Fix ping request handling from non-dart clients. (#239)

Fixes #238

- Updates `PingRequest` to wrap `Map<String, Object?>` instead of `Null` to allow empty parameters handling from non-Dart clients.

Author: ksokolovskyi

pkgs/dart_mcp/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.3.3-wip
+
+- Fix `PingRequest` handling when it is sent from a non-Dart client.
+
 ## 0.3.2
 
 - Deprecate the `EnumSchema` type in favor of the `StringSchema` with an

pkgs/dart_mcp/lib/src/api/api.dart

@@ -225,9 +225,12 @@ extension type RequestId( /*String|int*/ Parameter _) {}
 ///
 /// The receiver must promptly respond, or else may be disconnected.
 ///
-/// The request itself has no parameters and should always be just `null`.
-extension type PingRequest._(Null _) {
+/// The request itself has no parameters.
+extension type PingRequest._(Map<String, Object?> _) implements Request {
   static const methodName = 'ping';
+
+  factory PingRequest({MetaWithProgressToken? meta}) =>
+      PingRequest._({if (meta != null) '_meta': meta});
 }
 
 /// An out-of-band notification used to inform the receiver of a progress

pkgs/dart_mcp/lib/src/shared.dart

@@ -131,8 +131,6 @@ base class MCPBase {
 
   /// The peer may ping us at any time, and we should respond with an empty
   /// response.
-  ///
-  /// Note that [PingRequest] is always actually just `null`.
   EmptyResult _handlePing([PingRequest? _]) => EmptyResult();
 
   /// Handles [ProgressNotification]s and forwards them to the streams returned
@@ -172,11 +170,13 @@ base class MCPBase {
   ///
   /// If the timeout is reached, future values or errors from the ping request
   /// are ignored.
-  Future<bool> ping({Duration timeout = const Duration(seconds: 1)}) =>
-      sendRequest<EmptyResult>(
-        PingRequest.methodName,
-        null,
-      ).then((_) => true).timeout(timeout, onTimeout: () => false);
+  Future<bool> ping({
+    Duration timeout = const Duration(seconds: 1),
+    PingRequest? request,
+  }) => sendRequest<EmptyResult>(
+    PingRequest.methodName,
+    request,
+  ).then((_) => true).timeout(timeout, onTimeout: () => false);
 
   /// If [protocolLogSink] is non-null, emits messages to it for all messages
   /// sent over [channel].

pkgs/dart_mcp/pubspec.yaml

@@ -1,5 +1,5 @@
 name: dart_mcp
-version: 0.3.2
+version: 0.3.3-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/client_and_server_test.dart

@@ -127,6 +127,21 @@ void main() {
     );
   });
 
+  // Regression test for https://github.com/dart-lang/ai/issues/238.
+  test('client and server can handle ping with non-null parameters', () async {
+    final environment = TestEnvironment(TestMCPClient(), TestMCPServer.new);
+    await environment.initializeServer();
+
+    await expectLater(
+      environment.serverConnection.ping(request: PingRequest()),
+      completes,
+    );
+    await expectLater(
+      environment.server.ping(request: PingRequest()),
+      completes,
+    );
+  });
+
   test(
     'server can handle initialized notification with null parameters',
     () async {