cc.hbuf.Reset()
	if req.URL == nil {
		return nil, http2errNilRequestURL
	}

	host := req.Host
	if host == "" {
		host = req.URL.Host
	}
	host, err := httpguts.PunycodeHostPort(host)
	if err != nil {
		return nil, err
	}
	if !httpguts.ValidHostHeader(host) {
		return nil, errors.New("http2: invalid Host header")
	}

	var path string