Brian Moschel delivered this talk at the JS.Chi() April 2009 meetup. This talk provides an overview of Comet, also known as HTTP Push, covering how it works on the server and client, several implementation options, and using a new Comet API called Jabbify in an interactive demo.

1. Comet Overview
Brian Moschel
Jupiter IT

2. Overview
Why Comet How It Showcase
Jabbify Demo
Comet? Overview Works

3. Why Comet?
• Web 2.0 Trends
1. Time Spent on a Page

4. Why Comet?
• Web 2.0 Trends
2. Half life of a Page’s Content

5. Why Comet?
• Demand for Comet is growing
• Desktop apps moving to the web
• Chat
• Real time updates
• Don’t like to reload
• Ajax:2003::Comet:2009

6. Uses
• Multi user collaboration apps
– Wiki
– Presentation
• Communication
– Chat
• Preventing stale data
– Stock ticker
– Social web updates
• Others?

7. Polling vs. Comet
Polling
Server
Are we Are we Are we
No No No
There yet? There yet? There yet?
Client
Comet Long Polling
Server
Wait for data
Wait for data
Client

8. How Comet Works: Client Side
• Long Poll
– How?
• XHR, JSONP, or any transport, with connection held open
– Pro
• It works cross browser
– Con
• More overhead
• Forever Frame
– How?
• Iframe
• Multipart XHR
– Pro
• Less overhead, quicker responses
– Con
• Lack of error handling, not cross browser

9. Client Side Issues
• Cross Browser
– Duh
• 2 Connection Limit
– Use wildcard DNS
– Xxx.mywebsite.com -> mywebsite.com
• Synchronous request s (for JSONP)
– Long poll has to close to allow other requests to
process

10. How Comet Works: Server Side
• Simultaneous connections
– Traditional servers can’t scale
– A thread shared multiple connections
• Wake up when you’re ready to send data

11. How Comet Works: Server Side
• Python
– Orbited
– Cometd
• Java
– Jetty
• Erlang
– ErlyComet
• .NET
– Lightstreamer
• Service
– Jabbify

12. Server Side Issues
• Scaling
– Every user = 1 connection
• Complexity
– Threading
– Learning Curve

13. What is Jabbify?
• Comet, simplified
• No server
• No setup
• JavaScript API and GET requests

14. Why Jabbify?
Simple to use
Scale easily
Rapid setup

15. Simple to use
synchronized (_continuations) {
for(Iterator<Map.Entry <String, ArrayList<Continuation>>> iter =
_continuations.entrySet().iterator(); iter.hasNext();){
Map.Entry<String, ArrayList<Continuation>> entry = iter.next();
ArrayList<Continuation> continuations = entry.getValue();
for(Continuation c : continuations){
c.resume();
}
}
_continuations.clear();
}
vs
Jabbify.connect({name: this.username}, this.continue_to('after_connect'))
after_connect: function(){
Jabbify.send('vote','submit', {result: this.result})
}

16. Scale easily
• Scaling comet >> Scaling traditional web
applications
• Resource intensive
• Jabbify is built to scale as usage grows

17. Rapid Setup
<New id=quot;cfquot; class=quot;org.mortbay.jetty.plus.naming.Resourcequot;>
<Arg>jms/connectionFactory</Arg>
<Arg>
<New class=quot;org.apache.activemq.ActiveMQConnectionFactoryquot;>
<Arg>failover:(tcp://localhost:61616)?initialReconnectDelay=20&amp;maxReconnectDe
lay=900</Arg>
</New>
</Arg>
</New>
vs
<script language=quot;javascriptquot; type=quot;text/javascriptquot; src=quot;jabbify.jsquot;></script>

18. Comet is complex
• Client
– Transports (JSONP, Window.name, Flash, XHR, iframe)
• Server
– Special server
– Setup time
– Learning curve
• Scaling
– Resource consumption
– Threading issues

19. Jabbify is simple
• Client to Client Comet
– JavaScript API
• Jabbify.send(“message”,”create”,{message: “hi there”});
• Server to Client Comet
– GET requests
• https://jabbify.com/message_push?key=123&type=message...

20. How It Works

21. Demo

22. Take Home Points
Comet is coming
Jabbify = easy Comet

23. Showcase
• Jabbify Simple Chat Client
• Keyboard Demo
• Chat.unwrongest.com