Add simple benchmark

Author: simolus3

dart/benchmark/apply_lines.dart

@@ -0,0 +1,48 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import '../test/utils/native_test_utils.dart';
+
+/// Usage: dart run benchmark/apply_lines.dart path/to/lines.bin
+///
+/// This creates a new in-memory database and applies concatenated BSON sync
+/// lines from a file.
+void main(List<String> args) {
+  if (args.length != 1) {
+    throw 'Usage: dart run benchmark/apply_lines.dart path/to/lines.bin';
+  }
+
+  final [path] = args;
+  final file = File(path).openSync();
+  final db = openTestDatabase();
+
+  db
+    ..execute('select powersync_init()')
+    ..execute('select powersync_control(?, null)', ['start']);
+
+  final stopwatch = Stopwatch()..start();
+
+  final lengthBuffer = Uint8List(4);
+  while (file.positionSync() < file.lengthSync()) {
+    // BSON document: <int32LE length, ... bytes>
+    final bytesRead = file.readIntoSync(lengthBuffer);
+    if (bytesRead != 4) {
+      throw 'short read, expected length';
+    }
+    final length = lengthBuffer.buffer.asByteData().getInt32(0, Endian.little);
+    file.setPositionSync(file.positionSync() - 4);
+
+    final syncLineBson = file.readSync(length);
+    if (syncLineBson.length != length) {
+      throw 'short read for bson document';
+    }
+
+    db
+      ..execute('BEGIN')
+      ..execute('SELECT powersync_control(?, ?)', ['line_binary', syncLineBson])
+      ..execute('COMMIT;');
+  }
+
+  stopwatch.stop();
+  print('Applying $path took ${stopwatch.elapsed}');
+}