add test

Author: jba

mcp/server.go

@@ -203,6 +203,26 @@ func (s *Server) RemoveResourceTemplates(uriTemplates ...string) {
 		func() bool { return s.resourceTemplates.remove(uriTemplates...) })
 }
 
+func (s *Server) capabilities() *serverCapabilities {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	caps := &serverCapabilities{
+		Completions: &completionCapabilities{},
+		Logging:     &loggingCapabilities{},
+	}
+	if s.tools.len() > 0 {
+		caps.Tools = &toolCapabilities{ListChanged: true}
+	}
+	if s.prompts.len() > 0 {
+		caps.Prompts = &promptCapabilities{ListChanged: true}
+	}
+	if s.resources.len() > 0 || s.resourceTemplates.len() > 0 {
+		caps.Resources = &resourceCapabilities{ListChanged: true}
+	}
+	return caps
+}
+
 func (s *Server) complete(ctx context.Context, ss *ServerSession, params *CompleteParams) (Result, error) {
 	if s.opts.CompletionHandler == nil {
 		return nil, jsonrpc2.ErrMethodNotFound
@@ -645,30 +665,11 @@ func (ss *ServerSession) initialize(ctx context.Context, params *InitializeParam
 		version = v
 	}
 
-	caps := &serverCapabilities{
-		Completions: &completionCapabilities{},
-		Logging:     &loggingCapabilities{},
-	}
-	ss.server.mu.Lock()
-	hasTools := ss.server.tools.len() > 0
-	hasPrompts := ss.server.prompts.len() > 0
-	hasResources := ss.server.resources.len() > 0
-	ss.server.mu.Unlock()
-	if hasTools {
-		caps.Tools = &toolCapabilities{ListChanged: true}
-	}
-	if hasPrompts {
-		caps.Prompts = &promptCapabilities{ListChanged: true}
-	}
-	if hasResources {
-		caps.Resources = &resourceCapabilities{ListChanged: true}
-	}
-
 	return &InitializeResult{
 		// TODO(rfindley): alter behavior when falling back to an older version:
 		// reject unsupported features.
 		ProtocolVersion: version,
-		Capabilities:    caps,
+		Capabilities:    ss.server.capabilities(),
 		Instructions:    ss.server.opts.Instructions,
 		ServerInfo: &implementation{
 			Name:    ss.server.name,

mcp/server_test.go

@@ -227,3 +227,96 @@ func TestServerPaginateVariousPageSizes(t *testing.T) {
 		}
 	}
 }
+
+func TestServerCapabilities(t *testing.T) {
+	// An empty handler that can be used for tools, prompts, and resources.
+	emptyHandler := func(context.Context, *ServerSession, any) (any, error) {
+		return &emptyResult{}, nil
+	}
+
+	testCases := []struct {
+		name             string
+		configureServer  func(s *Server)
+		wantCapabilities *serverCapabilities
+	}{
+		{
+			name:            "No capabilities",
+			configureServer: func(s *Server) {},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+			},
+		},
+		{
+			name: "With prompts",
+			configureServer: func(s *Server) {
+				s.AddPrompts(NewServerPrompt(&Prompt{Name: "p"}, emptyHandler))
+			},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+				Prompts:     &promptCapabilities{ListChanged: true},
+			},
+		},
+		{
+			name: "With resources",
+			configureServer: func(s *Server) {
+				s.AddResources(NewServerResource(&Resource{URI: "file:///r"}, emptyHandler))
+			},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+				Resources:   &resourceCapabilities{ListChanged: true},
+			},
+		},
+		{
+			name: "With resource templates",
+			configureServer: func(s *Server) {
+				s.AddResourceTemplates(NewServerResourceTemplate(&ResourceTemplate{URITemplate: "file:///rt"}, emptyHandler))
+			},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+				Resources:   &resourceCapabilities{ListChanged: true},
+			},
+		},
+		{
+			name: "With tools",
+			configureServer: func(s *Server) {
+				s.AddTools(NewServerTool(&Tool{Name: "t"}, emptyHandler))
+			},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+				Tools:       &toolCapabilities{ListChanged: true},
+			},
+		},
+		{
+			name: "With all capabilities",
+			configureServer: func(s *Server) {
+				s.AddPrompts(NewServerPrompt(&Prompt{Name: "p"}, emptyHandler))
+				s.AddResources(NewServerResource(&Resource{URI: "file:///r"}, emptyHandler))
+				s.AddResourceTemplates(NewServerResourceTemplate(&ResourceTemplate{URITemplate: "file:///rt"}, emptyHandler))
+				s.AddTools(NewServerTool(&Tool{Name: "t"}, emptyHandler))
+			},
+			wantCapabilities: &serverCapabilities{
+				Completions: &completionCapabilities{},
+				Logging:     &loggingCapabilities{},
+				Prompts:     &promptCapabilities{ListChanged: true},
+				Resources:   &resourceCapabilities{ListChanged: true},
+				Tools:       &toolCapabilities{ListChanged: true},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			server := NewServer(nil, nil, nil)
+			tc.configureServer(server)
+			gotCapabilities := server.capabilities()
+			if diff := cmp.Diff(tc.wantCapabilities, gotCapabilities); diff != "" {
+				t.Errorf("capabilities() mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}