header.go
func (h *RequestHeader) RequestURI() []byte {
	requestURI := h.requestURI
	if len(requestURI) == 0 {
		requestURI = strSlash
	}
	return requestURI
}
func (h *RequestHeader) RequestURI() []byte {
	requestURI := h.requestURI
	if len(requestURI) == 0 {
		requestURI = strSlash
	}
	return requestURI
}
// RequestURI returns RequestURI from the first HTTP request line.