Stateful session in pedestal

stateful_session.clj

(ns stateful-session
  (:refer-clojure :exclude (get)))

(def ^:dynamic *session*)

(def stateful-session
  {:name ::stateful-session
   :enter
   (fn [context]
     (let [old-value (get-in context [:request :session] {})]
       (-> context
           (assoc ::session-old-value old-value)
           (assoc-in [:bindings #'*session*] (atom old-value)))))
   :leave
   (fn [context]
     (let [old-value (-> context ::session-old-value)
           new-value (deref *session*)]
       (if (not= old-value new-value)
         (assoc-in context [:response :session] new-value)
         context)))})

(defn get
  "Get a key from the session."
  ([k]
   (get k nil))
  ([k not-found]
   (get (deref *session*) k not-found)))

(defn put!
  "Set an entry in the session."
  [k v]
  (swap! *session* assoc k v))

(defn remove-session!
  "Clear the session."
  []
  (reset! *session* nil))