doxn43207 2018-03-15 14:53
浏览 52
已采纳

如何返回一个空的io.Reader?

I have a function which returns an io.Reader:

func getData(bucket string, key string) (io.Reader, error) {
  svc := s3.New(cfg)

  req := svc.GetObjectRequest(&s3.GetObjectInput{
    Bucket: aws.String(bucket),
    Key:    aws.String(key),
  })

  res, err := req.Send()
  if err != nil {
    // How to return a empty io.Reader here?
    return bytes.NewReader([]byte), err
  }
  return res.Body, nil
}

And I would like to know, how to return a empty io.Reader from the err block.

Thank you.

  • 写回答

1条回答 默认 最新

  • dongyuqie4322 2018-03-15 14:55
    关注

    In case of a non-nil error return value, usually other parameters are left to the zero value of their type, which in case of io.Reader (which is an interface type) should be nil:

    return nil, err
    

    Callers are responsible to first always check the returned error, and only proceed to use other return values if the error is nil. This is the general "rule". There may be exceptions of course, in which case you should document the deviant behavior.

    Actually there's nothing wrong with providing other values along with non-nil errors, and often it's useful. Typical example is the io.Reader.Read() method, which documents how implementations should (must) work:

    It returns the number of bytes read (0 <= n <= len(p)) and any error encountered.

    ... When Read encounters an error or end-of-file condition after successfully reading n > 0 bytes, it returns the number of bytes read.

    So even if Reader.Read() returns a non-nil error, it also reports how many bytes it was able to read successfully before the error was encountered, so you may process / use up to n bytes from the slice.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论

报告相同问题?

悬赏问题

  • ¥15 envi深度学习模块错误原因
  • ¥15 孟德尔随机化混杂因素
  • ¥15 关于react-hook组件用函数控制是否渲染的及时性问题。
  • ¥50 Linux下的软件,要做模块化拆分。进程间通信是否有开源框架可以借用?
  • ¥100 修改原有的MYSQL存储代码,在最右边添加多列数据
  • ¥20 Open Interpreter 使用时报错: still has pending operation at deallocation, the process may crash
  • ¥15 qt中链接动态链接库,调用其中的函数,该函数的参数需要传入回调函数,自己创建的回调函数无法作为参数传递进去
  • ¥15 matlab svm二分类代码问题
  • ¥40 求一款能支持ios15以上的屏蔽越狱插件。比较好用的
  • ¥15 C++ QT对比内存字符(形式不定)