with-channel-exmaple.clj

(ns example
  (:use [org.httpkit.server
         compojure.core]))

(defn- handle-client-data [data]
  (let [data (read-json data)]
    ;; routing can implented here. like socket.io's event routing
    ))

;;; when streaming/polling, client post data to server,
;;; mimic websocket's two way communication
(defn receive-data-handler [req]
  (handle-client-data (slurp (:body req))) ; assume data is in the :body
  {:status 200})

;;; use the unified with-channel API
(defn realtime-handler [req]
  ;; client use WebSocket if supported, long polling if no WebSocket support
  (with-channel req channel
    ;; client/server close the channel(connection), do some clean up
    ;; eg: remove it from a channel-hub
    (on-close channel (fn [status]
                        ;; DO clean up.
                        ))
    ;; setup handler for receive websocket message from client.
    ;; for streaming /post is used.
    (on-receive channel (fn [data]       ; data is raw string
                          (handle-client-data data)))

    ;; save channel somewhere (eg, a channel-hub) for later use,
    ;; waiting some event, then push sever data to client
    ;; sample channel-hub http://http-kit.org/channel.html#channel-group

    ;; if disingush here, there is no need to distingush them in on-interesting-server-events
    (when-not (websocket? channel)
      ;; sent the header to client, tell client this a Chunked HTTP reponse
      ;; more json encoded data expected to come later,
      (send! channel {:status 200
                      :headers {"Content-Type" "application/json"
                                "X-other-header" "value"}}
             false))  ;do not close the channel
    ))



(on-interesting-server-events event
  (let [channels (get-relevant-channels event)
        data (compute-the-data-sent-to-client event)]
    (doseq [ch channels]
      (if (websocket? ch)
        (send! ch (json-str data) false) ; do not close the channel, default is false
        (send! ch {:status 200
                   ;; tell client the body is json encoded
                   :headers {"Content-Type" "application/json"}
                   :body (json-str data)}
               ;; close the channel, allow javascript to comsume the data
               ;; the default value is true
               true)))))

(defroutes app
  (POST "/post" [] receive-data-handler)
  (GET "/realtime" [] realtime-handler))

(run-server app {:port 9090})