fix: implement SessionWithClientInfo for streamableHttpSession (#640)

- Add clientInfo and clientCapabilities fields to streamableHttpSession struct
- Implement GetClientInfo, SetClientInfo, GetClientCapabilities, SetClientCapabilities methods
- Add SessionWithClientInfo interface declaration
- Enable client capability checking for StreamableHTTP transport in stateful mode

Fixes #639

Author: Anko59

server/streamable_http.go

@@ -986,6 +986,8 @@ type streamableHttpSession struct {
 	resourceTemplates   *sessionResourceTemplatesStore
 	upgradeToSSE        atomic.Bool
 	logLevels           *sessionLogLevelsStore
+	clientInfo          atomic.Value // stores session-specific client info
+	clientCapabilities  atomic.Value // stores session-specific client capabilities
 
 	// Sampling support for bidirectional communication
 	samplingRequestChan    chan samplingRequestItem    // server -> client sampling requests
@@ -1063,11 +1065,38 @@ func (s *streamableHttpSession) SetSessionResourceTemplates(templates map[string
 	s.resourceTemplates.set(s.sessionID, templates)
 }
 
+func (s *streamableHttpSession) GetClientInfo() mcp.Implementation {
+	if value := s.clientInfo.Load(); value != nil {
+		if clientInfo, ok := value.(mcp.Implementation); ok {
+			return clientInfo
+		}
+	}
+	return mcp.Implementation{}
+}
+
+func (s *streamableHttpSession) SetClientInfo(clientInfo mcp.Implementation) {
+	s.clientInfo.Store(clientInfo)
+}
+
+func (s *streamableHttpSession) GetClientCapabilities() mcp.ClientCapabilities {
+	if value := s.clientCapabilities.Load(); value != nil {
+		if clientCapabilities, ok := value.(mcp.ClientCapabilities); ok {
+			return clientCapabilities
+		}
+	}
+	return mcp.ClientCapabilities{}
+}
+
+func (s *streamableHttpSession) SetClientCapabilities(clientCapabilities mcp.ClientCapabilities) {
+	s.clientCapabilities.Store(clientCapabilities)
+}
+
 var (
 	_ SessionWithTools             = (*streamableHttpSession)(nil)
 	_ SessionWithResources         = (*streamableHttpSession)(nil)
 	_ SessionWithResourceTemplates = (*streamableHttpSession)(nil)
 	_ SessionWithLogging           = (*streamableHttpSession)(nil)
+	_ SessionWithClientInfo        = (*streamableHttpSession)(nil)
 )
 
 func (s *streamableHttpSession) UpgradeToSSEWhenReceiveNotification() {

server/streamable_http_client_info_test.go

@@ -0,0 +1,60 @@
+package server
+
+import (
+	"testing"
+
+	"github.com/mark3labs/mcp-go/mcp"
+)
+
+func TestStreamableHttpSessionImplementsSessionWithClientInfo(t *testing.T) {
+	// Create the session stores
+	toolStore := newSessionToolsStore()
+	resourceStore := newSessionResourcesStore()
+	templatesStore := newSessionResourceTemplatesStore()
+	logStore := newSessionLogLevelsStore()
+	
+	// Create a streamable HTTP session
+	session := newStreamableHttpSession("test-session", toolStore, resourceStore, templatesStore, logStore)
+	
+	// Verify it implements SessionWithClientInfo
+	var clientSession ClientSession = session
+	clientInfoSession, ok := clientSession.(SessionWithClientInfo)
+	if !ok {
+		t.Fatal("streamableHttpSession should implement SessionWithClientInfo")
+	}
+	
+	// Test GetClientInfo with no data set (should return empty)
+	clientInfo := clientInfoSession.GetClientInfo()
+	if clientInfo.Name != "" || clientInfo.Version != "" {
+		t.Errorf("expected empty client info, got %+v", clientInfo)
+	}
+	
+	// Test SetClientInfo and GetClientInfo
+	expectedClientInfo := mcp.Implementation{
+		Name:    "test-client",
+		Version: "1.0.0",
+	}
+	clientInfoSession.SetClientInfo(expectedClientInfo)
+	
+	actualClientInfo := clientInfoSession.GetClientInfo()
+	if actualClientInfo.Name != expectedClientInfo.Name || actualClientInfo.Version != expectedClientInfo.Version {
+		t.Errorf("expected client info %+v, got %+v", expectedClientInfo, actualClientInfo)
+	}
+	
+	// Test GetClientCapabilities with no data set (should return empty)
+	capabilities := clientInfoSession.GetClientCapabilities()
+	if capabilities.Sampling != nil || capabilities.Roots != nil {
+		t.Errorf("expected empty client capabilities, got %+v", capabilities)
+	}
+	
+	// Test SetClientCapabilities and GetClientCapabilities
+	expectedCapabilities := mcp.ClientCapabilities{
+		Sampling: &struct{}{},
+	}
+	clientInfoSession.SetClientCapabilities(expectedCapabilities)
+	
+	actualCapabilities := clientInfoSession.GetClientCapabilities()
+	if actualCapabilities.Sampling == nil {
+		t.Errorf("expected sampling capability to be set")
+	}
+}