request<R> method

Future<R> request<R>(String command, { Map<String, Object?>? data, Duration timeout = const Duration(seconds: 3), })

Send a typed request to Web Worker and await the response.

Creates a dedicated MessageChannel for the reply, sends the request, and waits for exactly one response. Perfect for offloading CPU-intensive work to Web Workers while maintaining type safety.

Parameters:

• command: Command string for the worker
• data: Optional data payload
• timeout: Maximum wait time (default: 3 seconds)

Usage: {@tool snippet example/web_example.dart} {@end-tool}

Implementation

Future<R> request<R>(
  String command, {
  Map<String, Object?>? data,
  Duration timeout = const Duration(seconds: 3),
}) async {
  final completer = Completer<Object?>();
  final reply = MessageChannel();

  reply.port2.onmessage = ((MessageEvent msg) {
    if (completer.isCompleted) return;
    completer.complete(msg.data?.dartify());
  }).toJS;

  sendCmd(
    command,
    data: {...?data, 'reply': reply.port1},
    transfer: reply.port1,
  );

  try {
    final obj = await completer.future.timeout(
      timeout,
      onTimeout: () {
        throw TimeoutException(
          'request("$command") timed out after $timeout',
        );
      },
    );

    if (obj is Map && obj['error'] != null) {
      throw StateError('request("$command") failed: ${obj['error']}');
    }

    try {
      return obj as R;
    } on TypeError {
      throw StateError(
        'request("$command") returned incompatible type: ${obj.runtimeType} expected: $R',
      );
    }
  } finally {
    reply.port1.close();
    reply.port2.close();
  }
}