COMET in Plone

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Information about COMET in Plone

Published on February 11, 2008

Author: mrtopf



COMET is an upcoming method for delivering real-time interaction to a website by using server-push technologies. At the Snow Sprint 2008 Jean-Nicolas Bes and Ramon Bartl worked on making COMET work for the Open Source CMS Plone.

This is their presentation from the final sprint summary.

Bringing Comet to Plone KSS + Eventpush A first quick and dirty approach dr_jnut & ramonski

• „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 Backend Frontend eventPush VirtualHost

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. Backend Frontend eventPush VirtualHost


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 • • Buildout: plonekss/eventPush/buildout/trunk

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

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