fetch method

@override Future<ResponseBody> fetch(RequestOptions options, Stream<Uint8List>? requestStream, Future? cancelFuture)

We should implement this method to make real http requests.

options: The request options

requestStream The request stream, It will not be null only when http method is one of "POST","PUT","PATCH" and the request body is not empty.

We should give priority to using requestStream(not options.data) as request data. because supporting stream ensures the onSendProgress works.

cancelFuture: When cancelled the request, cancelFuture will be resolved! you can listen cancel event by it, for example:

 cancelFuture?.then((_)=>print("request cancelled!"))

cancelFuture: will be null when the request is not set CancelToken.

Implementation

@override
Future<ResponseBody> fetch(RequestOptions options,
    Stream<Uint8List>? requestStream, Future? cancelFuture) async {
  var xhr = HttpRequest();
  _xhrs.add(xhr);
  xhr
    ..open(options.method, '${options.uri}')
    ..responseType = 'arraybuffer';

  var _withCredentials = options.extra['withCredentials'];

  if (_withCredentials != null) {
    xhr.withCredentials = _withCredentials == true;
  } else {
    xhr.withCredentials = withCredentials;
  }

  options.headers.remove(Headers.contentLengthHeader);
  options.headers.forEach((key, v) => xhr.setRequestHeader(key, '$v'));

  if (options.connectTimeout > 0 && options.receiveTimeout > 0) {
    xhr.timeout = options.connectTimeout + options.receiveTimeout;
  }

  var completer = Completer<ResponseBody>();

  xhr.onLoad.first.then((_) {
    Uint8List body = (xhr.response as ByteBuffer).asUint8List();
    completer.complete(
      ResponseBody.fromBytes(
        body,
        xhr.status,
        headers: xhr.responseHeaders.map((k, v) => MapEntry(k, v.split(','))),
        statusMessage: xhr.statusText,
        isRedirect: xhr.status == 302 || xhr.status == 301,
      ),
    );
  });

  bool haveSent = false;

  if (options.connectTimeout > 0) {
    Future.delayed(Duration(milliseconds: options.connectTimeout)).then(
      (value) {
        if (!haveSent) {
          completer.completeError(
            DioError(
              requestOptions: options,
              error: 'Connecting timed out [${options.connectTimeout}ms]',
              type: DioErrorType.connectTimeout,
            ),
            StackTrace.current,
          );
          xhr.abort();
        }
      },
    );
  }

  int sendStart = 0;
  xhr.upload.onProgress.listen((event) {
    haveSent = true;
    if (options.sendTimeout > 0) {
      if (sendStart == 0) {
        sendStart = DateTime.now().millisecondsSinceEpoch;
      }
      var t = DateTime.now().millisecondsSinceEpoch;
      print(t - sendStart);
      if (t - sendStart > options.sendTimeout) {
        completer.completeError(
          DioError(
            requestOptions: options,
            error: 'Sending timed out [${options.sendTimeout}ms]',
            type: DioErrorType.sendTimeout,
          ),
          StackTrace.current,
        );
        xhr.abort();
      }
    }
    if (options.onSendProgress != null &&
        event.loaded != null &&
        event.total != null) {
      options.onSendProgress!(event.loaded!, event.total!);
    }
  });

  int receiveStart = 0;
  xhr.onProgress.listen((event) {
    if (options.receiveTimeout > 0) {
      if (receiveStart == 0) {
        receiveStart = DateTime.now().millisecondsSinceEpoch;
      }
      if (DateTime.now().millisecondsSinceEpoch - receiveStart >
          options.receiveTimeout) {
        completer.completeError(
          DioError(
            requestOptions: options,
            error: 'Receiving timed out [${options.receiveTimeout}ms]',
            type: DioErrorType.receiveTimeout,
          ),
          StackTrace.current,
        );
        xhr.abort();
      }
    }
    if (options.onReceiveProgress != null) {
      if (event.loaded != null && event.total != null) {
        options.onReceiveProgress!(event.loaded!, event.total!);
      }
    }
  });

  xhr.onError.first.then((_) {
    // Unfortunately, the underlying XMLHttpRequest API doesn't expose any
    // specific information about the error itself.
    completer.completeError(
      DioError(
        type: DioErrorType.response,
        error: 'XMLHttpRequest error.',
        requestOptions: options,
      ),
      StackTrace.current,
    );
  });

  cancelFuture?.then((err) {
    if (xhr.readyState < 4 && xhr.readyState > 0) {
      try {
        xhr.abort();
      } catch (e) {
        // ignore
      }

      // xhr.onError will not triggered when xhr.abort() called.
      // so need to manual throw the cancel error to avoid Future hang ups.
      // or added xhr.onAbort like axios did https://github.com/axios/axios/blob/master/lib/adapters/xhr.js#L102-L111
      if (!completer.isCompleted) {
        completer.completeError(err);
      }
    }
  });

  if (requestStream != null) {
    var _completer = Completer<Uint8List>();
    var sink = ByteConversionSink.withCallback(
        (bytes) => _completer.complete(Uint8List.fromList(bytes)));
    requestStream.listen(
      sink.add,
      onError: _completer.completeError,
      onDone: sink.close,
      cancelOnError: true,
    );
    var bytes = await _completer.future;
    xhr.send(bytes);
  } else {
    xhr.send();
  }

  return completer.future.whenComplete(() {
    _xhrs.remove(xhr);
  });
}