MCP Server Runner

Note: This project is currently under active development and in WIP (Work In Progress) status. Features and APIs may change significantly.

A WebSocket server implementation for running Model Context Protocol (MCP) servers. This application enables MCP servers to be accessed via WebSocket connections, facilitating integration with web applications and other network-enabled clients.

Development Status

• 🚧 Work In Progress: This software is in active development
• ⚠️ API Stability: APIs and features may change without notice
• 🧪 Testing: Currently undergoing testing and refinement
• 📝 Documentation: Documentation is being actively updated

Overview

MCP Server Runner acts as a bridge between WebSocket clients and MCP server implementations. It:

• Launches an MCP server process
• Manages WebSocket connections
• Handles bidirectional communication between clients and the MCP server
• Supports graceful shutdown and error handling

Features

• WebSocket server implementation with single-client support
• Process management for MCP server instances
• Bidirectional message passing between client and server
• Graceful shutdown handling
• Comprehensive error logging
• Cross-platform support (Unix/Windows)

Prerequisites

• Rust 1.70 or higher
• An MCP server implementation executable

Configuration

Environment Variables

The application can be configured through environment variables:

PROGRAM=        # Path to the MCP server executable (required if no config file)
ARGS=           # Comma-separated list of arguments for the MCP server
HOST=0.0.0.0    # Host address to bind to (default: 0.0.0.0)
PORT=8080       # Port to listen on (default: 8080)
CONFIG_FILE=    # Path to JSON configuration file

Additional environment variables will be passed through to the MCP server process.

JSON Configuration

Alternatively, you can provide a JSON configuration file:

{
  "servers": {
    "filesystem": {
      "command": "npx",
      "args": [
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/path/to/workspace"
      ]
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "your_token_here"
      }
    }
  },
  "default_server": "filesystem",
  "host": "0.0.0.0",
  "port": 8080
}

You can specify the configuration file in two ways:

1. As a command-line argument: mcp-server-runner config.json
2. Using the CONFIG_FILE environment variable: CONFIG_FILE=config.json mcp-server-runner

The JSON configuration allows you to define multiple server configurations and select one as the default.

Configuration Priority

1. Command-line specified config file
2. CONFIG_FILE environment variable
3. Environment variables (PROGRAM, ARGS, etc.)
4. Default values

Usage

1. Using environment variables:

   export PROGRAM=npx
   export ARGS=-y,@modelcontextprotocol/server-github
   export PORT=8080
   export GITHUB_PERSONAL_ACCESS_TOKEN=github_pat_***
   cargo run
   

2. Using a configuration file:

   # Either specify the config file as an argument
   cargo run config.json
   
   # Or use the CONFIG_FILE environment variable
   CONFIG_FILE=config.json cargo run
   

3. Connect to the WebSocket server:

   const ws = new WebSocket("ws://localhost:8080");
   

Docker Support

A Dockerfile and docker-compose.yml are provided for containerized deployment:

docker-compose up --build

Development

Build the project:

cargo build

Run tests:

cargo test

Run with debug logging:

RUST_LOG=debug cargo run

Architecture

The application follows a modular architecture:

• main.rs: Application entry point and server setup
• config/: Configuration loading and management
• process/: Process management and I/O handling
• websocket/: WebSocket connection management
• state.rs: Global state management
• shutdown.rs: Graceful shutdown handling

Error Handling

• Standard error output from the MCP server is logged but not forwarded to clients
• WebSocket connection errors are handled gracefully
• Process errors are logged with detailed information

Limitations

• Supports only one client connection at a time
• Does not support WebSocket SSL/TLS (use a reverse proxy for secure connections)
• No built-in authentication mechanism

Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

License

This project is licensed under the MIT License - see the LICENSE file for details.

Additional Resources

• Model Context Protocol Specification
• WebSocket Protocol (RFC 6455)