README.md

metadata

title: DOS MQTT LAB
emoji: 🖥️
colorFrom: green
colorTo: blue
sdk: static
pinned: false

DOS MQTT LAB — DOS programs that really go online

Two FreeDOS machines run in the page (v86 x86 emulator). Each has an emulated NE2000 network card. Inside DOS:

1. the Crynwr NE2000 packet driver is loaded,
2. mTCP's DHCP.EXE obtains an address (192.168.86.100),
3. A.EXE (listener) and B.EXE (sender) are real DOS programs, built with Open Watcom against the mTCP TCP/IP stack. They do their own DNS lookup, TCP handshake and speak MQTT 3.1.1.

Program	Behaviour
A.EXE	Connects, subscribes to the shared topic, and prints each received message. One second later it prints an echo line.
B.EXE	Run once: connects, publishes Hello from DOS B at HH:MM:SS (DOS clock), disconnects, exits.

The page types A into machine A once and types B into machine B every 5 seconds (DOS has no scheduler). Both DOS screens and an observation log show whether A received what B sent.

How the packets reach a public broker

Browsers cannot open raw TCP sockets, and Hugging Face static Spaces have no server. v86 terminates the guest's TCP streams; bridge.js plays a tiny in-page WISP server that relays every stream the guest opens on port 1883 to a public broker's MQTT-over-WebSocket (WSS) endpoint. MQTT is identical on both transports, so the bytes DOS writes are exactly what the broker receives. DNS goes through DNS-over-HTTPS (Cloudflare) via v86.

So the DOS side is genuine TCP/IP; only the last hop (browser → broker) is a WebSocket.

Things to know

• Default broker is wss://broker.emqx.io:8084/mqtt. Public brokers vary: in our tests broker.hivemq.com often took ~10 s to answer a CONNECT (or never did), while EMQX and test.mosquitto.org answered every time. Pick another from the list if one misbehaves.
• "Background" A is a separate DOS machine, because DOS itself is single-tasking.
• The DOS clock is UTC.
• Both machines are on isolated virtual networks, so they can both use 192.168.86.100.
• If a B run has not finished when the next 5-second tick arrives, that tick is skipped and logged.
• Copy the topic to another tab or device to see messages travel between separate browsers.
• The page needs a modern browser (WebAssembly, DecompressionStream).

Sources and licenses

See LICENSE, NOTICE.md and src/ (DOS program sources, build scripts, boot-disk scripts). GPL-3.0-or-later.

DOS × Gradio (gradio.html)

G.EXE is a third DOS program: it sends a question to a public Gradio Space (default tencent/Hy3) with plain HTTP through the same emulated NE2000/mTCP stack, reads the streamed answer and prints it. The page forwards the plain HTTP as HTTPS, but only to *.hf.space paths starting with /gradio_api/, and checks that the answer shown on the DOS screen equals the one Gradio returned. Use English (DOS shows ASCII). Open gradio.html.

Developer package

dev/dosmqtt-dev.zip holds the sources, build scripts, tests and the developer handover (dev/HANDOFF.md). It also contains the mTCP source archive that A.EXE / B.EXE are linked against. Rebuild everything with tools/build_all.sh.