| --- |
| title: DOS MQTT LAB |
| emoji: 🖥️ |
| colorFrom: green |
| colorTo: blue |
| sdk: static |
| pinned: false |
| --- |
| |
| # DOS MQTT LAB — DOS programs that really go online |
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| Two **FreeDOS** machines run in the page (v86 x86 emulator). Each has an emulated **NE2000** network card. Inside DOS: |
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| 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**. |
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| | 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. | |
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| 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. |
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| ## How the packets reach a public broker |
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| 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. |
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| So the DOS side is genuine TCP/IP; only the last hop (browser → broker) is a WebSocket. |
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| ## Things to know |
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| - **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`). |
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| ## Sources and licenses |
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| See `LICENSE`, `NOTICE.md` and `src/` (DOS program sources, build scripts, boot-disk scripts). GPL-3.0-or-later. |
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| ## DOS × Gradio (`gradio.html`) |
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| `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`. |
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| ## Developer package |
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| `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`. |
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