[flutter_tools] fix top web crasher (#83272)

packages/flutter_tools/lib/src/isolated/devfs_web.dart

@@ -660,45 +660,15 @@ class WebDevFS implements DevFS {
 
   Dwds get dwds => webAssetServer.dwds;
 
-  Future<DebugConnection> _cachedExtensionFuture;
-  StreamSubscription<void> _connectedApps;
+  @visibleForTesting
+  Future<DebugConnection> cachedExtensionFuture;
+
+  @visibleForTesting
+  StreamSubscription<void> connectedApps;
 
   /// Connect and retrieve the [DebugConnection] for the current application.
-  ///
-  /// Only calls [AppConnection.runMain] on the subsequent connections.
   Future<ConnectionResult> connect(bool useDebugExtension) {
-    final Completer<ConnectionResult> firstConnection =
-        Completer<ConnectionResult>();
-    _connectedApps =
-        dwds.connectedApps.listen((AppConnection appConnection) async {
-      try {
-        final DebugConnection debugConnection = useDebugExtension
-            ? await (_cachedExtensionFuture ??=
-                dwds.extensionDebugConnections.stream.first)
-            : await dwds.debugConnection(appConnection);
-        if (firstConnection.isCompleted) {
-          appConnection.runMain();
-        } else {
-          final vm_service.VmService vmService = await createVmServiceDelegate(
-            Uri.parse(debugConnection.uri),
-            logger: globals.logger,
-          );
-          firstConnection
-              .complete(ConnectionResult(appConnection, debugConnection, vmService));
-        }
-      } on Exception catch (error, stackTrace) {
-        if (!firstConnection.isCompleted) {
-          firstConnection.completeError(error, stackTrace);
-        }
-      }
-    }, onError: (dynamic error, StackTrace stackTrace) {
-      globals.printError(
-          'Unknown error while waiting for debug connection:$error\n$stackTrace');
-      if (!firstConnection.isCompleted) {
-        firstConnection.completeError(error, stackTrace);
-      }
-    });
-    return firstConnection.future;
+    return connectToApplication(useDebugExtension, this, globals.logger, createVmServiceDelegate);
   }
 
   @override
@@ -753,7 +723,7 @@ class WebDevFS implements DevFS {
   @override
   Future<void> destroy() async {
     await webAssetServer.dispose();
-    await _connectedApps?.cancel();
+    await connectedApps?.cancel();
   }
 
   @override
@@ -1068,3 +1038,35 @@ To serve from a subpath "foo" (i.e. http://localhost:8080/foo/ instead of http:/
 
 For more information, see: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/base
 ''';
+
+
+/// Connect and retrieve the [DebugConnection] for the current application.
+@visibleForTesting
+Future<ConnectionResult> connectToApplication(bool useDebugExtension, WebDevFS devFS, Logger logger, Future<vm_service.VmService> Function(Uri, {Logger logger}) createVmService) {
+  final Completer<ConnectionResult> firstConnection = Completer<ConnectionResult>();
+  devFS.connectedApps = devFS.dwds.connectedApps.listen((AppConnection appConnection) async {
+    try {
+      final DebugConnection debugConnection = useDebugExtension
+          ? await (devFS.cachedExtensionFuture ??=
+              devFS.dwds.extensionDebugConnections.stream.first)
+          : await devFS.dwds.debugConnection(appConnection);
+      if (!firstConnection.isCompleted) {
+        final vm_service.VmService vmService = await createVmService(
+          Uri.parse(debugConnection.uri),
+          logger: logger,
+        );
+        firstConnection.complete(ConnectionResult(appConnection, debugConnection, vmService));
+      }
+    } on Exception catch (error, stackTrace) {
+      if (!firstConnection.isCompleted) {
+        firstConnection.completeError(error, stackTrace);
+      }
+    }
+  }, onError: (dynamic error, StackTrace stackTrace) {
+    logger.printError('Unknown error while waiting for debug connection:$error\n$stackTrace');
+    if (!firstConnection.isCompleted) {
+      firstConnection.completeError(error, stackTrace);
+    }
+  });
+  return firstConnection.future;
+}

packages/flutter_tools/test/general.shard/web/devfs_web_test.dart

@@ -4,10 +4,14 @@
 
 // @dart = 2.8
 
+import 'dart:async';
 import 'dart:io' hide Directory, File;
 
+import 'package:dwds/dwds.dart';
 import 'package:flutter_tools/src/artifacts.dart';
+import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
 import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/build_system/targets/web.dart';
@@ -19,8 +23,11 @@ import 'package:flutter_tools/src/web/compile.dart';
 import 'package:package_config/package_config.dart';
 import 'package:shelf/shelf.dart';
 import 'package:test/fake.dart';
+import 'package:vm_service/vm_service.dart' as vm_service;
 
 import '../../src/common.dart';
+import '../../src/context.dart';
+import '../../src/fake_vm_services.dart';
 import '../../src/testbed.dart';
 
 const List<int> kTransparentImage = <int>[
@@ -1053,6 +1060,48 @@ void main() {
   }, overrides: <Type, Generator>{
     Artifacts: () => Artifacts.test(),
   }));
+
+  testWithoutContext('connectToApplication completes the future', () async {
+    final FakeDwds dwds = FakeDwds();
+    final FakeDevFS devfs = FakeDevFS()..dwds = dwds;
+    final BufferLogger logger = BufferLogger.test();
+
+    final Future<void> result = connectToApplication(false, devfs, logger, (Uri uri, {Logger logger}) async {
+      return FakeVmService();
+    });
+
+    dwds.controller.add(FakeAppConnection());
+
+    await expectLater(result, completes);
+  });
+
+  testWithoutContext('Multiple runs of connectToApplication does not complete the future more than once', () async {
+    final FakeDwds dwds = FakeDwds();
+    final FakeDevFS devfs = FakeDevFS()..dwds = dwds;
+    final BufferLogger logger = BufferLogger.test();
+    final Future<void> result = connectToApplication(false, devfs, logger, (Uri uri, {Logger logger}) async {
+      return FakeVmService();
+    });
+
+    dwds.controller.add(FakeAppConnection());
+    dwds.controller.add(FakeAppConnection());
+    unawaited(dwds.controller.close());
+
+    await expectLater(result, completes);
+  });
+
+  testWithoutContext('connectToApplication surfaces errors', () async {
+    final FakeDwds dwds = FakeDwds();
+    final FakeDevFS devfs = FakeDevFS()..dwds = dwds;
+    final BufferLogger logger = BufferLogger.test();
+    final Future<void> result = connectToApplication(false, devfs, logger, (Uri uri, {Logger logger}) async {
+      return FakeVmService();
+    });
+
+    dwds.controller.addError(Exception('test'));
+
+    await expectLater(() => result, throwsException);
+  });
 }
 
 class FakeHttpServer extends Fake implements HttpServer {
@@ -1081,3 +1130,38 @@ class FakeResidentCompiler extends Fake implements ResidentCompiler {
     return output;
   }
 }
+
+class FakeDevFS extends Fake implements WebDevFS {
+  @override
+  StreamSubscription<void> connectedApps;
+
+  @override
+  Future<DebugConnection> cachedExtensionFuture;
+
+  @override
+  Dwds dwds;
+
+  void dispose() {
+    connectedApps.cancel();
+  }
+}
+
+class FakeDwds extends Fake implements Dwds {
+  final StreamController<AppConnection> controller = StreamController<AppConnection>();
+
+  @override
+  Stream<AppConnection> get connectedApps => controller.stream;
+
+  @override
+  Future<DebugConnection> debugConnection(AppConnection appConnection) async {
+    return FakeDebugConnection();
+  }
+}
+
+class FakeAppConnection extends Fake implements AppConnection {}
+class FakeDebugConnection extends Fake implements DebugConnection {
+  @override
+  String get uri => '';
+}
+
+class FakeVmService extends Fake implements vm_service.VmService {}