获取Header的字段，比如Referer:

func handler(w http.ResponseWriter, r *http.Request) {
	log.Println(r.Header["Referer"])
}

获取某个Cookie，或者打印所有的Cookie:

func UpdGET(w http.ResponseWriter, r *http.Request) {
	log.Println(r.Cookies())
	log.Println(r.Cookie("abc"))
}

输出类似这样：

[abc=1 xyz=3]
1