Export SendNotificationToAllClients

[First PR to project]

Export sendNotificationToAllClients so it can be called from the MCP
server to send unsolicited notifications to all clients (sessions).

I have a use-case for my MCP server where I need to send notifications
of state change to all sessions.  My MCP server is fronting a device
hub, and the device's on the hub would like to send notifications up
to the LLM.

There is probably a reason why this was not exported, so please forgive
this PR if that's the case.  I just could not figure out what the spec
says about this.

In any case, I added a test and tested with the Inspector.  The
Inspectory sees the unsolicited notifications.  Cool!  I also tried with
Cursor and Claude, but neither seem to recognize notifications, no
matter how hard I tried to convince them.

Author: scottfeldman

server/server.go

@@ -211,8 +211,8 @@ func (s *MCPServer) UnregisterSession(
 	s.sessions.Delete(sessionID)
 }
 
-// sendNotificationToAllClients sends a notification to all the currently active clients.
-func (s *MCPServer) sendNotificationToAllClients(
+// SendNotificationToAllClients sends a notification to all the currently active clients.
+func (s *MCPServer) SendNotificationToAllClients(
 	method string,
 	params map[string]any,
 ) {
@@ -472,7 +472,7 @@ func (s *MCPServer) AddTools(tools ...ServerTool) {
 	s.toolsMu.Unlock()
 
 	// Send notification to all initialized sessions
-	s.sendNotificationToAllClients("notifications/tools/list_changed", nil)
+	s.SendNotificationToAllClients("notifications/tools/list_changed", nil)
 }
 
 // SetTools replaces all existing tools with the provided list
@@ -492,7 +492,7 @@ func (s *MCPServer) DeleteTools(names ...string) {
 	s.toolsMu.Unlock()
 
 	// Send notification to all initialized sessions
-	s.sendNotificationToAllClients("notifications/tools/list_changed", nil)
+	s.SendNotificationToAllClients("notifications/tools/list_changed", nil)
 }
 
 // AddNotificationHandler registers a new handler for incoming notifications

server/server_test.go

@@ -573,6 +573,75 @@ func TestMCPServer_SendNotificationToClient(t *testing.T) {
 	}
 }
 
+func TestMCPServer_SendNotificationToAllClients(t *testing.T) {
+
+	contextPrepare := func(ctx context.Context, srv *MCPServer) context.Context {
+		// Create 5 active sessions
+		for i := 0; i < 5; i++ {
+			err := srv.RegisterSession(ctx, &fakeSession{
+				sessionID:           fmt.Sprintf("test%d", i),
+				notificationChannel: make(chan mcp.JSONRPCNotification, 10),
+				initialized:         true,
+			})
+			require.NoError(t, err)
+		}
+		return ctx
+	}
+
+	validate := func(t *testing.T, ctx context.Context, srv *MCPServer) {
+		// Send 10 notifications to all sessions
+		for i := 0; i < 10; i++ {
+			srv.SendNotificationToAllClients("method", map[string]any{
+				"count": i,
+			})
+		}
+
+		// Verify each session received all 10 notifications
+		srv.sessions.Range(func(k, v any) bool {
+			session := v.(ClientSession)
+			fakeSess := session.(*fakeSession)
+			notificationCount := 0
+
+			// Read all notifications from the channel
+			for notificationCount < 10 {
+				select {
+				case notification := <-fakeSess.notificationChannel:
+					// Verify notification method
+					assert.Equal(t, "method", notification.Method)
+					// Verify count parameter
+					count, ok := notification.Params.AdditionalFields["count"]
+					assert.True(t, ok, "count parameter not found")
+					assert.Equal(t, notificationCount, count.(int), "count should match notification count")
+					notificationCount++
+				case <-time.After(100 * time.Millisecond):
+					t.Errorf("timeout waiting for notification %d for session %s", notificationCount, session.SessionID())
+					return false
+				}
+			}
+
+			// Verify no more notifications
+			select {
+			case notification := <-fakeSess.notificationChannel:
+				t.Errorf("unexpected notification received: %v", notification)
+			default:
+				// Channel empty as expected
+			}
+			return true
+		})
+	}
+
+	t.Run("all sessions", func(t *testing.T) {
+		server := NewMCPServer("test-server", "1.0.0")
+		ctx := contextPrepare(context.Background(), server)
+		_ = server.HandleMessage(ctx, []byte(`{
+				"jsonrpc": "2.0",
+				"id": 1,
+				"method": "initialize"
+			}`))
+		validate(t, ctx, server)
+	})
+}
+
 func TestMCPServer_PromptHandling(t *testing.T) {
 	server := NewMCPServer("test-server", "1.0.0",
 		WithPromptCapabilities(true),