if cksum == nil {
			continue
		}
		if cksum.Valid() {
			w.Header().Set(cksum.Type.Key(), v)
		}
	}
}

// GetContentChecksum returns content checksum.
// Returns ErrInvalidChecksum if so.
// Returns nil, nil if no checksum.
func GetContentChecksum(h http.Header) (*Checksum, error) {
	if trailing := h.Values(xhttp.AmzTrailer); len(trailing) > 0 {
		var res *Checksum
		for _, header := range trailing {

		want, err := base64.StdEncoding.DecodeString(mdFive)
		if err != nil {
			return false
		}
		r.Body = hash.NewChecker(r.Body, md5.New(), want, r.ContentLength)
		return true
	}
	cs, err := hash.GetContentChecksum(r.Header)
	if err != nil {
		return false
	}
	if cs == nil || !cs.Type.IsSet() {
		return false
	}
	if cs.Valid() && !cs.Type.Trailing() {