Rust: Crud upload on reconnect

Author: simolus3

packages/powersync_core/lib/src/sync/streaming_sync.dart

@@ -586,6 +586,7 @@ typedef BucketDescription = ({
 final class _ActiveRustStreamingIteration {
   final StreamingSyncImplementation sync;
   var _isActive = true;
+  var _hadSyncLine = false;
 
   StreamSubscription<void>? _completedUploads;
   final Completer<void> _completedStream = Completer();
@@ -621,8 +622,10 @@ final class _ActiveRustStreamingIteration {
 
       switch (event) {
         case ReceivedLine(line: final Uint8List line):
+          _triggerCrudUploadOnFirstLine();
           await _control('line_binary', line);
         case ReceivedLine(line: final line as String):
+          _triggerCrudUploadOnFirstLine();
           await _control('line_text', line);
         case UploadCompleted():
           await _control('completed_upload');
@@ -634,6 +637,17 @@ final class _ActiveRustStreamingIteration {
     }
   }
 
+  /// Triggers a local CRUD upload when the first sync line has been received.
+  ///
+  /// This allows uploading local changes that have been made while offline or
+  /// disconnected.
+  void _triggerCrudUploadOnFirstLine() {
+    if (!_hadSyncLine) {
+      sync._internalCrudTriggerController.add(null);
+      _hadSyncLine = true;
+    }
+  }
+
   Future<void> _stop() {
     return _control('stop');
   }

packages/powersync_core/test/in_memory_sync_test.dart

@@ -104,8 +104,8 @@ void _declareTests(String name, SyncOptions options) {
       addTearDown(status.cancel);
 
       syncService.addKeepAlive();
-      await expectLater(
-          status, emits(isSyncStatus(connected: true, hasSynced: false)));
+      await expectLater(status,
+          emitsThrough(isSyncStatus(connected: true, hasSynced: false)));
       return status;
     }
 
@@ -774,6 +774,58 @@ void _declareTests(String name, SyncOptions options) {
       await Future<void>.delayed(const Duration(milliseconds: 500));
       expect(syncService.controller.hasListener, isTrue);
     });
+
+    test('uploads writes made while offline', () async {
+      // Local write while not connected
+      await database.execute(
+          'insert into customers (id, name) values (uuid(), ?)',
+          ['local customer']);
+      uploadData = (db) async {
+        final batch = await db.getNextCrudTransaction();
+        if (batch != null) {
+          await batch.complete();
+        }
+      };
+      syncService.writeCheckpoint = () => {
+            'data': {'write_checkpoint': '1'}
+          };
+
+      final query = StreamQueue(database
+          .watch('SELECT name FROM customers')
+          .map((e) => e.single['name']));
+      expect(await query.next, 'local customer');
+
+      await waitForConnection();
+
+      syncService
+        ..addLine({
+          'checkpoint': Checkpoint(
+            lastOpId: '1',
+            writeCheckpoint: '1',
+            checksums: [BucketChecksum(bucket: 'a', priority: 3, checksum: 0)],
+          )
+        })
+        ..addLine({
+          'data': {
+            'bucket': 'a',
+            'data': <Map<String, Object?>>[
+              {
+                'op_id': '1',
+                'op': 'PUT',
+                'object_type': 'customers',
+                'object_id': '1',
+                'checksum': 0,
+                'data': json.encode({'name': 'from server'}),
+              }
+            ],
+          }
+        })
+        ..addLine({
+          'checkpoint_complete': {'last_op_id': '1'}
+        });
+
+      expect(await query.next, 'from server');
+    });
   });
 }