Reduce warnings for sync after uploads

crates/core/src/sync/storage_adapter.rs

@@ -459,6 +459,24 @@ impl StorageAdapter {
         self.delete_subscription.exec()?;
         Ok(())
     }
+
+    pub fn local_state(&self) -> Result<Option<LocalState>, PowerSyncError> {
+        let stmt = self
+            .db
+            .prepare_v2("SELECT target_op FROM ps_buckets WHERE name = ?")?;
+        stmt.bind_text(1, "$local", sqlite_nostd::Destructor::STATIC)?;
+
+        Ok(if stmt.step()? == ResultCode::ROW {
+            let target_op = stmt.column_int64(0);
+            Some(LocalState { target_op })
+        } else {
+            None
+        })
+    }
+}
+
+pub struct LocalState {
+    pub target_op: i64,
 }
 
 pub struct BucketInfo {

crates/core/src/sync/streaming_sync.rs

@@ -448,6 +448,12 @@ impl StreamingSyncIteration {
                     |s| s.start_tracking_checkpoint(progress, subscription_state),
                     &mut event.instructions,
                 );
+
+                // Technically, we could still try to apply a pending checkpoint after receiving a
+                // new one. However, sync_local assumes it's only called in a state where there's no
+                // pending checkpoint, so we'd have to take the oplog state at the time we've
+                // originally received the validated-but-not-applied checkpoint. This is likely not
+                // something worth doing.
                 self.validated_but_not_applied = None;
                 *target = updated_target;
             }
@@ -515,28 +521,7 @@ impl StreamingSyncIteration {
                 SyncEvent::BinaryLine { data } => bson::from_bytes(data)
                     .map_err(|e| PowerSyncError::sync_protocol_error("invalid binary line", e))?,
                 SyncEvent::UploadFinished => {
-                    if let Some(checkpoint) = self.validated_but_not_applied.take() {
-                        let result = self.sync_local(&checkpoint, None)?;
-
-                        match result {
-                            SyncLocalResult::ChangesApplied => {
-                                event.instructions.push(Instruction::LogLine {
-                                    severity: LogSeverity::DEBUG,
-                                    line: "Applied pending checkpoint after completed upload"
-                                        .into(),
-                                });
-
-                                self.handle_checkpoint_applied(event, self.adapter.now()?);
-                            }
-                            _ => {
-                                event.instructions.push(Instruction::LogLine {
-                                    severity: LogSeverity::WARNING,
-                                    line: "Could not apply pending checkpoint even after completed upload"
-                                        .into(),
-                                });
-                            }
-                        }
-                    }
+                    self.try_applying_write_after_completed_upload(event)?;
 
                     continue;
                 }
@@ -608,6 +593,43 @@ impl StreamingSyncIteration {
         Ok(progress)
     }
 
+    fn try_applying_write_after_completed_upload(
+        &mut self,
+        event: &mut ActiveEvent,
+    ) -> Result<(), PowerSyncError> {
+        let Some(checkpoint) = self.validated_but_not_applied.take() else {
+            return Ok(());
+        };
+
+        let target_write = self.adapter.local_state()?.map(|e| e.target_op);
+        if checkpoint.write_checkpoint < target_write {
+            // Note: None < Some(x). The pending checkpoint does not contain the write
+            // checkpoint created during the upload, so we don't have to try applying it, it's
+            // guaranteed to be outdated.
+            return Ok(());
+        }
+
+        let result = self.sync_local(&checkpoint, None)?;
+        match result {
+            SyncLocalResult::ChangesApplied => {
+                event.instructions.push(Instruction::LogLine {
+                    severity: LogSeverity::DEBUG,
+                    line: "Applied pending checkpoint after completed upload".into(),
+                });
+
+                self.handle_checkpoint_applied(event, self.adapter.now()?);
+            }
+            _ => {
+                event.instructions.push(Instruction::LogLine {
+                    severity: LogSeverity::WARNING,
+                    line: "Could not apply pending checkpoint even after completed upload".into(),
+                });
+            }
+        }
+
+        Ok(())
+    }
+
     /// Reconciles local stream subscriptions with service-side state received in a checkpoint.
     ///
     /// This involves:

crates/core/src/sync_local.rs

@@ -102,17 +102,10 @@ impl<'a> SyncOperation<'a> {
         if needs_check {
             // language=SQLite
             let statement = self.db.prepare_v2(
-                "\
-    SELECT group_concat(name)
-    FROM ps_buckets
-    WHERE target_op > last_op AND name = '$local'",
+                "SELECT 1 FROM ps_buckets WHERE target_op > last_op AND name = '$local'",
             )?;
 
-            if statement.step()? != ResultCode::ROW {
-                return Err(PowerSyncError::unknown_internal());
-            }
-
-            if statement.column_type(0)? == ColumnType::Text {
+            if statement.step()? == ResultCode::ROW {
                 return Ok(false);
             }
 

dart/test/sync_test.dart

@@ -121,8 +121,14 @@ void _syncTests<T>({
   }
 
   List<Object?> pushCheckpoint(
-      {int lastOpId = 1, List<Object> buckets = const []}) {
-    return syncLine(checkpoint(lastOpId: lastOpId, buckets: buckets));
+      {int lastOpId = 1,
+      List<Object> buckets = const [],
+      String? writeCheckpoint}) {
+    return syncLine(checkpoint(
+      lastOpId: lastOpId,
+      buckets: buckets,
+      writeCheckpoint: writeCheckpoint,
+    ));
   }
 
   List<Object?> pushCheckpointComplete({int? priority, String lastOpId = '1'}) {
@@ -676,6 +682,123 @@ void _syncTests<T>({
     });
   });
 
+  group('applies pending changes', () {
+    test('write checkpoint before upload complete', () {
+      // local write while offline
+      db.execute("insert into items (id, col) values ('local', 'data');");
+      invokeControl('start', null);
+
+      // Start upload process. Assume data has been uploaded and a write
+      // checkpoint has been requested, but not received yet.
+      db.execute('DELETE FROM ps_crud');
+      pushCheckpoint(buckets: priorityBuckets, writeCheckpoint: '1');
+      pushSyncData('prio1', '1', 'row-0', 'PUT', {'col': 'hi'});
+      expect(pushCheckpointComplete(), [
+        containsPair('LogLine', {
+          'severity': 'INFO',
+          'line': contains('Will retry at completed upload')
+        })
+      ]);
+
+      // Now complete the upload process.
+      db.execute(r"UPDATE ps_buckets SET target_op = 1 WHERE name = '$local'");
+      invokeControl('completed_upload', null);
+
+      // This should apply the pending write checkpoint.
+      expect(fetchRows(), [
+        {'id': 'row-0', 'col': 'hi'}
+      ]);
+    });
+
+    test('write checkpoint with synced data', () {
+      // local write while offline
+      db.execute("insert into items (id, col) values ('local', 'data');");
+      invokeControl('start', null);
+
+      // Complete upload process
+      db.execute('DELETE FROM ps_crud');
+      db.execute(r"UPDATE ps_buckets SET target_op = 1 WHERE name = '$local'");
+      expect(invokeControl('completed_upload', null), isEmpty);
+
+      // Sync afterwards containing data and write checkpoint.
+      pushCheckpoint(buckets: priorityBuckets, writeCheckpoint: '1');
+      pushSyncData('prio1', '1', 'row-0', 'PUT', {'col': 'hi'});
+      pushCheckpointComplete();
+      expect(fetchRows(), [
+        {'id': 'row-0', 'col': 'hi'}
+      ]);
+    });
+
+    test('write checkpoint after synced data', () {
+      // local write while offline
+      db.execute("insert into items (id, col) values ('local', 'data');");
+      invokeControl('start', null);
+
+      // Upload changes, assume that triggered a checkpoint.
+      db.execute('DELETE FROM ps_crud');
+      pushCheckpoint(buckets: priorityBuckets);
+      pushSyncData('prio1', '1', 'row-0', 'PUT', {'col': 'hi'});
+      expect(pushCheckpointComplete(), [
+        containsPair('LogLine', {
+          'severity': 'INFO',
+          'line': contains('Will retry at completed upload')
+        })
+      ]);
+
+      // Now the upload is complete and requests a write checkpoint
+      db.execute(r"UPDATE ps_buckets SET target_op = 1 WHERE name = '$local'");
+      expect(invokeControl('completed_upload', null), isEmpty);
+
+      // Which triggers a new iteration
+      pushCheckpoint(buckets: priorityBuckets, writeCheckpoint: '1');
+      expect(
+          pushCheckpointComplete(),
+          contains(containsPair('LogLine', {
+            'severity': 'DEBUG',
+            'line': contains('Validated and applied checkpoint')
+          })));
+
+      expect(fetchRows(), [
+        {'id': 'row-0', 'col': 'hi'}
+      ]);
+    });
+
+    test('second local write', () {
+      // first local write while offline
+      db.execute("insert into items (id, col) values ('local', 'data');");
+      invokeControl('start', null);
+
+      // Upload changes, assume that triggered a checkpoint.
+      db.execute('DELETE FROM ps_crud');
+      pushCheckpoint(buckets: priorityBuckets, writeCheckpoint: '1');
+      pushSyncData('prio1', '1', 'row-0', 'PUT', {'col': 'hi'});
+      expect(pushCheckpointComplete(), [
+        containsPair('LogLine', {
+          'severity': 'INFO',
+          'line': contains('Will retry at completed upload')
+        })
+      ]);
+
+      // Second local write during sync
+      db.execute("insert into items (id, col) values ('local2', 'data2');");
+
+      // Now the upload is complete and requests a write checkpoint
+      db.execute(r"UPDATE ps_buckets SET target_op = 1 WHERE name = '$local'");
+      expect(invokeControl('completed_upload', null), [
+        containsPair('LogLine', {
+          'severity': 'WARNING',
+          'line':
+              'Could not apply pending checkpoint even after completed upload'
+        })
+      ]);
+
+      expect(fetchRows(), [
+        {'id': 'local', 'col': 'data'},
+        {'id': 'local2', 'col': 'data2'},
+      ]);
+    });
+  });
+
   group('errors', () {
     syncTest('diff without prior checkpoint', (_) {
       invokeControl('start', null);

dart/test/utils/test_utils.dart

@@ -11,7 +11,7 @@ Object checkpoint({
   return {
     'checkpoint': {
       'last_op_id': '$lastOpId',
-      'write_checkpoint': null,
+      'write_checkpoint': writeCheckpoint,
       'buckets': buckets,
       'streams': streams,
     }