Merge pull request #279 from powersync-ja/test-disconnect-while-fetching-credentials

Allow disconnecting in `fetchCredentials` callback

Author: simolus3

packages/powersync_core/lib/src/abort_controller.dart

@@ -25,7 +25,7 @@ class AbortController {
       _abortRequested.complete();
     }
 
-    await _abortCompleter.future;
+    await onCompletion;
   }
 
   /// Signal that an abort has completed.

packages/powersync_core/lib/src/database/native/native_powersync_database.dart

@@ -120,6 +120,7 @@ class PowerSyncDatabaseImpl
     required PowerSyncBackendConnector connector,
     required Duration crudThrottleTime,
     required AbortController abort,
+    required Zone asyncWorkZone,
     Map<String, dynamic>? params,
   }) async {
     final dbRef = database.isolateConnectionFactory();
@@ -157,7 +158,7 @@ class PowerSyncDatabaseImpl
       await waitForShutdown();
     }
 
-    receiveMessages.listen((data) async {
+    Future<void> handleMessage(Object? data) async {
       if (data is List) {
         String action = data[0] as String;
         if (action == "getCredentials") {
@@ -192,7 +193,14 @@ class PowerSyncDatabaseImpl
               record.level, record.message, record.error, record.stackTrace);
         }
       }
-    });
+    }
+
+    // This function is called in a Zone marking the connection lock as locked.
+    // This is used to prevent reentrant calls to the lock (which would be a
+    // deadlock). However, the lock is returned as soon as this function
+    // returns - and handleMessage may run later. So, make sure we run those
+    // callbacks in the parent zone.
+    receiveMessages.listen(asyncWorkZone.bindUnaryCallback(handleMessage));
 
     receiveUnhandledErrors.listen((message) async {
       // Sample error:

packages/powersync_core/lib/src/database/powersync_database_impl_stub.dart

@@ -114,6 +114,7 @@ class PowerSyncDatabaseImpl
       {required PowerSyncBackendConnector connector,
       required Duration crudThrottleTime,
       required AbortController abort,
+      required Zone asyncWorkZone,
       Map<String, dynamic>? params}) {
     throw UnimplementedError();
   }

packages/powersync_core/lib/src/database/powersync_db_mixin.dart

@@ -282,6 +282,7 @@ mixin PowerSyncDatabaseMixin implements SqliteConnection {
 
     clientParams = params;
     var thisConnectAborter = AbortController();
+    final zone = Zone.current;
 
     late void Function() retryHandler;
 
@@ -296,6 +297,9 @@ mixin PowerSyncDatabaseMixin implements SqliteConnection {
         crudThrottleTime: crudThrottleTime,
         params: params,
         abort: thisConnectAborter,
+        // Run follow-up async tasks in the parent zone, a new one is introduced
+        // while we hold the lock (and async tasks won't hold the sync lock).
+        asyncWorkZone: zone,
       );
 
       thisConnectAborter.onCompletion.whenComplete(retryHandler);
@@ -347,6 +351,7 @@ mixin PowerSyncDatabaseMixin implements SqliteConnection {
     required PowerSyncBackendConnector connector,
     required Duration crudThrottleTime,
     required AbortController abort,
+    required Zone asyncWorkZone,
     Map<String, dynamic>? params,
   });
 
@@ -372,7 +377,7 @@ mixin PowerSyncDatabaseMixin implements SqliteConnection {
         _abortActiveSync = null;
       } else {
         /// Wait for the abort to complete. Continue updating the sync status after completed
-        await disconnector.onAbort;
+        await disconnector.onCompletion;
       }
     }
   }

packages/powersync_core/lib/src/database/web/web_powersync_database.dart

@@ -116,6 +116,7 @@ class PowerSyncDatabaseImpl
     required PowerSyncBackendConnector connector,
     required Duration crudThrottleTime,
     required AbortController abort,
+    required Zone asyncWorkZone,
     Map<String, dynamic>? params,
   }) async {
     final crudStream =

packages/powersync_core/test/streaming_sync_test.dart

@@ -9,6 +9,7 @@ import 'package:logging/logging.dart';
 import 'package:powersync_core/powersync_core.dart';
 import 'package:test/test.dart';
 
+import 'server/sync_server/in_memory_sync_server.dart';
 import 'test_server.dart';
 import 'utils/abstract_test_utils.dart';
 import 'utils/test_utils_impl.dart';
@@ -61,6 +62,45 @@ void main() {
       server.close();
     });
 
+    test('can disconnect in fetchCredentials', () async {
+      final service = MockSyncService();
+      final server = await createServer(mockSyncService: service);
+      final ignoreLogger = Logger.detached('powersync.test');
+
+      final pdb =
+          await testUtils.setupPowerSync(path: path, logger: ignoreLogger);
+      pdb.retryDelay = Duration(milliseconds: 50);
+      final connector = TestConnector(expectAsync0(() async {
+        return PowerSyncCredentials(endpoint: server.endpoint, token: 'token');
+      }));
+
+      await pdb.connect(connector: connector);
+      while (server.connectionCount != 1) {
+        await Future<void>.delayed(const Duration(milliseconds: 100));
+      }
+
+      service.addKeepAlive(60);
+
+      final didDisconnect = Completer<void>();
+
+      connector.fetchCredentialsCallback = expectAsync0(() async {
+        didDisconnect.complete(pdb.disconnect());
+
+        throw 'deliberate disconnect';
+      });
+
+      service.addKeepAlive(0);
+      await didDisconnect.future;
+      expect(pdb.currentStatus.connected, isFalse);
+      // The error should be cleared after calling disconnect
+      expect(pdb.currentStatus.downloadError, isNull);
+
+      // Wait for a short while to make sure the database doesn't reconnect.
+      for (var i = 0; i < 10; i++) {
+        expect(pdb.currentStatus.connecting, isFalse);
+      }
+    });
+
     test('can connect as initial operation', () async {
       final server = await createServer();
       final ignoreLogger = Logger.detached('powersync.test');

packages/powersync_core/test/test_server.dart

@@ -8,18 +8,21 @@ import 'package:shelf/shelf.dart';
 import 'package:shelf/shelf_io.dart' as shelf_io;
 import 'package:shelf_router/shelf_router.dart';
 
-class TestServer {
+import 'server/sync_server/in_memory_sync_server.dart';
+
+final class TestServer {
   late HttpServer server;
   Router app = Router();
   int maxConnectionCount = 0;
   int tokenExpiresIn;
 
   TestServer({this.tokenExpiresIn = 65});
 
-  Future<void> init() async {
+  Future<void> init({MockSyncService? mockSyncService}) async {
     app.post('/sync/stream', handleSyncStream);
     // Open on an arbitrary open port
-    server = await shelf_io.serve(app.call, 'localhost', 0);
+    server = await shelf_io.serve(
+        mockSyncService?.router.call ?? app.call, 'localhost', 0);
   }
 
   String get endpoint {
@@ -34,6 +37,9 @@ class TestServer {
     return server.connectionsInfo();
   }
 
+  /// The default response if no [MockSyncService] has been passed to [init].
+  ///
+  /// This will emit keepalive messages frequently.
   Future<Response> handleSyncStream(Request request) async {
     maxConnectionCount = max(connectionCount, maxConnectionCount);
 
@@ -61,9 +67,9 @@ class TestServer {
   }
 }
 
-Future<TestServer> createServer() async {
+Future<TestServer> createServer({MockSyncService? mockSyncService}) async {
   var server = TestServer();
-  await server.init();
+  await server.init(mockSyncService: mockSyncService);
   return server;
 }
 

packages/powersync_core/test/utils/abstract_test_utils.dart

@@ -125,21 +125,21 @@ abstract class AbstractTestUtils {
 }
 
 class TestConnector extends PowerSyncBackendConnector {
-  final Future<PowerSyncCredentials> Function() _fetchCredentials;
-  final Future<void> Function(PowerSyncDatabase)? _uploadData;
+  Future<PowerSyncCredentials> Function() fetchCredentialsCallback;
+  Future<void> Function(PowerSyncDatabase)? uploadDataCallback;
 
-  TestConnector(this._fetchCredentials,
+  TestConnector(this.fetchCredentialsCallback,
       {Future<void> Function(PowerSyncDatabase)? uploadData})
-      : _uploadData = uploadData;
+      : uploadDataCallback = uploadData;
 
   @override
   Future<PowerSyncCredentials?> fetchCredentials() {
-    return _fetchCredentials();
+    return fetchCredentialsCallback();
   }
 
   @override
   Future<void> uploadData(PowerSyncDatabase database) async {
-    await _uploadData?.call(database);
+    await uploadDataCallback?.call(database);
   }
 }