Comet服务器介绍.pdf

Time for Comet? Simon Willison Yahoo! Web Development Summit 5th December 2007 Header image: /shortbus/trunk/cometd-perl/html/ A new name for a very old technique Alex Russell coins “Comet” Deliberately named after a kitchen cleaner Fundamentally, [Comet applications] all use long-lived HTTP connections to reduce the latency with which messages are passed to the server. In “ essence, they do not poll the server occasionally. Instead the server has an open line of communication with which it can push data to the client. ” Who’s using it? More Ajax Time spent on a single page Less Ajax (Slides courtesy of Joe Walker) Long time to change Time before a page changes Short time to change (Slides courtesy of Joe Walker) Time spent on More Ajax a single page Time before a page changes Less Ajax (Slides courtesy of Joe Walker) Early Comet Netscape 1.1, March 1995 Netscape 1.1 new features • Tables • Background images • “Dynamic Documents” • Client Pull •Server Push • This predates JavaScript by an entire year Server Push, Client Pull “Client Pull” META HTTP-EQUIV=Refresh CONTENT=1 “Server Push” Content-type: multipart/x-mixed-replace;boundary=XXooXX --XXooXX Content-type: text/plain Data f