code: func (w *writer) StartBody() error {
  	if _, err := w.Write([]byte("\r\n")); err != nil {
  		return err
  	}
  	err := w.Writer.(*bufio.Writer).Flush()
  	w.Writer, w.tmp = w.tmp, nil
  	w.phase = body
  	return err
  }
docs: // StartBody moves the Conn into the body phase, no further headers may be sent at this point.