Bringing Comet
to Plone
KSS + Eventpush
A first quick and dirty approach
dr_jnut & ramonski
http://plone.org

• „Comet is a giant Hack“
- Jacob Rus
• use mechanisms unforseen by browser
Vendors and unspecified by web standards

Traditional Web
Applications
• Page-by-page web
• Pages load on user request
• No real time

AJAX Web Application
• Updating parts of the page with JS
• Closes each connection after a response is
served
• No real time

Ajax with polling
• Browser polls regulary the server for
updates.
• Wastes server resources and bandwith.
• No real real time
• Trade-off between latency and server
load

Comet Web Application
• Sending data to the client without explicit
request
• Rely on persistent connection between
server and client
• REAL real time!!!

2 Strategies
• Streaming
- Single persistent connection
• Long Polling
- New request for each event
- No response until an event occurs

„Forever Frame“
IFrame
streaming approach
• Gradually filled with script tags to be
executed in the browser
• Rendered incrementally, so each script tag
is executed as it is received.
• Can grow to an unreasonable size...

eventPush
ClientSide HttpWizard Zope/Plone
HTTP proxy
eventPush iFrame /@@feeder

HttpWizard internals
Proxy
(rewrites URI)
VirtualHost
www.plone.org Backend
Frontend eventPush
VirtualHost
www.plone.net

eventPush fileupload
ClientSide HttpWizard Zope/Plone
Upload iframe HTTP proxy
eventPush iFrame /@@feeder

File upload in HttpWizard
FileUpload
hook
4.
3.
4.
Proxy
2. (rewrites URI)
5.
VirtualHost
1. www.plone.org Backend
Frontend eventPush
VirtualHost
www.plone.net

DEMO Time

How will this evolve?
• HTML 5 draft from WHATWG *
• Introduces server-sent events
• Much more straightforward
• Avoids comet downsides
* Web Hypertext Application Technology Working Group

Links
• http://plone.org
• Buildout:
https://svn.plone.org/svn/collective/
plonekss/eventPush/buildout/trunk

Thanks to...
• KSS guys (__gotcha, ree et al.)
• Lovely systems
• Berggasthof Piz-Buin
• idSoftware (Q3 Rocketarena)
• beer in all variants