如何在 Go 中检索 cookie？

Question

我在undefined: msg以tmpl.Execute. 你应该如何在 Go 中检索 cookie？func contact(w http.ResponseWriter, r *http.Request) {    if r.Method == "POST" {        r.ParseForm()        for k, v := range r.Form {            fmt.Println("k:", k, "v:", v)        }        http.SetCookie(w, &http.Cookie{Name: "msg", Value: "Thanks"})        http.Redirect(w, r, "/contact/", http.StatusFound)    }    if msg, err := r.Cookie("msg"); err != nil {        msg := ""    }    tmpl, _ := template.ParseFiles("templates/contact.tmpl")    tmpl.Execute(w, map[string]string{"Msg": msg})}