Print a more helpful error if DDS is enabled when running integration_test and enableTimeline is called (#92509)

dev/bots/test.dart

@@ -883,7 +883,7 @@ Future<void> _runFrameworkTests() async {
     await _runFlutterTest(path.join(flutterRoot, 'dev', 'tools', 'gen_keycodes'));
     await _runFlutterTest(path.join(flutterRoot, 'dev', 'benchmarks', 'test_apps', 'stocks'));
     await _runFlutterTest(path.join(flutterRoot, 'packages', 'flutter_driver'), tests: <String>[path.join('test', 'src', 'real_tests')], options: soundNullSafetyOptions);
-    await _runFlutterTest(path.join(flutterRoot, 'packages', 'integration_test'));
+    await _runFlutterTest(path.join(flutterRoot, 'packages', 'integration_test'), options: <String>['--enable-vmservice']);
     await _runFlutterTest(path.join(flutterRoot, 'packages', 'flutter_goldens'), options: soundNullSafetyOptions);
     await _runFlutterTest(path.join(flutterRoot, 'packages', 'flutter_localizations'), options: soundNullSafetyOptions);
     await _runFlutterTest(path.join(flutterRoot, 'packages', 'flutter_test'), options: soundNullSafetyOptions);

packages/integration_test/lib/integration_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:developer' as developer;
+import 'dart:io' show SocketException, WebSocket, HttpClient;
 import 'dart:ui';
 
 import 'package:flutter/foundation.dart';
@@ -12,7 +13,6 @@ import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:vm_service/vm_service.dart' as vm;
-import 'package:vm_service/vm_service_io.dart' as vm_io;
 
 import '_callback_io.dart' if (dart.library.html) '_callback_web.dart' as driver_actions;
 import '_extension_io.dart' if (dart.library.html) '_extension_web.dart';
@@ -235,6 +235,7 @@ https://flutter.dev/docs/testing/integration-tests#testing-on-firebase-test-lab
   Future<void> enableTimeline({
     List<String> streams = const <String>['all'],
     @visibleForTesting vm.VmService? vmService,
+    @visibleForTesting HttpClient? httpClient,
   }) async {
     assert(streams != null);
     assert(streams.isNotEmpty);
@@ -244,9 +245,18 @@ https://flutter.dev/docs/testing/integration-tests#testing-on-firebase-test-lab
     if (_vmService == null) {
       final developer.ServiceProtocolInfo info = await developer.Service.getInfo();
       assert(info.serverUri != null);
-      _vmService = await vm_io.vmServiceConnectUri(
-        'ws://localhost:${info.serverUri!.port}${info.serverUri!.path}ws',
-      );
+      final String address = 'ws://localhost:${info.serverUri!.port}${info.serverUri!.path}ws';
+      try {
+        _vmService = await _vmServiceConnectUri(address, httpClient: httpClient);
+      } on SocketException catch(e, s) {
+        throw StateError(
+          'Failed to connect to VM Service at $address.\n'
+          'This may happen if DDS is enabled. If this test was launched via '
+          '`flutter drive`, try adding `--no-dds`.\n'
+          'The original exception was:\n'
+          '$e\n$s',
+        );
+      }
     }
     await _vmService!.setVMTimelineFlags(streams);
   }
@@ -447,3 +457,29 @@ class _GarbageCollectionInfo {
   final int oldCount;
   final int newCount;
 }
+
+// Connect to the given uri and return a new [VmService] instance.
+//
+// Copied from vm_service_io so that we can pass a custom [HttpClient] for
+// testing. Currently, the WebSocket API reuses an HttpClient that
+// is created before the test can change the HttpOverrides.
+Future<vm.VmService> _vmServiceConnectUri(
+  String wsUri, {
+  HttpClient? httpClient,
+}) async {
+  final WebSocket socket = await WebSocket.connect(wsUri, customClient: httpClient);
+  final StreamController<dynamic> controller = StreamController<dynamic>();
+  final Completer<void> streamClosedCompleter = Completer<void>();
+
+  socket.listen(
+    (dynamic data) => controller.add(data),
+    onDone: () => streamClosedCompleter.complete(),
+  );
+
+  return vm.VmService(
+    controller.stream,
+    (String message) => socket.add(message),
+    disposeHandler: () => socket.close(),
+    streamClosed: streamClosedCompleter.future,
+  );
+}

packages/integration_test/test/socket_fail_test.dart

@@ -0,0 +1,32 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test.dart';
+
+class SocketExceptionHttpClient extends Fake implements HttpClient {
+  @override
+  Future<HttpClientRequest> openUrl(String method, Uri url) {
+    throw const SocketException('always throw');
+  }
+}
+
+Future<void> main() async {
+  final IntegrationTestWidgetsFlutterBinding binding = IntegrationTestWidgetsFlutterBinding.ensureInitialized() as IntegrationTestWidgetsFlutterBinding;
+
+  test('Prints an appropriate message on socket exception', () async {
+    bool gotStateError = false;
+    try {
+      await binding.enableTimeline(httpClient: SocketExceptionHttpClient());
+    } on StateError catch (e) {
+      gotStateError = true;
+      expect(e.toString(), contains('This may happen if DDS is enabled'));
+    } on SocketException catch (_) {
+      fail('Did not expect a socket exception.');
+    }
+    expect(gotStateError, true);
+  });
+}