class MultipartRequest extends http.MultipartRequest {
  /// Creates a new [MultipartRequest].
  var client = http.Client();

  MultipartRequest(
    String method,
    Uri url, {
    this.onProgress,
  }) : super(method, url);

  final void Function(int bytes, int totalBytes) onProgress;

  void cancel() => client.close();

  @override
  Future<http.StreamedResponse> send() async {
    try {
      var response = await client.send(this);
      var stream = onDone(response.stream, client.close);
      return http.StreamedResponse(
        http.ByteStream(stream),
        response.statusCode,
        contentLength: response.contentLength,
        request: response.request,
        headers: response.headers,
        isRedirect: response.isRedirect,
        persistentConnection: response.persistentConnection,
        reasonPhrase: response.reasonPhrase,
      );
    } catch (_) {
      client.close();
      rethrow;
    }
  }

  Stream<T> onDone<T>(Stream<T> stream, void Function() onDone) =>
      stream.transform(StreamTransformer.fromHandlers(handleDone: (sink) {
        sink.close();
        onDone();
      }));

  /// Freezes all mutable fields and returns a single-subscription [ByteStream]
  /// that will emit the request body.
  @override
  http.ByteStream finalize() {
    final byteStream = super.finalize();
    if (onProgress == null) return byteStream;

    final total = contentLength;
    var bytes = 0;

    final t = StreamTransformer.fromHandlers(
      handleData: (List<int> data, EventSink<List<int>> sink) {
        bytes += data.length;
        if (onProgress != null) onProgress(bytes, total);
        sink.add(data);
      },
    );
    final stream = byteStream.transform(t);
    return http.ByteStream(stream);
  }
}