code: void postProgress(final DownloadRequest request, final long bytesWritten, final long totalBytes) {
      downloadPoster.execute(new Runnable() {
        @Override public void run() {
          request.downloadCallback().onProgress(request.downloadId(), bytesWritten, totalBytes);
        }
      });
    }
docs: Post download progress event.
  
  @param request download request
  @param bytesWritten the bytes have written to file
  @param totalBytes the total bytes of currnet file in downloading