Example of JSON message exchange and world update in Aleph using websockets

ws.clj

(ns test.ws
   (:use
    lamina.core
    compojure.core
    compojure.response
    aleph.core
    aleph.http
    aleph.formats
    hiccup.core
    ring.middleware.reload
    ring.middleware.file
    hiccup.form-helpers
    ring.adapter.jetty
    [ring.util.response :only (response content-type)]
   )
   (:require
     [compojure.handler :as handler]
   )
)


(def clients (agent 0))

(def broadcast-channel (named-channel :broadcast))

(def world-channel (named-channel :world))

(defn start-messaging [channel]
  (enqueue world-channel {:t 0 :clients 0})
   (let
    [clock (sample-every 1000 world-channel)]
    (receive-all clock
      (fn [m] (enqueue world-channel {:t (+ (:t m) 1) :clients @clients}) )
    )
    (siphon world-channel channel)
   )
)

(defn websocket-handler [channel request]
  (println request)
  (siphon (map* decode-json channel) broadcast-channel)
  (siphon (map* encode-json->string broadcast-channel) channel)
  (on-closed channel #(send clients dec))
  (send clients inc)
)

(defn page [request]
(html
[:script
"
function openWebSocket()
{
 if (window.WebSocket)
 {
 socket = new WebSocket('ws://localhost:8080/ws');
 socket.onopen = function(event) { console.log('WebSocket open!');};
 socket.onclose   = function(event) { console.log('WebSocket closed'); };
 socket.onmessage = function(event) { console.log(event.data);};
 }
else
{
 alert('Your browser does not support WebSockets yet.');
}
}
function closeWebSocket()
{
    socket.close();
}
function send(message)
{
if (!window.WebSocket) { return; }
if (socket.readyState == WebSocket.OPEN) {
    socket.send(message);
} else {
    alert('The WebSocket is not open!');
}
}
"
]
[:body
 [:button {:onclick "openWebSocket()"} "open"]
 [:button {:onclick "closeWebSocket()"} "close"]
 [:input#message {:type "text" :value "{ \"q\": 2 }"} ]
 [:button {:onclick "send(document.getElementById('message').value)"} "send"]
]
)
)

(defroutes routez
  (GET "/" [] page)
  (GET "/ws" [] (wrap-aleph-handler websocket-handler ))
)

(start-http-server (wrap-ring-handler (handler/site routez)) {:port 8080 :websocket true})

(start-messaging broadcast-channel)