight.io/docs/general/company/open-source/hosting/self-host-enterprise	Self-hosted [Enterprise] Star us on GitHub Star Docs Sign in Sign up General Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Menu Highlight Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Highlight Docs / Company / Open Source / Self-hosting / Self-hosted [Enterprise] Self-hosted [Enterprise] Our Enterprise Self-hosted Deployment Interested in deploying Highlight to your own VPC at a larger scale than the hobby deployment? Please contact us via our booking link . Self-hosted Enterprise Feature Set: Features Hobby Enterprise Native Platform Integrations (Teams, Slack, Sendgrid, etc..) ❌ ✅ Native Email Integrations (Sendgrid, SMTP, etc..) ❌ ✅ User Management Support (RBAC, SSO, SSL, etc..) ❌ ✅ HA Deploy & Persistent Storage ❌ ✅ Custom Retention Policies ❌ ✅ Automatic Upgrades ❌ ✅ Availability Guarantees ❌ ✅ Self Hosted Deployment Options We have multiple flexible options for running highlight on your own infrastructure. While the simplest way to get going is our docker compose single deploy, we support complex deployments that provide better scalability and availability. Docker Compose : Deploy Highlight on a single VM for a simpler deploy. Kubernetes Helm Chart : Deploy Highlight on your kubernetes cluster with our clustered HA Helm deploy. CloudFormation / Terraform / Pulumi : Deploy Highlight on your cloud provider of choice. Schedule a technical comparison call via our booking link . Pricing Pricing for our self-hosted enterprise deployment starts at $3k / month. Contact us via our booking link . Self-hosted [Hobby] Telemetry Community / Support Suggest Edits? Follow us! [object Object]	2026-01-13T08:48:55
https://www.algolia.com/	The AI Retrieval Platform - Agentic \| Generative \| Search Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. 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We got you covered! Brand guidelines Download logo pack Agentic. Generative. Search One AI retrieval platform to power them all Explore the platform Powering AI retrieval across use cases More than 18,000 customers across 150+ countries use Algolia to power agentic, generative, and search experiences across these use cases and more. Product Discovery Help users find the right products instantly with retrieval that identifies relevant items and features—like filtering, facets, and business rules—that optimize results for the KPIs you care about most. Learn more . Generative AI Ensure every AI response is accurate and on-brand with RAG that grounds outputs in your verified data and stays consistent with your search logic. Learn more . Guided Shopping Guide shoppers to a confident purchase faster with intent-aware retrieval that adapts to their needs instantly.  Learn more . Documentation Reduce support load and speed up problem-solving with retrieval that quickly identifies the right content and delivers precise answers. Learn more . See more capabilities Your browser does not support the video tag. A recognized Leader, two years in a row Algolia is recognized in the 2025 Gartner® Magic Quadrant™ Report for Search and Product Discovery two years running. Download a complimentary copy of the report today. Download --> Solutions that fulfill your business goals Here are just some of the ways Algolia technology provides value from day 1. Quickly surface the right content Your   customers get relevant results to find precisely what they’re looking for — in milliseconds. Learn more Understand user intent AI algorithms are used to predict and show results from the most likely category of content in your index. Learn more Stay on top of trends See how customers are interacting with your content to improve user experience and improve your KPIs. Learn more Personalize for more engagement Build unique visitor journeys that lead your customers to convert over and over again . Learn more Create buying urgency Algolia AI is always learning what drives conversion and reranks content to push better outcomes. Learn more Easily integrate search in any environment Index your content with our API clients or partner integrations, fine-tune your rankings, and launch with our UI components. All in minutes. View developer hub Proven impact Find out how Algolia performs for some of the world’s most dynamic businesses. +112% CVR boost +30% conversion rate 4x conversion rate improvement 100x faster workflow 34% increased search revenue 360% increased conversion rate +35% conversion rate improvement +10% more page views View all customer stories Trusted integrations and partnerships Get   up and running quickly with pre-built integrations on some of the most popular platforms.  See all integrations Compliant. Secure. Award-winning. 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Harness the power of goal driven AI search with Algolia Get Started Get a demo Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://dev.to/loiconlyone/jai-galere-pendant-3-semaines-pour-monter-un-cluster-kubernetes-et-voila-ce-que-jai-appris-30l6#gal%C3%A8re-4-ansible-qui-relance-tout-%C3%A0-chaque-fois	J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse BeardDemon Posted on Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # kubernetes # devops # learning Le contexte Bon, soyons honnêtes. Au début, j'avais un gros bordel de scripts bash éparpillés partout. Genre 5-6 fichiers avec des noms comme install-docker.sh , setup-k8s-FINAL-v3.sh (oui, le v3...). À chaque fois que je devais recréer mon infra, c'était 45 minutes de galère + 10 minutes à me demander pourquoi ça marchait pas. J'avais besoin de quelque chose de plus propre pour mon projet SAE e-commerce. Ce que je voulais vraiment Pas un truc de démo avec minikube. Non. Je voulais: 3 VMs qui tournent vraiment (1 master + 2 workers) Tout automatisé - je tape une commande et ça se déploie ArgoCD pour faire du GitOps (parce que push to deploy c'est quand même cool) Des logs centralisés (Loki + Grafana) Et surtout : pouvoir tout péter et tout recréer en 10 minutes L'architecture (spoiler: ça marche maintenant) ┌─────────────────────────────────────────┐ │ Mon PC (Debian) │ │ ┌──────────┐ ┌──────────┐ ┌─────────┐ │ │ Master │ │ Worker 1 │ │ Worker 2│ │ │ .56.10 │ │ .56.11 │ │ .56.12 │ │ └──────────┘ └──────────┘ └─────────┘ └─────────────────────────────────────────┘ Enter fullscreen mode Exit fullscreen mode Chaque VM a 4Go de RAM et 4 CPUs. Oui, ça bouffe des ressources. Non, ça passe pas sur un laptop pourri. Comment c'est organisé J'ai tout mis dans un repo bien rangé (pour une fois): ansible-provisioning/ ├── Vagrantfile # Les 3 VMs ├── playbook.yml # Le chef d'orchestre ├── manifests/ # Mes applis K8s │ ├── apiclients/ │ ├── apicatalogue/ │ ├── databases/ │ └── ... (toutes mes APIs) └── roles/ # Les briques Ansible ├── docker/ ├── kubernetes/ ├── k8s-master/ └── argocd/ Enter fullscreen mode Exit fullscreen mode Chaque rôle fait UN truc. C'est ça qui a changé ma vie. Shell scripts → Ansible : pourquoi j'ai migré Avant (la galère) J'avais un script prepare-system.sh qui ressemblait à ça: #!/bin/bash swapoff -a sed -i '/swap/d' /etc/fstab modprobe br_netfilter # ... 50 lignes de commandes # Aucune gestion d'erreur # Si ça plante au milieu, bonne chance Enter fullscreen mode Exit fullscreen mode Le pire ? Si je relançais le script après un fail, tout pétait. Genre le sed essayait de supprimer une ligne qui existait plus. Classique. Après (je respire enfin) Maintenant j'ai un rôle Ansible system-prepare : - name : Virer le swap shell : swapoff -a ignore_errors : yes - name : Enlever le swap du fstab lineinfile : path : /etc/fstab regexp : ' .swap.' state : absent - name : Charger br_netfilter modprobe : name : br_netfilter state : present Enter fullscreen mode Exit fullscreen mode La différence ? Je peux relancer 10 fois, ça fait pas de conneries C'est lisible par un humain Si ça plante, je sais exactement où Le Vagrantfile (ou comment lancer 3 VMs d'un coup) Vagrant . configure ( "2" ) do \| config \| config . vm . box = "debian/bullseye64" # Config libvirt (KVM/QEMU) config . vm . provider "libvirt" do \| libvirt \| libvirt . memory = 4096 libvirt . cpus = 4 libvirt . management_network_address = "192.168.56.0/24" end # NFS pour partager les manifests config . vm . synced_folder "." , "/vagrant" , type: "nfs" , nfs_version: 4 # Le master config . vm . define "vm-master" do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.10" vm . vm . hostname = "master" end # Les 2 workers ( 1 .. 2 ). each do \| i \| config . vm . define "vm-slave- #{ i } " do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.1 #{ i } " vm . vm . hostname = "slave- #{ i } " end end # Ansible se lance automatiquement config . vm . provision "ansible" do \| ansible \| ansible . playbook = "playbook.yml" ansible . groups = { "master" => [ "vm-master" ], "workers" => [ "vm-slave-1" , "vm-slave-2" ] } end end Enter fullscreen mode Exit fullscreen mode Un vagrant up et boom, tout se monte tout seul. Le playbook : l'ordre c'est important --- # 1. Tous les nœuds en même temps - name : Setup de base hosts : k8s_cluster roles : - system-prepare # Swap off, modules kernel - docker # Docker + containerd - kubernetes # kubelet, kubeadm, kubectl # 2. Le master d'abord - name : Init master hosts : master roles : - k8s-master # kubeadm init + Flannel # 3. Les workers ensuite, un par un - name : Join workers hosts : workers serial : 1 # IMPORTANT: un à la fois roles : - k8s-worker # 4. Les trucs bonus sur le master - name : Dashboard + ArgoCD + Monitoring hosts : master roles : - k8s-dashboard - argocd - logging - metrics-server Enter fullscreen mode Exit fullscreen mode Le serial: 1 c'est crucial. J'avais essayé sans, les deux workers essayaient de join en même temps et ça partait en cacahuète. Les rôles en détail Rôle: k8s-master (le chef d'orchestre) C'est lui qui initialise le cluster. Voici les parties importantes: - name : Init cluster k8s command : kubeadm init --apiserver-advertise-address=192.168.56.10 --pod-network-cidr=10.244.0.0/16 when : not k8s_initialise.stat.exists - name : Copier config kubectl copy : src : /etc/kubernetes/admin.conf dest : /home/vagrant/.kube/config owner : vagrant group : vagrant - name : Installer Flannel (réseau pod) shell : \| kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml environment : KUBECONFIG : /home/vagrant/.kube/config - name : Générer commande join pour les workers copy : content : " kubeadm join 192.168.56.10:6443 --token {{ k8s_token.stdout }} --discovery-token-ca-cert-hash sha256:{{ k8s_ca_hash.stdout }}" dest : /vagrant/join.sh mode : ' 0755' - name : Créer fichier .master-ready copy : content : " Master initialized" dest : /vagrant/.master-ready Enter fullscreen mode Exit fullscreen mode Le fichier .master-ready c'est un flag pour dire aux workers "go, vous pouvez join maintenant". Rôle: k8s-worker (le suiveur patient) - name : Attendre que le fichier .master-ready existe wait_for : path : /vagrant/.master-ready timeout : 600 - name : Joindre le cluster shell : bash /vagrant/join.sh args : creates : /etc/kubernetes/kubelet.conf register : join_result failed_when : - join_result.rc != 0 - " 'already exists in the cluster' not in join_result.stderr" - name : Attendre que le node soit Ready shell : \| for i in {1..60}; do STATUS=$(kubectl get node $(hostname) -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}') if [ "$STATUS" = "True" ]; then exit 0 fi sleep 5 done exit 1 Enter fullscreen mode Exit fullscreen mode Le worker attend gentiment que le master soit prêt avant de faire quoi que ce soit. Les galères que j'ai rencontrées Galère #1: NFS qui marche pas Au début, le partage NFS entre l'hôte et les VMs plantait. Symptôme: mount.nfs: Connection timed out Enter fullscreen mode Exit fullscreen mode Solution: # Sur l'hôte sudo apt install nfs-kernel-server sudo systemctl start nfs-server sudo ufw allow from 192.168.56.0/24 Enter fullscreen mode Exit fullscreen mode Le firewall bloquait les connexions NFS. Classique. Galère #2: Kubeadm qui timeout Le kubeadm init prenait 10 minutes et finissait par timeout. Cause: Pas assez de RAM sur les VMs (j'avais mis 2Go). Solution: Passer à 4Go par VM. Ça bouffe mais c'est nécessaire. Galère #3: Les workers qui join pas Les workers restaient en NotReady même après le join. Cause: Flannel (le CNI) était pas encore installé sur le master. Solution: Attendre que Flannel soit complètement déployé avant de faire join les workers: - name : Attendre Flannel command : kubectl wait --for=condition=ready pod -l app=flannel -n kube-flannel --timeout=300s environment : KUBECONFIG : /etc/kubernetes/admin.conf Enter fullscreen mode Exit fullscreen mode Galère #4: Ansible qui relance tout à chaque fois Au début, chaque vagrant provision refaisait TOUT depuis zéro. Solution: Ajouter des conditions when partout: - name : Init cluster k8s command : kubeadm init ... when : not k8s_initialise.stat.exists # ← Ça sauve des vies Enter fullscreen mode Exit fullscreen mode L'idempotence c'est vraiment la base avec Ansible. Les commandes utiles au quotidien # Lancer tout cd ansible-provisioning && vagrant up # Vérifier l'état du cluster vagrant ssh vm-master -c 'kubectl get nodes' # Voir les pods vagrant ssh vm-master -c 'kubectl get pods -A' # Refaire le provisioning (sans détruire les VMs) vagrant provision # Tout péter et recommencer vagrant destroy -f && vagrant up # SSH sur le master vagrant ssh vm-master # Logs d'un pod vagrant ssh vm-master -c 'kubectl logs -n apps apicatalogue-xyz' Enter fullscreen mode Exit fullscreen mode ArgoCD et les applications Une fois le cluster monté, ArgoCD déploie automatiquement mes apps. Voici comment je déclare l'API Catalogue: apiVersion : argoproj.io/v1alpha1 kind : Application metadata : name : catalogue-manager-application namespace : argocd spec : destination : namespace : apps server : https://kubernetes.default.svc source : path : ansible-provisioning/manifests/apicatalogue repoURL : https://github.com/uha-sae53/Vagrant.git targetRevision : main project : default syncPolicy : automated : prune : true selfHeal : true Enter fullscreen mode Exit fullscreen mode ArgoCD surveille mon repo GitHub. Dès que je change un manifest, ça se déploie automatiquement. Metrics Server et HPA J'ai aussi ajouté le Metrics Server pour l'auto-scaling: - name : Installer Metrics Server shell : \| kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml environment : KUBECONFIG : /etc/kubernetes/admin.conf - name : Patcher pour ignorer TLS (dev seulement) shell : \| kubectl patch deployment metrics-server -n kube-system --type='json' \ -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/-", "value": "--kubelet-insecure-tls"}]' Enter fullscreen mode Exit fullscreen mode Avec ça, mes pods peuvent scaler automatiquement en fonction de la charge CPU/RAM. Le résultat final Après tout ça, voici ce que je peux faire: # Démarrer tout de zéro vagrant up # ⏱️ 8 minutes plus tard... # Vérifier que tout tourne vagrant ssh vm-master -c 'kubectl get pods -A' # Résultat: # NAMESPACE NAME READY STATUS # apps apicatalogue-xyz 1/1 Running # apps apiclients-abc 1/1 Running # apps apicommandes-def 1/1 Running # apps api-panier-ghi 1/1 Running # apps frontend-jkl 1/1 Running # argocd argocd-server-xxx 1/1 Running # logging grafana-yyy 1/1 Running # logging loki-0 1/1 Running # kube-system metrics-server-zzz 1/1 Running Enter fullscreen mode Exit fullscreen mode Tout fonctionne, tout est automatisé. Conclusion Ce que j'ai appris: Ansible > scripts shell (vraiment, vraiment) L'idempotence c'est pas un luxe Tester chaque rôle séparément avant de tout brancher Les workers doivent attendre le master (le serial: 1 sauve des vies) 4Go de RAM minimum par VM pour K8s Le code complet est sur GitHub: https://github.com/uha-sae53/Vagrant Des questions ? Ping moi sur Twitter ou ouvre une issue sur le repo. Et si vous galérez avec Kubernetes, vous êtes pas seuls. J'ai passé 3 semaines là-dessus, c'est normal que ce soit compliqué au début. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse BeardDemon Follow Nananère je suis très sérieux... Location Alsace Education UHA - Université Haute Alsace Work Administrateur réseau Joined Jul 19, 2024 Trending on DEV Community Hot How to Crack Any Software Developer Interview in 2026 (Updated for AI & Modern Hiring) # softwareengineering # programming # career # interview The First Week at a Startup Taught Me More Than I Expected # startup # beginners # career # learning The First Week at a Startup Taught Me More Than I Expected # startup # beginners # career # learning 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/tatyanabayramova/glaucoma-awareness-month-363o#main-content	Glaucoma Awareness Month - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com           Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis Glaucoma Vision Simulator NoCoffee vision simulator for Firefox WCAG (Web Content Accessibility Guidelines) PDF/UA (PDF for Universal Access) European standard EN 301 549 Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer \| CPACC \| IAAP Member \| Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/alifunk/why-ownership-is-the-best-certification-building-infrastructure-for-an-aws-legend-4nd5#main-content	Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Ali-Funk Posted on Jan 12           Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend # aws # community # cloud # career After 8 years in IT Operations, I made a conscious decision: I’m not just going to "learn" Cloud Security. I’m going to live it. I am currently in the middle of a full career pivot. My days are spent on foundational IT retraining, my nights are dedicated to AWS certifications and Cloud Security. But certificates are just paper if you don't apply them. I promised myself that I wouldn't use this time to just "park" and wait for a degree. I am building a "launchpad". The Project: Building a Home for Cloud Architects Recently, I had the opportunity to support Marko Sluga a true authority in the AWS world and someone I’ve looked up to for learning cloud architecture. His community needed a new home, a place to discuss complex AWS topics, share knowledge, and grow together. I volunteered to design and build the infrastructure for his new Discord Community. This wasn't just about creating channels. It was about: Designing a logical structure for discussions Implementing security best practices for community management Creating a space where knowledge can scale When It clicked for me: Validation over Certification We often obsess over passing exams (and I am grinding for them too!). But in the real world, soft skills and mindset often beat raw data retention. After the launch, Marko gave me feedback that hit harder than any "Exam Passed" badge ever could: "Ali Funk being willing to take ownership like you did is a rare trait and I am grateful for your help. You deserve every ounce of recognition!" Marko Sluga He didn't thank me for "configuring a bot." He thanked me for taking ownership. Why I aim to be an AWS Community Builder This experience clarified my path. I realized that my biggest strength isn't just configuring systems It´s enabling others. I love bridging the gap between "Old School Ops" reliability and "Cloud Native" agility I love building infrastructures where communities can thrive I love the "hybrid war" of learning and doing simultaneously This is why I have set my sights on becoming an AWS Community Builder. I want to be part of the global group of people who don't just consume cloud technology, but who actively shape how it is understood and used. I want to share my journey from the Data Center floor to the cloud architecture board, helping others who are making the same pivot. The Takeaway If you are early in your cloud journey, or pivoting like me: Don't wait for permission. Don't wait until you have 5 certs to build something. Find a problem. Fix it. Take ownership. That’s how you build a "launchpad" If you’re early in your cloud journey: build something real, even if it’s small. Like I did with a Discord Server. Run it. Break it. Fix it. Document it. That experience will stay with you longer than any exam score ." Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Ali-Funk Follow Learning in Public. Transitioning into Cloud Security. Currently wrestling with AWS CCP and the Imposter Syndrome. I am here sharing what I learn so you don't have to make the same mistakes as I did. Location Germany Work Aspiring Cloud Security Architect Joined Jan 7, 2026 More from Ali-Funk More Than a Bootcamp: Why I Chose the German 'Umschulung' Path into Tech # career # watercooler # devops # beginners LLMs are like Humans - They make mistakes. Here is how we limit them with Guardrails # aws # ai # guardrails # architecture Why I rescheduled my AWS exam today # aws # beginners # cloud # career 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://www.algolia.com/use-cases/mobile-search	Build Mobile & App Search, fast \| Algolia Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. Integrations Connect to your existing stack via pre-built libraries and APIs. Infrastructure Overview Data Centers Choose from 70+ data centers across 17 regions. Data Centers Choose from 70+ data centers across 17 regions. Security & Compliance Built for peace of mind. Security & Compliance Built for peace of mind. Solutions Industries SEE ALL Ecommerce Ecommerce B2B Commerce B2B Commerce Fashion Fashion Grocery Grocery Media Media Marketplaces Marketplaces SaaS SaaS Higher Education Higher Education Use Cases SEE ALL Documentation search Documentation search Enterprise search Enterprise search Headless commerce Headless commerce Image search Image search Mobile & App search Mobile & App search Retail Media Network Retail Media Network Site search Site search Visual search Visual search Voice search Voice search Departments Digital Experience Digital Experience Ecommerce Ecommerce Engineering Engineering Merchandising Merchandising Product Management Product Management Pricing Developers Get started Developer Hub Developer Hub Documentation Documentation Integrations Integrations UI Components UI Components Autocomplete Autocomplete Resources Code Exchange Code Exchange Engineering Blog Engineering Blog MCP MCP Discord Discord Webinars & Events Webinars & Events Quick Links Quick Start Guide Quick Start Guide For Open Source For Open Source API Status API Status Support Support Resources Discover Algolia Blog Algolia Blog Resource Center Resource Center Customer Stories Customer Stories Webinars & Events Webinars & Events Newsroom Newsroom Customers Customer Hub Customer Hub What's New What's New Knowledge Base Knowledge Base Documentation Documentation Algolia Academy Algolia Academy Professional Services Professional Services Quick Access Company Partners Support Login Logout Request demo Get started Search Algolia Close Request demo Get started Other Types Filter --> Clear All Filters Filters Looking for our logo? We got you covered! Brand guidelines Download logo pack Mobile Search Create intelligent Search & Discovery for mobile Create AI-driven mobile-native experiences with Algolia APIs for mobile websites and apps. Get a demo Start building for free ]:border-l md:[&>:nth-child(1)]:border-none md:[&>*:nth-child(4n+1)]:border-none"> 1.7+ Trillion searches every year 99.999% uptime SLA available 382% ROI according to Forrester Research 18,000+ customers across 150+ countries Easily integrate search, browse, and recommendations into your mobile applications Integrate in your iOS & Android mobile apps Developers can quickly build excellent mobile search and discovery experiences with our front-end components for  iOS ,  Android , and mobile web. Our components and UI libraries reflect the concepts, coding patterns, and  UX/UI best practices  for each framework. Build on Android Build on iOS Add voice search capabilities Web browsing is the primary action people do on their mobile devices, but voice searching is in second place. Let users easily  voice search  with native browser  speech-to-text support . And you can add voice search to your mobile apps with voice overlay for  Android  and  iOS  developers. Read more about voice search Be location focused People using mobile devices are more likely to be searching for information related to their physical location, such as a restaurant or retail store. If you want more engagement or conversions, it’s smart to serve relevant local search content and results. Whether someone is surfing the web at home, or walking around a foreign city, they’ll get relevant local mobile search results. Read your mobile searchers’ minds with analytics Our analytics features reveal what your mobile users are trying to locate, which search results they’re selecting, and how they proceed based on what they discover while searching. You can use this insight to  do things  like fine-tune search relevance, improve your app’s user interface, and decide which content or products to promote for your smartphone users.  Read more about analytics Mobile & App search and recommendations that fast to build and scale With Algolia, create personalized experiences that improve your customer journey. Increase your conversion rates, shopper and user engagement, and elevate your brand. Maximize small-screen real estate By focusing functionality on what people want when they’re on their smartphones Reduce friction And improve engagement by correcting users’ text-entry typos and spelling mistakes Help users find what they need fast With out-of-the-box search-as-you-type autocomplete with real-time results Recommended content 7 ways to get more out of Algolia search A checklist of practical, easy ways for Algolia customers to improve their search and boost conversion rates. Recommendations range from core relevance and UI design to improving search merchandising. Read more How to improve search and discoverability in eCommerce Learn how to build search, discovery, and browse foundations for headless commerce, hosted by one of Algolia's Solutions Engineers.  Read more Shopping at the edge: Solving for infinite customer experience journeys A real-life scenario of the modern-day product discovery flow. Learn best-practices from our panel of experts.  Read more See more Mobile & App Search FAQs What is mobile search? 0 Mobile search is search conducted using a mobile device, for instance, an Apple iPhone or iPad, or an Android phone. An estimated 48% of U.S. web traffic is generated by people using mobile devices (e.g., an Apple iPhone or an Android phone), according to  Statista  (2021). Globally the percentage is higher—more than 50%. More than when they're using a desktop computer or laptop, mobile users often do local searches: those related to their geographical area (for example, "near me" searches). In addition, someone entering a search query using a mobile device is likely to want relatively simple information (as opposed to needing to conduct an online search for data on an information-intensive web page), such as the distance to a nearby pizza restaurant or which neighborhood retailers carry a product they've decided to buy using Google search or Amazon. There are various types of mobile apps. Some mobile search engines provide answers to questions (e.g., when someone asks for the local weather forecast). Some make personalized product recommendations based on entered search terms and collected shopper preferences. Some give directions, hail rides, or let people search for news articles. Some include the option of voice search, allowing users to speak their search queries. Mobile search presents unique challenges to mobile-app designers, product marketers, and others because mobile device screens are obviously much smaller than those on desktop and laptop PCs. The mobile search experience can be optimized to overlook typos caused while trying to tap keys on a tiny screen, as well as to offer mobile users shortcuts by suggesting queries based on the text they seem to be entering. Mobile search is a dynamic field that is continually changing as new technology, such as the ability to make AI-related recommendations and personalize the shopping experience in an ecommerce app, become available. Voice search on a mobile device is another new option that's popular with people who get impatient with trying to tap letters on a tiny screen. Many companies and organizations have yet to optimize their apps for mobile search, but as more do, and their mobile users are delighted, the practice of using mobile devices to search is sure to become an even more ingrained part of everyday American life. How many searches happen on mobile? 0 According to  Statista  (2021) about 48% of U.S. web traffic is generated by people using mobile devices (e.g., an Apple iPhone or an Android phone). For the world as a whole, the percentage is higher—more than 50%. An older report (2016), "Mobile Search: Topics and Themes" (Hitwise), concluded that almost 60% of all searches are done on mobile devices. This study also found that the most popular sector for a mobile search was the food and beverage category. This makes sense given that people often use their mobile phones while out in a town or a particular geographical area to do a local search for a restaurant near them. What percentage of people look at websites on their phone? 0 According to  Statista  (2021), about 50% of the world's web traffic is generated by people using mobile devices, such as an Apple iPhone or an Android phone. This percentage has been consistent since early 2017. Watching movies and videos (via mobile apps Netflix, Tencent, or Amazon Prime from the Apple app store), surfing social media sites, and emailing were found to be the most popular things for mobile users to do on their devices. What is the best search pattern for mobile phones? 0 In a book called  Mobile Design Pattern Gallery  (2014), author Theresa Neil focuses on the value of autocompletion in enhancing basic searching on a mobile phone. Autocomplete functionality suggests search queries as a user enters search terms on their mobile device; when the search they want appears, they can simply tap it. The final touch in terms of usefulness: providing a mobile search engine progress indicator, such as a ticking clock or the word "Searching...". Another popular mobile app pattern for maximizing small-screen real estate during a mobile search is faceted search, which lets the searcher narrow their results by applying filters, typically by selecting options provided in a "tray"-style overlay. Faceted search is often utilized by retailers in ecommerce (and the mobile equivalent, m-commerce) and by travel service providers, as well as in online search tools on media websites. One relatively new application for searching on mobile devices is voice search. According to eMarketer, in 2019, 40% of all U.S. Internet users were using voice search, which has grown more popular, albeit slowly. Try the AI search that understands Get a demo Start Free Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://www.highlight.io/docs/getting-started/browser/remix	Remix Star us on GitHub Star Docs Sign in Sign up Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Menu Highlight Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Getting Started / Browser / Remix Using highlight.io with Remix Learn how to set up highlight.io with your Remix application. 1 Install the npm package & SDK. Install the @highlight-run/remix npm package in your terminal. # with npm npm install @highlight-run/remix # with yarn yarn add @highlight-run/remix # with pnpm pnpm add @highlight-run/remix 2 Initialize the client SDK. Grab your project ID from app.highlight.io/setup , inject it into your client application using the loader export from your root.tsx file, and set the projectID in the <HighlightInit/> component. // app/root.tsx import { useLoaderData } from '@remix-run/react' import { HighlightInit } from '@highlight-run/remix/client' import { json } from '@remix-run/node' export async function loader() { return json({ ENV: { HIGHLIGHT_PROJECT_ID: process.env.HIGHLIGHT_PROJECT_ID, }, }) } export default function App() { const { ENV } = useLoaderData() return ( <html lang="en"> <HighlightInit projectId={ENV.HIGHLIGHT_PROJECT_ID} serviceName="my-remix-frontend" tracingOrigins networkRecording={{ enabled: true, recordHeadersAndBody: true }} /> {/* Render head, body, <Outlet />, etc. */} </html> ) } 3 Export a custom ErrorBoundary handler (optional) The ErrorBoundary component wraps your component tree and catches crashes/exceptions from your react app. When a crash happens, your users will be prompted with a modal to share details about what led up to the crash. Read more here . // app/components/error-boundary.tsx import { isRouteErrorResponse, useRouteError } from '@remix-run/react' import { ReportDialog } from '@highlight-run/remix/report-dialog' export function ErrorBoundary() { const error = useRouteError() if (isRouteErrorResponse(error)) { return ( <div> <h1> {error.status} {error.statusText} </h1> <p>{error.data}</p> </div> ) } else if (error instanceof Error) { return ( <div> <script src="https://unpkg.com/highlight.run"></script> <script dangerouslySetInnerHTML={{ __html: ` H.init('${process.env.HIGHLIGHT_PROJECT_ID}'); `, }} /> <h1>Error</h1> <p>{error.message}</p> <p>The stack trace is:</p> <pre>{error.stack}</pre> <ReportDialog /> </div> ) } else { return <h1>Unknown Error</h1> } } // app/root.tsx export { ErrorBoundary } from '~/components/error-boundary' 4 Identify users. Identify users after the authentication flow of your web app. We recommend doing this in a useEffect call or in any asynchronous, client-side context. The first argument of identify will be searchable via the property identifier , and the second property is searchable by the key of each item in the object. For more details, read about session search or how to identify users . import { H } from '@highlight-run/remix/client'; function RenderFunction() { useEffect(() => { // login logic... H.identify('jay@highlight.io', { id: 'very-secure-id', phone: '867-5309', bestFriend: 'jenny' }); }, []) return null; // Or your app's rendering code. } 5 Initialize the server SDK. Send errors to Highlight from your Remix server using the entry.server.tsx file. // app/entry.server.tsx import { H, HandleError } from '@highlight-run/remix/server' const nodeOptions = { projectID: process.env.HIGHLIGHT_PROJECT_ID } export const handleError = HandleError(nodeOptions) // Handle server requests 6 Verify installation Check your dashboard for a new session. Make sure to remove the Status is Completed filter to see ongoing sessions. Don't see anything? Send us a message in our community and we can help debug. 7 More Remix features? See our fullstack Remix guide for more information on how to use Highlight with Remix. Next.js Vue.js [object Object]	2026-01-13T08:48:55
https://www.highlight.io/docs/general/integrations/height-integration	Height Integration Star us on GitHub Star Docs Sign in Sign up General Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Menu Highlight Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Highlight Docs / Integrations / Height Integration Height Integration When you enable the Height integration, Highlight will allow creating Tasks from the session replay and errors viewer. Track bugs or enhancements for your app as you triage frontend and backend errors or watch your users' replays. To get started, go to the integrations and click the "Connect" button in the Height section. Features Comments can create a Height task filled out with the body of the comment and link back to the Session. Grouping Errors shows a shortcut to create a Height task pre-populated with the error linking to the full context of how the error occurred. Alerts Intercom Integration Community / Support Suggest Edits? Follow us! [object Object]	2026-01-13T08:48:55
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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Follow User actions Art light Trust yourself🌞your capabilities are your true power. ❤Telegram - ✔lighthouse4661 ❤Discord - ✔lighthouse4661 Joined Joined on Nov 21, 2025 Email address art.miclight@gmail.com github website twitter website Pronouns He/him Work CTO More info about @art_light Badges 4 Week Community Wellness Streak Keep contributing to discussions by posting at least 2 comments per week for 4 straight weeks. Unlock the 8 Week Badge next. Got it Close 2 Week Community Wellness Streak Keep the community conversation going! Post at least 2 comments for 2 straight weeks and unlock the 4 Week Badge. Got it Close 1 Week Community Wellness Streak For actively engaging with the community by posting at least 2 comments in a single week. 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Got it Close Skills/Languages Python, TypeScript, PyTorch, Transformers, vLLM, SGLang, FastAPI, React, Next.js, Vite, Rust, Zustand, Redux Toolkit, TanStack Query, Tailwind, CSS architecture, component systems Currently learning Mixture-of-Experts (MoE) architectures LoRA fine-tuning with quantized weights (Q-LoRA, GPTQ, AWQ) Continuous batching inference engines (vLLM, SGLang) Available for I’m looking for a reliable, talented collaborator who’s interested in long-term growth and building something truly impactful together with my technical support Post 9 posts published Comment 302 comments written Tag 31 tags followed We Didn’t “Align” — We Argued (and Shipped a Better System) Art light Art light Art light Follow Jan 11 We Didn’t “Align” — We Argued (and Shipped a Better System) # discuss # career # programming # developer 29 reactions Comments 6 comments 2 min read Want to connect with Art light? Create an account to connect with Art light. 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https://www.highlight.io/docs/general/product-features/dashboards/overview	Dashboards Star us on GitHub Star Docs Sign in Sign up General Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Menu Highlight Docs Welcome to highlight.io Get Started Roadmap Company Values Compliance & Security Open Source Contributing Overview GraphQL Backend Frontend (app.highlight.io) Landing Site (highlight.io) Documentation End to End SDK Example Apps Adding an SDK Application Architecture GitHub Code Spaces Code Style Good First Issues Self-hosting Self-hosted [Dev] Self-hosted [Hobby] Self-hosted [Enterprise] Telemetry Our Competitors Product Philosophy Product Features Session Replay Overview Canvas & Iframe Dev-tool Window Recording Tracking Users & Recording Events Filtering Sessions GraphQL Live Mode Performance Impact Player Session Caching Rage Clicks Request Proxying Session Search Extracting the Session URL Session Search Deep Linking Shadow Dom + Web Components Error Monitoring Overview Enhancing Errors with GitHub Error Search Filtering Errors Grouping Errors Managing Errors Manually Reporting Errors Sourcemaps General Features Overview Alerts Comments Digests Environments Search Segments Services Webhooks Logging Overview Log Alerts Log Search Tracing Overview Trace Search Dashboards Overview Dashboard Management Metrics Tutorials Service Latency Web Vitals & Page Speed User Engagement User Analytics Graphing Drilldown Event Search Dashboard Variables SQL Editor Metrics (beta) Overview Frequently Asked Questions. Integrations Integrations Overview Amplitude Integration ClickUp Integration Discord Integration Electron Support Front Integration GitHub Integration Grafana Integration Overview Setup Dashboards Alerts Height Integration Intercom Integration Jira Integration LaunchDarkly Integration Linear Integration Mixpanel Integration Nuxt Integration Pendo Integration Segment Integration Slack Integration Vercel Integration WordPress Plugin Highlight.io Changelog Overview Changelog 12 (02/17) Changelog 13 (02/24) Changelog 14 (03/03) Changelog 15 (03/11) Changelog 16 (03/19) Changelog 17 (04/07) Changelog 18 (04/26) Changelog 19 (05/22) Changelog 20 (06/06) Changelog 21 (06/21) Changelog 22 (08/07) Changelog 23 (08/22) Changelog 24 (09/11) Changelog 25 (10/03) Changelog 26 (11/08) Changelog 27 (12/22) Changelog 28 (3/6) Changelog 29 (4/2) Getting Started Getting Started with Highlight Fullstack Mapping Browser React.js Next.js Remix Vue.js Angular Gatsby.js SvelteKit Electron highlight.run SDK Overview Canvas & WebGL Console Messages Content-Security-Policy Identifying Users iframe Recording Monkey Patches Browser OpenTelemetry Persistent Asset Storage Privacy Proxying Highlight React.js Error Boundary Recording Network Requests and Responses Recording WebSocket Events Salesforce Lightning Web Components (LWC) Data Export Sourcemap Configuration Tracking Events Troubleshooting Upgrading Highlight Versioning Sessions & Errors Other React Native (beta) Server Go Overview chi Echo Fiber Gin GORM gqlgen Logrus Manual Tracing gorilla mux JS Overview Apollo AWS Lambda Cloudflare Workers Express.js Firebase Hono Nest.js Next.js Node.js Pino tRPC Winston Python Overview AWS Lambda Azure Functions Django FastAPI Flask Google Cloud Functions Loguru Other Frameworks Python AI / LLM Libraries Python Libraries Ruby Overview Other Frameworks Ruby on Rails Rust Overview actix-web No Framework Hosting Providers Overview Metrics in AWS Logging in AWS Logging in Azure Fly.io NATS Log Shipper Logging in GCP Heroku Log Drain Render Log Stream Logging in Trigger.dev Vercel Log Drain Elixir Overview Elixir App Java: All Frameworks PHP: All Frameworks C# .NET ASP C# .NET 4 ASP Docker / Docker Compose File Fluent Forward curl OpenTelemetry Protocol (OTLP) Syslog RFC5424 Systemd / Journald Native OpenTelemetry Overview Error Monitoring Logging Tracing Browser Instrumentation Metrics Fullstack Frameworks Overview Next.js Fullstack Overview Next.js Page Router Guide Next.js App Router Guide Edge Runtime Advanced Config Remix Walkthrough Self Host & Local Dev Overview Development deployment guide. Integrations Microsoft Teams self-hosted Hobby deployment guide. Traefik SSL Proxying. Docs Home SDK Client SDK API Reference Cloudflare Worker SDK API Reference Go SDK API Reference Hono SDK API Reference Java SDK API Reference Next.JS SDK API Reference Node.JS SDK API Reference Python SDK API Reference Ruby SDK API Reference Rust SDK API Reference Docs / Highlight Docs / Product Features / Dashboards / Dashboards Dashboards Dashboards are representations of your sessions, errors, logs, and traces that you can graph, analyze, and monitor. When understanding your business or application, the reality is that a lot of the data you need is already in highlight.io. Tutorial Videos Learn more about how to use our dashboards product with the following tutorial videos: How-to: Service Latency Learn how to measure and analyze service latency for optimal performance. How-to: Web Vitals & Page Speed Discover how to optimize your website's web vitals and page speed for a better user experience. How-to: User Engagement Explore methods to track and improve user engagement metrics for enhanced customer satisfaction. You can find our dashboards product at app.highlight.io/dashboards . Features Read more about the dashboard features below: Dashboard management. Create, find, and manage dashboards. Creating / editing a graph. Create and edit graphs in your dashboards. Drilldown Take a closer look at the underlying data. Variables Use variables to reuse filters across many graphs in a dashboard. Search Make the most of the search capabilities. Dashboards Dashboard Management Community / Support Suggest Edits? Follow us! [object Object]	2026-01-13T08:48:55
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Right menu CloudWatch Investigations: Your AI-Powered Troubleshooting Sidekick vikasbanage vikasbanage vikasbanage Follow for AWS Community Builders Jan 4 CloudWatch Investigations: Your AI-Powered Troubleshooting Sidekick # aws # genai # cloud # sre 1 reaction Comments Add Comment 4 min read AWS Control Tower Alternatives: From Console to Code Danny Steenman Danny Steenman Danny Steenman Follow for AWS Community Builders Dec 30 '25 AWS Control Tower Alternatives: From Console to Code # aws # controltower # landingzone # infrastructureascode Comments Add Comment 17 min read My Experience Using the BMAD Framework on a Personal Project (Patience Required) Dan Gurgui Dan Gurgui Dan Gurgui Follow Dec 30 '25 My Experience Using the BMAD Framework on a Personal Project (Patience Required) # aws # architecture # engineering # testing Comments Add Comment 8 min read AWS in the AI era: Bedrock, SageMaker, and the enterprise-first tradeoff Dan Gurgui Dan Gurgui Dan Gurgui Follow Dec 30 '25 AWS in the AI era: Bedrock, SageMaker, and the enterprise-first tradeoff # aws # architecture # engineering # kubernetes Comments Add Comment 8 min read The Last Deploy of 2025: Exposing my Lambda to the World with API Gateway Eric Rodríguez Eric Rodríguez Eric Rodríguez Follow Dec 31 '25 The Last Deploy of 2025: Exposing my Lambda to the World with API Gateway # aws # apigateway # serverless # python Comments Add Comment 1 min read My Perspective on Amazon Inspector's 2025 Updates for DevSecOps andre aliaman andre aliaman andre aliaman Follow for AWS Community Builders Dec 31 '25 My Perspective on Amazon Inspector's 2025 Updates for DevSecOps # aws # devsecops # cicd # security Comments Add Comment 4 min read Implementing Container Signing in Your CI/CD Pipeline: A DevSecOps Approach with AWS andre aliaman andre aliaman andre aliaman Follow for AWS Community Builders Dec 31 '25 Implementing Container Signing in Your CI/CD Pipeline: A DevSecOps Approach with AWS # cicd # cybersecurity # aws # devsecops Comments Add Comment 7 min read DEV Track Spotlight: Building Scalable, Self-Orchestrating AI Workflows with A2A and MCP (DEV415) Gunnar Grosch Gunnar Grosch Gunnar Grosch Follow for AWS Jan 4 DEV Track Spotlight: Building Scalable, Self-Orchestrating AI Workflows with A2A and MCP (DEV415) # aws # ai # mcp # serverless 1 reaction Comments Add Comment 12 min read Identify AWS Compute Services Ntombizakhona Mabaso Ntombizakhona Mabaso Ntombizakhona Mabaso Follow for AWS Community Builders Jan 4 Identify AWS Compute Services # aws # cloud # cloudcomputing # cloudpractitioner 1 reaction Comments Add Comment 3 min read Lifecycle rules in Terraform. 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https://dev.to/mohammadidrees/thinking-in-first-principles-how-to-question-an-async-queue-based-design-5cf1#step-2-introduce-time-what-happens-later	Thinking in First Principles: How to Question an Async Queue–Based Design - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Mohammad-Idrees Posted on Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Async queues are one of the most commonly suggested “solutions” in system design interviews. But many candidates jump straight to using queues without understanding: What problems they actually solve What new problems they introduce How to systematically discover those problems This post teaches a first-principles questioning process you can apply to any async queue design—without assuming prior knowledge. Why This Matters In interviews, interviewers are not evaluating whether you know Kafka, SQS, or RabbitMQ. They are evaluating whether you can: Reason about time Reason about failure Reason about order Reason about user experience Async queues change all four. What “First Principles” Means Here First principles means: We do not start with solutions We do not assume correctness We ask basic, unavoidable questions that every system must answer Async queues feel correct because they remove blocking—but correctness is not guaranteed by intuition. The Reference Mental Model (Abstract) We will reason about this abstract pattern , not a specific product: User → API → Storage → Queue → Worker → Storage Enter fullscreen mode Exit fullscreen mode No domain assumptions. This could be: Chat messages Emails Payments Notifications Image processing The questioning process stays the same. Step 1: The Root Question (Always Start Here) What is the system responsible for completing before it can respond? This is the most important question in system design. Why? Because it defines: Request boundaries Latency expectations Responsibility In an async queue design, the implicit answer is: “The request is complete once the work is enqueued.” This is different from synchronous designs, where the request completes after work finishes. So far, this seems good. Step 2: Introduce Time (What Happens Later?) Now ask: Which part of the work happens after the request is done? Answer: The worker processing This leads to an important realization: The system has split work across time Time separation is powerful—but it creates new questions. Step 3: Causality Question (Identity Across Time) Once work happens later, we must ask: How does the system know which output belongs to which input? This question always appears when time is decoupled. Typical answer: IDs in the job payload (request ID, entity ID) This introduces a new invariant: Each input must produce exactly one correct output Now we test whether the system can guarantee this. Step 4: Failure Question (The Queue Reality) Now ask the most important async-specific question: What happens if the worker crashes mid-processing? Realistic answers: The job is retried The work may run again The output may be produced twice This leads to a critical realization: Async queues are usually at-least-once , not exactly-once This is not a tooling issue. It is a fundamental property of distributed systems . Step 5: Duplication Question (Invariant Violation) Now ask: What happens if the same job is processed twice? Consequences: Duplicate outputs Duplicate side effects Conflicting state This violates the earlier invariant: “Exactly one output per input” At this point, we have discovered a correctness problem , not a performance problem. Step 6: Ordering Question (Time Without Synchrony) Now consider multiple inputs. Ask: What defines the order of processing? Important realization: Queue order ≠ business order Different workers process at different speeds Later inputs may finish first Now ask: Does correctness depend on order? If yes (and many systems do): Async queues alone are insufficient This problem emerges only when you question order explicitly. Step 7: Visibility Question (User Experience) Now switch perspectives. How does the user know the work is finished? Possible answers: Polling Guessing Timeouts Each answer reveals a problem: Polling wastes resources Guessing is unreliable Timeouts fail under load This violates a core system principle: Users should not wait blindly Case Study: A Simple Example (Problem-Agnostic) Imagine a system where users upload photos to be processed. Flow: User uploads photo API stores metadata Job is enqueued Worker processes photo Result is stored Now apply the questions: When does the upload request complete? → After enqueue What if the worker crashes? → Job retried What if it runs twice? → Two processed images What if two photos depend on order? → Order not guaranteed How does the user know processing is done? → Polling None of these issues are about images. They are about time, failure, identity, and visibility . What Async Queues Actually Trade Async queues solve one problem: They remove blocking from the request path But they introduce others: Solved Introduced Blocking Duplicate work Latency coupling Ordering ambiguity Resource exhaustion Completion uncertainty This is not bad. It just must be understood and handled . The One-Page Interview Checklist (Memorize This) For any async queue design , ask these five questions: What completes the request? What runs later? What happens if it runs twice? What defines order? How does the user observe completion? If you cannot answer all five clearly, the design is incomplete. Final Mental Model Async systems remove time coupling but destroy causality by default Your job as an engineer is not to “use queues” Your job is to restore correctness explicitly That is what interviewers are looking for. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Mohammad-Idrees Follow Joined Mar 16, 2023 More from Mohammad-Idrees How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://stackoverflow.com/users/385378/nikic	User NikiC - Stack Overflow Skip to main content Stack Overflow About Products For Teams Stack Internal Implement a knowledge platform layer to power your enterprise and AI tools. Stack Data Licensing Get access to top-class technical expertise with trusted & attributed content. Stack Ads Connect your brand to the world’s most trusted technologist communities. Releases Keep up-to-date on features we add to Stack Overflow and Stack Internal. About the company Visit the blog s-popover#show" data-s-popover-placement="bottom-start" /> Loading… current community Stack Overflow help chat Meta Stack Overflow your communities Sign up or log in to customize your list. more stack exchange communities company blog Log in Sign up Home Questions AI Assist Tags Challenges Chat Articles Users Companies Collectives Communities for your favorite technologies. Explore all Collectives Stack Internal Stack Overflow for Teams is now called Stack Internal . Bring the best of human thought and AI automation together at your work. Try for free Learn more Stack Internal Bring the best of human thought and AI automation together at your work. Learn more Collectives™ on Stack Overflow Find centralized, trusted content and collaborate around the technologies you use most. Learn more about Collectives Stack Internal Knowledge at work Bring the best of human thought and AI automation together at your work. Explore Stack Internal NikiC Member for 15 years, 6 months Last seen this week Twitter GitHub nikic.github.io Berlin, Germany Profiles Meta user Network profile Profile Activity Stats 102,157 reputation 7.0m reached 600 answers 25 questions Loading… Communities View all Stack Overflow 102.2k Meta Stack Exchange 964 Software Engineering 643 Physics 342 Code Review 156 About PHP core developer working at JetBrains. Studied physics and computer science at TU Berlin. Blog Twitter GitHub PHP-Parser : A PHP parser written in PHP FastRoute : Fast request router for PHP scalar_objects : Extension adding support for method calls on primitive types in PHP iter : Iteration primitives using generators Contact mail: [email protected] Read more Badges View all badges 39 gold badges   php Sep 13, 2011   Marshal Jan 20, 2012   Publicist × 4 Dec 13, 2019 195 silver badges   Outspoken Aug 22, 2011   Pundit Feb 5, 2011   Deputy May 7, 2011 226 bronze badges   oop Apr 4, 2015   regex Sep 16, 2011   Synonymizer Jul 8, 2011 Top tags View all tags php 8,915 Score 603 Posts 96 Posts % php-internals 1,999 Score 18 Posts 3 Posts % regex 428 Score 69 Posts 11 Posts % mysql 411 Score 35 Posts 6 Posts % arrays 253 Score 48 Posts 8 Posts % string 245 Score 21 Posts 3 Posts % Top posts View all questions , answers , and articles All Questions Answers Articles Score Newest answer 1837 How does PHP 'foreach' actually work? Feb 13, 2013 answer 1205 PHP \| define() vs. const Jul 7, 2010 answer 577 How to check for null in Twig? Dec 23, 2010 answer 275 Import file size limit in PHPMyAdmin Oct 18, 2010 answer 238 is_null($x) vs $x === null in PHP Nov 22, 2011 answer 215 How to access class constants in Twig? Sep 30, 2011 answer 211 Type-juggling and (strict) greater/lesser-than comparisons in PHP Apr 4, 2013 question 182 Input placeholders for Internet Explorer Apr 2, 2011 answer 153 PHP: Split string Mar 1, 2011 answer 149 How to check if $_GET is empty? Aug 4, 2010 Top Meta posts 0 1 10 Synonyms for PHP Top network posts View all network posts 27 How important do you think IE-friendliness is? 24 Does a wing in a potential flow have lift? 21 Is using 'heading' Markdown okay in answers? 20 Lower the amount of reputation needed to comment 5 Allow placing caret only on first position in title input field Stack Overflow Questions Help Chat Business Stack Internal Stack Data Licensing Stack Ads Company About Press Work Here Legal Privacy Policy Terms of Service Contact Us cookie-settings#toggle" class="s-btn s-btn__link py4 js-gps-track -link" data-gps-track="footer.click({ location: 4, link: 38 })" data-consent-popup-loader="footer"> Cookie Settings Cookie Policy Stack Exchange Network Technology Culture & recreation Life & arts Science Professional Business API Data Blog Facebook Twitter LinkedIn Instagram Site design / logo © 2026 Stack Exchange Inc; user contributions licensed under CC BY-SA . rev 2026.1.12.38533	2026-01-13T08:48:55
https://learn.interviewkickstart.com/privacy-policy	Privacy Policy \| Interview Kickstart Skip to content Our January 2026 cohorts are filling up quickly. Join our free webinar to uplevel your career. Register for Webinar About us Why us Instructors Reviews Cost FAQ Contact Blog Register for Webinar Register for our webinar Privacy Policy This Privacy Policy governs the manner in which Interview Kickstart collects, uses, maintains and discloses information collected from users (each, a “User”) of the https://interviewkickstart.com website (“Site”). This privacy policy applies to the Site and all products and services offered by Interview Kickstart. Personal identification information We may collect personal identification information from Users in a variety of ways, including, but not limited to, when Users visit our site, fill out a form, and in connection with other activities, services, features or resources we make available on our Site. 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https://dev.to/tatyanabayramova/glaucoma-awareness-month-363o#learn-more-about-needs-of-people-with-glaucoma	Glaucoma Awareness Month - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com           Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis Glaucoma Vision Simulator NoCoffee vision simulator for Firefox WCAG (Web Content Accessibility Guidelines) PDF/UA (PDF for Universal Access) European standard EN 301 549 Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer \| CPACC \| IAAP Member \| Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/t/jokes/page/3	jokes Page 3 - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close jokes Follow Hide plz post the lols Create Post submission guidelines no spam don't be offensive (sexist, racist, homophobic, crude, etc.), the DEV code of conduct is still in place! make the jokes programming related-ish Older #jokes posts 1 2 3 4 5 6 7 8 9 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Jun 9 '25 Meme Monday # discuss # watercooler # jokes 66 reactions Comments 85 comments 1 min read Too true... Austin Rizer Austin Rizer Austin Rizer Follow May 20 '25 Too true... # jokes # webdev Comments Add Comment 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Jun 2 '25 Meme Monday # discuss # jokes # watercooler 54 reactions Comments 81 comments 1 min read True story Gregory Chris Gregory Chris Gregory Chris Follow May 19 '25 True story # jokes # programming # funny 1 reaction Comments Add Comment 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow May 26 '25 Meme Monday # discuss # watercooler # jokes 82 reactions Comments 103 comments 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow May 19 '25 Meme Monday # discuss # watercooler # jokes 63 reactions Comments 119 comments 1 min read Accidentally Building Cluster OS - Part 1 - How It All Started Oleksandr Hulyi Oleksandr Hulyi Oleksandr Hulyi Follow Jun 7 '25 Accidentally Building Cluster OS - Part 1 - How It All Started # jokes # linux # archlinux # devops 1 reaction Comments 1 comment 3 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow May 12 '25 Meme Monday # jokes # watercooler # discuss 64 reactions Comments 121 comments 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow May 5 '25 Meme Monday # discuss # watercooler # jokes 57 reactions Comments 80 comments 1 min read Programming joke Anonymous Anonymous Anonymous Follow May 22 '25 Programming joke # jokes # programming # darkmode Comments 1 comment 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Apr 28 '25 Meme Monday # watercooler # discuss # jokes 41 reactions Comments 80 comments 1 min read Tried printing 'Hello' in Malbolge... Yejju Sathya Sai Yejju Sathya Sai Yejju Sathya Sai Follow Apr 14 '25 Tried printing 'Hello' in Malbolge... # jokes # programming # malbolge Comments Add Comment 1 min read API in Mini-Micro Kartik Patel Kartik Patel Kartik Patel Follow May 16 '25 API in Mini-Micro # jokes # miniscript # minimicro # api 1 reaction Comments 1 comment 3 min read A Star Wars inspired dating app - my FIRST Hackathon experience WLeah WLeah WLeah Follow Jun 4 '25 A Star Wars inspired dating app - my FIRST Hackathon experience # discuss # jokes # beginners # learning 7 reactions Comments 20 comments 2 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Apr 21 '25 Meme Monday # discuss # watercooler # jokes 33 reactions Comments 93 comments 1 min read RAM – The Forgetful Girl, Loyal Yet Tragic Phuc Nguyen Phuc Nguyen Phuc Nguyen Follow Apr 6 '25 RAM – The Forgetful Girl, Loyal Yet Tragic # jokes # cpp # devjournal Comments Add Comment 2 min read The Compiler – A Grumpy and Irresponsible Translator Phuc Nguyen Phuc Nguyen Phuc Nguyen Follow Apr 6 '25 The Compiler – A Grumpy and Irresponsible Translator # jokes # cpp # devjournal Comments Add Comment 2 min read Professional Programmer Proves Prolog Prolongs Productivity Timothy Foster Timothy Foster Timothy Foster Follow Apr 1 '25 Professional Programmer Proves Prolog Prolongs Productivity # jokes # prolog 1 reaction Comments Add Comment 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Apr 14 '25 Meme Monday # jokes # watercooler # discuss 32 reactions Comments 64 comments 1 min read April 1st: The Nuclear Pranks Only Real Developers Will Respect (and Regret) HotfixHero HotfixHero HotfixHero Follow Apr 1 '25 April 1st: The Nuclear Pranks Only Real Developers Will Respect (and Regret) # jokes # devlive # softwaredevelopment # softwareengineering 1 reaction Comments Add Comment 2 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Apr 7 '25 Meme Monday # discuss # jokes # watercooler 63 reactions Comments 92 comments 1 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Mar 31 '25 Meme Monday # discuss # jokes # watercooler 78 reactions Comments 92 comments 1 min read You're Not a Programmer Until... Cesar Aguirre Cesar Aguirre Cesar Aguirre Follow Mar 24 '25 You're Not a Programmer Until... # watercooler # discuss # programming # jokes 141 reactions Comments 64 comments 3 min read Meme Monday Ben Halpern Ben Halpern Ben Halpern Follow Mar 24 '25 Meme Monday # discuss # jokes # watercooler 64 reactions Comments 84 comments 1 min read Introducing HTML++ – The Future of Web Development ronynn ronynn ronynn Follow Apr 1 '25 Introducing HTML++ – The Future of Web Development # jokes # programming # discuss # webdev Comments Add Comment 1 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23563#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Career Follow Hide This tag is for anything relating to careers! Job offers, workplace conflict, interviews, resumes, promotions, etc. Create Post submission guidelines All articles and discussions should relate to careers in some way. Pretty much everything on dev.to is about our careers in some way. Ideally, though, keep the tag related to getting, leaving, or maintaining a career or job. about #career A career is the field in which you work, while a job is a position held in that field. Related tags include #resume and #portfolio as resources to enhance your #career Older #career posts 10 11 12 13 14 15 16 17 18 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu The Vibe Coding Hangover Is Real: What Nobody Tells You About AI-Generated Code in Production Paul Courage Labhani Paul Courage Labhani Paul Courage Labhani Follow Jan 8 The Vibe Coding Hangover Is Real: What Nobody Tells You About AI-Generated Code in Production # ai # webdev # programming # career 11 reactions Comments 6 comments 6 min read The Unwritten Rubric: Why Senior Engineers Fail "Google SRE" Interviews Ace Interviews Ace Interviews Ace Interviews Follow Dec 17 '25 The Unwritten Rubric: Why Senior Engineers Fail "Google SRE" Interviews # google # interview # career # devops Comments Add Comment 5 min read Unfortunately, I have to close my daily.dev account because of my own mistake Muhammad Usman Muhammad Usman Muhammad Usman Follow Dec 31 '25 Unfortunately, I have to close my daily.dev account because of my own mistake # discuss # webdev # career # learning 5 reactions Comments 6 comments 4 min read The Tanegashima Shift: The Tragedy and the Ascension of the Samurai Coder Quan Nguyen Quan Nguyen Quan Nguyen Follow Dec 16 '25 The Tanegashima Shift: The Tragedy and the Ascension of the Samurai Coder # ai # softwaredevelopment # career # history Comments Add Comment 6 min read Mastering Data Science Skills for Beginners and Aspiring Analysts Excellence Academy Excellence Academy Excellence Academy Follow Dec 17 '25 Mastering Data Science Skills for Beginners and Aspiring Analysts # beginners # career # learning # datascience Comments Add Comment 3 min read Se você se sente perdido como dev leia esse texto Augusto Galego Augusto Galego Augusto Galego Follow Dec 18 '25 Se você se sente perdido como dev leia esse texto # beginners # career # motivation 11 reactions Comments Add Comment 5 min read The Great Tech Reshuffle: AI-Driven Layoffs and the Golden Age of Specialized Funding DataFormatHub DataFormatHub DataFormatHub Follow Dec 17 '25 The Great Tech Reshuffle: AI-Driven Layoffs and the Golden Age of Specialized Funding # news # career # technology # software Comments Add Comment 6 min read Junior Broken Feedback Loop John Mitchell John Mitchell John Mitchell Follow Dec 17 '25 Junior Broken Feedback Loop # discuss # beginners # career # learning Comments Add Comment 1 min read I Built an AI-Powered Job Application Factory (And You Can Too) Henry Ohanga Henry Ohanga Henry Ohanga Follow Jan 7 I Built an AI-Powered Job Application Factory (And You Can Too) # ai # productivity # career # careerdevelopment 1 reaction Comments Add Comment 5 min read I Reviewed 50 Junior Developer Resumes — Here’s What Actually Works Resumemind Resumemind Resumemind Follow Jan 9 I Reviewed 50 Junior Developer Resumes — Here’s What Actually Works # beginners # career # codenewbie Comments 3 comments 2 min read Most Engineering Problems Are Communication Problems Shamim Ali Shamim Ali Shamim Ali Follow Jan 9 Most Engineering Problems Are Communication Problems # coding # community # career Comments Add Comment 1 min read From Scripter to Architect in the Age of AI Pedro Arantes Pedro Arantes Pedro Arantes Follow for Terezinha Tech Operations Dec 17 '25 From Scripter to Architect in the Age of AI # ai # career # architecture Comments Add Comment 3 min read How Pre-Sales Techies can use BANT to qualify opportunities effectively Sarah Lean 🏴󠁧󠁢 Sarah Lean 🏴󠁧󠁢 Sarah Lean 🏴󠁧󠁢 Follow Dec 16 '25 How Pre-Sales Techies can use BANT to qualify opportunities effectively # career Comments Add Comment 3 min read Don't kill the bearer of bad news marian-varga marian-varga marian-varga Follow Dec 15 '25 Don't kill the bearer of bad news # discuss # management # leadership # career Comments 1 comment 3 min read Why job boards are failing UX/UI designers (and what works better today) Alizetihr – Tech Talent Scouting Alizetihr – Tech Talent Scouting Alizetihr – Tech Talent Scouting Follow Dec 16 '25 Why job boards are failing UX/UI designers (and what works better today) # uxdesign # career # opensource # github Comments 1 comment 1 min read I Stopped Chasing New Frameworks. My Code Got Better Gelo Gelo Gelo Follow Jan 5 I Stopped Chasing New Frameworks. My Code Got Better # programming # learning # career # softwaredevelopment 27 reactions Comments 1 comment 2 min read Stop Writing Comments: Why Senior Devs Hate "Stale Lies" Doogal Simpson Doogal Simpson Doogal Simpson Follow Dec 19 '25 Stop Writing Comments: Why Senior Devs Hate "Stale Lies" # beginners # cleancode # javascript # career Comments Add Comment 3 min read Inside Google Jobs Series (Part 11): Cross-Domain & Payment Roles jackma jackma jackma Follow Dec 14 '25 Inside Google Jobs Series (Part 11): Cross-Domain & Payment Roles # programming # career Comments Add Comment 20 min read Profile MD. ANAWAR HOSSAIN MD. ANAWAR HOSSAIN MD. ANAWAR HOSSAIN Follow Dec 15 '25 Profile # android # java # career # kotlin Comments Add Comment 2 min read Refection Feyisayo Lasisi Feyisayo Lasisi Feyisayo Lasisi Follow Dec 29 '25 Refection # motivation # leadership # devjournal # career 5 reactions Comments Add Comment 2 min read Why Focusing on People Still Matters in the Age of Artificial Intelligence DIAMANTINO ALMEIDA DIAMANTINO ALMEIDA DIAMANTINO ALMEIDA Follow Dec 14 '25 Why Focusing on People Still Matters in the Age of Artificial Intelligence # ai # productivity # career Comments Add Comment 4 min read A Day in the Life of a Web Developer at Prateeksha Web Design: Inside the Workflow, Tools, and Culture prateekshaweb prateekshaweb prateekshaweb Follow Dec 15 '25 A Day in the Life of a Web Developer at Prateeksha Web Design: Inside the Workflow, Tools, and Culture # performance # career # webdev # productivity Comments Add Comment 3 min read Are senior developers misused in your company? Andreas Müller Andreas Müller Andreas Müller Follow Dec 14 '25 Are senior developers misused in your company? # discuss # management # career # productivity Comments Add Comment 2 min read My 2025 in Review—And My Most Read Posts Cesar Aguirre Cesar Aguirre Cesar Aguirre Follow Jan 5 My 2025 in Review—And My Most Read Posts # showdev # career # yearinreview # writing 6 reactions Comments 2 comments 3 min read Intuitive.ai (Intuitive.Cloud)-Oncampus Interview Experience \| 10LPA Vrajkumar Patel Vrajkumar Patel Vrajkumar Patel Follow Dec 27 '25 Intuitive.ai (Intuitive.Cloud)-Oncampus Interview Experience \| 10LPA # interview # interviewexperience # intuitivecloud # career 1 reaction Comments Add Comment 2 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/codemouse92/updated-beginner-tag-guidelines-1m2e#guideline-enforcement	Updated #beginner Tag Guidelines - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Jason C. McDonald Posted on Aug 2, 2019 • Edited on Aug 3, 2019           Updated #beginner Tag Guidelines # beginners # meta Co-authored with @highcenburg DEV.to has a reputation for being incredibly beginner-friendly, and we like to think that the #beginners tag is a big part of that. More recently, however, it's been getting hard to predict what belongs on the tag and what doesn't. What designates a "beginner"? Is it someone new to programming, new to Javascript, new to React, or just new to Bootstrap? Those of us who have been at this a while know where to find answers to our questions, and that includes knowing what tags to search for... A complete beginner knows none of this. He or she should be able to subscribe to one tag and get content specifically geared towards their experience level, no further intervention required! We ( @codemouse92 and @highcenburg ) decided to clean up the #beginners tag to achieve this goal. We know this is going to be a big transition, but we're convinced that everyone will benefit in the end: True beginners find content specifically for them, Article authors get their beginner-oriented content noticed more easily by their target audience, DEV.to gets that much more organized. New Guidelines To start with, from here on in we'll be defining a "beginner" as someone who is new to programming, development, networking, or to a particular language. Simply being new to a framework, a library, a toolkit, or an IDE doesn't automatically count. If you think about it, almost all articles on DEV.to teach concepts anyway. We want #beginners to focus only on those developers who have 0-2 out of 10 knowledge in their field or language. All articles on #beginners should be written for true beginners. Articles should require no prerequisite knowledge about the language . This means authors should be prepared to introduce prerequisite concepts fresh in their article or series. It's okay to assume some knowledge of general programming basics, but these expectations should be clearly delineated at the top of your article. Asking a question with the #beginners tag should imply that answers should assume no prerequisite knowledge. What Changed? We used to allow articles teaching frameworks, tools, or libraries to developers who were familiar with the language , but not the discussed topic itself. The new guidelines ensure #beginners focuses on informing true beginners. Here are a few theoretical articles which would have been acceptable on #beginners at some point, but (probably) aren't now: "Building a Blockchain in React" "Combining Pandas and Deep Learning" "Let's build a P2P calendar webapp in Perl" "Executing Assembly Code from C#" Promotional Guidelines Articles should NOT primarily promote an external work, such as a Udemy course, website, or book (yours or someone else's). This is what Listings is for. It IS acceptable to include a brief (1-2 sentence) plug for another resource at the bottom of your article, so long as the article contains complete and substantial content in its own right. If you want to write up a list of resources (paid or free) for beginners, this IS acceptable on the following conditions: Resources should be by at least three different distinct authors/creators. (Don't just make a list all of one person's work.) Clearly indicate which resources are FREE (no cost or data whatsoever), which require personally identifiable information PII , and which cost money. Do not use personal affiliate links to monetize. Use the exact same URLs that anyone else could provide. It should be clear at the first paragraph that the article contains promotional links. What SHOULD Be Here? Articles in this tag should be geared towards new developers, to introduce concepts, coding principles, and language features. In other words. we're looking for articles like this: Neural Networks 101 What I have learned so far with Python 4 Design Patterns in Web Develkopment 4 Common Data Structures Lookaheads in Javascript Dead Simple Python: Generators and Coroutines Questions are also welcomed! All questions on the #beginners tag should be seeking answers without assumptions about prerequisite knowledge. (They should also include the #help tag.) For example... What is a generator? What is the best framework for ERP? What is a segmentation fault? Why can't Python find my class? Guideline Enforcement We may cleaning up some prior posts, so if you find that this tag was removed from a bunch of your posts, don't despair. We just want this tag to be a safe harbor for beginners, even if they scroll back. If you want to go back and edit any of your posts to fit with the new standards, you're welcome to; if the tag was already removed from said posts, you can email yo@dev.to to get it reinstated. If the #beginners tag is used incorrectly in new posts, we'll remove it and provide a friendly reminder, along with suggestions on better tags to use. It takes time to get used to updated rules, so don't worry if this happens to you once or twice or several dozen times. We know you'll get the hang of it! Top comments (3) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Collapse Expand   Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Author. Speaker. Time Lord. (Views are my own) Email codemouse92@outlook.com Location Time Vortex Pronouns he/him Work Author of "Dead Simple Python" (No Starch Press) Joined Jan 31, 2017 • Aug 5 '19 Dropdown menu Copy link Hide P.S. I reeeeeeeally have to say, we're super excited to have @desi joining the #beginners tag moderators. She's the author of the "Best DEV.to Posts For Beginners" series. Best DEV.to Posts for Beginners: Week of July 29, 2019 Desi ・ Aug 5 ・ 2 min read #codenewbie #beginners #tutorial #bestofdev Like comment: Like comment: 3  likes Like Comment button Reply Collapse Expand   Desi Desi Desi Follow she/her. bug hunter. UI/UX copywriter. I want to make the internet more usable and accessible. Location Chicago Education Superhi \| Ferris State University Work QA Analyst at Bandzoogle Joined Mar 5, 2019 • Aug 5 '19 Dropdown menu Copy link Hide 🤗 excited to be helping out! Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Angela Whisnant Angela Whisnant Angela Whisnant Follow Former Computer Operator at SAS Institute. Budding web developer looking for small projects to gain experience. Email arwhisnant@gmail.com Location Raleigh, North Carolina Education B.S.Ed. Western Carolina University Work Student at Udemy.com Joined May 26, 2019 • Aug 7 '19 Dropdown menu Copy link Hide Makes good sense! Thanks for looking out for us Newbies!:o) Like comment: Like comment: 1  like Like Comment button Reply Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Jason C. McDonald Follow Author. Speaker. Time Lord. (Views are my own) Location Time Vortex Pronouns he/him Work Author of "Dead Simple Python" (No Starch Press) Joined Jan 31, 2017 More from Jason C. McDonald Writing Zenlike Python (Talk) # python # beginners Social Lifespan of Posts # meta # discuss Dead Simple Python: Working with Files # python # beginners 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV Forem — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account Forem Core Close Code of Conduct Last updated July 31, 2023 All participants of DEV Community are expected to abide by our Code of Conduct and Terms of Service , both online and during in-person events that are hosted and/or associated with DEV Community. Our Pledge In the interest of fostering an open and welcoming environment, we as moderators of DEV Community pledge to make participation in our project and our community a harassment-free experience for everyone, regardless of age, body size, disability, ethnicity, gender identity and expression, level of experience, nationality, personal appearance, race, religion, or sexual identity and orientation. 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We will not act on complaints regarding: 'Reverse' -isms, including 'reverse racism,' 'reverse sexism,' and 'cisphobia' Reasonable communication of boundaries, such as 'leave me alone,' 'go away,' or 'I'm not discussing this with you.' Someone's refusal to explain or debate social justice concepts Criticisms of racist, sexist, cissexist, or otherwise oppressive behavior or assumptions Enforcement Violations of the Code of Conduct may be reported by contacting the team via the abuse report form or by sending an email to support@dev.to . All reports will be reviewed and investigated and will result in a response that is deemed necessary and appropriate to the circumstances. Further details of specific enforcement policies may be posted separately. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Community Follow Hide Create Post Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend Ali-Funk Ali-Funk Ali-Funk Follow Jan 12 Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend # aws # community # career # cloud 5 reactions Comments Add Comment 2 min read How to Become a Google Developer Expert (GDE): The Complete Guide Muhammad Ahsan Ayaz Muhammad Ahsan Ayaz Muhammad Ahsan Ayaz Follow Jan 13 How to Become a Google Developer Expert (GDE): The Complete Guide # community # webdev # ai # leadership Comments Add Comment 17 min read The Clubhouse Protocol: A Thought Experiment in Distributed Governance Morten Olsen Morten Olsen Morten Olsen Follow Jan 12 The Clubhouse Protocol: A Thought Experiment in Distributed Governance # discuss # architecture # community # opensource Comments Add Comment 7 min read LINE Taiwan Developer Relations: 2020 Review and 2021 Community Plans Evan Lin Evan Lin Evan Lin Follow Jan 11 LINE Taiwan Developer Relations: 2020 Review and 2021 Community Plans # community # developer # devjournal Comments Add Comment 8 min read LINE Taiwan Developer Relations 2020 Review and 2021 Developer Community Plan Report (Part 2: Internal Evangelism) Evan Lin Evan Lin Evan Lin Follow Jan 11 LINE Taiwan Developer Relations 2020 Review and 2021 Developer Community Plan Report (Part 2: Internal Evangelism) # community # developer # devjournal Comments Add Comment 4 min read Sharing My Article's Impact on Developers - Thank you! 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Caterpillar # watercooler # community # devjournal Comments Add Comment 2 min read [TW_DevRel] Company Visit to NTU Software Engineering Course on October 28, 2022 Evan Lin Evan Lin Evan Lin Follow Jan 11 [TW_DevRel] Company Visit to NTU Software Engineering Course on October 28, 2022 # learning # softwareengineering # community # career Comments Add Comment 5 min read Refactoring How I Learn Richard Pascoe Richard Pascoe Richard Pascoe Follow Jan 11 Refactoring How I Learn # community # learning # programming # webdev Comments Add Comment 2 min read [TW_DevRel] Campus Resources for LINE Taiwan Developer Relations and Technical Promotion Evan Lin Evan Lin Evan Lin Follow Jan 11 [TW_DevRel] Campus Resources for LINE Taiwan Developer Relations and Technical Promotion # learning # community # resources # career Comments Add Comment 8 min read AI Co-Authorship: The Tool That's Changing Romance Novels in 2026 Anas Kayssi Anas Kayssi Anas Kayssi Follow Jan 11 AI Co-Authorship: The Tool That's Changing Romance Novels in 2026 # ai # creativecoding # writingtools # community Comments Add Comment 4 min read Build a Bookstore Page Richard Pascoe Richard Pascoe Richard Pascoe Follow Jan 10 Build a Bookstore Page # community # learning # programming # webdev Comments Add Comment 1 min read AceHack 5.0 Theme Reveal: Inspired by Minecraft, Built for Builders AceHack AceHack AceHack Follow Jan 9 AceHack 5.0 Theme Reveal: Inspired by Minecraft, Built for Builders # community # devchallenge # motivation Comments Add Comment 2 min read Why do developers like dark mode? Because light attracts bugs. Mehmet Bulat Mehmet Bulat Mehmet Bulat Follow Jan 9 Why do developers like dark mode? Because light attracts bugs. # jokes # community # devbugsmash # devlive Comments Add Comment 1 min read The Commit Message Comedy Club: Drop your funniest "git commit -m" lines Mehmet Bulat Mehmet Bulat Mehmet Bulat Follow Jan 8 The Commit Message Comedy Club: Drop your funniest "git commit -m" lines # jokes # community # devbugsmash # git Comments Add Comment 1 min read Communication is a Superpower Shamim Ali Shamim Ali Shamim Ali Follow Jan 8 Communication is a Superpower # career # community # workplace Comments Add Comment 12 min read 👋 Hello DEV Community! Excited to Start Sharing & Learning Alindev Alindev Alindev Follow Jan 9 👋 Hello DEV Community! Excited to Start Sharing & Learning # community # learning # webdev Comments Add Comment 1 min read My 2025 year in review whykay 👩🏻‍💻🐈🏳️‍🌈 (she/her) whykay 👩🏻‍💻🐈🏳️‍🌈 (she/her) whykay 👩🏻‍💻🐈🏳️‍🌈 (she/her) Follow Jan 5 My 2025 year in review # personal # community # reflection 4 reactions Comments Add Comment 3 min read Call for Speakers: AgentCamp – Gurugram 2026 Ganesh Sharma Ganesh Sharma Ganesh Sharma Follow Jan 8 Call for Speakers: AgentCamp – Gurugram 2026 # techtalks # agents # ai # community Comments Add Comment 1 min read DevRel na prática: meu artigo acadêmico ainda faz sentido em 2026? Awdren Fontão Awdren Fontão Awdren Fontão Follow Jan 7 DevRel na prática: meu artigo acadêmico ainda faz sentido em 2026? # discuss # community # llm # softwareengineering Comments Add Comment 3 min read Build a Travel Agency Page Richard Pascoe Richard Pascoe Richard Pascoe Follow Jan 12 Build a Travel Agency Page # community # learning # programming # webdev 3 reactions Comments Add Comment 2 min read LINE Taiwan DevRel: 2020 Review and 2021 Community Plans (Part 3: Technical Branding and Hiring) Evan Lin Evan Lin Evan Lin Follow Jan 11 LINE Taiwan DevRel: 2020 Review and 2021 Community Plans (Part 3: Technical Branding and Hiring) # devjournal # community # marketing # career 1 reaction Comments 1 comment 8 min read 7 AI Companion App Secrets to Build a Deeper Connection in 2026 Anas Kayssi Anas Kayssi Anas Kayssi Follow Jan 10 7 AI Companion App Secrets to Build a Deeper Connection in 2026 # ai # mentalhealth # developer # community Comments Add Comment 5 min read 7 Personalized Romance Novel Apps That Are Changing Digital Reading in 2026 Anas Kayssi Anas Kayssi Anas Kayssi Follow Jan 9 7 Personalized Romance Novel Apps That Are Changing Digital Reading in 2026 # generativeai # interactivefiction # digitalpublishing # community Comments Add Comment 6 min read 7 AI Assistant Secrets to Discover Hidden Gem Date Spots in 2026 Anas Kayssi Anas Kayssi Anas Kayssi Follow Jan 9 7 AI Assistant Secrets to Discover Hidden Gem Date Spots in 2026 # ai # recommendationsystems # community # indiedev Comments Add Comment 5 min read A small web app where people quietly appear on a world map Digiwares Digiwares Digiwares Follow Jan 3 A small web app where people quietly appear on a world map # showdev # webdev # community # networking Comments Add Comment 2 min read loading... trending guides/resources How to Become an AWS Community Builder How to Become an AWS Community Builder: Complete Guide for 2026 Applications KMP 밋업 202512 후기 Comunidades de desenvolvedores (JavaScript,TypeScript) Bringing Cursor Café to Guadalajara ☕💻 Why Blogging Still Matters in the Age of AI Apache Dev List Digest: Iceberg, Polaris, Arrow & Parquet (Nov 24-Dec 8, 2025) 2025 Wrapped: still building, sharing, and finding my place in the community 2025 Retrospective The Now Go Build Award: Celebrating Global Builders Who Inspire the AWS Community Public Speaking at Tech Events 101: From Acceptance to the Stage What makes a good tech Meet-up? 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https://www.algolia.com/products/ai/agent-studio	Agent Studio Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. Integrations Connect to your existing stack via pre-built libraries and APIs. Infrastructure Overview Data Centers Choose from 70+ data centers across 17 regions. Data Centers Choose from 70+ data centers across 17 regions. Security & Compliance Built for peace of mind. Security & Compliance Built for peace of mind. 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We got you covered! Brand guidelines Download logo pack Agent Studio Build faster with Agent Studio Now in beta: A new way to create, test, and deploy AI agents Get a demo Sign up for beta What is Agent Studio? Agent Studio is a framework for developers that accelerates the creation of AI agents. Built on Algolia’s AI-first infrastructure, it gives you the power to combine large language models (LLMs) with real-time search, behavioral data, and configurable logic. Launch personalized, brand-centric AI assistants that deliver a powerful user experience immersed in your product. More than 18,000 customers in 150+ countries trust Algolia See all customer stories Composable by design Combining industry-leading LLMs with the precision of Algolia Retrieval, Agent Studio lets you orchestrate smarter AI experiences that reflect your brand and business logic. Build with composable building blocks Configure flexible workflows using developer APIs and LangChain components. Define prompts, permissions, and LLMs through a self-service dashboard or code. Plug in your own LLM Use the model that fits your needs — OpenAI at launch, with more coming soon — no vendor lock-in. You control your infrastructure and costs. Search-native retrieval Powered by Algolia’s 1.75 trillion yearly searches, Agent Studio gives your agents the same instant access to personalization, business logic, and index control trusted by the world’s top brands. Integrated tooling Bring your own tools or use Algolia’s analytics, recommendation engines, and customer data—all with the security and scale of our platform. Benefits for developers and product teams Built for developers who want to move fast, Agent Studio provides full control while removing the need to build infrastructure from scratch. Launch faster Go from idea to production in weeks, not months. Keep control Own your data, logic, and LLM integrations. Adapt quickly Iterate with built-in observability and prompt management. Scale securely Define permissions, avoid shadow data, and maintain brand safety. Cut complexity, not performance We handle the orchestration, AI engineering, and cloud infrastructure setup—at no extra GenAI cost to you. Use any LLM Bring-your-own-LLM flexibility with no vendor lock-in and transparent pricing. Real-world use cases From retrieval-powered chatbots to personalized product assistants, Agent Studio supports agentic experiences across industries. Ecommerce 0 Shopping assistants, size & fit recommenders, cart recovery agents. Learn more Media 0 Content recommenders, editorial copilots, research assistants. Learn more Enterprise 0 Internal knowledge bots, support agents, document Q&A tools. Learn more SaaS 0 In-product guidance, onboarding copilots, troubleshooting flows. Learn more Sign Up for Early Access Be among the first developers to explore the future of AI-powered applications with Algolia.   To learn more about how to use the Agent Studio, check out Algolia's documentation or join our Discord community. * First name * Last name * Email * Company * Country Yes, I'd like to receive more information on Algolia products, events and promotions via email. Refer to Algolia's Privacy Policy for more information on how we use and protect your data. By submitting this form, I understand that I may receive email communication about Algolia products, events and promotion according to Algolia's Privacy Policy . (You can unsubscribe at anytime here ) Submit Success! Someone will be in touch with you soon. Algolia Agent Studio FAQs Is Agent Studio available now? 0 Agent Studio is now available in beta. Sign up to try it today, or connect with our team to learn more. What makes Agent Studio different from other agentic solutions? 0 Agent Studio is the only agent framework built on ten years of search expertise and leadership, combining real-time retrieval with customizable orchestration, LLM flexibility, and developer-first tools. How are you grounding your agentic experiences in real-time, accurate data? 0 While many AI solutions can be helpful, they can "hallucinate" answers. Agent Studio prevents hallucinations because it uses your up-to-the-minute data. It retrieves information from your structured search index to augment its generated responses with that data, an approach appropriately called Retrieval Augmented Generation, or RAG.  Is Agent Studio designed for my industry? 0 Yes. Agent Studio supports use cases across every industry—from SaaS and media to enterprise search and beyond—making it adaptable to virtually any AI agent need. Which LLMs are supported? 0 Algolia supports OpenAI, Azure OpenAI, Google Gemini, and OpenAI-compatible LLMs. See the complete list of supported models in our docs . Can I use non-product data in agents? 0 Yes. Agents can access any data indexed in Algolia, including help docs, guides, and more. Does it store chat data? 0 No server-side chat history is stored during beta. How does Agent Studio use my data? 0 Agent Studio uses your first-party data—such as search interactions, transaction history, and user behavior—to generate highly relevant, brand-specific responses. Unlike generic agent frameworks, it integrates this data directly from your Algolia indices, giving your agents context-aware intelligence out of the box. Enable anyone to build great Search & Discovery Get a demo Start free Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://www.algolia.com/industries/b2b-ecommerce	Build Search & Discovery for B2B Ecommerce \| Algolia Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark white Algolia logo white Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. Integrations Connect to your existing stack via pre-built libraries and APIs. Integrations Connect to your existing stack via pre-built libraries and APIs. Infrastructure Overview Data Centers Choose from 70+ data centers across 17 regions. Data Centers Choose from 70+ data centers across 17 regions. Security & Compliance Built for peace of mind. Security & Compliance Built for peace of mind. Solutions Industries SEE ALL Ecommerce Ecommerce B2B Commerce B2B Commerce Fashion Fashion Grocery Grocery Media Media Marketplaces Marketplaces SaaS SaaS Higher Education Higher Education Use Cases SEE ALL Documentation search Documentation search Enterprise search Enterprise search Headless commerce Headless commerce Image search Image search Mobile & App search Mobile & App search Retail Media Network Retail Media Network Site search Site search Visual search Visual search Voice search Voice search Departments Digital Experience Digital Experience Ecommerce Ecommerce Engineering Engineering Merchandising Merchandising Product Management Product Management Pricing Developers Get started Developer Hub Developer Hub Documentation Documentation Integrations Integrations UI Components UI Components Autocomplete Autocomplete Resources Code Exchange Code Exchange Engineering Blog Engineering Blog MCP MCP Discord Discord Webinars & Events Webinars & Events Quick Links Quick Start Guide Quick Start Guide For Open Source For Open Source API Status API Status Support Support Resources Discover Algolia Blog Algolia Blog Resource Center Resource Center Customer Stories Customer Stories Webinars & Events Webinars & Events Newsroom Newsroom Customers Customer Hub Customer Hub What's New What's New Knowledge Base Knowledge Base Documentation Documentation Algolia Academy Algolia Academy Professional Services Professional Services Quick Access Company Partners Support Login Logout Request demo Get started Search Algolia Close Request demo Get started Other Types Filter --> Clear All Filters Filters Looking for our logo? We got you covered! Brand guidelines Download logo pack B2B & MANUFACTURING Build seamless B2B buyer journeys with Algolia Guide buyers to the products they need with intuitive, AI-driven search solutions Get a demo Start building for free More than 1700 manufacturers and distributors choose Algolia “Ergodyne saw 5X CTR growth and 1.9X uplift in search interactions.” Read their story “King Arthur Baking Company saw an 18% increase in conversions. We now have total control over the look and feel of our search results. ” Mike Hoefer Director of Web Development King Arthur Baking Company Read their story “Algolia has become so mission critical for navigating our application that users instantly notice whenever we ship a new enhancement to our Algolia implementation.” Desmond Brand Engineering Manager Flexport Read their story “Swedol saw their conversion rate grow by 22% and a 7.5% increase in searches. The speed of Algolia has been incredibly impactful, along with the visibility and control we get through the dashboard. Best of all, we get the help we need from Algolia to find the best way forward on things really important to us.” Clint Fischerström Head of Ecommerce @ Swedol Read their story All the tools you need to build best-in-class B2B ecommerce experiences Your browser does not support the video tag. AI Search Quickly show your customers exactly what they need with industry-leading AI Search that understands buyer intent. Search by keyword, description, part #, SKU, or any other product attribute.  Combine results from all your data sources in a single search experience – from product results, to case studies, FAQs and more. Deliver relevant results for all queries, even those in the ‘long tail’. Automate category reporting & ranking with Query Categorization. Display best-sellers automatically with Dynamic Reranking. Learn more about AI Search Your browser does not support the video tag. AI Recommendations Boost average order value with tailored product and content suggestions using behavioral and contextual data.  Drive cross-sell with predictive models including “related products”, “trending items” and “frequent combinations”. Add personalized recommendations on your homepage, product landing pages, shopping cart and almost anywhere else. Image-based recommendations can help buyers find even more. Learn more about AI Recommendations Your browser does not support the video tag. AI Browse Automatically build category, collection, and other pages to show your buyers what they need based on their behavior and preferences. Deliver results instantly with our UI components and SDKs. A/B test different category ranking algorithms and push the highest converting results live. 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https://dev.to/mohammadidrees/thinking-in-first-principles-how-to-question-an-async-queue-based-design-5cf1#step-1-the-root-question-always-start-here	Thinking in First Principles: How to Question an Async Queue–Based Design - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Mohammad-Idrees Posted on Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Async queues are one of the most commonly suggested “solutions” in system design interviews. But many candidates jump straight to using queues without understanding: What problems they actually solve What new problems they introduce How to systematically discover those problems This post teaches a first-principles questioning process you can apply to any async queue design—without assuming prior knowledge. Why This Matters In interviews, interviewers are not evaluating whether you know Kafka, SQS, or RabbitMQ. They are evaluating whether you can: Reason about time Reason about failure Reason about order Reason about user experience Async queues change all four. What “First Principles” Means Here First principles means: We do not start with solutions We do not assume correctness We ask basic, unavoidable questions that every system must answer Async queues feel correct because they remove blocking—but correctness is not guaranteed by intuition. The Reference Mental Model (Abstract) We will reason about this abstract pattern , not a specific product: User → API → Storage → Queue → Worker → Storage Enter fullscreen mode Exit fullscreen mode No domain assumptions. This could be: Chat messages Emails Payments Notifications Image processing The questioning process stays the same. Step 1: The Root Question (Always Start Here) What is the system responsible for completing before it can respond? This is the most important question in system design. Why? Because it defines: Request boundaries Latency expectations Responsibility In an async queue design, the implicit answer is: “The request is complete once the work is enqueued.” This is different from synchronous designs, where the request completes after work finishes. So far, this seems good. Step 2: Introduce Time (What Happens Later?) Now ask: Which part of the work happens after the request is done? Answer: The worker processing This leads to an important realization: The system has split work across time Time separation is powerful—but it creates new questions. Step 3: Causality Question (Identity Across Time) Once work happens later, we must ask: How does the system know which output belongs to which input? This question always appears when time is decoupled. Typical answer: IDs in the job payload (request ID, entity ID) This introduces a new invariant: Each input must produce exactly one correct output Now we test whether the system can guarantee this. Step 4: Failure Question (The Queue Reality) Now ask the most important async-specific question: What happens if the worker crashes mid-processing? Realistic answers: The job is retried The work may run again The output may be produced twice This leads to a critical realization: Async queues are usually at-least-once , not exactly-once This is not a tooling issue. It is a fundamental property of distributed systems . Step 5: Duplication Question (Invariant Violation) Now ask: What happens if the same job is processed twice? Consequences: Duplicate outputs Duplicate side effects Conflicting state This violates the earlier invariant: “Exactly one output per input” At this point, we have discovered a correctness problem , not a performance problem. Step 6: Ordering Question (Time Without Synchrony) Now consider multiple inputs. Ask: What defines the order of processing? Important realization: Queue order ≠ business order Different workers process at different speeds Later inputs may finish first Now ask: Does correctness depend on order? If yes (and many systems do): Async queues alone are insufficient This problem emerges only when you question order explicitly. Step 7: Visibility Question (User Experience) Now switch perspectives. How does the user know the work is finished? Possible answers: Polling Guessing Timeouts Each answer reveals a problem: Polling wastes resources Guessing is unreliable Timeouts fail under load This violates a core system principle: Users should not wait blindly Case Study: A Simple Example (Problem-Agnostic) Imagine a system where users upload photos to be processed. Flow: User uploads photo API stores metadata Job is enqueued Worker processes photo Result is stored Now apply the questions: When does the upload request complete? → After enqueue What if the worker crashes? → Job retried What if it runs twice? → Two processed images What if two photos depend on order? → Order not guaranteed How does the user know processing is done? → Polling None of these issues are about images. They are about time, failure, identity, and visibility . What Async Queues Actually Trade Async queues solve one problem: They remove blocking from the request path But they introduce others: Solved Introduced Blocking Duplicate work Latency coupling Ordering ambiguity Resource exhaustion Completion uncertainty This is not bad. It just must be understood and handled . The One-Page Interview Checklist (Memorize This) For any async queue design , ask these five questions: What completes the request? What runs later? What happens if it runs twice? What defines order? How does the user observe completion? If you cannot answer all five clearly, the design is incomplete. Final Mental Model Async systems remove time coupling but destroy causality by default Your job as an engineer is not to “use queues” Your job is to restore correctness explicitly That is what interviewers are looking for. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Mohammad-Idrees Follow Joined Mar 16, 2023 More from Mohammad-Idrees How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://tinyhack.com/archive/	Archive – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Archive 2 thoughts on “Archive” Michael Packard says: November 7, 2009 at 1:26 pm I have been having great fun with the Apple II emulator for the Wii. The only real problem I have with is is selecting disk images – I have over 800 of them on my sd card (downloaded the whole asimov archive!), and even when separated into folders alphabetically, the emulator chokes for several MINUTES when I go select a folder with, say, 75-100 disk images. Eventually it shows me the file list, but it takes forever. Can you fix this? I’d like to explore what is available for the apple, but it’s REALLY hard when it takes so long to just open one of many folders I have. Otherwise it’s a fantastic emulator. Thanx. Reply Abel Miranda says: February 19, 2022 at 7:07 pm Love the apple II emulator. Is there a way to emulate the Apple IIGS on the Wii? Thank you Reply Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. Δ Pages About Archive Search for: Search Follow x.com/yohanes Mastodon Recent Posts CVE-2025-31931 Arbitrary Shared Library Loading in Intel ITT API on Android (affects OpenCV <= 4.10) Decrypting Encrypted files from Akira Ransomware (Linux/ESXI variant 2024) using a bunch of GPUs Patching .so files of an installed Android App Extracting WhatsApp Database (or any app data) from Android 12/13 using CVE-2024-0044 Zygisk-based reFlutter Recent Comments Eitan Porat on About admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 admin on Using U-Boot to extract Boot Image from Pritom P7 lpt2007 on Using U-Boot to extract Boot Image from Pritom P7 Archives November 2025 March 2025 November 2024 June 2024 April 2024 January 2024 December 2023 September 2022 March 2021 January 2021 May 2019 January 2019 November 2018 July 2018 May 2018 February 2018 October 2017 September 2017 March 2017 November 2016 November 2015 July 2014 March 2014 February 2014 June 2013 January 2013 November 2011 March 2011 February 2011 July 2010 April 2010 January 2010 December 2009 September 2009 August 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 2009 December 2008 October 2008 September 2008 August 2008 July 2008 June 2008 May 2008 March 2008 February 2008 October 2007 June 2007 February 2007 January 2007 December 2006 Categories agestar android blog ctf debian flareon flex freebsd google hacks hardware hostmonster linux mac os x misc mobile opensource phone raspberry reverse-engineering sdr security Uncategorized wii writeup Meta Log in Entries feed Comments feed WordPress.org Tinyhack.com Proudly powered by WordPress	2026-01-13T08:48:55
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https://dev.to/loiconlyone/jai-galere-pendant-3-semaines-pour-monter-un-cluster-kubernetes-et-voila-ce-que-jai-appris-30l6#les-gal%C3%A8res-que-jai-rencontr%C3%A9es	J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse BeardDemon Posted on Jan 10 J'ai galéré pendant 3 semaines pour monter un cluster Kubernetes (et voilà ce que j'ai appris) # kubernetes # devops # learning Le contexte Bon, soyons honnêtes. Au début, j'avais un gros bordel de scripts bash éparpillés partout. Genre 5-6 fichiers avec des noms comme install-docker.sh , setup-k8s-FINAL-v3.sh (oui, le v3...). À chaque fois que je devais recréer mon infra, c'était 45 minutes de galère + 10 minutes à me demander pourquoi ça marchait pas. J'avais besoin de quelque chose de plus propre pour mon projet SAE e-commerce. Ce que je voulais vraiment Pas un truc de démo avec minikube. Non. Je voulais: 3 VMs qui tournent vraiment (1 master + 2 workers) Tout automatisé - je tape une commande et ça se déploie ArgoCD pour faire du GitOps (parce que push to deploy c'est quand même cool) Des logs centralisés (Loki + Grafana) Et surtout : pouvoir tout péter et tout recréer en 10 minutes L'architecture (spoiler: ça marche maintenant) ┌─────────────────────────────────────────┐ │ Mon PC (Debian) │ │ ┌──────────┐ ┌──────────┐ ┌─────────┐ │ │ Master │ │ Worker 1 │ │ Worker 2│ │ │ .56.10 │ │ .56.11 │ │ .56.12 │ │ └──────────┘ └──────────┘ └─────────┘ └─────────────────────────────────────────┘ Enter fullscreen mode Exit fullscreen mode Chaque VM a 4Go de RAM et 4 CPUs. Oui, ça bouffe des ressources. Non, ça passe pas sur un laptop pourri. Comment c'est organisé J'ai tout mis dans un repo bien rangé (pour une fois): ansible-provisioning/ ├── Vagrantfile # Les 3 VMs ├── playbook.yml # Le chef d'orchestre ├── manifests/ # Mes applis K8s │ ├── apiclients/ │ ├── apicatalogue/ │ ├── databases/ │ └── ... (toutes mes APIs) └── roles/ # Les briques Ansible ├── docker/ ├── kubernetes/ ├── k8s-master/ └── argocd/ Enter fullscreen mode Exit fullscreen mode Chaque rôle fait UN truc. C'est ça qui a changé ma vie. Shell scripts → Ansible : pourquoi j'ai migré Avant (la galère) J'avais un script prepare-system.sh qui ressemblait à ça: #!/bin/bash swapoff -a sed -i '/swap/d' /etc/fstab modprobe br_netfilter # ... 50 lignes de commandes # Aucune gestion d'erreur # Si ça plante au milieu, bonne chance Enter fullscreen mode Exit fullscreen mode Le pire ? Si je relançais le script après un fail, tout pétait. Genre le sed essayait de supprimer une ligne qui existait plus. Classique. Après (je respire enfin) Maintenant j'ai un rôle Ansible system-prepare : - name : Virer le swap shell : swapoff -a ignore_errors : yes - name : Enlever le swap du fstab lineinfile : path : /etc/fstab regexp : ' .swap.' state : absent - name : Charger br_netfilter modprobe : name : br_netfilter state : present Enter fullscreen mode Exit fullscreen mode La différence ? Je peux relancer 10 fois, ça fait pas de conneries C'est lisible par un humain Si ça plante, je sais exactement où Le Vagrantfile (ou comment lancer 3 VMs d'un coup) Vagrant . configure ( "2" ) do \| config \| config . vm . box = "debian/bullseye64" # Config libvirt (KVM/QEMU) config . vm . provider "libvirt" do \| libvirt \| libvirt . memory = 4096 libvirt . cpus = 4 libvirt . management_network_address = "192.168.56.0/24" end # NFS pour partager les manifests config . vm . synced_folder "." , "/vagrant" , type: "nfs" , nfs_version: 4 # Le master config . vm . define "vm-master" do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.10" vm . vm . hostname = "master" end # Les 2 workers ( 1 .. 2 ). each do \| i \| config . vm . define "vm-slave- #{ i } " do \| vm \| vm . vm . network "private_network" , ip: "192.168.56.1 #{ i } " vm . vm . hostname = "slave- #{ i } " end end # Ansible se lance automatiquement config . vm . provision "ansible" do \| ansible \| ansible . playbook = "playbook.yml" ansible . groups = { "master" => [ "vm-master" ], "workers" => [ "vm-slave-1" , "vm-slave-2" ] } end end Enter fullscreen mode Exit fullscreen mode Un vagrant up et boom, tout se monte tout seul. Le playbook : l'ordre c'est important --- # 1. Tous les nœuds en même temps - name : Setup de base hosts : k8s_cluster roles : - system-prepare # Swap off, modules kernel - docker # Docker + containerd - kubernetes # kubelet, kubeadm, kubectl # 2. Le master d'abord - name : Init master hosts : master roles : - k8s-master # kubeadm init + Flannel # 3. Les workers ensuite, un par un - name : Join workers hosts : workers serial : 1 # IMPORTANT: un à la fois roles : - k8s-worker # 4. Les trucs bonus sur le master - name : Dashboard + ArgoCD + Monitoring hosts : master roles : - k8s-dashboard - argocd - logging - metrics-server Enter fullscreen mode Exit fullscreen mode Le serial: 1 c'est crucial. J'avais essayé sans, les deux workers essayaient de join en même temps et ça partait en cacahuète. Les rôles en détail Rôle: k8s-master (le chef d'orchestre) C'est lui qui initialise le cluster. Voici les parties importantes: - name : Init cluster k8s command : kubeadm init --apiserver-advertise-address=192.168.56.10 --pod-network-cidr=10.244.0.0/16 when : not k8s_initialise.stat.exists - name : Copier config kubectl copy : src : /etc/kubernetes/admin.conf dest : /home/vagrant/.kube/config owner : vagrant group : vagrant - name : Installer Flannel (réseau pod) shell : \| kubectl apply -f https://github.com/flannel-io/flannel/releases/latest/download/kube-flannel.yml environment : KUBECONFIG : /home/vagrant/.kube/config - name : Générer commande join pour les workers copy : content : " kubeadm join 192.168.56.10:6443 --token {{ k8s_token.stdout }} --discovery-token-ca-cert-hash sha256:{{ k8s_ca_hash.stdout }}" dest : /vagrant/join.sh mode : ' 0755' - name : Créer fichier .master-ready copy : content : " Master initialized" dest : /vagrant/.master-ready Enter fullscreen mode Exit fullscreen mode Le fichier .master-ready c'est un flag pour dire aux workers "go, vous pouvez join maintenant". Rôle: k8s-worker (le suiveur patient) - name : Attendre que le fichier .master-ready existe wait_for : path : /vagrant/.master-ready timeout : 600 - name : Joindre le cluster shell : bash /vagrant/join.sh args : creates : /etc/kubernetes/kubelet.conf register : join_result failed_when : - join_result.rc != 0 - " 'already exists in the cluster' not in join_result.stderr" - name : Attendre que le node soit Ready shell : \| for i in {1..60}; do STATUS=$(kubectl get node $(hostname) -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}') if [ "$STATUS" = "True" ]; then exit 0 fi sleep 5 done exit 1 Enter fullscreen mode Exit fullscreen mode Le worker attend gentiment que le master soit prêt avant de faire quoi que ce soit. Les galères que j'ai rencontrées Galère #1: NFS qui marche pas Au début, le partage NFS entre l'hôte et les VMs plantait. Symptôme: mount.nfs: Connection timed out Enter fullscreen mode Exit fullscreen mode Solution: # Sur l'hôte sudo apt install nfs-kernel-server sudo systemctl start nfs-server sudo ufw allow from 192.168.56.0/24 Enter fullscreen mode Exit fullscreen mode Le firewall bloquait les connexions NFS. Classique. Galère #2: Kubeadm qui timeout Le kubeadm init prenait 10 minutes et finissait par timeout. Cause: Pas assez de RAM sur les VMs (j'avais mis 2Go). Solution: Passer à 4Go par VM. Ça bouffe mais c'est nécessaire. Galère #3: Les workers qui join pas Les workers restaient en NotReady même après le join. Cause: Flannel (le CNI) était pas encore installé sur le master. Solution: Attendre que Flannel soit complètement déployé avant de faire join les workers: - name : Attendre Flannel command : kubectl wait --for=condition=ready pod -l app=flannel -n kube-flannel --timeout=300s environment : KUBECONFIG : /etc/kubernetes/admin.conf Enter fullscreen mode Exit fullscreen mode Galère #4: Ansible qui relance tout à chaque fois Au début, chaque vagrant provision refaisait TOUT depuis zéro. Solution: Ajouter des conditions when partout: - name : Init cluster k8s command : kubeadm init ... when : not k8s_initialise.stat.exists # ← Ça sauve des vies Enter fullscreen mode Exit fullscreen mode L'idempotence c'est vraiment la base avec Ansible. Les commandes utiles au quotidien # Lancer tout cd ansible-provisioning && vagrant up # Vérifier l'état du cluster vagrant ssh vm-master -c 'kubectl get nodes' # Voir les pods vagrant ssh vm-master -c 'kubectl get pods -A' # Refaire le provisioning (sans détruire les VMs) vagrant provision # Tout péter et recommencer vagrant destroy -f && vagrant up # SSH sur le master vagrant ssh vm-master # Logs d'un pod vagrant ssh vm-master -c 'kubectl logs -n apps apicatalogue-xyz' Enter fullscreen mode Exit fullscreen mode ArgoCD et les applications Une fois le cluster monté, ArgoCD déploie automatiquement mes apps. Voici comment je déclare l'API Catalogue: apiVersion : argoproj.io/v1alpha1 kind : Application metadata : name : catalogue-manager-application namespace : argocd spec : destination : namespace : apps server : https://kubernetes.default.svc source : path : ansible-provisioning/manifests/apicatalogue repoURL : https://github.com/uha-sae53/Vagrant.git targetRevision : main project : default syncPolicy : automated : prune : true selfHeal : true Enter fullscreen mode Exit fullscreen mode ArgoCD surveille mon repo GitHub. Dès que je change un manifest, ça se déploie automatiquement. Metrics Server et HPA J'ai aussi ajouté le Metrics Server pour l'auto-scaling: - name : Installer Metrics Server shell : \| kubectl apply -f https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml environment : KUBECONFIG : /etc/kubernetes/admin.conf - name : Patcher pour ignorer TLS (dev seulement) shell : \| kubectl patch deployment metrics-server -n kube-system --type='json' \ -p='[{"op": "add", "path": "/spec/template/spec/containers/0/args/-", "value": "--kubelet-insecure-tls"}]' Enter fullscreen mode Exit fullscreen mode Avec ça, mes pods peuvent scaler automatiquement en fonction de la charge CPU/RAM. Le résultat final Après tout ça, voici ce que je peux faire: # Démarrer tout de zéro vagrant up # ⏱️ 8 minutes plus tard... # Vérifier que tout tourne vagrant ssh vm-master -c 'kubectl get pods -A' # Résultat: # NAMESPACE NAME READY STATUS # apps apicatalogue-xyz 1/1 Running # apps apiclients-abc 1/1 Running # apps apicommandes-def 1/1 Running # apps api-panier-ghi 1/1 Running # apps frontend-jkl 1/1 Running # argocd argocd-server-xxx 1/1 Running # logging grafana-yyy 1/1 Running # logging loki-0 1/1 Running # kube-system metrics-server-zzz 1/1 Running Enter fullscreen mode Exit fullscreen mode Tout fonctionne, tout est automatisé. Conclusion Ce que j'ai appris: Ansible > scripts shell (vraiment, vraiment) L'idempotence c'est pas un luxe Tester chaque rôle séparément avant de tout brancher Les workers doivent attendre le master (le serial: 1 sauve des vies) 4Go de RAM minimum par VM pour K8s Le code complet est sur GitHub: https://github.com/uha-sae53/Vagrant Des questions ? Ping moi sur Twitter ou ouvre une issue sur le repo. Et si vous galérez avec Kubernetes, vous êtes pas seuls. J'ai passé 3 semaines là-dessus, c'est normal que ce soit compliqué au début. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse BeardDemon Follow Nananère je suis très sérieux... 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https://www.algolia.com/products/ai-recommendations	AI recommendation engine for products and content \| Algolia Niket --> Deutsch English français News: Meet us at NRF 2026 Learn more Company Partners Support Login Logout Algolia mark blue Algolia logo blue Products AI Search & Retrieval Overview Search Show users what they're looking for with AI-driven resuts. Search Show users what they're looking for with AI-driven resuts. Recommendations Use behavioral cues to drive higher engagement. Recommendations Use behavioral cues to drive higher engagement. Personalization Show each user what they need across their journey. Personalization Show each user what they need across their journey. Analytics All your insights in one dashboard. Analytics All your insights in one dashboard. Browse Move customers down the funnel with curated category pages. Browse Move customers down the funnel with curated category pages. Artificial Intelligence OVERVIEW Agent Studio Create, test, and deploy AI agents, fast. Agent Studio Create, test, and deploy AI agents, fast. Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Generative Experiences Build conversational solutions with retrieval augmented generation (RAG). Ask AI Deliver conversational answers—right from your search bar. Ask AI Deliver conversational answers—right from your search bar. MCP Server Search, analyze, or monitor your index within your agentic workflow. MCP Server Search, analyze, or monitor your index within your agentic workflow. Intelligent Data Kit Overview Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Enrichment Modify, enhance, or restructure data as it’s indexed for search. Data Transformation Streamline data preparation and enhance data quality. Data Transformation Streamline data preparation and enhance data quality. 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We got you covered! Brand guidelines Download logo pack AI RECOMMENDATION ENGINE Suggestions that just make sense Use AI-powered behavioral cues to recommend items and content that your audience is actually interested in Get a demo Get started for free AI-Powered Product & Content Recommendations Your browser does not support the video tag. Inspire undecided visitors No matter where your users are in their journey, AI Recommendations drives higher site engagement and cart/conversion metrics.   Algolia’s AI surfaces personal recommendations in a smart carousel, to match user affinities. Advanced filters let you apply more granular preferences at a user or customer segment level. Maximize catalog exposure and drive cross-sell A seamless integration with your backend CMS and product catalogs will help expose the full breadth of your products or content to users throughout their journey. How Algolia’s AI Recommendations Engine Works Algolia’s AI recommendations engine turns first-party behavioral signals and catalog data into revenue-driving suggestions in four fast steps: Ingest & enrich your data Sync your full product or content index and stream real-time events (views, clicks, add-to-cart, purchases). The engine enriches each record with vector embeddings and image fingerprints, laying the groundwork for high-quality matches. Train purpose-built ML models Supervised machine-learning algorithms—collaborative, content-based, and hybrid—spot patterns in what shoppers browse and buy to predict what each person is most likely to want next. Serve lightning-fast recommendations via API A single API call returns a ranked JSON list in <10 ms. Choose from out-of-the-box models (Related Products, Frequently Bought Together, Trending Items) or spin up custom ones without slowing the page. Learn & optimize continuously As fresh events stream in, models retrain automatically and feed dashboards so you can A/B-test, merchandise, and fine-tune relevance over time. AI-powered recommendation models and tools Frequently bought together 0 Drive cross-sales and increase average cart value by showing your shoppers products that complement their current selection. Read the docs Looking similar 0 Algolia's 'Looking Similar' feature uses image recognition technology to identify related items, helping users discover products that fit a specific theme, vibe or mood and increase cart size through additional purchases. Read the docs Related items 0 Whether an item is unavailable, or a user is looking for inspiration, Algolia’s AI model compares images to your index in real time, to find related items. Read the docs Trending items 0 Algolia AI Recommendation's Trending Items model showcases the hottest products in your catalog, capturing customer interest and boosting engagement. Read the docs Personalized recommendations 0 Use Algolia’s AI capabilities to go beyond recommendations based on customer segment, to 1:1 marketing based on context and behavior signals. More than 18,000 customers in 150+ countries trust Algolia Featured Customer Stories END. Clothing lifts conversions with AI Recommendations Streetwear retailer END. boosted product-listing click-throughs and delivered a 2 % site-wide conversion lift after adding Algolia Recommendations. Read the END. Clothing case study Auto Mercado grows baskets & revenue online Costa Rica’s premium grocer saw a 50 %+ post-search conversion jump and larger basket sizes, while unlocking new ad-revenue streams thanks to Algolia’s Recommend plus Search. Explore the Auto Mercado story Gymshark’s Black Friday orders soar 150 % During peak traffic, Gymshark recorded a 150 % increase in order rate and 32 % more “add-to-cart” actions from new users after switching to Algolia Recommend. See Gymshark’s results The one-stop shop for your AI recommendations Easy to use Launch personalized carousels in minutes—just sync your catalog and events, drag-and-drop our pre-built Recommend widgets, and stay in full control with no-code tuning. Fast Serve AI-driven product or content recommendations in < 10 ms, keeping pages—and add-to-cart clicks—blazing fast even at holiday traffic peaks. Scalable Work with a partner who handles 30 billion records and nearly 1.7 trillion searches and recommendations a year with 99.999% availability. Addressing a wide range of industries B2C ecommerce 0 Boost AOV with AI-powered product recommendations that adapt to every click—from homepage inspiration to checkout upsells. Read more on B2C ecommerce B2B ecommerce 0 Guide buyers to the exact SKUs, parts, and cross-sell add-ons they need with account-aware recommendations. Read more on B2B ecommerce Marketplaces 0 Surface the most relevant listings for each user and seller, increasing GMV and engagement across your multi-vendor catalog. Read more on marketplaces Media 0 Keep audiences bingeing with content recommendations that learn from viewing history, trending topics, and seasonal interests. Read more on media SaaS 0 Drive feature adoption and retention by recommending in-app tutorials, integrations, and plan upgrades based on real-time usage. Read more on SaaS Solutions for multiple use-cases Enterprise search 0 Connects your customers to the right content, and your employees to the right information. Read more on Enterprise search Mobile & app search 0 Create mobile search and discovery sessions that your users love. Read more on mobile search Image search 0 Build image search for your website or app. Read more on image search Headless ecommerce 0 Rich product- and content-based customer experiences in a headless ecommerce framework. Read more on headless ecommerce Voice search 0 Contextual understanding capabilities, NLP, natural-language understanding, and AI tools. Read more on voice search AI Recommendations FAQs What is Algolia’s AI Recommendations? 0 Algolia’s AI Recommendations is a powerful API-driven AI recommendation engine that uses behavioral cues to suggest items and content that your audience is actually interested in.  It's designed to deliver personalized suggestions anywhere in the user journey, helping businesses drive higher site engagement and improve conversion metrics. How does Algolia's recommendation engine work technically? 0 Under the hood recommendations rely on supervised machine learning models and the Algolia foundation. For both models, the data corresponding to the past 30 days is collected. This results in a matrix where columns are  userTokens  and rows are  objectIDs . Each cell represents the number of interactions (click and/or conversions) between a  userToken  and an  objectID . Then, Algolia Recommend applies a  collaborative filtering algorithm : for each item, it finds other items that share similar buying patterns across customers. Items would be considered similar if the same users set interacted with them. Items would be considered bought together if the same set of users bought them. Can AI Recommendations be used for products and content? 0 Yes! Algolia’s AI Recommendations can work for both products and content For retail and e-commerce, it can suggest relevant products, accessories, or bundles based on browsing and purchase behavior. In media, publishing, and SaaS, it can recommend articles, videos, courses, or documentation tailored to each user’s interests. What features and capabilities does Algolia’s AI Recommendations offer? 0 Algolia’s AI Recommendations provides several features and capabilities that allow you to provide visitors, users, or shoppers with relevant, highly-personalized suggestions: Related Products: Shows shoppers products that complement their current selection Looking Similar: Uses image recognition technology to identify related items, helping users discover products that fit a specific theme, vibe or mood Trending Items: Showcases the hottest products in your catalog, capturing customer interest and boosting engagement Frequently Bought Together: Suggests items commonly purchased in combination Personalized Recommendations: Goes beyond recommendations based on customer segment, to 1:1 marketing based on context and behavior signals What industries can benefit from Algolia’s AI recommendation engine? 0 Algolia’s AI Recommendations serves a wide range of industries like B2C and B2B ecommerce, marketplaces, media, SaaS, fashion, and more.  Each industry can leverage the recommendation engine's flexibility to create tailored experiences that match their specific user needs and business objectives. How fast are Algolia's AI recommendation responses? 0 Very fast. Most recommendation requests will take from 1 to 20 milliseconds to process. This lightning-fast response time gives users instant suggestions without any noticeable delay. What is the implementation process for AI Recommendations? 0 Implementing AI Recommendations is straightforward, four-step process: Capture your users' conversion events - Track user interactions like clicks, views, and purchases Send your data to Algolia - Upload your behavioral data to the platform Train the models with the push of a button - Let Algolia's AI process and learn from your data Add recommendations to your UI - Integrate the recommendation widgets into your website or app Learn more about getting started with AI Recommendations   Does Algolia AI Recommendations support multiple languages? 0 Yes, Algolia's recommendation engine is completely language-agnostic. It supports alphabet-based and symbol-based languages such as Chinese, Japanese, and Korean, making it suitable for global businesses operating in diverse markets. How are AI-powered recommendation engines different from traditional recommendation engines? 0 AI recommendation engines analyze the full sequence and context of a user’s behavior. Traditional recommendation engines, on the other hand, often base their suggestions on only a single action like the most recent item viewed or purchased.  By leveraging AI, recommendation engines can detect patterns, predict intent, and deliver more relevant, personalized recommendations that adapt in real time as the user interacts with your site or app. How does Algolia ensure scalability for large businesses? 0 Algolia is built to handle enterprise-scale operations with exceptional reliability. The platform handles 30 billion records and nearly 1.7 trillion searches and recommendations a year with 99.999% availability, making it suitable for businesses of any size. What's the difference between content-based and personalized recommendations? 0 Content-based recommendations rely solely on item descriptions, while personalized recommendations incorporate user interactions to create individualized experiences.  What are the benefits of an AI-powered recommendation engine? 0 An AI-powered recommendation engine can lead to higher average order value, conversion rates , and customer lifetime value while also reducing bounce rates. For example, global retailer END increased conversions by 2% using Algolia’s AI Recommendations. What makes Algolia AI Recommendations different from other solutions? 0 Algolia stands out through several key differentiators: Speed : Sub-20 millisecond response times for real-time recommendations Scale : Proven ability to handle enterprise-level traffic and data volumes Ease of Implementation: Implement our APIs in minutes and gain easy control over rankings Comprehensive Models: Multiple recommendation types from collaborative filtering to image-based suggestions Global Language Support: Works across all major languages and character sets Integration Flexibilit y: Seamless connection with existing CMS and product catalogs The platform combines technical sophistication with user-friendly implementation, making advanced AI recommendations accessible to businesses of all sizes. Enable anyone to build great Search & Discovery Get a demo Start free Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Developers Developer Hub Documentation Integrations Engineering blog Discord community API status DocSearch For Open Source Live demos GDPR AI Act Industries Overview B2C ecommerce B2B ecommerce Marketplaces SaaS Media Startups Fashion Tools Search Grader Ecommerce Search Audit Products Overview AI Search AI Browse AI Recommendations Ask AI Intelligent Data Kit Use cases Overview Enterprise search Headless commerce Mobile & app search Voice search Image search OEM Site search Integrations Salesforce Commerce Cloud B2C Shopify Adobe Commerce Netlify Commercetools BigCommerce Distributed & secure Global infrastructure Security & compliance Azure AWS Company About Algolia Careers Newsroom Events Leadership Social impact Contact us Anti-Modern Slavery Statement Awards Social networks Algolia mark white ©2026 Algolia - All rights reserved. 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https://dev.to/t/beginners/page/3378	Beginners Page 3378 - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Beginners Follow Hide "A journey of a thousand miles begins with a single step." -Chinese Proverb Create Post submission guidelines UPDATED AUGUST 2, 2019 This tag is dedicated to beginners to programming, development, networking, or to a particular language. Everything should be geared towards that! For Questions... Consider using this tag along with #help, if... You are new to a language, or to programming in general, You want an explanation with NO prerequisite knowledge required. You want insight from more experienced developers. Please do not use this tag if you are merely new to a tool, library, or framework. See also, #explainlikeimfive For Articles... Posts should be specifically geared towards true beginners (experience level 0-2 out of 10). Posts should require NO prerequisite knowledge, except perhaps general (language-agnostic) essentials of programming. Posts should NOT merely be for beginners to a tool, library, or framework. If your article does not meet these qualifications, please select a different tag. Promotional Rules Posts should NOT primarily promote an external work. This is what Listings is for. Otherwise accepable posts MAY include a brief (1-2 sentence) plug for another resource at the bottom. Resource lists ARE acceptable if they follow these rules: Include at least 3 distinct authors/creators. Clearly indicate which resources are FREE, which require PII, and which cost money. Do not use personal affiliate links to monetize. Indicate at the top that the article contains promotional links. about #beginners If you're writing for this tag, we recommend you read this article . If you're asking a question, read this article . Older #beginners posts 3375 3376 3377 3378 3379 Posts Left menu 👋 Sign in for the ability to sort posts by relevant , latest , or top . Right menu loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
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https://dev.to/mohammadidrees/thinking-in-first-principles-how-to-question-an-async-queue-based-design-5cf1#why-this-matters	Thinking in First Principles: How to Question an Async Queue–Based Design - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Mohammad-Idrees Posted on Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Async queues are one of the most commonly suggested “solutions” in system design interviews. But many candidates jump straight to using queues without understanding: What problems they actually solve What new problems they introduce How to systematically discover those problems This post teaches a first-principles questioning process you can apply to any async queue design—without assuming prior knowledge. Why This Matters In interviews, interviewers are not evaluating whether you know Kafka, SQS, or RabbitMQ. They are evaluating whether you can: Reason about time Reason about failure Reason about order Reason about user experience Async queues change all four. What “First Principles” Means Here First principles means: We do not start with solutions We do not assume correctness We ask basic, unavoidable questions that every system must answer Async queues feel correct because they remove blocking—but correctness is not guaranteed by intuition. The Reference Mental Model (Abstract) We will reason about this abstract pattern , not a specific product: User → API → Storage → Queue → Worker → Storage Enter fullscreen mode Exit fullscreen mode No domain assumptions. This could be: Chat messages Emails Payments Notifications Image processing The questioning process stays the same. Step 1: The Root Question (Always Start Here) What is the system responsible for completing before it can respond? This is the most important question in system design. Why? Because it defines: Request boundaries Latency expectations Responsibility In an async queue design, the implicit answer is: “The request is complete once the work is enqueued.” This is different from synchronous designs, where the request completes after work finishes. So far, this seems good. Step 2: Introduce Time (What Happens Later?) Now ask: Which part of the work happens after the request is done? Answer: The worker processing This leads to an important realization: The system has split work across time Time separation is powerful—but it creates new questions. Step 3: Causality Question (Identity Across Time) Once work happens later, we must ask: How does the system know which output belongs to which input? This question always appears when time is decoupled. Typical answer: IDs in the job payload (request ID, entity ID) This introduces a new invariant: Each input must produce exactly one correct output Now we test whether the system can guarantee this. Step 4: Failure Question (The Queue Reality) Now ask the most important async-specific question: What happens if the worker crashes mid-processing? Realistic answers: The job is retried The work may run again The output may be produced twice This leads to a critical realization: Async queues are usually at-least-once , not exactly-once This is not a tooling issue. It is a fundamental property of distributed systems . Step 5: Duplication Question (Invariant Violation) Now ask: What happens if the same job is processed twice? Consequences: Duplicate outputs Duplicate side effects Conflicting state This violates the earlier invariant: “Exactly one output per input” At this point, we have discovered a correctness problem , not a performance problem. Step 6: Ordering Question (Time Without Synchrony) Now consider multiple inputs. Ask: What defines the order of processing? Important realization: Queue order ≠ business order Different workers process at different speeds Later inputs may finish first Now ask: Does correctness depend on order? If yes (and many systems do): Async queues alone are insufficient This problem emerges only when you question order explicitly. Step 7: Visibility Question (User Experience) Now switch perspectives. How does the user know the work is finished? Possible answers: Polling Guessing Timeouts Each answer reveals a problem: Polling wastes resources Guessing is unreliable Timeouts fail under load This violates a core system principle: Users should not wait blindly Case Study: A Simple Example (Problem-Agnostic) Imagine a system where users upload photos to be processed. Flow: User uploads photo API stores metadata Job is enqueued Worker processes photo Result is stored Now apply the questions: When does the upload request complete? → After enqueue What if the worker crashes? → Job retried What if it runs twice? → Two processed images What if two photos depend on order? → Order not guaranteed How does the user know processing is done? → Polling None of these issues are about images. They are about time, failure, identity, and visibility . What Async Queues Actually Trade Async queues solve one problem: They remove blocking from the request path But they introduce others: Solved Introduced Blocking Duplicate work Latency coupling Ordering ambiguity Resource exhaustion Completion uncertainty This is not bad. It just must be understood and handled . The One-Page Interview Checklist (Memorize This) For any async queue design , ask these five questions: What completes the request? What runs later? What happens if it runs twice? What defines order? How does the user observe completion? If you cannot answer all five clearly, the design is incomplete. Final Mental Model Async systems remove time coupling but destroy causality by default Your job as an engineer is not to “use queues” Your job is to restore correctness explicitly That is what interviewers are looking for. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Mohammad-Idrees Follow Joined Mar 16, 2023 More from Mohammad-Idrees How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/ben/my-public-inbox-4bj8	My Public Inbox - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Ben Halpern Posted on Feb 23, 2021           My Public Inbox # publicinbox # ama I'm going to pin this post to the top of my profile so there's a place for anyone to publicly ask me a question, and I'll do my best to reply when I can. I'm happy to offer advice primarily on the intersection of software, entrepreneurship and career. Happy coding! Top comments (115) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Collapse Expand   Reid Burton Reid Burton Reid Burton Follow I am an amateur programmer. I program in more languages than I care to remember. Location string Location = null; Education Homeschooled Pronouns He/Him Work Ceo of unemployment. Joined Nov 7, 2024 • Aug 1 '25 Dropdown menu Copy link Hide Hey, can you explain how @dumb_dev_meme_bot works? Like comment: Like comment: 2  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Aug 1 '25 Dropdown menu Copy link Hide Scraping the latest Meme Monday and then using the API to post. If you have any questions about the API feel free to post over at core.forem.com Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Reid Burton Reid Burton Reid Burton Follow I am an amateur programmer. I program in more languages than I care to remember. Location string Location = null; Education Homeschooled Pronouns He/Him Work Ceo of unemployment. Joined Nov 7, 2024 • Aug 2 '25 Dropdown menu Copy link Hide Neat! Also, how does someone make or suggest a tag? Like comment: Like comment: 1  like Like Thread Thread   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Aug 2 '25 Dropdown menu Copy link Hide We don’t have any official place right now but I’ll come up with one and get back to you. In the meantime just let me know your idea. Like comment: Like comment: 1  like Like Thread Thread   Reid Burton Reid Burton Reid Burton Follow I am an amateur programmer. I program in more languages than I care to remember. Location string Location = null; Education Homeschooled Pronouns He/Him Work Ceo of unemployment. Joined Nov 7, 2024 • Aug 2 '25 Dropdown menu Copy link Hide Fan theories for both Gamer and Popcorn Movies and TV Forems, as they are vital parts of both communities. Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   George Nance George Nance George Nance Follow I make the code do pretty things Location Phoenix, AZ Joined Aug 15, 2018 • Feb 23 '21 Dropdown menu Copy link Hide How did you grow enough of a following to launch a social network? Any advice for someone who wants to do the same? Like comment: Like comment: 13  likes Like Comment button Reply Collapse Expand   Lorenzo Lorenzo Lorenzo Follow Joined Jan 31, 2021 • Feb 23 '21 Dropdown menu Copy link Hide Yes, can you please give us advice about how to grow an audience as a dev? Like comment: Like comment: 3  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Feb 24 '21 Dropdown menu Copy link Hide I made a promise to myself that I wouldn't stop working on the project for 10 years, even if traction took forever. Then I methodically worked on content creation and observing what stuck and could lead to further opportunities. It was years of growing on Twitter before even typing rails new for what became DEV. Giving myself the room to do a lot of observing while methodically building helped ensure some amount of success. But it's also an area that combines several different skillsets of mine. FWIW it's going to be way easier for folks to build from scratch on Forem (the extraction from DEV we're working hard on).... We'll soon launch a Forem app which will act as a discovery mechanism for independent Forem social networks hosted in a distributed way, but discoverable through one app.... It's going to be really really cool. Like comment: Like comment: 41  likes Like Thread Thread   Syed Faraaz Ahmad Syed Faraaz Ahmad Syed Faraaz Ahmad Follow I like to build stuff Email faraaz98@live.com Location Bengaluru, India Education B.Tech. (Computer Engineering) Work Software Engineer at Deepsource Joined Aug 20, 2018 • Feb 24 '21 Dropdown menu Copy link Hide I made a promise to myself that I wouldn't stop working on the project for 10 years You must have had exceptional belief in DEV community then Like comment: Like comment: 7  likes Like Thread Thread   Lorenzo Lorenzo Lorenzo Follow Joined Jan 31, 2021 • Feb 24 '21 • Edited on Feb 24 • Edited Dropdown menu Copy link Hide Thanks for answering! Like comment: Like comment: 3  likes Like Thread Thread   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Feb 24 '21 Dropdown menu Copy link Hide You must have had exceptional belief in DEV community then I had belief in my own interest in seeing an improvement in online communities. My sense was that I wouldn't get bored of trying to help because I really cared. So with that in mind I also promised myself I wouldn't give up . In prior ventures I'd either gotten bored or given up primarily because I either didn't truly care about the mission deep down, or got involved with people I didn't like or respect as founders and people. I made sure with this venture to solve for some of those fundamentals early on and let the success come with patience. Like comment: Like comment: 12  likes Like Thread Thread   Elena Williams Elena Williams Elena Williams Follow Joined Apr 26, 2018 • Mar 18 '21 Dropdown menu Copy link Hide Sorry if I missed it, but how many years has it been (since the 10-year stop watch started, anathem-style)? My snooping suggests ... 8-ish? Though this could be completely misguided. Like comment: Like comment: 3  likes Like Comment button Reply Collapse Expand   Yuki Kimoto Yuki Kimoto Yuki Kimoto Follow I'm developing SPVM programing language and GitPrep now. Facebook https://www.facebook.com/profile/61550470287438 Location Japan/Tokyo Joined Mar 8, 2021 • Jan 2 '23 Dropdown menu Copy link Hide Thanks for your public inbox. I'm searching for the way to communicated with people. Like comment: Like comment: 4  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Jan 2 '23 Dropdown menu Copy link Hide 🙂 Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Christopher Wray Christopher Wray Christopher Wray Follow Email chris@sol.company Location Pasco, WA Education Western Governors University Work Senior Software Engineer at Soltech Joined Jan 14, 2020 • Feb 23 '21 Dropdown menu Copy link Hide Do you now make enough money to support yourself with DEV? Like comment: Like comment: 9  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Feb 24 '21 Dropdown menu Copy link Hide DEV (Forem) was once a ramen story (not paying ourselves, running out of money etc)... But now the company is pretty well funded and building a very sustainable business model around hosting Forems. Special Announcement From the DEV Founders Ben Halpern for The DEV Team ・ Nov 7 '19 #meta #news Like comment: Like comment: 9  likes Like Comment button Reply Collapse Expand   Christopher Wray Christopher Wray Christopher Wray Follow Email chris@sol.company Location Pasco, WA Education Western Governors University Work Senior Software Engineer at Soltech Joined Jan 14, 2020 • Feb 24 '21 Dropdown menu Copy link Hide Awesome 👏 Congratulations. I will do my best to read that other article. Like comment: Like comment: 3  likes Like Comment button Reply Collapse Expand   Temani Afif Temani Afif Temani Afif Follow Your favorite CSS Hacker Joined Feb 11, 2021 • Jun 8 '21 Dropdown menu Copy link Hide Hi Ben, I hope you don't mind I used your avatar to create a Loader meme: dev.to/afif/i-made-100-more-css-lo... ? PS: You may have missed my ping so I am writing you here. Cheers! Like comment: Like comment: 4  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Jun 8 '21 Dropdown menu Copy link Hide Sorry I saw it, but didn't react. I love it 😅. Like comment: Like comment: 4  likes Like Comment button Reply Collapse Expand   Iain Freestone Iain Freestone Iain Freestone Follow A Web developer from Hampshire in the south of England. Location Hampshire UK Work Web Developer Joined May 28, 2019 • Feb 24 '21 • Edited on Feb 24 • Edited Dropdown menu Copy link Hide Hi Ben, is there any way to get analytics on a post made to dev.to? The number of views figures are nice to see but would love to be able to track where the visitors came from. Thanks for the great work on this site. Like comment: Like comment: 4  likes Like Comment button Reply Collapse Expand   krishna kakade krishna kakade krishna kakade Follow console.log(' Open for UI/UX design roles') Email krishnadevz@protonmail.com Location India Education Computer Science & Engineering Work Unemployed Joined Jun 17, 2019 • Jul 22 '21 Dropdown menu Copy link Hide Hello Ben i hope you know me a little bit about but still I am krishna kakade. Currently I am in my last year of computer science and engineering from India and mostly working in web development related technologies. and i am interested in joining the devto/forem frontend development team as fresher student because i love to write blogs for forem and also i would to like to join core development team of forem and i also have to learn ruby and rails but i will learn it i can join within next 15 days you can also check my personal website here:- krishnadevz.github.io and resume here : I am ready to work hard and consistently for the betterment of the company's products. thank you have a nice day kind regards krishna kakade Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Jul 22 '21 Dropdown menu Copy link Hide Would you be thinking of this as an internship/apprenticeship sort of opportunity? Like comment: Like comment: 2  likes Like Comment button Reply Collapse Expand   krishna kakade krishna kakade krishna kakade Follow console.log(' Open for UI/UX design roles') Email krishnadevz@protonmail.com Location India Education Computer Science & Engineering Work Unemployed Joined Jun 17, 2019 • Jul 23 '21 • Edited on Jul 24 • Edited Dropdown menu Copy link Hide Yes and also I am about too graduate in next two months thank you 😊 Like comment: Like comment: 1  like Like Thread Thread   krishna kakade krishna kakade krishna kakade Follow console.log(' Open for UI/UX design roles') Email krishnadevz@protonmail.com Location India Education Computer Science & Engineering Work Unemployed Joined Jun 17, 2019 • Jul 24 '21 Dropdown menu Copy link Hide any updates ? Like comment: Like comment: 1  like Like Thread Thread   krishna kakade krishna kakade krishna kakade Follow console.log(' Open for UI/UX design roles') Email krishnadevz@protonmail.com Location India Education Computer Science & Engineering Work Unemployed Joined Jun 17, 2019 • Aug 4 '21 Dropdown menu Copy link Hide ? Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Peter H. Boling Peter H. Boling Peter H. Boling Follow AI is my Sidekiq. Human of Earth, maker of code, director, team leader, mentor, linux system admin, FLOSS advocate, barista, student, and builder of web applications great and small for 25 years. Email floss@galtzo.com Location Detroi, MI Education Ball State University, Purdue University Pronouns he/him/his Work You should hire me Joined Jan 17, 2021 • Apr 1 '23 • Edited on Apr 1 • Edited Dropdown menu Copy link Hide Are you familiar with the concept of "invariants"? It is a query you write with SQL, or via ActiveRecord, that should have a specific count result, usually 0 . For example, the count of users with invalid data should be zero. I have no idea how my Forem account broke, though I suspect it was related to when my Dev.to account was deleted/banned and accused of being a bot. Even since then my Dev.to access has worked, but I can't login to Forem, and the reset password, just goes in circles, never showing an error, but also never actually resetting my password. I'm guessing it is because user.save is returning false. Might be worthwhile having an invariant that check for users with a particular type of data characteristic, like my Forem account currently has, to make sure they are able to use the product. Account is peter dot boling at gmail dot com. Cheers! Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Peter H. Boling Peter H. Boling Peter H. Boling Follow AI is my Sidekiq. Human of Earth, maker of code, director, team leader, mentor, linux system admin, FLOSS advocate, barista, student, and builder of web applications great and small for 25 years. Email floss@galtzo.com Location Detroi, MI Education Ball State University, Purdue University Pronouns he/him/his Work You should hire me Joined Jan 17, 2021 • Apr 10 '23 • Edited on Apr 10 • Edited Dropdown menu Copy link Hide I am unable to sign up for an account on Forem. I am unable to login to Forem. I am unable to request a password reset on Forem. When you accidentally deleted my dev.to account, it must have banned me on Forem also. Is this something that can be resolved? I would ask support, but they lied to me (or you did, still unclear?) about the manner in which my account was deleted, so I am not comfortable messaging them again. You have a public face, so I'm inclined to believe your explanations over theirs. Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Peter H. Boling Peter H. Boling Peter H. Boling Follow AI is my Sidekiq. Human of Earth, maker of code, director, team leader, mentor, linux system admin, FLOSS advocate, barista, student, and builder of web applications great and small for 25 years. Email floss@galtzo.com Location Detroi, MI Education Ball State University, Purdue University Pronouns he/him/his Work You should hire me Joined Jan 17, 2021 • Apr 10 '23 • Edited on Apr 10 • Edited Dropdown menu Copy link Hide Shortly after posting that last comment I got an email that my Forem account had been locked due to too many failed login attempts. I used the link to unlock my account. I used the "forgot password" link to request a reset password link, and the email did actually come through! But upon attempting to set a new password, I was dumped back into the same cycle. Submitting the form clears it, and displays no messages. Logging in, in the hope that the reset might have worked, does the same. No error message. Just reloads the login form. Please unlock my account (for real this time)! In case you missed it in my first message, I suspect that my user record is unable to be saved, due to some invalid state. Like comment: Like comment: 2  likes Like Comment button Reply Collapse Expand   Max Phillips Max Phillips Max Phillips Follow Software engineer working on smart tv's Pronouns he/him Work Software Engineer Joined Sep 22, 2020 • Oct 24 '21 Dropdown menu Copy link Hide Hi Ben, I read the manifesto essay for Forem recently and was quite excited to see so many of the issues with the current state of the internet expressed so eloquently :) I was wondering if you have any advice for building successful business models for open source software? Thanks for starting this, I'm excited to see more community focused software in the future! Like comment: Like comment: 2  likes Like Comment button Reply Collapse Expand   Ben Halpern Ben Halpern Ben Halpern Follow A Canadian software developer who thinks he’s funny. Email ben@forem.com Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 • Oct 24 '21 Dropdown menu Copy link Hide I was wondering if you have any advice for building successful business models for open source software? Pay a lot of attention to what is established and working (read up on open core), but merge that with an exploration of what hasn’t been tried in the space you’re in — what is the unique way you’ll apply some good established ideas? Like comment: Like comment: 3  likes Like Comment button Reply Collapse Expand   Max Phillips Max Phillips Max Phillips Follow Software engineer working on smart tv's Pronouns he/him Work Software Engineer Joined Sep 22, 2020 • Oct 24 '21 Dropdown menu Copy link Hide Thanks for the reply! I hadn't heard of open core I'll read up on that. I'm currently studying arts and social media at university, and its been very interesting to see how the design choices made by platforms are impacting their use (although also a bit maddening at times). I think Forem's community-first approach is definitely the right track to be on. The values of open source seem to be pretty well aligned with the direction social media should be taking, though its surprising how rarely open source is considered as an option for that sort of every-day-person-facing software. Like comment: Like comment: 1  like Like Comment button Reply Collapse Expand   Uzondu Uzondu Uzondu Follow 🛠️ Earth’s in beta. Buggy, no undo button. I’m building anyway — SaaS is the strategy. Email uzondu.chubauzo21@gmail.com Location Enugu, Nigeria Pronouns Innovative front-end developer Creative UI-focused developer Joined Mar 22, 2024 • Apr 8 '25 Dropdown menu Copy link Hide I was wondering, how are dev challenges typically judged? Any additional insights would really be appreciated. I'm asking so I can better plan and set expectations for future ones. I know the post already touches on this a bit, but I’d love to hear something a bit more relatable — like whether judging is influenced by reactions or engagement, or if it’s purely technical. Thanks again in advance! 😊 Like comment: Like comment: 2  likes Like Comment button Reply View full discussion (115 comments) Some comments may only be visible to logged-in visitors. Sign in to view all comments. Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Ben Halpern Follow A Canadian software developer who thinks he’s funny. Location NY Education Mount Allison University Pronouns He/him Work Co-founder at Forem Joined Dec 27, 2015 More from Ben Halpern Still time to get your questions in! # ama # ai # machinelearning # discuss I created DEV and have other positive qualities, ask me anything! # ama # meta I created @ThePracticalDev and dev.to, ask me anything! # ama 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/mohammadidrees/thinking-in-first-principles-how-to-question-an-async-queue-based-design-5cf1#main-content	Thinking in First Principles: How to Question an Async Queue–Based Design - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Mohammad-Idrees Posted on Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Async queues are one of the most commonly suggested “solutions” in system design interviews. But many candidates jump straight to using queues without understanding: What problems they actually solve What new problems they introduce How to systematically discover those problems This post teaches a first-principles questioning process you can apply to any async queue design—without assuming prior knowledge. Why This Matters In interviews, interviewers are not evaluating whether you know Kafka, SQS, or RabbitMQ. They are evaluating whether you can: Reason about time Reason about failure Reason about order Reason about user experience Async queues change all four. What “First Principles” Means Here First principles means: We do not start with solutions We do not assume correctness We ask basic, unavoidable questions that every system must answer Async queues feel correct because they remove blocking—but correctness is not guaranteed by intuition. The Reference Mental Model (Abstract) We will reason about this abstract pattern , not a specific product: User → API → Storage → Queue → Worker → Storage Enter fullscreen mode Exit fullscreen mode No domain assumptions. This could be: Chat messages Emails Payments Notifications Image processing The questioning process stays the same. Step 1: The Root Question (Always Start Here) What is the system responsible for completing before it can respond? This is the most important question in system design. Why? Because it defines: Request boundaries Latency expectations Responsibility In an async queue design, the implicit answer is: “The request is complete once the work is enqueued.” This is different from synchronous designs, where the request completes after work finishes. So far, this seems good. Step 2: Introduce Time (What Happens Later?) Now ask: Which part of the work happens after the request is done? Answer: The worker processing This leads to an important realization: The system has split work across time Time separation is powerful—but it creates new questions. Step 3: Causality Question (Identity Across Time) Once work happens later, we must ask: How does the system know which output belongs to which input? This question always appears when time is decoupled. Typical answer: IDs in the job payload (request ID, entity ID) This introduces a new invariant: Each input must produce exactly one correct output Now we test whether the system can guarantee this. Step 4: Failure Question (The Queue Reality) Now ask the most important async-specific question: What happens if the worker crashes mid-processing? Realistic answers: The job is retried The work may run again The output may be produced twice This leads to a critical realization: Async queues are usually at-least-once , not exactly-once This is not a tooling issue. It is a fundamental property of distributed systems . Step 5: Duplication Question (Invariant Violation) Now ask: What happens if the same job is processed twice? Consequences: Duplicate outputs Duplicate side effects Conflicting state This violates the earlier invariant: “Exactly one output per input” At this point, we have discovered a correctness problem , not a performance problem. Step 6: Ordering Question (Time Without Synchrony) Now consider multiple inputs. Ask: What defines the order of processing? Important realization: Queue order ≠ business order Different workers process at different speeds Later inputs may finish first Now ask: Does correctness depend on order? If yes (and many systems do): Async queues alone are insufficient This problem emerges only when you question order explicitly. Step 7: Visibility Question (User Experience) Now switch perspectives. How does the user know the work is finished? Possible answers: Polling Guessing Timeouts Each answer reveals a problem: Polling wastes resources Guessing is unreliable Timeouts fail under load This violates a core system principle: Users should not wait blindly Case Study: A Simple Example (Problem-Agnostic) Imagine a system where users upload photos to be processed. Flow: User uploads photo API stores metadata Job is enqueued Worker processes photo Result is stored Now apply the questions: When does the upload request complete? → After enqueue What if the worker crashes? → Job retried What if it runs twice? → Two processed images What if two photos depend on order? → Order not guaranteed How does the user know processing is done? → Polling None of these issues are about images. They are about time, failure, identity, and visibility . What Async Queues Actually Trade Async queues solve one problem: They remove blocking from the request path But they introduce others: Solved Introduced Blocking Duplicate work Latency coupling Ordering ambiguity Resource exhaustion Completion uncertainty This is not bad. It just must be understood and handled . The One-Page Interview Checklist (Memorize This) For any async queue design , ask these five questions: What completes the request? What runs later? What happens if it runs twice? What defines order? How does the user observe completion? If you cannot answer all five clearly, the design is incomplete. Final Mental Model Async systems remove time coupling but destroy causality by default Your job as an engineer is not to “use queues” Your job is to restore correctness explicitly That is what interviewers are looking for. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Mohammad-Idrees Follow Joined Mar 16, 2023 More from Mohammad-Idrees How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/tatyanabayramova/glaucoma-awareness-month-363o#for-digital-content-follow-wcag-and-pdfua-standards	Glaucoma Awareness Month - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com           Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis Glaucoma Vision Simulator NoCoffee vision simulator for Firefox WCAG (Web Content Accessibility Guidelines) PDF/UA (PDF for Universal Access) European standard EN 301 549 Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer \| CPACC \| IAAP Member \| Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/alifunk/more-than-a-bootcamp-why-i-chose-the-german-umschulung-path-into-tech-20co	More Than a Bootcamp: Why I Chose the German 'Umschulung' Path into Tech - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Ali-Funk Posted on Jan 11 More Than a Bootcamp: Why I Chose the German 'Umschulung' Path into Tech # career # watercooler # devops # beginners I have 8 years of experience. Why am I doing a 2-year apprenticeship? Because shortcuts don't build careers.** The "Zero to Hero" Trap If you scroll through LinkedIn or YouTube today, the narrative is loud and seductive: "Become a Full Stack Developer in 12 weeks!" "Break into Cyber with this 6-week crash course!" "Get a 6-figure remote job with zero experience!" It sounds great. It sells courses. But let’s be real for a second: You cannot speed-run experience. I had a choice to make. I could have tried to hack my way into a mid-level role based on my past work. Instead, I chose to take a step back to leap forward. I enrolled in a German "Umschulung" (retraining) to become a Fachinformatiker Systemintegration (FiSi). To my international friends: This is not a bootcamp. This is a commitment. And here is why I—a guy with 8 years in the industry—am doing it. I Am Not Starting From Zero (The Ops Advantage) I didn't wake up yesterday deciding I like computers. I have spent the last 8 years in IT Support and Administration. I have been in the trenches. I know the panic of a server going down at 3 AM. I know that "fixing it in production" is very different from "fixing it in a lab." I have the scar tissue that only comes from dealing with legacy systems and real users. So, why go back to school? Why get an entry-level degree? Because I realized that experience without a solid theoretical foundation has a ceiling. I knew how to fix things, but I wanted to understand exactly why they work (or break) on the architectural level. I didn't just want a job; I wanted mastery. What is an "Umschulung" anyway? For those outside of the DACH (Germany/Austria/Switzerland) region, the concept might be hard to grasp. A "FiSi" Umschulung is not a course you watch on Udemy. Duration : It is a 2-year full-time program. Dual System : It combines vocational school (theory) with working in a real company (practice). The Standard : The final exams are standardized by the IHK (Chamber of Commerce). They are rigorous. You can't fake your way through them. In Germany, this qualification is the " Gold Standard " for technical infrastructure roles. It separates the hobbyists from the professionals. My Strategy: Building the Cathedral , Not a Tent I see many people rushing into Cloud or Cybersecurity without knowing what an IP address is or how Linux permissions work. They are trying to build a penthouse on a foundation of sand. I am using these two years to harden my foundation: Formalizing the Basics : Networking (CCNA level), Linux Administration (Red Hat style), and electrical engineering basics. The Pivot : I am using this safe environment to transition from "General Ops" to Cloud Architecture & Kubernetes Security. The Proof : At the end, I won't just have a portfolio; I will have a state-recognized degree that proves I know my stuff. Conclusion There is a huge difference between "getting a job" and "building a career." If you want a job quickly, maybe a bootcamp works (though the market in 2026 disagrees). But if you want a career that lasts 20 years, don't be afraid to take the long road. Don't be afraid to go back to the basics, even if you are experienced. I am trading " speed " for " substance ". And in an industry full of hype, substance is the ultimate competitive advantage. I write about my journey from SysAdmin to Cloud Architect, covering AWS, Kubernetes, and the reality of the IT job market. Let's connect on LinkedIn! Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Ali-Funk Follow Learning in Public. Transitioning into Cloud Security. Currently wrestling with AWS CCP and the Imposter Syndrome. I am here sharing what I learn so you don't have to make the same mistakes as I did. Location Germany Work Aspiring Cloud Security Architect Joined Jan 7, 2026 More from Ali-Funk Why I rescheduled my AWS exam today # aws # beginners # cloud # career 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://dev.to/mohammadidrees/thinking-in-first-principles-how-to-question-an-async-queue-based-design-5cf1#what-first-principles-means-here	Thinking in First Principles: How to Question an Async Queue–Based Design - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Mohammad-Idrees Posted on Jan 13 Thinking in First Principles: How to Question an Async Queue–Based Design # architecture # interview # learning # systemdesign Async queues are one of the most commonly suggested “solutions” in system design interviews. But many candidates jump straight to using queues without understanding: What problems they actually solve What new problems they introduce How to systematically discover those problems This post teaches a first-principles questioning process you can apply to any async queue design—without assuming prior knowledge. Why This Matters In interviews, interviewers are not evaluating whether you know Kafka, SQS, or RabbitMQ. They are evaluating whether you can: Reason about time Reason about failure Reason about order Reason about user experience Async queues change all four. What “First Principles” Means Here First principles means: We do not start with solutions We do not assume correctness We ask basic, unavoidable questions that every system must answer Async queues feel correct because they remove blocking—but correctness is not guaranteed by intuition. The Reference Mental Model (Abstract) We will reason about this abstract pattern , not a specific product: User → API → Storage → Queue → Worker → Storage Enter fullscreen mode Exit fullscreen mode No domain assumptions. This could be: Chat messages Emails Payments Notifications Image processing The questioning process stays the same. Step 1: The Root Question (Always Start Here) What is the system responsible for completing before it can respond? This is the most important question in system design. Why? Because it defines: Request boundaries Latency expectations Responsibility In an async queue design, the implicit answer is: “The request is complete once the work is enqueued.” This is different from synchronous designs, where the request completes after work finishes. So far, this seems good. Step 2: Introduce Time (What Happens Later?) Now ask: Which part of the work happens after the request is done? Answer: The worker processing This leads to an important realization: The system has split work across time Time separation is powerful—but it creates new questions. Step 3: Causality Question (Identity Across Time) Once work happens later, we must ask: How does the system know which output belongs to which input? This question always appears when time is decoupled. Typical answer: IDs in the job payload (request ID, entity ID) This introduces a new invariant: Each input must produce exactly one correct output Now we test whether the system can guarantee this. Step 4: Failure Question (The Queue Reality) Now ask the most important async-specific question: What happens if the worker crashes mid-processing? Realistic answers: The job is retried The work may run again The output may be produced twice This leads to a critical realization: Async queues are usually at-least-once , not exactly-once This is not a tooling issue. It is a fundamental property of distributed systems . Step 5: Duplication Question (Invariant Violation) Now ask: What happens if the same job is processed twice? Consequences: Duplicate outputs Duplicate side effects Conflicting state This violates the earlier invariant: “Exactly one output per input” At this point, we have discovered a correctness problem , not a performance problem. Step 6: Ordering Question (Time Without Synchrony) Now consider multiple inputs. Ask: What defines the order of processing? Important realization: Queue order ≠ business order Different workers process at different speeds Later inputs may finish first Now ask: Does correctness depend on order? If yes (and many systems do): Async queues alone are insufficient This problem emerges only when you question order explicitly. Step 7: Visibility Question (User Experience) Now switch perspectives. How does the user know the work is finished? Possible answers: Polling Guessing Timeouts Each answer reveals a problem: Polling wastes resources Guessing is unreliable Timeouts fail under load This violates a core system principle: Users should not wait blindly Case Study: A Simple Example (Problem-Agnostic) Imagine a system where users upload photos to be processed. Flow: User uploads photo API stores metadata Job is enqueued Worker processes photo Result is stored Now apply the questions: When does the upload request complete? → After enqueue What if the worker crashes? → Job retried What if it runs twice? → Two processed images What if two photos depend on order? → Order not guaranteed How does the user know processing is done? → Polling None of these issues are about images. They are about time, failure, identity, and visibility . What Async Queues Actually Trade Async queues solve one problem: They remove blocking from the request path But they introduce others: Solved Introduced Blocking Duplicate work Latency coupling Ordering ambiguity Resource exhaustion Completion uncertainty This is not bad. It just must be understood and handled . The One-Page Interview Checklist (Memorize This) For any async queue design , ask these five questions: What completes the request? What runs later? What happens if it runs twice? What defines order? How does the user observe completion? If you cannot answer all five clearly, the design is incomplete. Final Mental Model Async systems remove time coupling but destroy causality by default Your job as an engineer is not to “use queues” Your job is to restore correctness explicitly That is what interviewers are looking for. Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. 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Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Mohammad-Idrees Follow Joined Mar 16, 2023 More from Mohammad-Idrees How to Identify System Design Problems from First Principles # architecture # interview # systemdesign # tutorial 🧱 The Blueprint of Success: Mastering the Technical Requirements Document (TRD) # architecture # career # systemdesign 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/tatyanabayramova/glaucoma-awareness-month-363o#support-your-local-glaucoma-organizations	Glaucoma Awareness Month - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. 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A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Add reaction Like Unicorn Exploding Head Raised Hands Fire Jump to Comments Save Boost More... Copy link Copy link Copied to Clipboard Share to X Share to LinkedIn Share to Facebook Share to Mastodon Share Post via... Report Abuse Tatyana Bayramova, CPACC Posted on Jan 11 • Originally published at tatanotes.com           Glaucoma Awareness Month # a11y # discuss # news Glaucoma is one of the leading causes of blindness worldwide, affecting millions of people. It is estimated that approximately 80 million people globally have glaucoma, and the number is projected to grow to over 111 million by 2040 . Glaucoma is commonly known as the "silent thief of sight" because it usually has no symptoms in its early stages. With this condition, the optic nerve gets damaged slowly, leading to vision field reduction and, if left untreated, blindness. High intraocular pressure (IOP) is a major risk factor for glaucoma. Elevated IOP can damage the optic nerve fibers, leading to progressive vision loss, resulting in glaucoma. However, glaucoma can also occur in individuals with normal IOP levels, known as normal-tension glaucoma. High IOP alone is not a definitive indicator of glaucoma. Unfortunately, due to late diagnosis, one person I know lost their vision. Even though glaucoma has no cure yet, blindness could be prevented with regular eye exams and early treatment, such as applying eye drops, or performing an SLT procedure that helps lower IOP to prevent further damage to the optic nerve. What can you do to support people with glaucoma? Learn more about needs of people with glaucoma Glaucoma affects the way people perceive the environment. Use vision simulators like Glaucoma Vision Simulator or NoCoffee vision simulator for Firefox to understand how glaucoma affects vision. Adapt your digital and physical projects so that they're easy to use with visual impairments. Similar simulators exist for other visual impairments as well. For digital content, follow WCAG and PDF/UA standards WCAG criteria like 1.1.1. Non-text Content (Level A) , 1.4.4 Resize Text (Level AA) , and 4.1.2 Name, Role, Value (Level A) address needs of people with visual impairments, including glaucoma. This is not an exhaustive list, and you should aim to follow other WCAG criteria to ensure your digital content is accessible to people with disabilities. To ensure PDF accessibility, follow PDF/UA (PDF for Universal Access) standard. This will help make your documents accessible by users of assistive technologies, such as screen readers. Ensure compliance with EN 301 549 standard for a wider range of products European standard EN 301 549 specifies accessibility requirements for a broad range of products and services, including hardware, software, websites, and electronic documents. By following this standard, you can make your digital content is accessible to people with disabilities, including those with visual impairments like glaucoma. Complying with these standards is a great first step, but keep in mind that no guideline or automated tool guarantees accessibility. An effective way to ensure accessibility is to conduct accessibility user testing with people with disabilities. Accomodate for people with visual impairments, including glaucoma Adopt accessible practices in the physical world. Design physical spaces with accessibility in mind — for example, provide printed materials and signage in Braille or large print, whenever possible. To help people with glaucoma navigate the environment, install tactile paving. Support your local glaucoma organizations There are many organizations around the world that support glaucoma research, provide guidance and support groups for people with glaucoma. You can find a glaucoma society in your country on the World Glaucoma Association's list of member societies . Here are some glaucoma organizations you can support: European Glaucoma Society National Glaucoma Patient Support Groups American Glaucoma Society Glaucoma Research Society of Canada Glaucoma Australia By keeping accessibility barriers in mind, we can help ensure that individuals with glaucoma and other visual impairments can access and benefit from the great variety of products and public services. Sources How fast does glaucoma progress without treatment? Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis Glaucoma Vision Simulator NoCoffee vision simulator for Firefox WCAG (Web Content Accessibility Guidelines) PDF/UA (PDF for Universal Access) European standard EN 301 549 Top comments (0) Subscribe Personal Trusted User Create template Templates let you quickly answer FAQs or store snippets for re-use. Submit Preview Dismiss Code of Conduct • Report abuse Are you sure you want to hide this comment? It will become hidden in your post, but will still be visible via the comment's permalink . Hide child comments as well Confirm For further actions, you may consider blocking this person and/or reporting abuse Tatyana Bayramova, CPACC Follow Senior Software Engineer \| CPACC \| IAAP Member \| Accessibility Joined Dec 3, 2024 More from Tatyana Bayramova, CPACC Accessibility Testing on Windows on Mac # a11y # testing # web # discuss Our Rights, Our Future, Right Now - Celebrating Human Rights Day # a11y # discuss # news # learning Today is the International Day of Persons with Disabilities # a11y # webdev # frontend # discuss 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. 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https://dev.to/codemouse92	Jason C. McDonald - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Follow User actions Jason C. McDonald Author. Speaker. Time Lord. (Views are my own) Location Time Vortex Joined Joined on Jan 31, 2017 Email address codemouse92@outlook.com Personal website https://codemouse92.com github website twitter website Pronouns he/him Work Author of "Dead Simple Python" (No Starch Press) Eight Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least eight years. Got it Close 5 Top 7 Awarded for having a post featured in the weekly "must-reads" list. 🙌 Got it Close Writing Debut Awarded for writing and sharing your first DEV post! Continue sharing your work to earn the 4 Week Writing Streak Badge. Got it Close Seven Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least seven years. Got it Close Six Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least six years. Got it Close Tag Moderator 2022 Awarded for being a tag moderator in 2022. Got it Close Trusted Member 2022 Awarded for being a trusted member in 2022. Got it Close 1 Week Community Wellness Streak For actively engaging with the community by posting at least 2 comments in a single week. Got it Close Five Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least five years. Got it Close Four Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least four years. Got it Close DevDiscuss Podcast Guest Awarded to DEV community members who appeared as guests on the DevDiscuss podcast Got it Close Three Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least three years. Got it Close Fab 5 Awarded for having at least one comment featured in the weekly "top 5 posts" list. Got it Close She Coded Rewarded to participants in our annual International Women's Day event, either via #shecoded, #theycoded or #shecodedally Got it Close 8 Week Writing Streak The streak continues! You've written at least one post per week for 8 consecutive weeks. Unlock the 16-week badge next! Got it Close 4 Week Writing Streak You've posted at least one post per week for 4 consecutive weeks! Got it Close Two Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least two years. Got it Close Beloved Comment Awarded for making a well-loved comment, as voted on with 25 heart (❤️) reactions by the community. Got it Close One Year Club This badge celebrates the longevity of those who have been a registered member of the DEV Community for at least one year. Got it Close Show all 23 badges More info about @codemouse92 Organizations MousePaw Media The Bug Hunters Café GitHub Repositories wordperil A word puzzle party game. Python dkim_manage A script to automate most tasks associated with OpenDKIM key rotation. Shell • 5 stars Timecard Track time beautifully. Python • 26 stars dicebox Roll dice, flip coins, and simulate other decision-making methods. Python • 5 stars DEVModInACan Canned moderation messages and comments for DEV. 13 stars Elements A modern music library application. Python • 1 star no-monster-minecraft A data pack for Minecrafters who like playing without monsters. mcfunction • 15 stars WacomTouchToggle Easily turn on and off touchpad capabilities for Wacom tablets (such as the Wacom Bamboo) Shell • 1 star Skills/Languages Management and business analysis for complex and high-risk projects. Python and C++ expert. Legacy code modernization. Mentorship, building high-performance teams, running internships. Currently hacking on Quantified Tasks Available for Speaking, podcasts, consulting. Post 121 posts published Comment 2138 comments written Tag 27 tags followed Pin Pinned Dead Simple Python: Working with Files Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Dec 21 '19 Dead Simple Python: Working with Files # python # beginners 182 reactions Comments 11 comments 12 min read Three Ground Rules for Sane Project Planning Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 1 '19 Three Ground Rules for Sane Project Planning # management # coding # project # planning 83 reactions Comments 3 comments 8 min read How To Become A Developer -- Part 1: Coding Skills Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 6 '19 How To Become A Developer -- Part 1: Coding Skills # beginners # career 325 reactions Comments 7 comments 7 min read The Rules of Debugging Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Feb 16 '19 The Rules of Debugging # coding # culture # humor 197 reactions Comments 8 comments 8 min read Clean, DRY, SOLID Spaghetti Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Jul 24 '18 Clean, DRY, SOLID Spaghetti # oop # coding # culture # design 287 reactions Comments 37 comments 9 min read Searching Outside the Box (OTB Ep 9: Anna Greene-Hicks) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Dec 13 '24 Searching Outside the Box (OTB Ep 9: Anna Greene-Hicks) # career # jobsearch # interview # resume 1 reaction Comments Add Comment 1 min read Want to connect with Jason C. McDonald? Create an account to connect with Jason C. McDonald. You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in Networking Your Next Role (OTB Ep 8: Marlon Peseke) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Dec 6 '24 Networking Your Next Role (OTB Ep 8: Marlon Peseke) # career # jobsearch # interview # resume Comments Add Comment 1 min read Navigating Expectations (OTB Ep 7: JJ Brenner) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 22 '24 Navigating Expectations (OTB Ep 7: JJ Brenner) # career # jobsearch # interview # resume Comments Add Comment 1 min read Challenging Bias in Hiring (OTB Ep 6: Todd Lucas) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 15 '24 Challenging Bias in Hiring (OTB Ep 6: Todd Lucas) # career # jobsearch # interview # resume 1 reaction Comments Add Comment 1 min read Transcending the Niche (OTB Ep 5: Paul Hardin) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 8 '24 Transcending the Niche (OTB Ep 5: Paul Hardin) # career # jobsearch # interview # resume Comments Add Comment 1 min read Taking on New Challenges (OTB Ep 4: Ned Batchelder) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 1 '24 Taking on New Challenges (OTB Ep 4: Ned Batchelder) # career # jobsearch # interview # resume 5 reactions Comments 1 comment 1 min read Leveraging Job Hopping (OTB Ep 3: Abraham Vanderpool) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 30 '24 Leveraging Job Hopping (OTB Ep 3: Abraham Vanderpool) # jobsearch # career # resume # interview 2 reactions Comments Add Comment 1 min read Overcoming Imposter Syndrome (OTB Ep 2: Monica Ayhens-Madon) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 28 '24 Overcoming Imposter Syndrome (OTB Ep 2: Monica Ayhens-Madon) # career # jobsearch # interview # resume 1 reaction Comments Add Comment 1 min read Finding the Right Job (OTB Ep 1: Jennifer Rorex) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 25 '24 Finding the Right Job (OTB Ep 1: Jennifer Rorex) # career # jobsearch # resume # interview 1 reaction Comments Add Comment 1 min read Introducing "On The Board" Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 25 '24 Introducing "On The Board" # career # resume # interview # jobsearch 7 reactions Comments 1 comment 1 min read How To Estimate Software Development Effort Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Sep 7 '23 How To Estimate Software Development Effort # agile # management # scrum # kanban 7 reactions Comments 1 comment 6 min read Training Juniors Remotely Is Possible. Here's How. Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 28 '23 Training Juniors Remotely Is Possible. Here's How. # remote # management # workplace 14 reactions Comments 4 comments 11 min read Ten Principles of Critique Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Sep 30 '21 Ten Principles of Critique # culture # communication # community # codereview 34 reactions Comments 3 comments 5 min read Episode 9: Sneeze Decor Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Jul 12 '21 Episode 9: Sneeze Decor # speaking # communities # mentorship # programming 2 reactions Comments Add Comment 1 min read Episode 8: More Power To You Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Jul 8 '21 Episode 8: More Power To You # management # mentorship # leadership # teams Comments Add Comment 1 min read Episode 7: Brain Scans and Networking Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Jun 16 '21 Episode 7: Brain Scans and Networking # datascience # python # career # ux Comments Add Comment 1 min read Episode 6: Mentorship with Cheese Sauce Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Jun 1 '21 Episode 6: Mentorship with Cheese Sauce # teaching # learning # programming # mentorship 10 reactions Comments 3 comments 1 min read Six Things You Thought Senior Devs Did (But We Don't) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow May 21 '21 Six Things You Thought Senior Devs Did (But We Don't) 295 reactions Comments 58 comments 3 min read Episode 5: Bojan Reads the Documentation Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café May 3 '21 Episode 5: Bojan Reads the Documentation # agile # scrum # management 2 reactions Comments Add Comment 1 min read Episode 4: Attack of the Fresh Fruit Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Apr 19 '21 Episode 4: Attack of the Fresh Fruit 4 reactions Comments Add Comment 1 min read Episode 3: To Boldly Debug Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for The Bug Hunters Café Apr 8 '21 Episode 3: To Boldly Debug # debugging # python # devops # sre 3 reactions Comments Add Comment 1 min read News: Call to remove RMS from FSF Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Mar 24 '21 News: Call to remove RMS from FSF # news # inclusion 19 reactions Comments 6 comments 4 min read Type Literal Tabs Anywhere Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 28 '20 Type Literal Tabs Anywhere # linux # tooling 14 reactions Comments 1 comment 2 min read Writing Zenlike Python (Talk) Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Sep 15 '20 Writing Zenlike Python (Talk) # python # beginners 13 reactions Comments Add Comment 1 min read How to rename 'master' in an organization Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media Jul 7 '20 How to rename 'master' in an organization # devops # inclusion # git 14 reactions Comments Add Comment 4 min read Ask Guido van Rossum a question! Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for EuroPython Jul 6 '20 Ask Guido van Rossum a question! # python 12 reactions Comments Add Comment 1 min read 5 Ways to Retain Open Source Contributors Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Jul 6 '20 5 Ways to Retain Open Source Contributors # opensource # culture # projectmanagement 41 reactions Comments 4 comments 5 min read Goodbye Master, Hello...What? Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media Jun 29 '20 Goodbye Master, Hello...What? # devops # culture # inclusion # git 29 reactions Comments 19 comments 3 min read Development Log: One Month In Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media Jun 29 '20 Development Log: One Month In # python # contributorswanted # hackathon # gamedev 8 reactions Comments 1 comment 3 min read Development Log: All About Structure Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media Jun 12 '20 Development Log: All About Structure # python # gamedev # hackathon # contributorswanted 33 reactions Comments Add Comment 6 min read Development Log: Planning a Game Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media May 26 '20 Development Log: Planning a Game # contributorswanted # hackathon # python # gamedev 28 reactions Comments 1 comment 3 min read How to Apologize Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow May 25 '20 How to Apologize # culture # triplebyte 170 reactions Comments 8 comments 5 min read Are you a ladder or a roadblock? Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow May 20 '20 Are you a ladder or a roadblock? # career # culture # diversity 28 reactions Comments 7 comments 8 min read Windows and Linux: A Sane Discussion Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow May 16 '20 Windows and Linux: A Sane Discussion # discuss # healthydebate 47 reactions Comments 55 comments 2 min read GAME MODE 2020: Building a Game in One Month Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow for MousePaw Media Apr 30 '20 GAME MODE 2020: Building a Game in One Month # contributorswanted # hackathon # python # gamedev 55 reactions Comments 9 comments 2 min read Debugging with SQrL Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Apr 1 '20 Debugging with SQrL # jokes 4 reactions Comments Add Comment 1 min read Pair Programming: Dog Edition Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Feb 1 '20 Pair Programming: Dog Edition # jokes 50 reactions Comments 4 comments 1 min read Social Lifespan of Posts Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Jan 29 '20 Social Lifespan of Posts # discuss # meta 54 reactions Comments 30 comments 4 min read Turning Bugs Into Features Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Jan 14 '20 Turning Bugs Into Features # healthydebate # debugging # discuss 51 reactions Comments 2 comments 2 min read Socks Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Jan 8 '20 Socks # watercooler 18 reactions Comments 5 comments 1 min read Introducing: Timecard Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Dec 30 '19 Introducing: Timecard # showdev # python 63 reactions Comments 11 comments 6 min read The Use-Case Paradox Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 30 '19 The Use-Case Paradox # coding # philosophy 7 reactions Comments Add Comment 1 min read 8 Ways to Be More Professional Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 7 '19 8 Ways to Be More Professional # career # beginners 240 reactions Comments 28 comments 9 min read Python SnakeBytes: Unpacking Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Nov 5 '19 Python SnakeBytes: Unpacking # python # coding 19 reactions Comments 2 comments 1 min read What's Your Costume? Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 31 '19 What's Your Costume? # watercooler # discuss 15 reactions Comments 9 comments 1 min read 10 Skills of a Professional Author Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 28 '19 10 Skills of a Professional Author # writing 57 reactions Comments 3 comments 8 min read A Day In The Life Of A Writer Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 24 '19 A Day In The Life Of A Writer # writing 25 reactions Comments 5 comments 6 min read Python SnakeBytes: The Walrus Operator Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 21 '19 Python SnakeBytes: The Walrus Operator # python # coding 41 reactions Comments 7 comments 1 min read Has Stack Overflow Become An Antipattern? Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 19 '19 Has Stack Overflow Become An Antipattern? # culture 316 reactions Comments 109 comments 7 min read Beware Counterfeit No Starch Books from Amazon! Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Oct 13 '19 Beware Counterfeit No Starch Books from Amazon! # news # books 11 reactions Comments Add Comment 1 min read Compiled! An Unobfuscated Glossary Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Sep 6 '19 Compiled! An Unobfuscated Glossary # programming # coding # compiling # building 68 reactions Comments 4 comments 13 min read What Is An "Interpreted" Language? Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Sep 1 '19 What Is An "Interpreted" Language? # healthydebate # discuss 33 reactions Comments 31 comments 3 min read Introducing #devjournal Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 30 '19 Introducing #devjournal # devjournal # meta 106 reactions Comments 8 comments 2 min read Stealing Isn't "Sharing" Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 22 '19 Stealing Isn't "Sharing" # culture # ethics 53 reactions Comments 50 comments 11 min read Let's Get Clever #2: Spades Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 20 '19 Let's Get Clever #2: Spades # challenge # fun # coding # programming 11 reactions Comments Add Comment 4 min read Let's Get Clever #1: Fibonacci Sequence Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 13 '19 Let's Get Clever #1: Fibonacci Sequence # challenge # fun # coding # programming 44 reactions Comments 56 comments 2 min read The Dark Side Of The Magic Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 12 '19 The Dark Side Of The Magic # career # beginners # programming 68 reactions Comments 50 comments 6 min read Dead Simple Python: Lambdas, Decorators, and Other Magic Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 7 '19 Dead Simple Python: Lambdas, Decorators, and Other Magic # python # beginners # functional 125 reactions Comments 15 comments 14 min read How To Become A Developer -- Part 4: Recommended Reading Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 6 '19 How To Become A Developer -- Part 4: Recommended Reading # beginners # career 118 reactions Comments 1 comment 2 min read How To Become A Developer -- Part 3: People Skills Jason C. McDonald Jason C. McDonald Jason C. McDonald Follow Aug 6 '19 How To Become A Developer -- Part 3: People Skills # beginners # career 89 reactions Comments 10 comments 5 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=48019#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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https://dev.to/alifunk	Ali-Funk - DEV Community Forem Feed Follow new Subforems to improve your feed DEV Community Follow A space to discuss and keep up software development and manage your software career Future Follow News and discussion of science and technology such as AI, VR, cryptocurrency, quantum computing, and more. Open Forem Follow A general discussion space for the Forem community. If it doesn't have a home elsewhere, it belongs here Gamers Forem Follow An inclusive community for gaming enthusiasts Music Forem Follow From composing and gigging to gear, hot music takes, and everything in between. Vibe Coding Forem Follow Discussing AI software development, and showing off what we're building. Popcorn Movies and TV Follow Movie and TV enthusiasm, criticism and everything in-between. DUMB DEV Community Follow Memes and software development shitposting Design Community Follow Web design, graphic design and everything in-between Security Forem Follow Your central hub for all things security. From ethical hacking and CTFs to GRC and career development, for beginners and pros alike Golf Forem Follow A community of golfers and golfing enthusiasts Crypto Forem Follow A collaborative community for all things Crypto—from Bitcoin to protocol development and DeFi to NFTs and market analysis. Parenting Follow A place for parents to the share the joys, challenges, and wisdom that come from raising kids. We're here for them and for each other. Forem Core Follow Discussing the core forem open source software project — features, bugs, performance, self-hosting. Maker Forem Follow A community for makers, hobbyists, and professionals to discuss Arduino, Raspberry Pi, 3D printing, and much more. HMPL.js Forem Follow For developers using HMPL.js to build fast, lightweight web apps. A space to share projects, ask questions, and discuss server-driven templating Dropdown menu Dropdown menu Skip to content Navigation menu Search Powered by Algolia Search Log in Create account DEV Community Close Follow User actions Ali-Funk Learning in Public. Transitioning into Cloud Security. Currently wrestling with AWS CCP and the Imposter Syndrome. I am here sharing what I learn so you don't have to make the same mistakes as I did. Location Germany Joined Joined on Jan 7, 2026 github website Work Aspiring Cloud Security Architect More info about @alifunk Badges Writing Debut Awarded for writing and sharing your first DEV post! Continue sharing your work to earn the 4 Week Writing Streak Badge. Got it Close Skills/Languages System Integration Generalist focusing on AWS & Cloud Security Available for Let´s talk about learning for AWS and Cloud in general. Post 4 posts published Comment 2 comments written Tag 0 tags followed Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend Ali-Funk Ali-Funk Ali-Funk Follow Jan 12 Why "Ownership" is the Best Certification: Building Infrastructure for an AWS Legend # aws # community # career # cloud 5 reactions Comments Add Comment 2 min read Want to connect with Ali-Funk? Create an account to connect with Ali-Funk. You can also sign in below to proceed if you already have an account. Create Account Already have an account? Sign in More Than a Bootcamp: Why I Chose the German 'Umschulung' Path into Tech Ali-Funk Ali-Funk Ali-Funk Follow Jan 11 More Than a Bootcamp: Why I Chose the German 'Umschulung' Path into Tech # watercooler # career # devops # beginners Comments Add Comment 3 min read LLMs are like Humans - They make mistakes. Here is how we limit them with Guardrails Ali-Funk Ali-Funk Ali-Funk Follow Jan 8 LLMs are like Humans - They make mistakes. Here is how we limit them with Guardrails # aws # ai # guardrails # architecture Comments Add Comment 2 min read Why I rescheduled my AWS exam today Ali-Funk Ali-Funk Ali-Funk Follow Jan 7 Why I rescheduled my AWS exam today # aws # beginners # cloud # career Comments Add Comment 2 min read loading... 💎 DEV Diamond Sponsors Thank you to our Diamond Sponsors for supporting the DEV Community Google AI is the official AI Model and Platform Partner of DEV Neon is the official database partner of DEV Algolia is the official search partner of DEV DEV Community — A space to discuss and keep up software development and manage your software career Home DEV++ Podcasts Videos DEV Education Tracks DEV Challenges DEV Help Advertise on DEV DEV Showcase About Contact Free Postgres Database Software comparisons Forem Shop Code of Conduct Privacy Policy Terms of Use Built on Forem — the open source software that powers DEV and other inclusive communities. Made with love and Ruby on Rails . DEV Community © 2016 - 2026. We're a place where coders share, stay up-to-date and grow their careers. Log in Create account	2026-01-13T08:48:55
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https://docs.python.org/3.13/	3.13.11 Documentation Theme Auto Light Dark Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide Navigation index modules \| Python » 3.13.11 Documentation » \| Theme Auto Light Dark \| Python 3.13.11 documentation Welcome! This is the official documentation for Python 3.13.11. Documentation sections: What's new in Python 3.13? Or all "What's new" documents since Python 2.0 Tutorial Start here: a tour of Python's syntax and features Library reference Standard library and builtins Language reference Syntax and language elements Python setup and usage How to install, configure, and use Python Python HOWTOs In-depth topic manuals Installing Python modules Third-party modules and PyPI.org Distributing Python modules Publishing modules for use by other people Extending and embedding For C/C++ programmers Python's C API C API reference FAQs Frequently asked questions (with answers!) Deprecations Deprecated functionality Indices, glossary, and search: Global module index All modules and libraries General index All functions, classes, and terms Glossary Terms explained Search page Search this documentation Complete table of contents Lists all sections and subsections Project information: Reporting issues Contributing to docs Download the documentation History and license of Python Copyright About the documentation Download Download these documents Docs by version Python 3.15 (in development) Python 3.14 (stable) Python 3.13 (stable) Python 3.12 (security-fixes) Python 3.11 (security-fixes) Python 3.10 (security-fixes) Python 3.9 (EOL) Python 3.8 (EOL) Python 3.7 (EOL) Python 3.6 (EOL) Python 3.5 (EOL) Python 3.4 (EOL) Python 3.3 (EOL) Python 3.2 (EOL) Python 3.1 (EOL) Python 3.0 (EOL) Python 2.7 (EOL) Python 2.6 (EOL) All versions Other resources PEP Index Beginner's Guide Book List Audio/Visual Talks Python Developer’s Guide « Navigation index modules \| Python » 3.13.11 Documentation » \| Theme Auto Light Dark \| © Copyright 2001-2026, Python Software Foundation. This page is licensed under the Python Software Foundation License Version 2. Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. See History and License for more information. The Python Software Foundation is a non-profit corporation. Please donate. Last updated on Jan 13, 2026 (07:50 UTC). Found a bug ? Created using Sphinx 8.2.3.	2026-01-13T08:48:55
https://tinyhack.com/2014/03/12/implementing-a-web-server-in-a-single-printf-call/?replytocom=23737#respond	Implementing a web server in a single printf() call – Tinyhack.com --> Skip to content Tinyhack.com A hacker does for love what others would not do for money. Implementing a web server in a single printf() call A guy just forwarded a joke that most of us will already know Jeff Dean Facts (also here and here ). Everytime I read that list, this part stands out: Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search. It is really possible to implement a web server using a single printf call, but I haven’t found anyone doing it. So this time after reading the list, I decided to implement it. So here is the code, a pure single printf call, without any extra variables or macros (don’t worry, I will explain how to this code works) #include <stdio.h> int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3", ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 + 2, (((unsigned long int)0x4005c8 + 12) & 0xffff)- ((((unsigned long int)0x4005c8 + 12) >> 16) & 0xffff), 0, 0x00000000006007D8 ); } This code only works on a Linux AMD64 bit system, with a particular compiler (gcc version 4.8.2 (Debian 4.8.2-16) ) And to compile it: gcc -g web1.c -O webserver As some of you may have guessed: I cheated by using a special format string . That code may not run on your machine because I have hardcoded two addresses. The following version is a little bit more user friendly (easier to change), but you are still going to need to change 2 values: FUNCTION_ADDR and DESTADDR which I will explain later: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) #define DESTADDR 0x00000000006007D8 #define a (FUNCTION_ADDR & 0xffff) #define b ((FUNCTION_ADDR >> 16) & 0xffff) int main(int argc, char argv[]) { printf("%c%hn%c%hn" "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3" , b, 0, DESTADDR + 2, a-b, 0, DESTADDR ); } I will explain how the code works through a series of short C codes. The first one is a code that will explain how that we can start another code without function call. See this simple code: #include <stdlib.h> #include <stdio.h> #define ADDR 0x00000000600720 void hello() { printf("hello world\n"); } int main(int argc, char argv[]) { (((unsigned long int)ADDR))= (unsigned long int)hello; } You can compile it, but it many not run on your system. You need to do these steps: 1. Compile the code: gcc run-finalizer.c -o run-finalizer 2. Examine the address of fini_array objdump -h -j .fini_array run-finalizer And find the VMA of it: run-finalizer: file format elf64-x86-64 Sections: Idx Name Size VMA LMA File off Algn 18 .fini_array 00000008 0000000000600720 0000000000600720 00000720 23 CONTENTS, ALLOC, LOAD, DATA Note that you need a recent GCC to do this, older version of gcc uses different mechanism of storing finalizers. 3. Change the value of ADDR on the code to the correct address 4. Compile the code again 5. Run it and now you will see “hello world” printed to your screen. How does this work exactly?: According to Chapter 11 of Linux Standard Base Core Specification 3.1 .fini_array This section holds an array of function pointers that contributes to a single termination array for the executable or shared object containing the section. We are overwriting the array so that our hello function is called instead of the default handler. If you are trying to compile the webserver code, the value of ADDR is obtained the same way (using objdump). Ok, now we know how to execute a function by overriding a certain address, we need to know how we can overwrite an address using printf . You can find many tutorials on how to exploit format string bugs, but I will try give a short explanation. The printf function has this feature that enables us to know how many characters has been printed using the “%n” format: #include <stdio.h> int main(){ int count; printf("AB%n", &count); printf("\n%d characters printed\n", count); } You will see that the output is: AB 2 characters printed Of course we can put any address to the count pointer to overwrite that address. But to overide an address with a large value we need to print a large amount of text. Fortunately there is another format string “%hn” that works on short instead of int. We can overwrite the value 2 bytes at a time to form the 4 byte value that we want. Lets try to use two printf calls to put a¡ value that we want (in this case the pointer to function “hello”) to the fini_array: #include <stdio.h> #include <stdlib.h> #include <stdint.h> #define FUNCTION_ADDR ((uint64_t)hello) #define DESTADDR 0x0000000000600948 void hello() { printf("\n\n\n\nhello world\n\n"); } int main(int argc, char argv[]) { short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("a = %04x b = %04x\n", a, b) uint64_t p = (uint64_t)DESTADDR; printf("before: %08lx\n", p); printf("%c%hn", b, 0, DESTADDR + 2 ); printf("after1: %08lx\n", p); printf("%c%hn", a, 0, DESTADDR); printf("after2: %08lx\n", p); return 0; } The important lines are: short a= FUNCTION_ADDR & 0xffff; short b = (FUNCTION_ADDR >> 16) & 0xffff; printf("%c%hn", b, 0, DESTADDR + 2 ); printf("%c%hn", a, 0, DESTADDR); The a and b are just halves of the function address, we can construct a string of length a and b to be given to printf, but I chose to use the “%” formatting which will control the length of the output through parameter. For example, this code: printf("%c", 10, 'A'); Will print 9 spaces followed by A, so in total, 10 characters will be printed. If we want to use just one printf, we need to take account that b bytes have been printed, and we need to print another b-a bytes (the counter is accumulative). printf("%c%hn%c%hn", b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); Currently we are using the “hello” function to call, but we can call any function (or any address). I have written a shellcode that acts as a web server that just prints “Hello world”. This is the shell code that I made: unsigned char hello[] = "\xeb\x3d\x48\x54\x54\x50\x2f\x31\x2e\x30\x20\x32" "\x30\x30\x0d\x0a\x43\x6f\x6e\x74\x65\x6e\x74\x2d" "\x74\x79\x70\x65\x3a\x74\x65\x78\x74\x2f\x68\x74" "\x6d\x6c\x0d\x0a\x0d\x0a\x3c\x68\x31\x3e\x48\x65" "\x6c\x6c\x6f\x20\x57\x6f\x72\x6c\x64\x21\x3c\x2f" "\x68\x31\x3e\x4c\x8d\x2d\xbc\xff\xff\xff\x48\x89" "\xe3\x48\x83\xeb\x10\x48\x31\xc0\x50\x66\xb8\x1f" "\x90\xc1\xe0\x10\xb0\x02\x50\x31\xd2\x31\xf6\xff" "\xc6\x89\xf7\xff\xc7\x31\xc0\xb0\x29\x0f\x05\x49" "\x89\xc2\x31\xd2\xb2\x10\x48\x89\xde\x89\xc7\x31" "\xc0\xb0\x31\x0f\x05\x31\xc0\xb0\x05\x89\xc6\x4c" "\x89\xd0\x89\xc7\x31\xc0\xb0\x32\x0f\x05\x31\xd2" "\x31\xf6\x4c\x89\xd0\x89\xc7\x31\xc0\xb0\x2b\x0f" "\x05\x49\x89\xc4\x48\x31\xd2\xb2\x3d\x4c\x89\xee" "\x4c\x89\xe7\x31\xc0\xff\xc0\x0f\x05\x31\xf6\xff" "\xc6\xff\xc6\x4c\x89\xe7\x31\xc0\xb0\x30\x0f\x05" "\x4c\x89\xe7\x31\xc0\xb0\x03\x0f\x05\xeb\xc3"; If we remove the function hello and insert that shell code, that code will be called. That code is just a string, so we can append it to the “%c%hn%c%hn” format string. This string is unnamed, so we will need to find the address after we compile it. To obtain the address, we need to compile the code, then disassemble it: objdump -d webserver 00000000004004fd <main>: 4004fd: 55 push %rbp 4004fe: 48 89 e5 mov %rsp,%rbp 400501: 48 83 ec 20 sub $0x20,%rsp 400505: 89 7d fc mov %edi,-0x4(%rbp) 400508: 48 89 75 f0 mov %rsi,-0x10(%rbp) 40050c: c7 04 24 d8 07 60 00 movl $0x6007d8,(%rsp) 400513: 41 b9 00 00 00 00 mov $0x0,%r9d 400519: 41 b8 94 05 00 00 mov $0x594,%r8d 40051f: b9 da 07 60 00 mov $0x6007da,%ecx 400524: ba 00 00 00 00 mov $0x0,%edx 400529: be 40 00 00 00 mov $0x40,%esi 40052e: bf c8 05 40 00 mov $0x4005c8,%edi 400533: b8 00 00 00 00 mov $0x0,%eax 400538: e8 a3 fe ff ff callq 4003e0 <printf@plt> 40053d: c9 leaveq 40053e: c3 retq 40053f: 90 nop We only need to care about this line: mov $0x4005c8,%edi That is the address that we need in: #define FUNCTION_ADDR ((uint64_t)0x4005c8 + 12) The +12 is needed because our shell code starts after the string “%c%hn%c%hn” which is 12 characters long. If you are curious about the shell code, it was created from the following C code. #include<stdio.h> #include<string.h> #include<stdlib.h> #include<unistd.h> #include<sys/types.h> #include<sys/stat.h> #include<sys/socket.h> #include<arpa/inet.h> #include<netdb.h> #include<signal.h> #include<fcntl.h> int main(int argc, char argv[]) { int sockfd = socket(AF_INET, SOCK_STREAM, 0); struct sockaddr_in serv_addr; bzero((char )&serv_addr, sizeof(serv_addr)); serv_addr.sin_family = AF_INET; serv_addr.sin_addr.s_addr = INADDR_ANY; serv_addr.sin_port = htons(8080); bind(sockfd, (struct sockaddr )&serv_addr, sizeof(serv_addr)); listen(sockfd, 5); while (1) { int cfd = accept(sockfd, 0, 0); char s = "HTTP/1.0 200\r\nContent-type:text/html\r\n\r\n<h1>Hello world!</h1>"; if (fork()==0) { write(cfd, s, strlen(s)); shutdown(cfd, SHUT_RDWR); close(cfd); } } return 0; } I have done an extra effort (although it is not really necessary in this case) to remove all NUL character from the shell code (since I couldn’t find one for X86-64 in the Shellcodes database ). Jeff Dean once implemented a web server in a single printf() call. Other engineers added thousands of lines of explanatory comments but still don’t understand exactly how it works. Today that program is the front-end to Google Search . It is left as an exercise for the reader to scale the web server to able to handle Google search load. Source codes for this post is available at https://github.com/yohanes/printf-webserver For people who thinks that this is useless: yes it is useless. I just happen to like this challenge, and it has refreshed my memory and knowledge for the following topics: shell code writing (haven’t done this in years), AMD64 assembly (calling convention, preserved registers, etc), syscalls, objdump, fini_array (last time I checked, gcc still used .dtors), printf format exploiting, gdb tricks (like writing memory block to file), and low level socket code (I have been using boost’s for the past few years). Update : Ubuntu adds a security feature that provides a read-only relocation table area in the final ELF. To be able to run the examples in ubuntu, add this in the command line when compiling -Wl,-z,norelro e.g: gcc -Wl,-z,norelro test.c Author admin Posted on March 12, 2014 April 28, 2017 Categories hacks 18 thoughts on “Implementing a web server in a single printf() call” dodi says: March 12, 2014 at 2:04 pm eh buset, serius nih lu ? 🙂 Reply priyo says: March 13, 2014 at 5:07 am scroll up… scroll down… scroll up… scroll down… 100x gagal paham* Reply terminalcommand says: March 13, 2014 at 5:19 am Thank you! Very interesting article. I also didn’t know about the one line webserver at google. Although this is a hard topic, you’ve made a great work simplifying it. Reply Basun says: March 13, 2014 at 10:02 am The one line webserver bit is a joke about Jeff Dean, who works at Google. Its not real. 🙂 Reply Cees Timmerman says: April 20, 2016 at 4:12 pm There are real webserver oneliners: https://gist.github.com/willurd/5720255 Reply anonim says: March 13, 2014 at 5:29 am Diskusinya di https://news.ycombinator.com/item?id=7389623 Reply Neil says: March 13, 2014 at 12:38 pm Shouldn’t there be an exit() somewhere in the fork==0 branch? Otherwise every time there is a request the new child process will become a server too and start accepting requests, right? I think the parent leaks its copy of the file descriptor too. Maybe the fork is a bit redundant. I don’t think the write or close will block with such a small amount of data. Cool post though! I’m not really sure why I’m nitpicking in the shell code. Sorry. Reply admin says: March 14, 2014 at 1:58 am Ah yes, there is an exit from the loop on the assembly code (myhttp.s) but it got removed from http.c when I removed the comment and debug code. And you are also right about the fork, it is unnecessary in this case. At first I was going to write the HTTP headers and then exec some external command. I changed my mind and didn’t bother deleting the fork call. Reply Kyle Ross says: March 13, 2014 at 11:02 pm This is really interesting, but I’m having trouble following whats actually happening. Could you explain how you reduced that C code with includes and methods into a string containing hex codes and how that is turned back into some sort of executable code? Thanks Reply admin says: March 14, 2014 at 2:01 am I think it is beyond the scope of this article to explain about shell code writing. There are many books and tutorials that you can read (just search for “buffer overflow” or “shell code writing”). Reply TTK Ciar says: March 14, 2014 at 1:05 am Alternatively: $ perl -Mojo -E ‘a({inline => “%= `uptime`”})->start’ daemon & Server available at http://127.0.0.1:3000 . $ lynx -dump -nolist http://127.0.0.1:3000/ 17:57:56 up 66 days, 6:45, 108 users, load average: 0.10, 0.12, 0.07 though, perl by definition is cheating. Reply Evan Danaher says: March 14, 2014 at 2:54 pm I’m not sure why you used finalizers instead of just changing the return address on the stack; this may be the first time I’ve ever said this, but stack smashing is much more portable. I’ve made a variant that I’d expect to work on any gcc 4.4-4.7 on x86_64 Linux, and have some ideas which, if they work out, may make it actually “portable” to any x86/x86_64 Unix running a reasonable compiler. https://github.com/edanaher/printf-webserver Reply admin says: March 17, 2014 at 3:02 pm Yes using the stack is also possible, but on most modern system, GCC is compiled with stack protection turned on (and needs to be disabled using -fno-stack-protector). Reply Pingback: Implementing a web server in a single printf() call « adafruit industries blog Itzik Kotler says: March 15, 2014 at 4:35 pm Pretty neat. I did something similar (all though simpler) back in the days. See: http://www.exploit-db.com/papers/13233/ Reply Pingback: Saving the world, one cpu cycle at a time \| Dav's bit o the web programath says: April 22, 2014 at 1:18 pm printf(“%c%hn%c%hn”, b, 0, DESTADDR + 2, b-a, 0, DESTADDR ); ————————————————— i think the fourth parameter should be ‘a-b’, not ‘b-a’, because a == b + (a – b) Reply Pingback: New top story on Hacker News: Implementing a web server in a single printf call (2014) – Latest news Leave a Reply Cancel reply Your email address will not be published. Required fields are marked * Comment * Name * Email * Website Save my name, email, and website in this browser for the next time I comment. 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