Tutorial 12

Transports

Demonstrates the five transport mechanisms available in finemcp for client-server communication.

Transport Comparison

Transport	Function	Sessions	Streaming	Bidirectional	Use Case
HTTP	`transport.StartHTTP(s, addr)`	No	No	No	Simple REST-like deployments
Streamable HTTP	`transport.StartStreamable(ctx, s, addr)`	Yes (`Mcp-Session-Id`)	Yes (SSE)	Yes (GET SSE)	Modern MCP standard (2025-03-26+)
SSE	`transport.StartSSE(s, addr)`	Yes (URL-based)	Yes	Yes	Legacy streaming
WebSocket	`transport.StartWebSocket(s, addr)`	Yes	Yes	Yes	Full-duplex real-time
Stdio	`transport.ServeStdio(ctx, s)`	No	Via stdout	Via stdin/stdout	CLI tools, subprocesses

Examples

http/

Simplest transport — stateless HTTP POST with JSON-RPC request/response:

transport.StartHTTP(s, ":8080")

curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 1, "method": "initialize",
  "params": { "protocolVersion": "2025-03-26", "clientInfo": { "name": "curl", "version": "1.0.0" }, "capabilities": {} }
}'

streamable/

Modern transport with session management and SSE streaming:

transport.StartStreamable(context.Background(), s, ":8080")

# Initialize (save Mcp-Session-Id from response headers)
curl -v -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 1, "method": "initialize",
  "params": { "protocolVersion": "2025-03-26", "clientInfo": { "name": "curl", "version": "1.0.0" }, "capabilities": {} }
}'

# Subsequent requests require the session header
curl -X POST http://localhost:8080 -H "Content-Type: application/json" \
  -H "Mcp-Session-Id: <session-id>" -d '{
  "jsonrpc": "2.0", "id": 2, "method": "tools/list"
}'

sse/

Legacy SSE transport — client connects to /sse for events, sends to /message:

transport.StartSSE(s, ":8080")

# Terminal 1: Connect to SSE stream (returns message URL)
curl -N http://localhost:8080/sse

# Terminal 2: Send requests to the message URL from SSE stream
curl -X POST "<message_url>" -H "Content-Type: application/json" -d '{
  "jsonrpc": "2.0", "id": 1, "method": "initialize",
  "params": { "protocolVersion": "2025-03-26", "clientInfo": { "name": "curl", "version": "1.0.0" }, "capabilities": {} }
}'

websocket/

Full-duplex WebSocket transport:

transport.StartWebSocket(s, ":8080")

# Using websocat
websocat ws://localhost:8080

# Type JSON-RPC messages interactively:
{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","clientInfo":{"name":"ws-client","version":"1.0.0"},"capabilities":{}}}
{"jsonrpc":"2.0","id":2,"method":"tools/list"}

stdio/

Subprocess transport over stdin/stdout:

transport.ServeStdio(context.Background(), s)

echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","clientInfo":{"name":"cli","version":"1.0.0"},"capabilities":{}}}' | go run ./12-transports/stdio

Choosing a Transport

Starting out? Use StartHTTP — simplest, no sessions, easy to curl.
Need streaming? Use StartStreamable — the modern MCP standard.
Full-duplex? Use StartWebSocket for real-time bidirectional communication.
CLI tool? Use ServeStdio for subprocess-based hosting.
Legacy clients? Use StartSSE for backwards compatibility.