MCP协议深度解析：Transport层实现全攻略

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前言

在之前的文章中，我们介绍了MCP的整体架构。今天我们来深入MCP的核心——**传输层（Transport Layer）**实现。

MCP定义了两种标准传输机制：

  1. stdio：本地进程通信
  2. Streamable HTTP：远程服务器通信（替代了旧版HTTP+SSE）

本文将从协议规范到完整代码，手把手带你实现MCP传输层。

MCP协议基础

JSON-RPC 2.0消息格式

MCP基于JSON-RPC 2.0，所有消息都是UTF-8编码的JSON：

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// Request
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "initialize",
  "params": { ... }
}

// Response
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": { ... }
}

// Error Response
{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": -32600,
    "message": "Invalid Request"
  }
}

// Notification (no id, no response)
{
  "jsonrpc": "2.0",
  "method": "notifications/initialized"
}

消息类型

类型 说明 是否需要响应
Request 请求，包含method和params ✅ 是
Response 响应，包含result或error ❌ 否
Notification 通知，没有id ❌ 否

传输层一：stdio实现

架构原理

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┌─────────────────────────────────────────────────┐
│              Client Process                      │
│                                                  │
│  ┌────────┐    stdin     ┌────────────────┐    │
│  │  MCP   │ ──────────▶  │ Server Process │    │
│  │ Client │ ◀──────────  │   (Subprocess) │    │
│  └────────┘    stdout    └────────────────┘    │
│                             │                  │
│                             ▼                  │
│                        stderr (logs)           │
└─────────────────────────────────────────────────┘

核心规则

  1. 消息分隔：使用换行符\n分隔
  2. 禁止内嵌换行：消息内部不能有换行
  3. stdout纯净：服务器只能输出有效的MCP消息
  4. stderr日志：日志输出到stderr，客户端可捕获或忽略

Golang完整实现

Server端

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package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"strings"
	"sync"
)

// JSON-RPC 消息结构
type Request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      *int64          `json:"id,omitempty"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type Response struct {
	JSONRPC string      `json:"jsonrpc"`
	ID      *int64      `json:"id,omitempty"`
	Result  interface{} `json:"result,omitempty"`
	Error   *ErrorInfo  `json:"error,omitempty"`
}

type ErrorInfo struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

type InitializeParams struct {
	ProtocolVersion string          `json:"protocolVersion"`
	Capabilities    map[string]any  `json:"capabilities"`
	ClientInfo      ClientInfo      `json:"clientInfo"`
}

type ClientInfo struct {
	Name    string `json:"name"`
	Version string `json:"version"`
}

type ServerInfo struct {
	Name    string `json:"name"`
	Version string `json:"version"`
}

// MCP Server
type MCPServer struct {
	sessionID    string
	capabilities map[string]any
	mu           sync.Mutex
}

func NewMCPServer() *MCPServer {
	return &MCPServer{
		capabilities: map[string]any{
			"tools":     map[string]bool{"listChanged": true},
			"resources": map[string]any{},
			"logging":   map[string]any{},
		},
	}
}

func (s *MCPServer) log(message string) {
	fmt.Fprintf(os.Stderr, "[LOG] %s\n", message)
}

func (s *MCPServer) sendMessage(msg Response) error {
	data, err := json.Marshal(msg)
	if err != nil {
		return err
	}

	// 确保没有内嵌换行
	if strings.Contains(string(data), "\n") {
		return fmt.Errorf("message contains embedded newlines")
	}

	fmt.Println(string(data))
	s.log(fmt.Sprintf("Sent: %s...", string(data)[:min(100, len(data))]))
	return nil
}

func (s *MCPServer) readMessage() (*Request, error) {
	reader := bufio.NewReader(os.Stdin)
	line, err := reader.ReadString('\n')
	if err != nil {
		return nil, err
	}

	line = strings.TrimSpace(line)
	if line == "" {
		return nil, nil
	}

	var req Request
	if err := json.Unmarshal([]byte(line), &req); err != nil {
		s.log(fmt.Sprintf("Invalid JSON: %v", err))
		return nil, err
	}

	return &req, nil
}

func (s *MCPServer) handleRequest(req *Request) *Response {
	s.log(fmt.Sprintf("Handling method: %s", req.Method))

	switch req.Method {
	case "initialize":
		return s.handleInitialize(req)
	case "tools/list":
		return s.handleToolsList(req)
	default:
		return &Response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error: &ErrorInfo{
				Code:    -32601,
				Message: fmt.Sprintf("Method not found: %s", req.Method),
			},
		}
	}
}

func (s *MCPServer) handleInitialize(req *Request) *Response {
	var params InitializeParams
	if err := json.Unmarshal(req.Params, &params); err != nil {
		return &Response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error: &ErrorInfo{
				Code:    -32700,
				Message: "Invalid params",
			},
		}
	}

	s.log(fmt.Sprintf("Client: %s v%s", params.ClientInfo.Name, params.ClientInfo.Version))
	s.log(fmt.Sprintf("Protocol version: %s", params.ProtocolVersion))

	// 生成 session ID
	s.sessionID = fmt.Sprintf("session-%d", os.Getpid())

	return &Response{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result: map[string]any{
			"protocolVersion": "2025-06-18",
			"capabilities":    s.capabilities,
			"serverInfo": ServerInfo{
				Name:    "example-server",
				Version: "1.0.0",
			},
		},
	}
}

func (s *MCPServer) handleToolsList(req *Request) *Response {
	return &Response{
		JSONRPC: "2.0",
		ID:      req.ID,
		Result: map[string]any{
			"tools": []map[string]any{
				{
					"name":        "echo",
					"description": "Echo back the input message",
					"inputSchema": map[string]any{
						"type": "object",
						"properties": map[string]any{
							"message": map[string]any{
								"type":        "string",
								"description": "Message to echo",
							},
						},
						"required": []string{"message"},
					},
				},
			},
		},
	}
}

func (s *MCPServer) Run() {
	s.log("MCP Server starting...")

	for {
		req, err := s.readMessage()
		if err != nil {
			s.log(fmt.Sprintf("Client disconnected: %v", err))
			break
		}

		if req == nil {
			s.log("Client disconnected (EOF)")
			break
		}

		resp := s.handleRequest(req)
		if resp != nil {
			if err := s.sendMessage(*resp); err != nil {
				s.log(fmt.Sprintf("Error sending response: %v", err))
			}
		}
	}

	s.log("MCP Server stopped")
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func main() {
	server := NewMCPServer()
	server.Run()
}

Client端

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package main

import (
	"bufio"
	"encoding/json"
	"fmt"
	"os"
	"os/exec"
	"sync"
	"time"
)

type Request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type Response struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Result  json.RawMessage `json:"result,omitempty"`
	Error   *ErrorInfo      `json:"error,omitempty"`
}

type ErrorInfo struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

type MCPStdioClient struct {
	cmd            *exec.Cmd
	stdin          *bufio.Writer
	stdout         *bufio.Reader
	stderr         *bufio.Reader
	messageID      int64
	pendingReqs    map[int64]chan *Response
	pendingReqsMu  sync.Mutex
	responses      map[int64]*Response
	responsesMu    sync.Mutex
}

func NewMCPClient(serverCmd string, args ...string) *MCPStdioClient {
	return &MCPStdioClient{
		cmd:         exec.Command(serverCmd, args...),
		pendingReqs: make(map[int64]chan *Response),
		responses:   make(map[int64]*Response),
	}
}

func (c *MCPStdioClient) Connect() error {
	stdin, err := c.cmd.StdinPipe()
	if err != nil {
		return err
	}

	stdout, err := c.cmd.StdoutPipe()
	if err != nil {
		return err
	}

	stderr, err := c.cmd.StderrPipe()
	if err != nil {
		return err
	}

	c.stdin = bufio.NewWriter(stdin)
	c.stdout = bufio.NewReader(stdout)
	c.stderr = bufio.NewReader(stderr)

	if err := c.cmd.Start(); err != nil {
		return err
	}

	// 启动读取 goroutine
	go c.readLoop()
	go c.logLoop()

	fmt.Println("Connected to MCP server")
	return nil
}

func (c *MCPStdioClient) readLoop() {
	for {
		line, err := c.stdout.ReadString('\n')
		if err != nil {
			fmt.Printf("Read error: %v\n", err)
			break
		}

		line = strings.TrimSpace(line)
		if line == "" {
			continue
		}

		var msg Response
		if err := json.Unmarshal([]byte(line), &msg); err != nil {
			fmt.Printf("Invalid JSON from server: %v\n", err)
			continue
		}

		c.handleMessage(&msg)
	}
}

func (c *MCPStdioClient) logLoop() {
	for {
		line, err := c.stderr.ReadString('\n')
		if err != nil {
			break
		}
		fmt.Printf("[Server Log] %s", line)
	}
}

func (c *MCPStdioClient) handleMessage(msg *Response) {
	c.pendingReqsMu.Lock()
	if ch, ok := c.pendingReqs[msg.ID]; ok {
		ch <- msg
		close(ch)
		delete(c.pendingReqs, msg.ID)
	} else {
		// Notification or server-initiated request
		fmt.Printf("Received: %+v\n", msg)
	}
	c.pendingReqsMu.Unlock()
}

func (c *MCPStdioClient) sendMessage(msg Request) error {
	data, err := json.Marshal(msg)
	if err != nil {
		return err
	}

	if _, err := c.stdin.WriteString(string(data) + "\n"); err != nil {
		return err
	}

	if err := c.stdin.Flush(); err != nil {
		return err
	}

	return nil
}

func (c *MCPStdioClient) Request(method string, params any) (json.RawMessage, error) {
	c.messageID++
	reqID := c.messageID

	var paramsJSON json.RawMessage
	if params != nil {
		var err error
		paramsJSON, err = json.Marshal(params)
		if err != nil {
			return nil, err
		}
	}

	req := Request{
		JSONRPC: "2.0",
		ID:      reqID,
		Method:  method,
		Params:  paramsJSON,
	}

	// 设置响应通道
	ch := make(chan *Response, 1)
	c.pendingReqsMu.Lock()
	c.pendingReqs[reqID] = ch
	c.pendingReqsMu.Unlock()

	// 发送请求
	fmt.Printf("Sending: %s\n", method)
	if err := c.sendMessage(req); err != nil {
		return nil, err
	}

	// 等待响应（30秒超时）
	select {
	case resp := <-ch:
		if resp.Error != nil {
			return nil, fmt.Errorf("server error: %s", resp.Error.Message)
		}
		return resp.Result, nil
	case <-time.After(30 * time.Second):
		return nil, fmt.Errorf("request %s timed out", method)
	}
}

func (c *MCPStdioClient) Notification(method string, params any) error {
	var paramsJSON json.RawMessage
	if params != nil {
		var err error
		paramsJSON, err = json.Marshal(params)
		if err != nil {
			return err
		}
	}

	notif := map[string]any{
		"jsonrpc": "2.0",
		"method":  method,
	}
	if params != nil {
		notif["params"] = params
	}

	data, _ := json.Marshal(notif)
	if _, err := c.stdin.WriteString(string(data) + "\n"); err != nil {
		return err
	}
	return c.stdin.Flush()
}

func (c *MCPStdioClient) Initialize() (json.RawMessage, error) {
	result, err := c.Request("initialize", map[string]any{
		"protocolVersion": "2025-06-18",
		"capabilities": map[string]any{
			"roots":    map[string]bool{"listChanged": true},
			"sampling": map[string]any{},
		},
		"clientInfo": map[string]string{
			"name":    "example-client",
			"version": "1.0.0",
		},
	})
	if err != nil {
		return nil, err
	}

	// 发送 initialized notification
	c.Notification("notifications/initialized", nil)

	return result, nil
}

func (c *MCPStdioClient) Close() error {
	if c.cmd != nil {
		c.cmd.Process.Kill()
		c.cmd = nil
		fmt.Println("Disconnected from MCP server")
	}
	return nil
}

func main() {
	// 连接本地服务器
	client := NewMCPClient("go", "run", "mcp_server.go")
	if err := client.Connect(); err != nil {
		fmt.Fprintf(os.Stderr, "Connect error: %v\n", err)
		os.Exit(1)
	}
	defer client.Close()

	// 初始化
	initResult, err := client.Initialize()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Initialize error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Initialized: %s\n", string(initResult))

	// 列出工具
	toolsResult, err := client.Request("tools/list", nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Tools list error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Available tools: %s\n", string(toolsResult))

	// 调用工具
	callResult, err := client.Request("tools/call", map[string]any{
		"name": "echo",
		"arguments": map[string]string{
			"message": "Hello MCP!",
		},
	})
	if err != nil {
		fmt.Fprintf(os.Stderr, "Tool call error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Tool result: %s\n", string(callResult))
}

测试运行

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# Terminal 1: Run server directly to see logs
go run mcp_server.go

# Terminal 2: Run client
go run mcp_client.go

传输层二：Streamable HTTP实现

架构原理

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┌─────────────────────────────────────────────────┐
│              Client                              │
│                                                  │
│  ┌─────────────────────────────────────────┐    │
│  │  POST /mcp  (JSON-RPC requests)         │    │
│  │  GET  /mcp  (SSE stream for responses)  │    │
│  └─────────────────────────────────────────┘    │
│                     │                           │
│                     ▼                           │
│  ┌─────────────────────────────────────────┐    │
│  │         MCP Endpoint: /mcp              │    │
│  │  - POST: Receive requests               │    │
│  │  - GET:  SSE stream                     │    │
│  └─────────────────────────────────────────┘    │
│                     │                           │
│                     ▼                           │
│              Server Process                     │
└─────────────────────────────────────────────────┘

核心特性

  1. POST发送请求：每个JSON-RPC消息一个新的POST请求
  2. SSE流式响应：服务器通过SSE流返回响应
  3. 会话管理：使用Mcp-Session-Id头维护会话
  4. 协议版本头：MCP-Protocol-Version

Golang完整实现

Server端（Gin + SSE）

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package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
)

// JSON-RPC 消息结构
type Request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      *int64          `json:"id,omitempty"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type Response struct {
	JSONRPC string      `json:"jsonrpc"`
	ID      *int64      `json:"id,omitempty"`
	Result  interface{} `json:"result,omitempty"`
	Error   *ErrorInfo  `json:"error,omitempty"`
}

type ErrorInfo struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

// Session 管理
type Session struct {
	ID             string
	ProtocolVersion string
	CreatedAt      time.Time
	MessageQueue   chan map[string]interface{}
}

type SessionManager struct {
	sessions map[string]*Session
	mu       sync.RWMutex
}

func NewSessionManager() *SessionManager {
	return &SessionManager{
		sessions: make(map[string]*Session),
	}
}

func (sm *SessionManager) CreateSession() *Session {
	sessionID := uuid.New().String()
	session := &Session{
		ID:           sessionID,
		CreatedAt:    time.Now(),
		MessageQueue: make(chan map[string]interface{}, 100),
	}

	sm.mu.Lock()
	sm.sessions[sessionID] = session
	sm.mu.Unlock()

	return session
}

func (sm *SessionManager) GetSession(sessionID string) *Session {
	sm.mu.RLock()
	defer sm.mu.RUnlock()
	return sm.sessions[sessionID]
}

func (sm *SessionManager) DeleteSession(sessionID string) {
	sm.mu.Lock()
	defer sm.mu.Unlock()

	if session, ok := sm.sessions[sessionID]; ok {
		close(session.MessageQueue)
		delete(sm.sessions, sessionID)
	}
}

func (sm *SessionManager) QueueMessage(sessionID string, msg map[string]interface{}) error {
	session := sm.GetSession(sessionID)
	if session == nil {
		return fmt.Errorf("session not found: %s", sessionID)
	}

	select {
	case session.MessageQueue <- msg:
		return nil
	default:
		return fmt.Errorf("message queue full")
	}
}

var sessionManager = NewSessionManager()

func handleInitialize(params map[string]interface{}) map[string]interface{} {
	protocolVersion, _ := params["protocolVersion"].(string)
	clientInfo, _ := params["clientInfo"].(map[string]interface{})

	fmt.Printf("Client: %v v%v\n", clientInfo["name"], clientInfo["version"])
	fmt.Printf("Protocol version: %s\n", protocolVersion)

	return map[string]interface{}{
		"protocolVersion": "2025-06-18",
		"capabilities": map[string]interface{}{
			"tools":     map[string]bool{"listChanged": true},
			"resources": map[string]interface{}{},
			"logging":   map[string]interface{}{},
		},
		"serverInfo": map[string]string{
			"name":    "example-server",
			"version": "1.0.0",
		},
	}
}

func handleToolsList() map[string]interface{} {
	return map[string]interface{}{
		"tools": []map[string]interface{}{
			{
				"name":        "echo",
				"description": "Echo back the input message",
				"inputSchema": map[string]interface{}{
					"type": "object",
					"properties": map[string]interface{}{
						"message": map[string]interface{}{
							"type":        "string",
							"description": "Message to echo",
						},
					},
					"required": []string{"message"},
				},
			},
		},
	}
}

func handleRequest(req Request, sessionID string) *Response {
	fmt.Printf("Handling method: %s\n", req.Method)

	switch req.Method {
	case "initialize":
		var params map[string]interface{}
		json.Unmarshal(req.Params, &params)

		result := handleInitialize(params)
		return &Response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result:  result,
		}

	case "tools/list":
		result := handleToolsList()
		return &Response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Result:  result,
		}

	case "notifications/initialized":
		// Notification, no response
		return nil

	default:
		return &Response{
			JSONRPC: "2.0",
			ID:      req.ID,
			Error: &ErrorInfo{
				Code:    -32601,
				Message: fmt.Sprintf("Method not found: %s", req.Method),
			},
		}
	}
}

func mcpPOST(c *gin.Context) {
	sessionID := c.GetHeader("Mcp-Session-Id")
	protocolVersion := c.GetHeader("MCP-Protocol-Version")

	var req Request
	if err := c.ShouldBindJSON(&req); err != nil {
		c.JSON(http.StatusBadRequest, Response{
			JSONRPC: "2.0",
			Error: &ErrorInfo{
				Code:    -32700,
				Message: "Parse error",
			},
		})
		return
	}

	fmt.Printf("Received POST: %s\n", req.Method)

	// Handle initialization
	if req.Method == "initialize" {
		session := sessionManager.CreateSession()

		var params map[string]interface{}
		json.Unmarshal(req.Params, &params)
		if pv, ok := params["protocolVersion"].(string); ok {
			session.ProtocolVersion = pv
		}

		response := handleRequest(req, session.ID)

		c.Header("Mcp-Session-Id", session.ID)
		c.Header("Content-Type", "text/event-stream")
		c.Header("Cache-Control", "no-cache")
		c.Header("Connection", "keep-alive")

		// Send SSE
		c.Stream(func(w io.Writer) bool {
			data, _ := json.Marshal(response)
			fmt.Fprintf(w, "data: %s\n\n", data)
			c.Writer.Flush()
			return false
		})
		return
	}

	// Validate session
	if sessionID == "" {
		c.JSON(http.StatusBadRequest, Response{
			JSONRPC: "2.0",
			Error: &ErrorInfo{
				Code:    -32000,
				Message: "Session ID required",
			},
		})
		return
	}

	session := sessionManager.GetSession(sessionID)
	if session == nil {
		c.JSON(http.StatusNotFound, Response{
			JSONRPC: "2.0",
			Error: &ErrorInfo{
				Code:    -32001,
				Message: "Session not found",
			},
		})
		return
	}

	response := handleRequest(req, sessionID)

	// Notifications don't need response
	if response == nil {
		c.Status(http.StatusAccepted)
		return
	}

	// Send as SSE
	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")

	c.Stream(func(w io.Writer) bool {
		data, _ := json.Marshal(response)
		fmt.Fprintf(w, "data: %s\n\n", data)
		c.Writer.Flush()
		return false
	})
}

func mcpGET(c *gin.Context) {
	sessionID := c.GetHeader("Mcp-Session-Id")

	if sessionID == "" {
		c.Status(http.StatusMethodNotAllowed)
		return
	}

	session := sessionManager.GetSession(sessionID)
	if session == nil {
		c.Status(http.StatusNotFound)
		return
	}

	fmt.Printf("SSE stream opened for session: %s\n", sessionID)

	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")

	c.Stream(func(w io.Writer) bool {
		select {
		case msg, ok := <-session.MessageQueue:
			if !ok {
				return false
			}
			data, _ := json.Marshal(msg)
			fmt.Fprintf(w, "data: %s\n\n", data)
			c.Writer.Flush()
			return true
		case <-c.Request.Context().Done():
			fmt.Printf("SSE stream closed for session: %s\n", sessionID)
			return false
		}
	})
}

func mcpDELETE(c *gin.Context) {
	sessionID := c.GetHeader("Mcp-Session-Id")

	if sessionID != "" {
		sessionManager.DeleteSession(sessionID)
		fmt.Printf("Session terminated: %s\n", sessionID)
	}

	c.Status(http.StatusOK)
}

func main() {
	r := gin.Default()

	r.POST("/mcp", mcpPOST)
	r.GET("/mcp", mcpGET)
	r.DELETE("/mcp", mcpDELETE)

	fmt.Println("MCP Server starting on :8080")
	r.Run(":8080")
}

Client端

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package main

import (
	"bufio"
	"bytes"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"strings"
	"sync/atomic"
)

type Request struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Method  string          `json:"method"`
	Params  json.RawMessage `json:"params,omitempty"`
}

type Response struct {
	JSONRPC string          `json:"jsonrpc"`
	ID      int64           `json:"id"`
	Result  json.RawMessage `json:"result,omitempty"`
	Error   *ErrorInfo      `json:"error,omitempty"`
}

type ErrorInfo struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
}

type MCPHTTPClient struct {
	baseURL         string
	sessionID       string
	protocolVersion string
	messageID       int64
	httpClient      *http.Client
}

func NewMCPHTTPClient(baseURL string) *MCPHTTPClient {
	return &MCPHTTPClient{
		baseURL:         baseURL,
		protocolVersion: "2025-06-18",
		httpClient:      &http.Client{},
	}
}

func (c *MCPHTTPClient) Initialize() (json.RawMessage, error) {
	reqBody := map[string]interface{}{
		"jsonrpc": "2.0",
		"id":      1,
		"method":  "initialize",
		"params": map[string]interface{}{
			"protocolVersion": c.protocolVersion,
			"capabilities": map[string]interface{}{
				"roots":    map[string]bool{"listChanged": true},
				"sampling": map[string]interface{}{},
			},
			"clientInfo": map[string]string{
				"name":    "example-client",
				"version": "1.0.0",
			},
		},
	}

	result, err := c.sendRequest(reqBody)
	if err != nil {
		return nil, err
	}

	// Send initialized notification
	c.Notification("notifications/initialized", nil)

	return result, nil
}

func (c *MCPHTTPClient) Request(method string, params interface{}) (json.RawMessage, error) {
	reqBody := map[string]interface{}{
		"jsonrpc": "2.0",
		"id":      atomic.AddInt64(&c.messageID, 1),
		"method":  method,
	}

	if params != nil {
		paramsJSON, _ := json.Marshal(params)
		reqBody["params"] = paramsJSON
	}

	return c.sendRequest(reqBody)
}

func (c *MCPHTTPClient) sendRequest(reqBody map[string]interface{}) (json.RawMessage, error) {
	reqJSON, err := json.Marshal(reqBody)
	if err != nil {
		return nil, err
	}

	req, err := http.NewRequest("POST", c.baseURL+"/mcp", bytes.NewReader(reqJSON))
	if err != nil {
		return nil, err
	}

	req.Header.Set("Accept", "application/json, text/event-stream")
	req.Header.Set("MCP-Protocol-Version", c.protocolVersion)
	if c.sessionID != "" {
		req.Header.Set("Mcp-Session-Id", c.sessionID)
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		body, _ := io.ReadAll(resp.Body)
		return nil, fmt.Errorf("HTTP error %d: %s", resp.StatusCode, string(body))
	}

	// Extract session ID
	if sessionID := resp.Header.Get("Mcp-Session-Id"); sessionID != "" {
		c.sessionID = sessionID
		fmt.Printf("Session ID: %s\n", sessionID)
	}

	// Parse SSE response
	body, err := io.ReadAll(resp.Body)
	if err != nil {
		return nil, err
	}

	// Extract data from SSE format
	lines := strings.Split(string(body), "\n")
	for _, line := range lines {
		if strings.HasPrefix(line, "data: ") {
			data := strings.TrimPrefix(line, "data: ")
			var result Response
			if err := json.Unmarshal([]byte(data), &result); err != nil {
				continue
			}

			if result.Error != nil {
				return nil, fmt.Errorf("server error: %s", result.Error.Message)
			}

			return result.Result, nil
		}
	}

	return nil, fmt.Errorf("no valid response in SSE stream")
}

func (c *MCPHTTPClient) Notification(method string, params interface{}) error {
	reqBody := map[string]interface{}{
		"jsonrpc": "2.0",
		"method":  method,
	}

	if params != nil {
		reqBody["params"] = params
	}

	reqJSON, _ := json.Marshal(reqBody)

	req, err := http.NewRequest("POST", c.baseURL+"/mcp", bytes.NewReader(reqJSON))
	if err != nil {
		return err
	}

	req.Header.Set("Accept", "application/json, text/event-stream")
	req.Header.Set("MCP-Protocol-Version", c.protocolVersion)
	if c.sessionID != "" {
		req.Header.Set("Mcp-Session-Id", c.sessionID)
	}

	resp, err := c.httpClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	fmt.Printf("Notification sent: %s, status: %d\n", method, resp.StatusCode)
	return nil
}

func (c *MCPHTTPClient) Close() error {
	if c.sessionID != "" {
		req, _ := http.NewRequest("DELETE", c.baseURL+"/mcp", nil)
		req.Header.Set("Mcp-Session-Id", c.sessionID)
		req.Header.Set("MCP-Protocol-Version", c.protocolVersion)

		resp, err := c.httpClient.Do(req)
		if err == nil {
			resp.Body.Close()
			fmt.Printf("Session terminated: %d\n", resp.StatusCode)
		}

		c.sessionID = ""
	}
	return nil
}

func main() {
	// 连接远程服务器
	client := NewMCPHTTPClient("http://127.0.0.1:8080")
	defer client.Close()

	// 初始化
	initResult, err := client.Initialize()
	if err != nil {
		fmt.Fprintf(os.Stderr, "Initialize error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Initialized: %s\n", string(initResult))

	// 列出工具
	toolsResult, err := client.Request("tools/list", nil)
	if err != nil {
		fmt.Fprintf(os.Stderr, "Tools list error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Available tools: %s\n", string(toolsResult))

	// 调用工具
	callResult, err := client.Request("tools/call", map[string]interface{}{
		"name": "echo",
		"arguments": map[string]string{
			"message": "Hello MCP!",
		},
	})
	if err != nil {
		fmt.Fprintf(os.Stderr, "Tool call error: %v\n", err)
		os.Exit(1)
	}
	fmt.Printf("Tool result: %s\n", string(callResult))
}

测试运行

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# Terminal 1: Start server
go get github.com/gin-gonic/gin
go get github.com/google/uuid
go run mcp_http_server.go

# Terminal 2: Run client
go run mcp_http_client.go

传输层对比

特性 stdio Streamable HTTP
适用场景 本地进程 远程服务器
连接方式 子进程 HTTP POST/GET
响应模式 直接stdout SSE流
会话管理 进程生命周期 Mcp-Session-Id
认证 无（本地信任） OAuth/API Key
多客户端 ❌ 单客户端 ✅ 多客户端
防火墙穿透 ❌ 不可用 ✅ 可用
性能 ⭐⭐⭐⭐⭐ 最优 ⭐⭐⭐ 网络开销

旧版HTTP+SSE vs 新版Streamable HTTP

旧版（2024-11-05）

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Client                          Server
  │                               │
  │── GET /sse ─────────────────▶│  打开SSE连接
  │◀─ endpoint: /message ────────│  返回POST端点
  │                               │
  │── POST /message ────────────▶│  发送请求
  │◀─ SSE message event ─────────│  接收响应

新版（2025-06-18）

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Client                          Server
  │                               │
  │── POST /mcp ────────────────▶│  发送请求
  │◀─ SSE stream ────────────────│  流式响应
  │                               │
  │── GET /mcp ─────────────────▶│  可选：独立SSE流
  │◀─ SSE messages ──────────────│  服务器主动推送

主要改进：

  1. 单端点：统一使用/mcp，简化配置
  2. 会话管理：标准的Mcp-Session-Id头
  3. 协议版本头：MCP-Protocol-Version
  4. DELETE终止：显式会话终止

安全考量

DNS重绑定防护

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# Server必须验证Origin头
@app.post("/mcp")
async def mcp_post(request: Request, origin: str = Header(None)):
    # 本地运行只允许特定Origin
    if origin and not origin.startswith(("http://localhost", "http://127.0.0.1")):
        return Response(status_code=403)

认证实现

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# Bearer Token认证
@app.post("/mcp")
async def mcp_post(authorization: str = Header(None)):
    if not authorization or not authorization.startswith("Bearer "):
        return Response(status_code=401)
    
    token = authorization[7:]
    if not validate_token(token):
        return Response(status_code=401)

总结

MCP传输层设计精妙：

  1. stdio：本地最优，零网络开销
  2. Streamable HTTP：远程标准，支持多客户端
  3. SSE流式：实时推送，低延迟
  4. 会话管理：状态维护，安全可控

理解并实现这些传输协议，是构建MCP生态的基础。

相关链接：

感谢你的阅读，如果文章对你有帮助，可以请作者喝杯茶!