clojure - 确保 var 在 Clojure 中绑定(bind)

Question

在我的中间件中，我检查 :session 的值以查看用户是否已登录。

如果设置了 :session 的值，效果会很好。虽然，我不确定检查 :session 是否已绑定(bind)的最佳方法是什么。

(defn logged-in-verify
  [ring-handler]
  (fn new-ring-handler
    [request]
    ;;verify that the scrypt hash of email and timestamp matches.
    (let [session   (:session request)
          email     (:ph-auth-email session)
          token     (:ph-auth-token session)
          timestamp (:ph-auth-timestamp session)]
      (if (scryptgen/check (str email timestamp) token)
        (do 
          ;; return response from wrapped handler
          (ring-handler request))
        ;; return error response
        {:status 400, :body "Please sign in."}))))

由于我不检查 :session 是否已绑定(bind)，因此使用此中间件的事物会在未设置时返回 NullPointerException 。最好的方法是什么？

Answer 1

使用when-let 或类似的if-let检查您是否确实有 session :

(defn logged-in-verify
  [ring-handler]
  (fn new-ring-handler
    [request]
    ;;verify that the scrypt hash of email and timestamp matches.
    (if-let [session   (:session request)]
        (let [email     (:ph-auth-email session)
              token     (:ph-auth-token session)
              timestamp (:ph-auth-timestamp session)]
          (if (scryptgen/check (str email timestamp) token)
             ;; return response from wrapped handler
             (ring-handler request))
             ;; return error response
             {:status 400, :body "Please sign in."}))
        ;; do something when there is no session yet
        (generate-new-session-and-redirect))))