if c == nil || !c.Valid() {
		return nil
	}
	return map[string]string{c.Type.String(): c.Encoded}
}

// TransferChecksumHeader will transfer any checksum value that has been checked.
// If checksum was trailing, they must have been added to r.Trailer.
func TransferChecksumHeader(w http.ResponseWriter, r *http.Request) {
	c, err := GetContentChecksum(r.Header)
	if err != nil || c == nil {
		return