Golang io.copy在请求正文中两次

您不能直接执行此操作，但可以编写在io.Copy上执行哈希处理的包装器

// this works for either a reader or writer, //  but if you use both in the same time the hash will be wrong.type Hasher struct {    io.Writer    io.Reader    hash.Hash    Size uint64}func (h *Hasher) Write(p []byte) (n int, err error) {    n, err = h.Writer.Write(p)    h.Hash.Write(p)    h.Size += uint64(n)    return}func (h *Hasher) Read(p []byte) (n int, err error) {    n, err = h.Reader.Read(p)    h.Hash.Write(p[:n]) //on error n is gonna be 0 so this is still safe.    return}func (h *Hasher) Sum() string {    return hex.EnpreToString(h.Hash.Sum(nil))}func (h *UploadHandle) Read() (io.Reader, string, int64, error) {    var b bytes.Buffer    hashedReader := &Hasher{Reader: h.Contents, Hash: sha1.New()}    n, err := io.Copy(&b, hashedReader)    if err != nil {        return nil, "", 0, err    }    return &b, hashedReader.Sum(), n, nil}

//由于我完全忘记了

io.TeeReader

func (h *UploadHandle) Read() (io.Reader, string, int64, error) {    var b bytes.Buffer    hash := sha1.New()    n, err := io.Copy(&b, io.TeeReader(h.Contents, hash))    if err != nil {        return nil, "", 0, err    }    return &b, hex.EnpreToString(hash.Sum(nil)), n, nil}