MCP Transport Types

mistral.rs supports three transport types for connecting to MCP servers, each optimized for different use cases.

HTTP Transport

Best for public APIs, RESTful services, and servers behind load balancers.

Configuration

json

{
  "source": {
    "type": "Http",
    "url": "https://api.example.com/mcp",
    "timeout_secs": 30,
    "headers": {
      "X-API-Version": "v1",
      "User-Agent": "mistral-rs/0.6.0"
    }
  },
  "bearer_token": "your-api-token"
}

Features

Server-Sent Events (SSE) support for streaming responses
Custom headers for API versioning or client identification
Bearer token authentication (added as Authorization: Bearer <token>)
Configurable timeouts
Standard HTTP semantics

Example: Hugging Face MCP

rust

McpServerSource::Http {
    url: "https://hf.co/mcp".to_string(),
    timeout_secs: Some(30),
    headers: None,
}

WebSocket Transport

Best for real-time applications, bidirectional communication, and low-latency requirements.

Configuration

json

{
  "source": {
    "type": "WebSocket",
    "url": "wss://realtime.example.com/mcp",
    "timeout_secs": 60,
    "headers": {
      "Origin": "https://mistral.rs",
      "Sec-WebSocket-Protocol": "mcp"
    }
  },
  "bearer_token": "your-websocket-token"
}

Features

Persistent connections reduce handshake overhead
Server-initiated notifications
Lower latency for frequent tool calls
Automatic reconnection handling
WebSocket-specific headers support

Example: Real-time Data Feed

rust

McpServerSource::WebSocket {
    url: "wss://data.example.com/mcp".to_string(),
    timeout_secs: Some(60),
    headers: Some(headers),
}

Process Transport

Best for local tools, development servers, and sandboxed environments.

Configuration

json

{
  "source": {
    "type": "Process",
    "command": "mcp-server-filesystem",
    "args": ["--root", "/tmp", "--readonly"],
    "work_dir": "/home/user/workspace",
    "env": {
      "MCP_LOG_LEVEL": "info",
      "MCP_TIMEOUT": "30"
    }
  }
}

Features

No network overhead
Process isolation for security
Direct stdin/stdout communication
Environment variable configuration
Working directory control
No authentication needed (process inherits permissions)

Example: Filesystem Server

rust

McpServerSource::Process {
    command: "mcp-server-filesystem".to_string(),
    args: vec!["--root".to_string(), "/tmp".to_string()],
    work_dir: None,
    env: None,
}

Transport Selection Guide

Use Case	Recommended Transport	Why
Public APIs	HTTP	Standard auth, caching, load balancing
Local tools	Process	No network, process isolation
Real-time data	WebSocket	Low latency, server push
Corporate proxies	HTTP	Proxy support, standard ports
Development	Process	Easy debugging, no network setup
Interactive apps	WebSocket	Bidirectional, persistent connection

Security Considerations

HTTP

Always use HTTPS in production
Bearer tokens transmitted with each request
Consider token rotation strategies

WebSocket

Use WSS (WebSocket Secure) in production
Bearer token sent during handshake
Connection persists with authenticated state

Process

Inherits user permissions
Sandboxing via work_dir and env
No network exposure

Performance Tips

HTTP: Enable keep-alive, use connection pooling
WebSocket: Reuse connections, handle reconnection gracefully
Process: Minimize startup time, use long-running processes

Error Handling

All transports implement automatic retry with exponential backoff:

Initial retry: 1 second
Max retry: 60 seconds
Max attempts: 5

Custom retry behavior can be configured per server.