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})

}