feat: Add GetHeader() Support for SSE Transport Sessions (ClientSession)

server/server_test.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"net/http"
 	"reflect"
 	"sort"
 	"testing"
@@ -1522,6 +1523,11 @@ func (f fakeSession) Initialized() bool {
 	return f.initialized
 }
 
+func (f fakeSession) GetHeader() http.Header {
+	// Test session doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 var _ ClientSession = fakeSession{}
 
 func TestMCPServer_WithHooks(t *testing.T) {

server/session.go

@@ -3,6 +3,7 @@ package server
 import (
 	"context"
 	"fmt"
+	"net/http"
 
 	"github.com/mark3labs/mcp-go/mcp"
 )
@@ -17,6 +18,8 @@ type ClientSession interface {
 	NotificationChannel() chan<- mcp.JSONRPCNotification
 	// SessionID is a unique identifier used to track user session.
 	SessionID() string
+	// GetHeader returns the HTTP headers from the initial request
+	GetHeader() http.Header
 }
 
 // SessionWithLogging is an extension of ClientSession that can receive log message notifications and set log level

server/session_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"net/http"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -42,6 +43,11 @@ func (f sessionTestClient) Initialized() bool {
 	return f.initialized
 }
 
+func (f sessionTestClient) GetHeader() http.Header {
+	// Test session doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 // sessionTestClientWithTools implements the SessionWithTools interface for testing
 type sessionTestClientWithTools struct {
 	sessionID           string
@@ -100,6 +106,11 @@ func (f *sessionTestClientWithTools) SetSessionTools(tools map[string]ServerTool
 	f.sessionTools = toolsCopy
 }
 
+func (f *sessionTestClientWithTools) GetHeader() http.Header {
+	// Test session doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 // sessionTestClientWithClientInfo implements the SessionWithClientInfo interface for testing
 type sessionTestClientWithClientInfo struct {
 	sessionID           string
@@ -137,6 +148,11 @@ func (f *sessionTestClientWithClientInfo) SetClientInfo(clientInfo mcp.Implement
 	f.clientInfo.Store(clientInfo)
 }
 
+func (f *sessionTestClientWithClientInfo) GetHeader() http.Header {
+	// Test session doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 // sessionTestClientWithTools implements the SessionWithLogging interface for testing
 type sessionTestClientWithLogging struct {
 	sessionID           string
@@ -172,6 +188,11 @@ func (f *sessionTestClientWithLogging) GetLogLevel() mcp.LoggingLevel {
 	return level.(mcp.LoggingLevel)
 }
 
+func (f *sessionTestClientWithLogging) GetHeader() http.Header {
+	// Test session doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 // Verify that all implementations satisfy their respective interfaces
 var (
 	_ ClientSession         = (*sessionTestClient)(nil)

server/sse.go

@@ -30,6 +30,7 @@ type sseSession struct {
 	loggingLevel        atomic.Value
 	tools               sync.Map     // stores session-specific tools
 	clientInfo          atomic.Value // stores session-specific client info
+	headers             http.Header  // stores HTTP headers from the initial request
 }
 
 // SSEContextFunc is a function that takes an existing context and the current
@@ -108,6 +109,10 @@ func (s *sseSession) SetClientInfo(clientInfo mcp.Implementation) {
 	s.clientInfo.Store(clientInfo)
 }
 
+func (s *sseSession) GetHeader() http.Header {
+	return s.headers
+}
+
 var (
 	_ ClientSession         = (*sseSession)(nil)
 	_ SessionWithTools      = (*sseSession)(nil)
@@ -353,6 +358,7 @@ func (s *SSEServer) handleSSE(w http.ResponseWriter, r *http.Request) {
 		eventQueue:          make(chan string, 100), // Buffer for events
 		sessionID:           sessionID,
 		notificationChannel: make(chan mcp.JSONRPCNotification, 100),
+		headers:             r.Header.Clone(), // Store HTTP headers from request
 	}
 
 	s.sessions.Store(sessionID, session)

server/stdio.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"net/http"
 	"os"
 	"os/signal"
 	"sync/atomic"
@@ -100,6 +101,11 @@ func (s *stdioSession) GetLogLevel() mcp.LoggingLevel {
 	return level.(mcp.LoggingLevel)
 }
 
+func (s *stdioSession) GetHeader() http.Header {
+	// stdio transport doesn't have HTTP headers, return empty header
+	return make(http.Header)
+}
+
 var (
 	_ ClientSession         = (*stdioSession)(nil)
 	_ SessionWithLogging    = (*stdioSession)(nil)

server/streamable_http.go

@@ -365,7 +365,7 @@ func (s *StreamableHTTPServer) handleGet(w http.ResponseWriter, r *http.Request)
 		sessionID = uuid.New().String()
 	}
 
-	session := newStreamableHttpSession(sessionID, s.sessionTools)
+	session := newStreamableHttpSessionWithHeaders(sessionID, s.sessionTools, r.Header)
 	if err := s.server.RegisterSession(r.Context(), session); err != nil {
 		http.Error(w, fmt.Sprintf("Session registration failed: %v", err), http.StatusBadRequest)
 		return
@@ -549,13 +549,24 @@ type streamableHttpSession struct {
 	notificationChannel chan mcp.JSONRPCNotification // server -> client notifications
 	tools               *sessionToolsStore
 	upgradeToSSE        atomic.Bool
+	headers             http.Header // stores HTTP headers from the initial request
 }
 
 func newStreamableHttpSession(sessionID string, toolStore *sessionToolsStore) *streamableHttpSession {
 	return &streamableHttpSession{
 		sessionID:           sessionID,
 		notificationChannel: make(chan mcp.JSONRPCNotification, 100),
 		tools:               toolStore,
+		headers:             make(http.Header), // Initialize empty headers for ephemeral sessions
+	}
+}
+
+func newStreamableHttpSessionWithHeaders(sessionID string, toolStore *sessionToolsStore, headers http.Header) *streamableHttpSession {
+	return &streamableHttpSession{
+		sessionID:           sessionID,
+		notificationChannel: make(chan mcp.JSONRPCNotification, 100),
+		tools:               toolStore,
+		headers:             headers.Clone(),
 	}
 }
 
@@ -595,6 +606,10 @@ func (s *streamableHttpSession) UpgradeToSSEWhenReceiveNotification() {
 
 var _ SessionWithStreamableHTTPConfig = (*streamableHttpSession)(nil)
 
+func (s *streamableHttpSession) GetHeader() http.Header {
+	return s.headers
+}
+
 // --- session id manager ---
 
 type SessionIdManager interface {