MPP Server (Rust)

Rust port of the Multiplayer Piano server with way better performance than the Node.js version. [Original]

Note: Some genius called my original README "AI slop" so I dumbed it down to their reading level. You're welcome.

2025-11-03.02-55-05.mp4

Why?

The Node.js version works fine, but it starts choking at around 1000 concurrent users. This rewrite handles 50k+ connections without breaking a sweat. Plus no garbage collection pauses, which is nice.

Performance differences:

• 3-5x faster message processing
• ~15MB memory vs ~50MB for Node
• <1ms latency even under heavy load
• 500k+ messages/sec throughput

All the same features as the original. WebSocket-based real-time piano playing, channels, chat, crown system, bans, the whole deal.

Setup

You need Rust 1.70+ from https://rustup.rs/

git clone https://github.com/nyxikitty/mpp-server-rust.git
cd mpp-server-rust

# Sound files are already included, you're good to go

cargo build --release

Running

Development:

cargo run

Production (much faster):

cargo run --release

Server runs at http://localhost:8080

Config

Optional .env file:

WS_PORT=8080
NODE_ENV=production
RUST_LOG=mpp_server=info
SALT1=random_string_here
SALT2=another_random_string

The salts are for hashing client IPs in production. If you don't set NODE_ENV to production, it'll just use random IDs.

How it works

Clients connect via WebSocket at ws://localhost:8080/ws and send JSON arrays:

[{"m": "hi"}]
[{"m": "ch", "_id": "lobby"}]
[{"m": "n", "t": 1234567890, "n": [{"n": "a1", "v": 0.5}]}]

Message types

• hi - Connect
• bye - Disconnect
• +ls/-ls - Subscribe/unsubscribe from channel list
• t - Time sync
• a - Chat
• n - Play notes
• m - Move cursor
• userset - Change name/color
• ch - Join/create channel
• chset - Change channel settings
• chown - Give crown to someone
• kickban - Ban user
• unban - Unban user
• devices - MIDI device list

Code structure

src/
├── main.rs       - Axum setup
├── server.rs     - Connection handling
├── handlers.rs   - Message handlers
├── types.rs      - Data structures
└── utils.rs      - Helpers
client/           - HTML/CSS/JS (from original)

Uses Tokio for async, Axum for WebSocket, DashMap for lock-free state, Serde for JSON.

Deployment

systemd

/etc/systemd/system/mpp-server.service:

[Unit]
Description=MPP Server
After=network.target

[Service]
Type=simple
User=mpp
WorkingDirectory=/opt/mpp-server
Environment="RUST_LOG=mpp_server=info"
Environment="NODE_ENV=production"
ExecStart=/opt/mpp-server/target/release/mpp-server
Restart=always

[Install]
WantedBy=multi-user.target

sudo systemctl enable mpp-server
sudo systemctl start mpp-server

nginx

server {
    listen 80;
    server_name mpp.example.com;

    location /ws {
        proxy_pass http://127.0.0.1:8080;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }

    location / {
        proxy_pass http://127.0.0.1:8080;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Docker

version: '3.8'

services:
  mpp-server:
    build: .
    ports:
      - "8080:8080"
    environment:
      - NODE_ENV=production
      - RUST_LOG=mpp_server=info
    restart: unless-stopped

Dockerfile:

FROM rust:1.75 as builder
WORKDIR /app
COPY Cargo.* ./
COPY src ./src
RUN cargo build --release

FROM debian:bookworm-slim
WORKDIR /app
COPY --from=builder /app/target/release/mpp-server .
COPY client ./client
EXPOSE 8080
CMD ["./mpp-server"]

Troubleshooting

WebSocket won't connect

• Check your firewall
• Make sure you're using ws:// not http://
• Look at browser console

Notes don't play

• Sound files should be in client/sounds/
• Check browser console for 404s

Memory issues

• Check if the banned users map is getting huge
• Use --release flag, debug builds use way more memory

Performance tips

• Always use --release for production (it's like 10-100x faster)
• Set RUST_LOG to info or warn in production
• Increase file descriptor limit: ulimit -n 65535

Tech stack

• tokio - async runtime
• axum - web framework
• serde - JSON
• dashmap - concurrent hashmap
• tower-http - middleware
• tracing - logging

License

MIT - same as the original

Contributing

PRs welcome. Just try to keep it compatible with the Node version's protocol.

Credits

Based on the original MPP server

Piano sounds from https://github.com/multiplayerpiano/piano-sounds