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 数据库获取信息反馈出错,直接查询了ref字段并且还使用了User文档的_id而不是自己的
  • ¥15 将安全信息用到以下对象时发生以下错误:c:dumpstack.log.tmp 另一个程序正在使用此文件,因此无法访问
  • ¥15 速度位置规划实现精确定位的问题
  • ¥15 代码问题:df = pd.read_excel('c:\User\18343\Desktop\wpsdata.xlxs')路径读不到
  • ¥15 为什么视频算法现在全是动作识别?
  • ¥15 编写一段matlab代码
  • ¥15 用Python做岩石类别鉴定软件
  • ¥15 关于调取、提交更新数据库记录的问题
  • ¥15 之前删了盘从下vs2022遇见这个问题 搞了一整天了
  • ¥15 从Freecad中宏下载的DesignSPHysics,出现如下问题是什么原因导致的(语言-python)