Make parameters nullable, if nullable in the spec.

mcp_examples/pubspec.yaml

@@ -10,7 +10,7 @@ dependencies:
   args: ^2.7.0
   async: ^2.13.0
   cli_util: ^0.4.2
-  dart_mcp: ^0.2.0
+  dart_mcp: ^0.4.0
   google_generative_ai: ^0.4.7
   path: ^1.9.1
   stream_channel: ^2.1.4

pkgs/dart_mcp/CHANGELOG.md

@@ -1,9 +1,9 @@
-## 0.3.4-wip
+## 0.4.0-wip
 
 - Update the tool calling example to include progress notifications.
-- Remove a reference to "screenshot" for a generic error that occurs for more
-  than just screenshots.
-- Mark the "root" parameter for create_project required.
+- **Breaking**: Update APIs to accept nullable parameters when the parameters
+  are not required for that method. This is only breaking if you override these
+  methods.
 
 ## 0.3.3
 

pkgs/dart_mcp/lib/src/client/client.dart

@@ -136,30 +136,30 @@ base class ServerConnection extends MCPBase {
   ///
   /// This is a broadcast stream, events are not buffered and only future events
   /// are given.
-  Stream<PromptListChangedNotification> get promptListChanged =>
+  Stream<PromptListChangedNotification?> get promptListChanged =>
       _promptListChangedController.stream;
   final _promptListChangedController =
-      StreamController<PromptListChangedNotification>.broadcast();
+      StreamController<PromptListChangedNotification?>.broadcast();
 
   /// Emits an event any time the server notifies us of a change to the list of
   /// tools it supports.
   ///
   /// This is a broadcast stream, events are not buffered and only future events
   /// are given.
-  Stream<ToolListChangedNotification> get toolListChanged =>
+  Stream<ToolListChangedNotification?> get toolListChanged =>
       _toolListChangedController.stream;
   final _toolListChangedController =
-      StreamController<ToolListChangedNotification>.broadcast();
+      StreamController<ToolListChangedNotification?>.broadcast();
 
   /// Emits an event any time the server notifies us of a change to the list of
   /// resources it supports.
   ///
   /// This is a broadcast stream, events are not buffered and only future events
   /// are given.
-  Stream<ResourceListChangedNotification> get resourceListChanged =>
+  Stream<ResourceListChangedNotification?> get resourceListChanged =>
       _resourceListChangedController.stream;
   final _resourceListChangedController =
-      StreamController<ResourceListChangedNotification>.broadcast();
+      StreamController<ResourceListChangedNotification?>.broadcast();
 
   /// Emits an event any time the server notifies us of a change to a resource
   /// that this client has subscribed to.
@@ -291,7 +291,7 @@ base class ServerConnection extends MCPBase {
       sendRequest(CallToolRequest.methodName, request);
 
   /// Lists all the [Resource]s from this server.
-  Future<ListResourcesResult> listResources(ListResourcesRequest request) =>
+  Future<ListResourcesResult> listResources([ListResourcesRequest? request]) =>
       sendRequest(ListResourcesRequest.methodName, request);
 
   /// Reads a [Resource] returned from the [ListResourcesResult] or matching
@@ -300,12 +300,12 @@ base class ServerConnection extends MCPBase {
       sendRequest(ReadResourceRequest.methodName, request);
 
   /// Lists all the [ResourceTemplate]s from this server.
-  Future<ListResourceTemplatesResult> listResourceTemplates(
-    ListResourceTemplatesRequest request,
-  ) => sendRequest(ListResourceTemplatesRequest.methodName, request);
+  Future<ListResourceTemplatesResult> listResourceTemplates([
+    ListResourceTemplatesRequest? request,
+  ]) => sendRequest(ListResourceTemplatesRequest.methodName, request);
 
   /// Lists all the prompts from this server.
-  Future<ListPromptsResult> listPrompts(ListPromptsRequest request) =>
+  Future<ListPromptsResult> listPrompts([ListPromptsRequest? request]) =>
       sendRequest(ListPromptsRequest.methodName, request);
 
   /// Gets the requested [Prompt] from the server.

pkgs/dart_mcp/lib/src/client/roots_support.dart

@@ -62,6 +62,6 @@ base mixin RootsSupport on MCPClient {
   }
 
   /// Handler for [ListRootsRequest]s - returns the available [Root]s.
-  FutureOr<ListRootsResult> handleListRoots(ListRootsRequest request) =>
+  FutureOr<ListRootsResult> handleListRoots([ListRootsRequest? request]) =>
       ListRootsResult(roots: _roots.toList());
 }

pkgs/dart_mcp/lib/src/server/prompts_support.dart

@@ -33,7 +33,7 @@ base mixin PromptsSupport on MCPServer {
   }
 
   /// Lists the available prompts.
-  ListPromptsResult _listPrompts(ListPromptsRequest request) =>
+  ListPromptsResult _listPrompts([ListPromptsRequest? request]) =>
       ListPromptsResult(prompts: _prompts.values.toList());
 
   /// Gets the response for a given prompt.

pkgs/dart_mcp/lib/src/server/resources_support.dart

@@ -148,9 +148,9 @@ base mixin ResourcesSupport on MCPServer {
   }
 
   /// Lists all the [ResourceTemplate]s currently available.
-  ListResourceTemplatesResult _listResourceTemplates(
-    ListResourceTemplatesRequest request,
-  ) {
+  ListResourceTemplatesResult _listResourceTemplates([
+    ListResourceTemplatesRequest? request,
+  ]) {
     return ListResourceTemplatesResult(
       resourceTemplates: [
         for (var descriptor in _resourceTemplates) descriptor.template,
@@ -191,7 +191,7 @@ base mixin ResourcesSupport on MCPServer {
   }
 
   /// Lists all the resources currently available.
-  ListResourcesResult _listResources(ListResourcesRequest request) {
+  ListResourcesResult _listResources(ListResourcesRequest? request) {
     return ListResourcesResult(resources: _resources.values.toList());
   }
 

pkgs/dart_mcp/lib/src/server/server.dart

@@ -26,8 +26,8 @@ part 'tools_support.dart';
 abstract base class MCPServer extends MCPBase {
   /// Completes when this server has finished initialization and gotten the
   /// final ack from the client.
-  Future<void> get initialized => _initialized.future;
-  final Completer<void> _initialized = Completer<void>();
+  Future<InitializedNotification?> get initialized => _initialized.future;
+  final Completer<InitializedNotification?> _initialized = Completer();
 
   /// Whether this server is still active and has completed initialization.
   bool get ready => isActive && _initialized.isCompleted;
@@ -65,9 +65,9 @@ abstract base class MCPServer extends MCPBase {
   ///
   /// This is a broadcast stream, events are not buffered and only future events
   /// are given.
-  Stream<RootsListChangedNotification>? get rootsListChanged =>
+  Stream<RootsListChangedNotification?>? get rootsListChanged =>
       _rootsListChangedController?.stream;
-  StreamController<RootsListChangedNotification>? _rootsListChangedController;
+  StreamController<RootsListChangedNotification?>? _rootsListChangedController;
 
   MCPServer.fromStreamChannel(
     super.channel, {
@@ -106,7 +106,7 @@ abstract base class MCPServer extends MCPBase {
     clientCapabilities = request.capabilities;
     if (clientCapabilities.roots?.listChanged == true) {
       _rootsListChangedController =
-          StreamController<RootsListChangedNotification>.broadcast();
+          StreamController<RootsListChangedNotification?>.broadcast();
       registerNotificationHandler(
         RootsListChangedNotification.methodName,
         _rootsListChangedController!.sink.add,
@@ -128,12 +128,12 @@ abstract base class MCPServer extends MCPBase {
   ///
   /// The server should not respond.
   @mustCallSuper
-  void handleInitialized(InitializedNotification notification) {
-    _initialized.complete();
+  void handleInitialized([InitializedNotification? notification]) {
+    _initialized.complete(notification);
   }
 
   /// Lists all the root URIs from the client.
-  Future<ListRootsResult> listRoots(ListRootsRequest request) =>
+  Future<ListRootsResult> listRoots([ListRootsRequest? request]) =>
       sendRequest(ListRootsRequest.methodName, request);
 
   /// A request to prompt the LLM owned by the client with a message.

pkgs/dart_mcp/lib/src/shared.dart

@@ -95,9 +95,7 @@ base class MCPBase {
     void Function(T) impl,
   ) => _peer.registerMethod(
     name,
-    (Parameters p) => impl(
-      (p.value as Map? ?? <String, Object?>{}).cast<String, Object?>() as T,
-    ),
+    (Parameters? p) => impl((p?.value as Map?)?.cast<String, Object?>() as T),
   );
 
   /// Sends a notification to the peer.

pkgs/dart_mcp/pubspec.yaml

@@ -1,5 +1,5 @@
 name: dart_mcp
-version: 0.3.4-wip
+version: 0.4.0-wip
 description: A package for making MCP servers and clients.
 repository: https://github.com/dart-lang/ai/tree/main/pkgs/dart_mcp
 issue_tracker: https://github.com/dart-lang/ai/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Adart_mcp

pkgs/dart_mcp/test/api/prompts_test.dart

@@ -24,9 +24,7 @@ void main() {
 
     final serverConnection = environment.serverConnection;
 
-    final promptsResult = await serverConnection.listPrompts(
-      ListPromptsRequest(),
-    );
+    final promptsResult = await serverConnection.listPrompts();
     expect(promptsResult.prompts, [TestMCPServerWithPrompts.greeting]);
 
     final greetingResult = await serverConnection.getPrompt(
@@ -58,6 +56,7 @@ void main() {
       emitsInOrder([
         PromptListChangedNotification(),
         PromptListChangedNotification(),
+        null,
       ]),
       reason: 'We should get a notification for new and removed prompts',
     );
@@ -68,6 +67,7 @@ void main() {
       (_) => GetPromptResult(messages: []),
     );
     server.removePrompt('new prompt');
+    server.sendNotification(PromptListChangedNotification.methodName);
     // Give the notifications a chance to propagate.
     await pumpEventQueue();
 

pkgs/dart_mcp/test/api/roots_test.dart

@@ -25,7 +25,7 @@ void main() {
     final server = environment.server;
     final events = StreamQueue(server.rootsListChanged!);
 
-    expect((await server.listRoots(ListRootsRequest())).roots, isEmpty);
+    expect((await server.listRoots()).roots, isEmpty);
 
     final a = Root(uri: 'test://a', name: 'a');
     final a2 = Root(uri: 'test://a', name: 'a2');
@@ -41,6 +41,11 @@ void main() {
 
     expect(await events.take(2), hasLength(2));
 
+    environment.serverConnection.sendNotification(
+      RootsListChangedNotification.methodName,
+    );
+    expect(await events.next, isNull);
+
     expect(
       (await server.listRoots(ListRootsRequest())).roots,
       unorderedEquals([a, b]),

pkgs/dart_mcp/test/client_and_server_test.dart

@@ -143,31 +143,35 @@ void main() {
   });
 
   test(
-    'server can handle initialized notification with null parameters',
+    'server can handle initialized notification with null or actual parameters',
     () async {
-      final serverLog = StreamController<String>();
-      final environment = TestEnvironment(
-        TestMCPClient(),
-        (c) => TestMCPServer(c, protocolLogSink: serverLog.sink),
-      );
-      await environment.serverConnection.initialize(
-        InitializeRequest(
-          protocolVersion: ProtocolVersion.latestSupported,
-          capabilities: environment.client.capabilities,
-          clientInfo: environment.client.implementation,
-        ),
-      );
-      // Send a notification that doesn't have any parameters.
-      environment.serverConnection.notifyInitialized();
-      await environment.server.initialized;
-      expect(
-        serverLog.stream,
-        emitsInOrder([
-          allOf(startsWith('<<<'), contains('initialize')),
-          allOf(startsWith('>>>'), contains('serverInfo')),
-          allOf(startsWith('<<<'), contains('notifications/initialized')),
-        ]),
-      );
+      for (final initializedMessage in [null, InitializedNotification()]) {
+        final serverLog = StreamController<String>();
+        final environment = TestEnvironment(
+          TestMCPClient(),
+          (c) => TestMCPServer(c, protocolLogSink: serverLog.sink),
+        );
+        await environment.serverConnection.initialize(
+          InitializeRequest(
+            protocolVersion: ProtocolVersion.latestSupported,
+            capabilities: environment.client.capabilities,
+            clientInfo: environment.client.implementation,
+          ),
+        );
+        // Send a notification that doesn't have any parameters.
+        environment.serverConnection.notifyInitialized(initializedMessage);
+        final result = await environment.server.initialized;
+        expect(result, initializedMessage);
+        expect(
+          serverLog.stream,
+          emitsInOrder([
+            allOf(startsWith('<<<'), contains('initialize')),
+            allOf(startsWith('>>>'), contains('serverInfo')),
+            allOf(startsWith('<<<'), contains('notifications/initialized')),
+          ]),
+        );
+        await environment.client.shutdown();
+      }
     },
   );
 

pkgs/dart_mcp/test/server/resources_support_test.dart

@@ -25,9 +25,7 @@ void main() {
 
     final serverConnection = environment.serverConnection;
 
-    final resourcesResult = await serverConnection.listResources(
-      ListResourcesRequest(),
-    );
+    final resourcesResult = await serverConnection.listResources();
     expect(resourcesResult.resources.length, 1);
 
     final resource = resourcesResult.resources.single;
@@ -127,6 +125,9 @@ void main() {
       ResourceListChangedNotification(),
     );
 
+    server.sendNotification(ResourceListChangedNotification.methodName);
+    expect(await resourceListChangedQueue.next, null);
+
     expect(resourceListChangedQueue.hasNext, completion(false));
 
     /// We need to manually shut down to so that the `hasNext` futures can
@@ -199,35 +200,36 @@ void main() {
     await environment.shutdown();
   });
 
-  test('Resource templates can be listed and queried', () async {
-    final environment = TestEnvironment(
-      TestMCPClient(),
-      (channel) => TestMCPServerWithResources(
-        channel,
-        fileContents: {'package:foo/foo.dart': 'hello world!'},
-      ),
-    );
-    await environment.initializeServer();
+  test(
+    'Resource templates can be listed, queried, and subscribed to',
+    () async {
+      final environment = TestEnvironment(
+        TestMCPClient(),
+        (channel) => TestMCPServerWithResources(
+          channel,
+          fileContents: {'package:foo/foo.dart': 'hello world!'},
+        ),
+      );
+      await environment.initializeServer();
 
-    final serverConnection = environment.serverConnection;
+      final serverConnection = environment.serverConnection;
 
-    final templatesResponse = await serverConnection.listResourceTemplates(
-      ListResourceTemplatesRequest(),
-    );
+      final templatesResponse = await serverConnection.listResourceTemplates();
 
-    expect(
-      templatesResponse.resourceTemplates.single,
-      TestMCPServerWithResources.packageUriTemplate,
-    );
+      expect(
+        templatesResponse.resourceTemplates.single,
+        TestMCPServerWithResources.packageUriTemplate,
+      );
 
-    final readResourceResponse = await serverConnection.readResource(
-      ReadResourceRequest(uri: 'package:foo/foo.dart'),
-    );
-    expect(
-      (readResourceResponse.contents.single as TextResourceContents).text,
-      'hello world!',
-    );
-  });
+      final readResourceResponse = await serverConnection.readResource(
+        ReadResourceRequest(uri: 'package:foo/foo.dart'),
+      );
+      expect(
+        (readResourceResponse.contents.single as TextResourceContents).text,
+        'hello world!',
+      );
+    },
+  );
 }
 
 final class TestMCPServerWithResources extends TestMCPServer

pkgs/dart_mcp/test/server/roots_tracking_support_test.dart

@@ -64,7 +64,7 @@ final class TestMCPClientWithRoots extends TestMCPClient with RootsSupport {
   Future<void>? waitToRespond;
 
   @override
-  FutureOr<ListRootsResult> handleListRoots(ListRootsRequest request) async {
+  FutureOr<ListRootsResult> handleListRoots([ListRootsRequest? request]) async {
     await waitToRespond;
     return super.handleListRoots(request);
   }