code: func dumpRespBody(resp *http.Response) ([]byte, error) {
  	if resp.Body == nil {
  		return nil, nil
  	}
  	var b bytes.Buffer
  	savecl := resp.ContentLength
  	var save io.ReadCloser
  	var err error
  	save, resp.Body, err = drainBody(resp.Body)
  	if err != nil {
  		return nil, err
  	}
  	_, err = io.Copy(&b, resp.Body)
  	if err != nil {
  		return nil, err
  	}
  	resp.Body = save
  	resp.ContentLength = savecl
  	if err != nil {
  		return nil, err
  	}
  	return b.Bytes(), nil
  }
docs: // Dump response body, strongly inspired from httputil.DumpResponse