fix(datastore): Restart Sync Engine when network on/off (#5218)

Author: Equartey

packages/amplify/amplify_flutter/lib/amplify_flutter.dart

@@ -6,7 +6,7 @@ library amplify_flutter;
 import 'package:amplify_core/amplify_core.dart';
 import 'package:amplify_flutter/src/amplify_impl.dart';
 
-export 'package:amplify_core/amplify_core.dart' hide Amplify;
+export 'package:amplify_core/amplify_core.dart' hide Amplify, WebSocketOptions;
 export 'package:amplify_secure_storage/amplify_secure_storage.dart';
 
 /// Top level singleton Amplify object.

packages/amplify_core/lib/amplify_core.dart

@@ -64,7 +64,9 @@ export 'src/state_machine/transition.dart';
 export 'src/types/analytics/analytics_types.dart';
 
 /// API
-export 'src/types/api/api_types.dart';
+export 'src/types/api/api_types.dart' hide WebSocketOptions;
+// ignore: invalid_export_of_internal_element
+export 'src/types/api/api_types.dart' show WebSocketOptions;
 
 /// App path provider
 export 'src/types/app_path_provider/app_path_provider.dart';

packages/amplify_core/lib/src/types/api/api_types.dart

@@ -22,6 +22,7 @@ export 'graphql/graphql_response.dart';
 export 'graphql/graphql_response_error.dart';
 export 'graphql/graphql_subscription_operation.dart';
 export 'graphql/graphql_subscription_options.dart';
+export 'graphql/web_socket_options.dart';
 export 'hub/api_hub_event.dart';
 export 'hub/api_subscription_hub_event.dart';
 // Types

packages/amplify_core/lib/src/types/api/graphql/web_socket_options.dart

@@ -0,0 +1,21 @@
+import 'package:meta/meta.dart'; // Importing the 'meta' package to use the @internal annotation
+
+/// An internal class to control websocket features after API plugin has been initialized.
+@internal
+class WebSocketOptions {
+  /// Private constructor to prevent instantiation
+  WebSocketOptions._();
+
+  /// Private static boolean field
+  static bool _autoReconnect = true;
+
+  /// Static getter method for the boolean field
+  @internal
+  static bool get autoReconnect => _autoReconnect;
+
+  /// Static setter method for the boolean field
+  @internal
+  static set autoReconnect(bool value) {
+    _autoReconnect = value;
+  }
+}

packages/amplify_datastore/android/src/main/kotlin/com/amazonaws/amplify/amplify_datastore/pigeons/NativePluginBindings.kt

@@ -162,11 +162,12 @@ class _MyAppState extends State<MyApp> {
   void listenToHub() {
     setState(() {
       hubSubscription = Amplify.Hub.listen(HubChannel.DataStore, (msg) {
-        if (msg.type case DataStoreHubEventType.networkStatus) {
-          print('Network status message: $msg');
+        final payload = msg.payload;
+        if (payload is NetworkStatusEvent) {
+          print('Network status active: ${payload.active}');
           return;
         }
-        print(msg);
+        print(msg.type);
       });
       _listeningToHub = true;
     });
@@ -317,6 +318,9 @@ class _MyAppState extends State<MyApp> {
             displayQueryButtons(
                 _isAmplifyConfigured, _queriesToView, updateQueriesToView),
 
+            // Start/Stop/Clear buttons
+            displaySyncButtons(),
+
             Padding(padding: EdgeInsets.all(5.0)),
             Text("Listen to DataStore Hub"),
             Switch(

packages/amplify_datastore/example/ios/Runner.xcodeproj/xcshareddata/xcschemes/Runner.xcscheme

@@ -175,3 +175,35 @@ Widget getWidgetToDisplayComment(
         }),
   );
 }
+
+Widget displaySyncButtons() {
+  return Row(mainAxisAlignment: MainAxisAlignment.center, children: [
+    VerticalDivider(
+      color: Colors.white,
+      width: 5,
+    ),
+    ElevatedButton.icon(
+      onPressed: () {
+        Amplify.DataStore.start();
+      },
+      icon: Icon(Icons.play_arrow),
+      label: const Text("Start"),
+    ),
+    divider,
+    ElevatedButton.icon(
+      onPressed: () {
+        Amplify.DataStore.stop();
+      },
+      icon: Icon(Icons.stop),
+      label: const Text("Stop"),
+    ),
+    divider,
+    ElevatedButton.icon(
+      onPressed: () {
+        Amplify.DataStore.clear();
+      },
+      icon: Icon(Icons.delete_sweep),
+      label: const Text("Clear"),
+    ),
+  ]);
+}

packages/amplify_datastore/example/ios/Runner/Info.plist

@@ -8,8 +8,9 @@ public class FlutterApiPlugin: APICategoryPlugin, AWSAPIAuthInformation
     private let apiAuthFactory: APIAuthProviderFactory
     private let nativeApiPlugin: NativeApiPlugin
     private let nativeSubscriptionEvents: PassthroughSubject<NativeGraphQLSubscriptionResponse, Never>
-    private var cancellables = AtomicDictionary<AnyCancellable, Void>()
+    private var cancellables = AtomicDictionary<AnyCancellable?, Void>()
     private var endpoints: [String: String]
+    private var networkMonitor: AmplifyNetworkMonitor
 
     init(
         apiAuthProviderFactory: APIAuthProviderFactory,
@@ -21,6 +22,23 @@ public class FlutterApiPlugin: APICategoryPlugin, AWSAPIAuthInformation
         self.nativeApiPlugin = nativeApiPlugin
         self.nativeSubscriptionEvents = subscriptionEventBus
         self.endpoints = endpoints
+        self.networkMonitor = AmplifyNetworkMonitor()
+        
+        // Listen to network events and send a notification to Flutter side when disconnected.
+        // This enables Flutter to clean up the websocket/subscriptions.
+        do {
+            let cancellable = try reachabilityPublisher()?.sink(receiveValue: { reachabilityUpdate in
+                if !reachabilityUpdate.isOnline {
+                    DispatchQueue.main.async {
+                       self.nativeApiPlugin.deviceOffline {}
+                   }
+                }
+            })
+            cancellables.set(value: (), forKey: cancellable) // the subscription is bind with class instance lifecycle, it should be released when stream is finished or unsubscribed
+
+        } catch {
+            print("Failed to create reachability publisher: \(error)")
+        }
     }
 
     public func defaultAuthType() throws -> AWSAuthorizationType {
@@ -122,6 +140,11 @@ public class FlutterApiPlugin: APICategoryPlugin, AWSAPIAuthInformation
                    errors.contains(where: self.isUnauthorizedError(graphQLError:)) {
                     return Fail(error: APIError.operationError("Unauthorized", "", nil)).eraseToAnyPublisher()
                 }
+                if case .data(.failure(let graphQLResponseError)) = event,
+                   case .error(let errors) = graphQLResponseError,
+                   errors.contains(where: self.isFlutterNetworkError(graphQLError:)){
+                    return Fail(error: APIError.networkError("FlutterNetworkException", nil, URLError(.networkConnectionLost))).eraseToAnyPublisher()
+                }
                 return Just(event).setFailureType(to: Error.self).eraseToAnyPublisher()
             }
             .eraseToAnyPublisher()
@@ -182,6 +205,13 @@ public class FlutterApiPlugin: APICategoryPlugin, AWSAPIAuthInformation
         }
         return errorTypeValue == "Unauthorized"
     }
+    
+    private func isFlutterNetworkError(graphQLError: GraphQLError) -> Bool {
+        guard case let .string(errorTypeValue) = graphQLError.extensions?["errorType"] else {
+            return false
+        }
+        return errorTypeValue == "FlutterNetworkException"
+    }
 
     func asyncQuery(nativeRequest: NativeGraphQLRequest) async -> NativeGraphQLResponse {
         await withCheckedContinuation { continuation in
@@ -236,14 +266,23 @@ public class FlutterApiPlugin: APICategoryPlugin, AWSAPIAuthInformation
     public func patch(request: RESTRequest) async throws -> RESTTask.Success {
         preconditionFailure("method not supported")
     }
-    
+        
     public func reachabilityPublisher(for apiName: String?) throws -> AnyPublisher<ReachabilityUpdate, Never>? {
-        preconditionFailure("method not supported")
+        return networkMonitor.publisher
+                .compactMap { event in
+                    switch event {
+                    case (.offline, .online):
+                        return ReachabilityUpdate(isOnline: true)
+                    case (.online, .offline):
+                        return ReachabilityUpdate(isOnline: false)
+                    default:
+                        return nil
+                    }
+                }
+                .eraseToAnyPublisher()
     }
 
     public func reachabilityPublisher() throws -> AnyPublisher<ReachabilityUpdate, Never>? {
-        return nil
+        return try reachabilityPublisher(for: nil)
     }
-    
-
 }

packages/amplify_datastore/example/lib/main.dart

@@ -145,8 +145,6 @@ public class SwiftAmplifyDataStorePlugin: NSObject, FlutterPlugin, NativeAmplify
                     nil
                 )
             }
-            // TODO: Migrate to Async Swift v2
-            //            AmplifyAWSServiceConfiguration.addUserAgentPlatform(.flutter, version: "\(version) /datastore")
             try Amplify.configure(with : .data(data))
             return completion(.success(()))
         } catch let error as ConfigurationError {

packages/amplify_datastore/example/lib/queries_display_widgets.dart

@@ -141,7 +141,14 @@ extension GraphQLResponse {
                 uniquingKeysWith: { _, a in a }
             )
         }
-
+        
+        if error.message?.stringValue?.contains("NetworkException") == true {
+            extensions = extensions.merging(
+                ["errorType": "FlutterNetworkException"],
+                uniquingKeysWith: { _, a in a }
+            )
+        }
+        
         return (try? jsonEncoder.encode(error))
             .flatMap { try? jsonDecoder.decode(GraphQLError.self, from: $0) }
             .map {

packages/amplify_datastore/ios/Classes/FlutterApiPlugin.swift

@@ -350,7 +350,9 @@ class NativeAmplifyApi
   Future<NativeGraphQLSubscriptionResponse> subscribe(
       NativeGraphQLRequest request) async {
     final flutterRequest = nativeRequestToGraphQLRequest(request);
-
+    // Turn off then default reconnection behavior to allow native side to trigger reconnect
+    // ignore: invalid_use_of_internal_member
+    WebSocketOptions.autoReconnect = false;
     final operation = Amplify.API.subscribe(flutterRequest,
         onEstablished: () => sendNativeStartAckEvent(flutterRequest.id));
 
@@ -376,6 +378,28 @@ class NativeAmplifyApi
     }
   }
 
+  @override
+  Future<void> deviceOffline() async {
+    await _notifySubscriptionsDisconnected();
+  }
+
+  Future<void> _notifySubscriptionsDisconnected() async {
+    _subscriptionsCache.forEach((subId, stream) async {
+      // Send Swift subscriptions an expected error message when network is lost.
+      // Swift side is expecting this string to transform into the correct error type.
+      // This will cause the Sync Engine to enter retry mode and in order to recover it
+      // later we must unsubscribe and close the websocket.
+      GraphQLResponseError error = GraphQLResponseError(
+        message: 'FlutterNetworkException - Network disconnected',
+      );
+      sendSubscriptionStreamErrorEvent(subId, error.toJson());
+      // Note: the websocket will still be closing after this line.
+      // There may be a small delay in shutdown.
+      await unsubscribe(subId);
+      await stream.cancel();
+    });
+  }
+
   /// Amplify.DataStore.Stop() callback
   ///
   /// Clean up subscriptions on stop.

packages/amplify_datastore/ios/Classes/SwiftAmplifyDataStorePlugin.swift

@@ -42,6 +42,9 @@ abstract class NativeApiPlugin {
   @async
   void unsubscribe(String subscriptionId);
 
+  @async
+  void deviceOffline();
+
   @async
   void onStop();
 }

packages/amplify_datastore/ios/Classes/api/GraphQLResponse+Decode.swift

@@ -4,7 +4,8 @@
 /// Amplify API for Dart
 library amplify_api_dart;
 
-export 'package:amplify_core/src/types/api/api_types.dart';
+export 'package:amplify_core/src/types/api/api_types.dart'
+    hide WebSocketOptions;
 
 export 'src/api_plugin_impl.dart';
 

packages/amplify_datastore/ios/Classes/pigeons/NativePluginBindings.swift

@@ -142,11 +142,7 @@ class SubscriptionBloc<T>
   }
 
   Stream<WsSubscriptionState<T>> _complete(SubscriptionComplete event) async* {
-    assert(
-      _currentState is SubscriptionListeningState,
-      'State should always be listening when completed.',
-    );
-    yield (_currentState as SubscriptionListeningState<T>).complete();
+    yield _currentState.complete();
     await close();
   }