.. _dojox/cometd:

dojox.cometd
============

:Status: Draft
:Version: beta
:Authors: Alex Russell, Greg Wilkins

Low-latency data transfer from servers to clients. dojox.cometd implements a
Bayeux protocol client for use with most Bayeux servers. See cometd.com for
details on Cometd or on the Bayeux protocol.

Basic Example
-------------

Using dojox.cometd to connect to a Bayeux-compliant server is very straightforward:

.. cv-compound::

  As a simple example, we'll setup a chat room; we will subscribe to a channel and log any messages received.
  When you send a message it is published on this channel. You can open a couple browsers to and send messages
  back and forth to see this in action. Just enter your name and type a message and click send.

  .. cv:: javascript

    <script type="text/javascript">
    dojo.require("dijit.form.TextBox"); // Those widgets are only included to make the example look nice
    dojo.require("dijit.form.Button"); // Those widgets are only included to make the example look nice

    dojo.require("dojo.io.script");
    dojo.require("dojox.cometd");
    dojo.require("dojox.cometd.callbackPollTransport");
    dojo.addOnLoad(function(){
		dojox.cometd.init("http://cometd.dojocampus.org:9000/cometd");
		dojox.cometd.subscribe("/demo",function(message){
			console.log("received",message);
			dojo.byId("messageLog").
				appendChild(document.createElement("div")).
				appendChild(document.createTextNode(message.data.from + ": " + message.data.text));
		});
		dojo.connect(dojo.byId("send"),"onclick",function(){
			if (!dojo.byId("sendName").value.length || !dojo.byId("sendText").value.length) { 
                                alert("Please enter some text"); 
                                return;
                        }
                        dojox.cometd.publish("/demo",{
			     from: dojo.byId("sendName").value, 
			     text: dojo.byId("sendText").value
			});
		});
    });
    </script>

  The html is a just a simple form to enter you name and message to send

  .. cv:: html

    <div id="chatroom"> 
    	<div style="clear: both;"><label for="sendName" style="float: left; width: 100px; padding: 3px;">Name:</label> <input id="sendName" type="text" dojoType="dijit.form.TextBox"></div>
    	<div style="clear: both;"><label for="sendText" style="float: left; width: 100px; padding: 3px;">Message:</label> <input id="sendText" type="text" dojoType="dijit.form.TextBox"><button id="send" dojoType="dijit.form.Button">Send Message</button></div>
    	<div id="messageLog"><strong>Messages:</strong></div>
    </div>

  .. cv:: css

    <style type="text/css">
      #messageLog {
        margin-top: 20px;
        padding: 5px;
        width: 400px;
      }
    </style>