This document discusses different techniques for pushing data from a server to a browser in real-time, including Comet, a umbrella term for techniques like long polling and server-sent events. It outlines several Comet implementations like Tornado and Twisted, and compares symmetric and asymmetric pub/sub architectures for user-centric and data-centric use cases. Key aspects of building a Comet system are asynchronous I/O, message dispatching, and scaling to handle large numbers of simultaneous connections.

1. How to push data to a browser?
chenchao01@baidu.com

2. Polling Vs
Push
HTTP functions as a request-response protocol

3. 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

4. Two kinds of Comet
• Streming
• Long Polling

5. Comet - Streaming

6. Comet - Long Polling

7. Design & Architecture

8. Comet is a
pub/sub System
rely on http & web

9. 产品功能上分
• User-centric
– Event based
– Web chat/notification/gmail
• Data-centric
– Data synchronization

10. Architecture model
• Symmetric pub/sub
– User-centric
• Asymmetric pub/sub
– Data-centric

11. Symmetric pub/sub
eg: Tornado + RabbitMQ 快速实现一个很好可扩展的 webchat

12. Asymmetric pub/sub
Data Feed ~= Adapter
Eg: Facebook’s webchat

13. Facebook’s webchat

14. The two Models
• 互相模拟对方的行为
• Mix the two model

15. How to Implement a Comet
Server?
Next

16. Lots of Connections
• How many connections to handle?
– 同时在线用户数
• C10k(http://www.kegel.com/c10k.html)
• Asynchronous IO

17. Communication
• Browser & server
– http
– JavaScript

18. key ingredients
• Asynchronous IO
• Message Dispatch
• HTTP
• Javascript

19. 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 )
• …

20. Scale

21. 空间 comet system overview

22. 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 ）

23. Message send

24. Q&A