Unique IDの生成【Go】

サードパーティのパッケージを使用します。
GitHub - satori/go.uuid: UUID package for Go

func main() {
    http.HandleFunc("/", index)
    http.HandleFunc("/read", read)
    http.Handle("/favicon.ico", http.NotFoundHandler())
    http.ListenAndServe(":8080", nil)
}

func index(w http.ResponseWriter, req *http.Request) {
    id, err := uuid.NewV4()    // unique idを生成
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
    }
    http.SetCookie(w, &http.Cookie{
        Name:     "session",
        Value:    id.String(),
        Path:     "/read",
        HttpOnly: true,
    })
    http.Redirect(w, req, "/read", http.StatusSeeOther)    // Cookieをセットしたらreadにリダイレクト
}

func read(w http.ResponseWriter, req *http.Request) {
    c, err := req.Cookie("session")
    if err == http.ErrNoCookie {
        http.Error(w, err.Error(), http.StatusBadRequest)
    }
    fmt.Fprintln(w, c)
}