code: private void makeBlock(String upHost, long offset, int blockSize, int chunkSize, ProgressHandler progress,
                             CompletionHandler _completionHandler, UpCancellationSignal c) {
          String path = format(Locale.ENGLISH, "/mkblk/%d", blockSize);
          try {
              file.seek(offset);
              file.read(chunkBuffer, 0, chunkSize);
          } catch (IOException e) {
              completionHandler.complete(key, ResponseInfo.fileError(e, token), null);
              return;
          }
          this.crc32 = Crc32.bytes(chunkBuffer, 0, chunkSize);
          String postUrl = String.format("%s%s", upHost, path);
          post(postUrl, chunkBuffer, 0, chunkSize, progress, _completionHandler, c);
      }
docs: 创建块，并上传第一个分片内容
  
  @param upHost             上传主机
  @param offset             本地文件偏移量
  @param blockSize          分块的块大小
  @param chunkSize          分片的片大小
  @param progress           上传进度
  @param _completionHandler 上传完成处理动作