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Moksha

Real-time TurboGears Introduction

This tutorial will describe how to set up an introductory “real time chat” application using the Orbited framework and TurboGears. Real-time web-sites are capable of far more than simple chat applications, but chat is the common “Hello World” of real-time developers.

Warning

You should already be fairly familiar with TurboGears, Javascript and JQuery before you begin this tutorial.

Note

The setup described here is not a production-ready real-time-web solution. MorbidQ is not a production Message Queue Server, and indeed most production solutions would want to use a more robust and efficient protocol such as AMQP. Currently AMQP protocols for Javascript are “in development”. This document is intended to let you get started with real-time-web development before you graduate to more mature technologies.

Setup

You will need to have a running TurboGears VirtualEnv to follow along in this tutorial. We recommend the TurboGears 2.1 Standard Installation if possible.

Architectural Overview

  • Orbited – a server process which provides “web socket proxying” support as well as Javascript client-side implementations for supported protocols.
  • MorbidQ – a simple (non-scalable) STOMP message queue for developers, its primary advantage is that the message queue is built into the Orbited server, so a simple config setting will enable and configure it
  • TurboGears – serves the HTML widget which references the Orbited Javascript. TurboGears does not connect to the MorbidQ service in this project, but sending STOMP messages to the server can be implemented.

Software Install

Orbited provides a “web socket” mechanism that allows Javascript code to connect to (defined) servers to recieve messages. The networking protocol spoken by the Javascript code can be any implemented TCP protocol. The following are the protocols commonly used with Orbited:

  • STOMP, a simple streaming text format we will use here
  • XMPP, such as spoken by jabberd
  • IRC, an older protocol for internet chat

Orbited’s model means that with a simple Javascript plugin which speaks a given protocol, your Javascript code can be connected to any server and port on the Internet (with the proper Orbited configuration).

To install the Orbited framework in your VirtualEnv we need to install the Orbited 0.7.10+ and Twisted 9.0+ packages. This will also pull in the morbidq package.

(tgenv)$ easy_install twisted orbited

MorbidQ

MorbidQ provides an easily configured message broker/queue which is not intended for large-scale production use. It uses the simple STOMP protocol. If you want to stick with STOMP as you scale up, you can explore the other STOMP servers available.

Note

There are (far) faster message queue engines than Morbid, but most of them use the AMQP binary protocol. There is an experimental AMQP implementation for Javascript available in Kamaloka-js. It is suggested that you become comfortable with real-time-web programming before switching to a full-featured Queue server.

To configure MorbidQ and Orbited, you need a config file. Something like the following, which we will save as “chat.ini” in our “rtchat” project’s directory.

[listen]
# this is the server which provides the socket-proxy for javascript
http://:9000
# the following enables the MorbidQ STOMP Message Queue
stomp://:61613

[access]
# allow incoming HTTP requests on port 9000 to connect to
# localhost:61613 (i.e. the MorbidQ STOMP server)
# The * refers to the
* -> localhost:61613

[global]
session.ping_interval = 20

You can now run Orbited with the embedded MorbidQ queue with the following command:

(tg2env)$ orbited --config=chat.ini

You should see messages telling you that Orbited/MorbidQ is listening on the defined ports. You can hit CTRL-C to stop the server, though we’ll want to use it in a moment, so you’ll likely want to leave it running and start another console.

Chat View (HTML)

We are going to be very simplistic with our chat widget in our first attempt. We’ll simply dump the text which is sent to the server into a div node. The view looks like this:

<?python
# we pull some values out of TurboGears config-file, with defaults
# for our tutorial settings.
from simplejson import dumps as d
orbited_server = config.get( 'orbited_server', 'localhost' )
orbited_port = config.get( 'orbited_port', 9000 )
stomp_server = config.get( 'stomp_server', 'localhost' )
stomp_port = config.get( 'stomp_port', 61613 )
orbited_files = 'http://%s:%s/static'%( orbited_server, orbited_port )
?>
  <div id="chat">
    <h2>Real-time Chat</h2>
    <div class="chat-trace">
    </div>
    <div class="chat-entry">
        Chat:
        <input class="chatter" />
        <button class="chat-trigger">Send</button>
    </div>
  </div>

Orbited/STOMP Javascript Setup

We are going to use JQuery for our javascript framework. Here we use the Google javascript APIs version of the library:

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>

The JSON javascript library provides for safe JSON parsing, that is, it actually parses the JSON data rather than doing an unsafe “eval” on the code. We linked it into our “public” directory above.

<script type="text/javascript" src="${orbited_files}/JSON.js"></script>

The Orbited javascript library implements the “proxied socket” mechanism which connects to the Orbited server we started above. We’ll use Orbited’s proxy-socket to connect to the MorbidQ server via STOMP. We configure the Orbited client before we import the STOMP client library as the STOMP client library references “TCPSocket” as seen here.

<script type="text/javascript" src="${orbited_files}/Orbited.js"></script>
<script type="text/javascript">
    // This line is required to allow our chat server and this
    // page to operate on different ports...
    document.domain = document.domain;
    // Establish the port and server for the Orbited server
    Orbited.settings.port = 9000;
    Orbited.settings.hostname = ${simplejson.dumps( chat_server )};
    // Enable streaming operation
    Orbited.settings.streaming = true;
    // This object is referenced by stomp.js
    TCPSocket = Orbited.TCPSocket;
</script>
<script type="text/javascript" src="${orbited_files}/protocols/stomp/stomp.js"></script>

The Chat Client

The chat client we show here is extremely simplistic. It is intended to show you the minimum required to get messages flowing across the MorbidQ server.

<script type="text/javascript">
    var add_message = function( text ) {
        var node = $('<div class="chat-message"></div>');
        node.append( text );
        $('.chat-trace').append( node );
    };
    $(document).ready( function() {
        stomp = new STOMPClient();
        stomp.onconnectedframe = function(frame) {
            stomp.subscribe( "/topic/chat" );
        };
        stomp.onmessageframe = function( frame ) {
            add_message( frame.body );
        };
        stomp.connect(${d(stomp_server)},${d(stomp_port)} );
        $('.chat-entry .chat-trigger').click( function() {
            var chatter = $('.chat-entry .chatter');
            var value = chatter.attr( 'value' );
            if (value.length) {
                stomp.send( value, "/topic/chat" );
                chatter.attr( 'value', '' );
            }
        });
    });
</script>

Testing and Revision

You should now be able to start your TurboGears server, browse to http://localhost:8080 and start chatting. Your messages should show up in the chat-trace DIV as you enter them.

You will immediately notice problems with the chat system, some obvious enhancements:

  • messages should include the user’s chosen nickname
  • the “enter” key should be hooked to send chat messages
  • it would be nice to log the messages on the server
  • you would normally use JSON.stringify() and JSON.parse() to send JSON structured messages
  • you likely want to implement some form of security

There are a number of callbacks of the STOMP object that you may wish to override to perform basic configuration and the like:

  • stomp.onopen( ) – called on initialization of the STOMP connection
  • stomp.onclose( code ) – connection was lost with an error-code describing the reason
  • stomp.onerrorframe( frame ) – error-describing frame was recieved * frame.body contains the payload
  • stomp.onconnectframe( frame ) – called when the connection to the server has been set up
  • stomp.onmessageframe( frame ) – a (normal) message was received from the server, frame.body is normally a JSON payload, but can be whatever the sender has put into the body

The methods to control the STOMP object are:

  • stomp.reset( ) – force the STOMP connection to reset/reconnect
  • stomp.connect( server, port ) – connect to the given address
  • stomp.send( payload, channel ) – send the given payload to the given channel
  • stomp.subscribe( channel ) – subscribe to messages sent to a given channel (onmessageframe( frame) will begin getting called).

What’s Next?

Note

The code on this page is loosely based on Django, Orbited, Stomp and Co.