MSMP — Minecraft Server Multiplexer Proxy

MSMP is a lightweight Rust-based reverse proxy that allows multiple Minecraft servers to be hosted behind a single port. It routes incoming connections to the correct backend server by intercepting the Minecraft handshake packet and reading the subdomain of the server address the client is connecting from.

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How It Works

When a Minecraft client connects, it sends a handshake packet containing the server address it is trying to reach (e.g. survival.example.com). MSMP intercepts this packet before any connection is forwarded, extracts the subdomain (survival), and looks it up in a config file to find the corresponding backend port.

Once the target port is found, MSMP:

1. Opens a TCP connection to the backend server on 127.0.0.1:<port>
2. Forwards the original handshake packet so the backend receives it normally
3. Spawns a thread to forward data from the backend server back to the client
4. Continuously forwards data from the client to the backend in the main loop

This creates a transparent TCP tunnel — the backend server and the client behave as if they are connected directly.

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Architecture

Client
  │
  ▼
MSMP :2001
  │  reads handshake
  │  extracts subdomain
  │
  ├──► survival   → 127.0.0.1:25565
  ├──► creative   → 127.0.0.1:25566
  └──► minigames  → 127.0.0.1:25567

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Configuration

Servers are defined in a file named servers in the project root. Each line follows the format:

server_name,port

Example:

survival,25565
creative,25566
minigames,25567

The server_name must match the subdomain the client uses to connect. For example, a client connecting to survival.example.com will be routed to port 25565.

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Usage

1. Configure your servers file

survival,25565
creative,25566

2. Start your Minecraft servers

Make sure each backend server is running on its configured port on 127.0.0.1.

3. Run MSMP

cargo run

MSMP will start listening on port 2001.

4. Connect from Minecraft

In the Minecraft client, connect to:

survival.yourdomain.com:2001

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Dependencies

Crate	Purpose
tokio	Async runtime for handling concurrent connections
dotenv	Loads environment variables from a .env file

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Limitations

• All backend servers must be running on 127.0.0.1 (localhost)
• No graceful error handling if a backend server is unreachable — the connection will panic
• Buffer size is fixed at 1024 bytes which may cause issues with large packets
• No TLS/SSL support