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Idiomatic usage of Compojure using sessionless cookies.
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Compojure Cookies Example 2011

Clojure, being a relatively new language, uses an even newer web framework: Compojure.

Compojure, still sporting a sub 1.0 version, being under active development and reduced to a thin veneer over Ring may prove challenging for developers. If for any reason because many examples and tutorials are just outdated.

I'm going to demonstrate the use of sessionless cookies in Compojure, with working examples.

The Bare Essentials

Example 1, a simple hello-world application is suitable for running on Heroku:

(ns example1
  (:use [ring.adapter.jetty :only [run-jetty]]
        [compojure.core     :only [defroutes GET]]))

(defroutes routes
  (GET  "/" [] "Hi there"))

(defn -main []
  (run-jetty routes {:port (if (nil? (System/getenv "PORT")) 
                             8000 ; localhost or heroku?
                             (Integer/parseInt (System/getenv "PORT")))}) )

After you check out the project from GitHub, it's easy to see in action:

$ lein run -m example1

Middleware: A Morality Tale in I Act

The addition of a very simple form requires some changes.

(ns example2
  (:use [ring.adapter.jetty             :only [run-jetty]]
        [compojure.core                 :only [defroutes GET POST]]
        [ring.middleware.params         :only [wrap-params]]))

(defroutes routes
  (POST "/" [name] (str "Thanks " name))
  (GET  "/" [] "<form method='post' action='/'> What's your name? <input type='text' name='name' /><input type='submit' /></form>"))

(def app (-> #'routes wrap-params))

(defn -main []
  (run-jetty app {:port (if (nil? (System/getenv "PORT")) 
                          8000 ; localhost or heroku?
                          (Integer/parseInt (System/getenv "PORT")))}) )

The new POST route uses the name variable from the form. This is possible because we're now leveraging middleware:

(def app (-> #'routes wrap-params))

Simply put: middleware is features. Rather than forcing you into a one-size-fits all model, it's a way to mix and match whichever features you need.

In this case, we need to process form variables. wrap-params is what does this for us by making the form variable name available as a local variable.

TODO: Everything In Between

  • middleware, they're really features
  • mention use/only
  • point out Hiccup
  • infinite wisdom of keyword params

The Final Result

Example 0 is the final result, say something witty and descriptive here.

(ns example0
  (:use [ring.adapter.jetty             :only [run-jetty]]
        [compojure.core                 :only [defroutes GET POST]]
        [ring.middleware.cookies        :only [wrap-cookies]]
        [ring.middleware.params         :only [wrap-params]]
        [ring.middleware.keyword-params :only [wrap-keyword-params]]))

(defn main-page [cookies]
  (str "Hi there "
       (if (empty? (:value (cookies "name")))
         "<form method='post' action='/'> What's your name? <input type='text' name='name' class='name' maxlength='10' /><input type='submit' name='submit' value='ok' /></form>"
         (:value (cookies "name")))))

(defn process-form [params cookies]
  (let [name (if (not (empty? (:name params)))
               (:name params)
               (:value (cookies "name")))]

    ;; set cookie, return html
    {:cookies {"name" name}
     :body (str "<html><head><meta HTTP-EQUIV='REFRESH' content='5; url='/'\"</head><body>Thanks!</body></html>")}))

(defroutes routes
  (POST "/" {params :params cookies :cookies} (process-form params cookies))
  (GET  "/" {cookies :cookies}                (main-page cookies)))

(def app (-> #'routes wrap-cookies wrap-keyword-params wrap-params))

(defn -main []
  (run-jetty routes {:port (if (nil? (System/getenv "PORT")) 
                             8000 ; localhost or heroku?
                             (Integer/parseInt (System/getenv "PORT")))}) )
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