header.go
func (h *RequestHeader) WriteTo(w io.Writer) (int64, error) {
	n, err := w.Write(h.Header())
	return int64(n), err
}
func (h *RequestHeader) WriteTo(w io.Writer) (int64, error) {
	n, err := w.Write(h.Header())
	return int64(n), err
}
// WriteTo writes request header to w.
//
// WriteTo implements io.WriterTo interface.