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proj# Plan: Stream Doom → Node.js Server → Browser

Context

The full pipeline already exists in code:

  • src/i/StdoutFrameWriter.java — writes binary RGBA frames to stdout
  • server/server.js — Node.js server parses frames, converts to JPEG, broadcasts via WebSocket
  • server/index.html — browser client renders JPEG frames on a canvas

The recent commits ("still trying to output over stream") indicate the stream is not working. The root cause is a stdout redirect bug explained below.

Root Cause: Stdout Redirect Bug

In Engine.main() (line 55), when -stdout is detected:

System.setOut(System.err);  // redirect ALL Java output to stderr

This runs before new Engine(argv) — and therefore before new StdoutFrameWriter().

In StdoutFrameWriter constructor (line 44):

this.out = new DataOutputStream(new BufferedOutputStream(System.out, 256 * 1024));

At this point System.out is already the redirected stream (i.e. stderr). So frame data is written to stderr, not stdout. The Node.js process piping stdout receives nothing.

Fix

1. src/i/StdoutFrameWriter.java — use FileDescriptor.out directly

Replace the constructor body with:

import java.io.FileDescriptor;
import java.io.FileOutputStream;

public StdoutFrameWriter() {
    // FileDescriptor.out is the real file descriptor 1 (stdout), unaffected
    // by System.setOut() which only redirects the Java PrintStream wrapper.
    this.out = new DataOutputStream(
        new BufferedOutputStream(new FileOutputStream(FileDescriptor.out), 256 * 1024)
    );
}

This bypasses System.setOut() entirely and writes directly to the OS-level stdout fd, which is what the Node.js pipe reads.

2. server/server.js — add game flags to spawn args

The current GAME_ARGS (line 40) lacks -nosound and a game-activity mode. Update:

const GAME_ARGS = [
  '-jar', 'src/mochadoom.jar',
  '-stdout',
  '-nosound',
  '-demokeys',   // drive game with synthetic keys so frames aren't static
];

Alternatively use -timedemo demo1 instead of -demokeys to replay a built-in demo. Ignore the demo all togerther

Files to Modify

File Change
src/i/StdoutFrameWriter.java Constructor: new FileOutputStream(FileDescriptor.out) instead of System.out
server/server.js Add -nosound and -demokeys to GAME_ARGS array

Run Instructions (Windows)

# 1. Install Node deps (once)
cd server; npm install; cd ..

# 2. Build the JAR
.\build-jar.ps1

# 3. Start the streaming server (spawns Java automatically)
cd server; node server.js --spawn

Then open http://localhost:8080 in a browser. The canvas should show live Doom frames.

Verification

  1. Terminal shows: DOOM stream server running at http://localhost:8080
  2. Browser status pill shows LIVE (green dot)
  3. Frame counter increments in the top-right stats
  4. FPS meter shows a positive value
  5. Canvas displays Doom gameplay frames