fix(auth): Uncaught Hosted UI cancellation

packages/amplify_core/lib/src/state_machine/event.dart

@@ -68,10 +68,10 @@ final class EventCompleter<Event extends StateMachineEvent,
   /// match the Zone in which its future is listened to, otherwise the future
   /// will never complete.
   ///
-  /// That is, running `_zone.run(completer.complete)` would still throw
-  /// the error in the Zone where the completer was instantiated. And due
-  /// to how Zone's work, a listener for a completer which completes in a
-  /// different error zone will never finish.
+  /// That is, running `_zone.run(() => completer.completeError(error))` would
+  /// still throw the error in the Zone where the completer was instantiated,
+  /// not `_zone`. And due to how Zone's work, a listener for a completer which
+  /// completes in a different error zone will never finish.
   ///
   /// The following example illustrates the problem we're trying to solve
   /// here:
@@ -168,5 +168,8 @@ final class EventCompleter<Event extends StateMachineEvent,
   ///
   /// Since state machine methods are marked with `@useResult`, this allows
   /// opting into fire-and-forget behavior explicitly.
-  void ignore() {}
+  void ignore() {
+    _acceptedCompleters.clear();
+    _completers.clear();
+  }
 }

packages/amplify_core/lib/src/state_machine/state_machine.dart

@@ -302,6 +302,8 @@ abstract class StateMachine<
 
     final resolution = resolveError(error, stackTrace);
 
+    logger.debug('Resolved error with state', resolution?.type);
+
     // Add the error to the state stream if it cannot be resolved to a new
     // state internally.
     if (resolution == null) {

packages/auth/amplify_auth_cognito/example/integration_test/hosted_ui_webview_test.dart

@@ -13,7 +13,6 @@ import 'package:amplify_auth_cognito_dart/src/flows/hosted_ui/hosted_ui_platform
 import 'package:amplify_auth_cognito_dart/src/model/hosted_ui/oauth_parameters.dart';
 import 'package:amplify_auth_cognito_dart/src/state/cognito_state_machine.dart';
 import 'package:amplify_auth_cognito_dart/src/state/state.dart';
-import 'package:amplify_auth_cognito_test/amplify_auth_cognito_test.dart';
 import 'package:amplify_flutter/amplify_flutter.dart';
 import 'package:amplify_integration_test/amplify_integration_test.dart';
 import 'package:flutter/material.dart';
@@ -56,21 +55,52 @@ void main() {
         );
       });
 
-      Future<void> signIn(WidgetTester tester) async {
+      Future<void> signIn(
+        WidgetTester tester, {
+        bool cancel = false,
+      }) async {
         stateMachine.addInstance<HostedUiPlatform>(
           HostedUiTestPlatform(
             tester,
             stateMachine,
             username: username,
             password: password,
+            cancel: cancel,
           ),
         );
         _logger.debug('Signing in with Web UI');
-        final result = await plugin.signInWithWebUI(
-          provider: AuthProvider.cognito,
-        );
-        _logger.debug('Signed in with Web UI');
-        expect(result.isSignedIn, isTrue);
+        if (cancel) {
+          final expectation = expectLater(
+            plugin.signInWithWebUI(
+              provider: AuthProvider.cognito,
+            ),
+            throwsA(isA<UserCancelledException>()),
+          );
+          final hostedUiMachine =
+              stateMachine.expect(HostedUiStateMachine.type);
+          expect(
+            hostedUiMachine.stream,
+            emitsInOrder([
+              isA<HostedUiSigningIn>(),
+              isA<HostedUiFailure>().having(
+                (s) => s.exception,
+                'exception',
+                isA<UserCancelledException>(),
+              ),
+              emitsDone,
+            ]),
+          );
+          await expectation;
+          // Ensure queue is flushed and done event is emitted after
+          // signInWithWebUI completes.
+          await hostedUiMachine.close();
+        } else {
+          final result = await plugin.signInWithWebUI(
+            provider: AuthProvider.cognito,
+          );
+          _logger.debug('Signed in with Web UI');
+          expect(result.isSignedIn, isTrue);
+        }
       }
 
       Future<void> signOut({required bool globalSignOut}) async {
@@ -112,14 +142,17 @@ void main() {
         await signOut(globalSignOut: false);
       });
 
+      testWidgets('cancel sign-in', (tester) async {
+        await signIn(tester, cancel: true);
+      });
+
       testWidgets('global sign out', (tester) async {
         await signIn(tester);
         await signOut(globalSignOut: true);
       });
     },
     // Add remaining platforms as `webview_flutter` adds support.
-    // TODO(dnys1): Investigate Android failures in CI on Android 33+
-    skip: zIsWeb || !((Platform.isAndroid && !isCI) || Platform.isIOS),
+    skip: zIsWeb || !(Platform.isAndroid || Platform.isIOS),
   );
 }
 
@@ -129,11 +162,15 @@ class HostedUiTestPlatform extends HostedUiPlatformImpl {
     DependencyManager manager, {
     required this.username,
     required this.password,
+    required this.cancel,
   }) : super(manager);
 
   final String username;
   final String password;
 
+  /// Whether to cancel the sign-in flow once initiated.
+  final bool cancel;
+
   final WidgetTester tester;
   final Completer<WebViewController> _controller = Completer();
   final Completer<OAuthParameters> _oauthParameters = Completer();
@@ -143,6 +180,9 @@ class HostedUiTestPlatform extends HostedUiPlatformImpl {
     required CognitoSignInWithWebUIPluginOptions options,
     AuthProvider? provider,
   }) async {
+    if (cancel) {
+      throw const UserCancelledException('Cancelled');
+    }
     final signInUri = await getSignInUri(provider: provider);
     await tester.pumpWidget(
       HostedUiApp(

packages/auth/amplify_auth_cognito/example/pubspec.yaml

@@ -40,6 +40,7 @@ dev_dependencies:
   io: ^1.0.0
   otp: ^3.1.4
   stack_trace: ^1.10.0
+  stream_transform: ^2.1.0
   test: ^1.22.1
   webdriver: ^3.0.0
   webview_flutter: ^4.0.0

packages/auth/amplify_auth_cognito/lib/src/flows/hosted_ui/hosted_ui_platform_flutter.dart

@@ -16,6 +16,7 @@ import 'package:amplify_auth_cognito_dart/src/model/hosted_ui/oauth_parameters.d
 // ignore: implementation_imports, invalid_use_of_internal_member
 import 'package:amplify_auth_cognito_dart/src/state/state.dart';
 import 'package:amplify_core/amplify_core.dart';
+import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
 /// {@template amplify_auth_cognito.hosted_ui_platform_flutter}
@@ -27,7 +28,17 @@ class HostedUiPlatformImpl extends io.HostedUiPlatformImpl {
   /// {@macro amplify_auth_cognito.hosted_ui_platform_flutter}
   HostedUiPlatformImpl(super.dependencyManager);
 
-  static final bool _isMobile = Platform.isAndroid || Platform.isIOS;
+  static bool get _isMobile {
+    if (Platform.isAndroid || Platform.isIOS) {
+      return true;
+    }
+    // Allow overrides for tests
+    if (zAssertsEnabled) {
+      return debugDefaultTargetPlatformOverride == TargetPlatform.android ||
+          debugDefaultTargetPlatformOverride == TargetPlatform.iOS;
+    }
+    return false;
+  }
 
   NativeAuthBridge get _nativeAuthBridge => dependencyManager.expect();
 
@@ -80,39 +91,37 @@ class HostedUiPlatformImpl extends io.HostedUiPlatformImpl {
         options.isPreferPrivateSession,
         options.browserPackageName,
       );
-      unawaited(
-        dispatcher.dispatchAndComplete(
-          HostedUiEvent.exchange(
-            OAuthParameters.fromJson(queryParameters.cast()),
-          ),
-        ),
-      );
+      dispatcher
+          .dispatch(
+            HostedUiEvent.exchange(
+              OAuthParameters.fromJson(queryParameters.cast()),
+            ),
+          )
+          .ignore();
     } on Exception catch (e) {
-      unawaited(
-        dispatcher.dispatchAndComplete(const HostedUiEvent.cancelSignIn()),
-      );
-      if (e is PlatformException) {
-        if (e.code == 'CANCELLED') {
+      switch (e) {
+        case PlatformException(code: 'CANCELLED'):
           throw const UserCancelledException(
             'The user cancelled the sign-in flow',
           );
-        }
-        // Generated Android message is `CLASS_NAME: message`
-        var message = e.message;
-        if (message != null && message.contains(': ')) {
-          message = message.split(': ')[1];
-        }
-        String? recoverySuggestion;
-        if (e.code == 'NOBROWSER') {
-          recoverySuggestion = "Ensure you've added the <queries> tag to your "
-              'AndroidManifest.xml as outlined in the docs';
-        }
-        throw UrlLauncherException(
-          message ?? 'An unknown error occurred',
-          recoverySuggestion: recoverySuggestion,
-        );
+        case PlatformException(:final code, :var message):
+          // Generated Android message is `CLASS_NAME: message`
+          if (message != null && message.contains(': ')) {
+            message = message.split(': ')[1];
+          }
+          String? recoverySuggestion;
+          if (code == 'NOBROWSER') {
+            recoverySuggestion =
+                "Ensure you've added the <queries> tag to your "
+                'AndroidManifest.xml as outlined in the docs';
+          }
+          throw UrlLauncherException(
+            message ?? 'An unknown error occurred',
+            recoverySuggestion: recoverySuggestion,
+          );
+        default:
+          rethrow;
       }
-      rethrow;
     }
   }
 

packages/auth/amplify_auth_cognito/pubspec.yaml

@@ -33,6 +33,7 @@ dependencies:
   plugin_platform_interface: ^2.0.0
 
 dev_dependencies:
+  amplify_auth_cognito_test: any
   amplify_lints: ">=3.0.0 <3.1.0"
   flutter_test:
     sdk: flutter

packages/auth/amplify_auth_cognito/test/hosted_ui_platform_flutter_test.dart

@@ -0,0 +1,90 @@
+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+// ignore_for_file: invalid_use_of_internal_member, non_constant_identifier_names
+
+import 'package:amplify_auth_cognito/amplify_auth_cognito.dart';
+import 'package:amplify_auth_cognito/src/flows/hosted_ui/hosted_ui_platform_flutter.dart';
+import 'package:amplify_auth_cognito/src/native_auth_plugin.g.dart';
+import 'package:amplify_auth_cognito_dart/src/flows/hosted_ui/hosted_ui_platform.dart';
+import 'package:amplify_auth_cognito_dart/src/state/cognito_state_machine.dart';
+import 'package:amplify_auth_cognito_dart/src/state/state.dart';
+import 'package:amplify_auth_cognito_test/amplify_auth_cognito_test.dart';
+import 'package:amplify_flutter/amplify_flutter.dart';
+import 'package:flutter/foundation.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  AWSLogger().logLevel = LogLevel.verbose;
+
+  group('HostedUiPlatformFlutter', () {
+    late AmplifyAuthCognito plugin;
+    late SecureStorageInterface secureStorage;
+    late DependencyManager dependencyManager;
+
+    setUp(() async {
+      secureStorage = MockSecureStorage();
+      dependencyManager = DependencyManager()
+        ..addInstance(hostedUiConfig)
+        ..addInstance<SecureStorageInterface>(secureStorage)
+        ..addInstance<NativeAuthBridge>(ThrowingNativeBridge());
+      plugin = AmplifyAuthCognito()
+        ..stateMachine = CognitoAuthStateMachine(
+          dependencyManager: dependencyManager,
+        );
+      plugin.stateMachine.addBuilder<HostedUiPlatform>(
+        HostedUiPlatformImpl.new,
+      );
+      await plugin.stateMachine.acceptAndComplete(
+        ConfigurationEvent.configure(mockConfig),
+      );
+    });
+
+    tearDown(() => plugin.close());
+
+    test('can cancel flow', () async {
+      // Pretend to be iOS so that the `ThrowingNativeBridge` is called,
+      // mimicking a failure from the platform channel.
+      debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+      addTearDown(() => debugDefaultTargetPlatformOverride = null);
+
+      final expectation = expectLater(
+        plugin.signInWithWebUI(
+          provider: AuthProvider.cognito,
+        ),
+        throwsA(isA<UserCancelledException>()),
+      );
+      final hostedUiMachine =
+          plugin.stateMachine.expect(HostedUiStateMachine.type);
+      expect(
+        hostedUiMachine.stream,
+        emitsInOrder([
+          isA<HostedUiSigningIn>(),
+          isA<HostedUiFailure>().having(
+            (s) => s.exception,
+            'exception',
+            isA<UserCancelledException>(),
+          ),
+          emitsDone,
+        ]),
+      );
+      await expectation;
+      // Ensure queue is flushed and done event is emitted after
+      // signInWithWebUI completes.
+      await hostedUiMachine.close();
+    });
+  });
+}
+
+final class ThrowingNativeBridge extends Fake implements NativeAuthBridge {
+  @override
+  Future<Map<String?, String?>> signInWithUrl(
+    String arg_url,
+    String arg_callbackUrlScheme,
+    bool arg_preferPrivateSession,
+    String? arg_browserPackageName,
+  ) async {
+    throw PlatformException(code: 'CANCELLED');
+  }
+}

packages/auth/amplify_auth_cognito_dart/lib/src/flows/hosted_ui/hosted_ui_platform_io.dart

@@ -250,13 +250,13 @@ class HostedUiPlatformImpl extends HostedUiPlatform {
           );
           continue;
         }
-        unawaited(
-          dispatcher.dispatchAndComplete(
-            HostedUiEvent.exchange(
-              OAuthParameters.fromJson(queryParams),
-            ),
-          ),
-        );
+        dispatcher
+            .dispatch(
+              HostedUiEvent.exchange(
+                OAuthParameters.fromJson(queryParams),
+              ),
+            )
+            .ignore();
         await _respond(
           request,
           HttpStatus.ok,
@@ -268,7 +268,7 @@ class HostedUiPlatformImpl extends HostedUiPlatform {
         break;
       }
     } finally {
-      unawaited(close());
+      close().ignore();
     }
   }
 
@@ -324,7 +324,7 @@ class HostedUiPlatformImpl extends HostedUiPlatform {
         break;
       }
     } finally {
-      unawaited(close());
+      close().ignore();
     }
   }