How to push data to a browser?

chenchao01@baidu.com

Polling Vs Push

HTTP functions as a request-response protocol

How to push?

• Comet– Long Polling/HTTP Streaming/Ajax Push/Reverse

Ajax, Two-way-web/HTTP serverpush

• Flash XMLSocket• Java/Silverlight socket• HTML5 Server-Sent Events• HTML5 WebSockets

Two kinds of Comet

• Streming• Long Polling

Comet - Streaming

Comet - Long Polling

Design & Architecture

Comet is a

pub/sub Systemrely on http & web

产品功能上分• User-centric

– Event based– Web chat/notification/gmail

• Data-centric – Data synchronization

Architecture model

• Symmetric pub/sub– User-centric

• Asymmetric pub/sub– Data-centric

Symmetric pub/sub

eg: Tornado + RabbitMQ 快速实现一个很好可扩展的 webchat

Asymmetric pub/sub

Data Feed ~= AdapterEg: Facebook’s webchat

Facebook’s webchat

The two Models

• 互相模拟对方的行为• Mix the two model

How to Implement a Comet Server?

Next

Lots of Connections

• How many connections to handle?–同时在线用户数

• C10k(http://www.kegel.com/c10k.html)• Asynchronous IO

Communication

• Browser & server– http– JavaScript

key ingredients

• Asynchronous IO• Message Dispatch• HTTP• Javascript

开源• Tornado• Twisted• Jeety• nginx_http_push_module• Bayeaux协议 (该协议对应有服务器端以及

js的实现 )• …

Scale

空间 comet system overview

backends

• Lighttpd– Mod_pack(hold链接，处理 long polling)– Mod_proxy_backend_pack( 与 control-center交互，macpack)

• Control-center– 类似于 ui，接受 lighty的请求向 register注册，接受message_pool的请求，向 lighty推送

• Register– 单点，维护 uid 和 ip的映射关系

• Message_pool– 接受来自 transfer的数据，存储数据库，然后推向 control-center）

Message send

Q&A