Doom, Played over Curl

DOOM, played over curl.

HTTP server rendering DOOM frames into ANSI half-blocks, streamed to the terminal over HTTP with cURL.

No install, no dependencies except curl and bash.

curl -sL http://localhost:3000 | bash

GET / is content-negotiated: a curl gets back play.sh with __SERVER__ rewritten to whichever host you fetched it from. The script runs the per-keystroke /tick loop, handles stty, the alternate screen, the cursor, and cleanup.

A browser hitting the same URL gets a tiny landing page that just shows the one-liner.

stty -echo -icanon min 1 time 0 && curl -sN -X POST -T - localhost:3000/play

• Default small screen. See below to set columns and rows.
• Press any key to start playing.
• Ctrl+C to quit. 'q' doesn't work here. reset to fix your terminal back.

If you don't want to use the default small screen here, set the columns and rows:

curl -sN -X POST -T - "localhost:3000/play?cols=200&rows=60"

One streaming HTTP request, two directions: keystrokes go up the request body, ANSI frames come down the response body. No key-loop wrapper, no per-keystroke round-trip. This is Just a single TCP connection doing both halves at once.

The catch: the shell normally puts the terminal in cooked mode, which (a) line-buffers stdin so curl doesn't see a key until you hit Enter, and (b) echoes everything you type on top of the frames. So you have to flip the terminal into raw mode first, and put it back when you're done. Hence the stty command before the curl and having to call reset to set it straight.

You can also do it cleanly this slightly longer way:

( stty -echo -icanon min 1 time 0 < /dev/tty
trap 'stty sane < /dev/tty' EXIT INT TERM
curl -sN -X POST -T - localhost:3000/play < /dev/tty )

Held-key behavior: the server releases each key 150 ms after the last byte for it, so holding w moves you smoothly forward. Press Ctrl-C to disconnect. The trap restores the terminal either way.

/play defaults to 15 fps, because curl with -T - doesn't service the response socket while stdin is silent (it's blocked in read(stdin)), so frames pile up in the kernel send buffer between keystrokes and burst-drain when you press something. 15 fps keeps the bursts small enough that the terminal can render each frame before the next one arrives. To override:

... "http://localhost:3000/play?cols=200&rows=60&fps=25" …

Frames overwrite the previous frame in place via cursor-home (no per-frame screen clear), so even when a slow terminal can't keep up the worst you'll see is a "torn" frame (a top from frame N+1, bottom from frame N) instead of a blank one.

If you just want to watch without playing (frames stream regardless of input), no stty is needed and no -T - blocking happens, so the default 15 fps is perfectly smooth and you can crank it higher:

curl -sN -X POST "http://localhost:3000/play?cols=200&rows=60&fps=30"

Doom plays itself idly. Hit Ctrl-C when bored.

terminal cURL DOOM server
------------- ----------------
curl GET / ----------> play.sh
<---------- (with __SERVER__ rewritten)
pipe to bash
stty raw mode
read keypress
curl POST /tick?s=&key= --------> feed key into doom session
<-------- ANSI frame from doom's framebuffer
print to /dev/tty
loop

The server keeps one doomgeneric process per session. Each session has:

• a stdin pipe used to push text commands (K keypress, T advance tics, F dump a frame, Q quit),
• a dedicated frame pipe on fd 3 so doom's own printf logging on stderr can't corrupt the binary framebuffer,
• a virtual clock that the headless backend bumps inside DG_SleepMs, so doom's "wait until next tic" loop unblocks instantly instead of sleeping.

Each frame from doom is 640×400 BGRA pixels (1 MB). The server downsamples to the terminal's cols x rows*2 pixel grid using the upper-half-block glyph ▀ (foreground = top pixel, background = bottom pixel, that's how you get vertical resolution doubling for free), and only emits an SGR escape when the color actually changes. That shrinks the response ~5x.

Idle sessions are reaped after 60 seconds. Killing the Node process kills every child doom along with it.

This is only for hosting the game, not playing it.

• Node.js 18+
• A C compiler (cc/clang/gcc) and make
• doom1 shareware WAD
• doomgeneric source code

# 1. Install Node deps
npm install
# 2. Build the headless doom binary (once)
cd doomgeneric/doomgeneric && make -f Makefile.server && cd ../..
# 3. Start the server
npm start
# -> cURL DOOM running on http://localhost:3000
# -> Play with: curl -sL http://localhost:3000 | bash

The code assumes on doom1.wad (the freely-distributed shareware episode). To use a different WAD, drop it in the project root and edit the WAD constant in index.js.

| Key | Action | |---|---| | W / ↑ | Move forward | | S / ↓ | Move backward | | A / ← | Turn left | | D / → | Turn right | | , / . | Strafe left / right | | F | Fire | | Space / E | Use / open door | | Tab | Automap | | Enter | Menu confirm | | Esc | Menu / back | | Y / N | Yes / no in menu dialogs | | Q | Quit |

The session jumps straight into E1M1 on Hurt me plenty (-warp 1 1 -skill 3), so you skip the title screen and the menu dance.

| Env var | Default | Effect | |---|---|---| | DOOM_SERVER | http://localhost:3000 | Where the client connects | | DOOM_COLS | terminal width | Force a viewport width | | DOOM_ROWS | terminal height − 1 | Force a viewport height | | PORT | 3000 | Server-side: listening port |

The client auto-detects terminal size with stty size < /dev/tty (reading the kernel's TTY state via ioctl(TIOCGWINSZ), falling back to tput and $LINES/$COLUMNS only if that fails). Doom's native resolution under the half-block glyph is 320x200 pixels = 320 columns x 100 rows of terminal cells, so anything bigger gets clamped (it'd just be upscaling).

# Force a small viewport on a big terminal
DOOM_COLS=120 DOOM_ROWS=40 ./doom.sh
# Point at a remote server
DOOM_SERVER=https://doom.example.com ./doom.sh

All routes accept ?cols=N&rows=N to override the rendered viewport.

GET /: Content-negotiated landing, script for curl, HTML for browsers POST /new: Create session, return 1st frame, X-Session header for session id POST /tick?s=&key=: Push one key, advance ~5 tics, return next frame POST /play?cols=&rows=&fps=: Bidi streaming, request body = keystrokes, response body = ANSI frames (default 15 fps, range 5-35) POST /quit?s=: Tear down a session immediately (instead of waiting 60 s) GET /health: {"sessions": N}

Author: Sawyer X. Doom: id Software, 1993. doomgeneric: by ozkl, the abstraction that lets me swap in a custom rendering backend. doom1.wad: the shareware episode, freely distributable.