Cowboy and Websockets

Theory and practice of building a webchat with Cowboy

Loïc Hoguin - @lhoguin

Erlang Cowboy and Nine Nines Founder

Background

Cowboy

• Nearing release of version 0.8
• 100% Websocket standard compliant
• Tested with > 1 million Websocket connections
• Now with a user guide!

Websocket

• RFC 6455 The Websocket Protocol
• HTTP Upgrade
• Two-way connection between the client and the server
• Text and binary

Theory

Webchat architecture

• Users
• One or more room
• One or more users per room
• Messages sent to one room broadcasted to all members

Practice

• This is gonna be LEGEN-- wait for it!

High five!

• ... DARY!

More theory

Many connections per user

• User session processes buffer messages
• User sends messages to rooms
• Room broadcasts to session processes
• Session processes broadcast to connections

Handle disconnects

• Messages get tagged with an auto-incremented id
• Client sends last known eid on connect
• Server atomically replies with all messages > eid
• Connection continues as before

Thanks!

• http://ninenines.eu
• https://github.com/extend/cowboy
• #ninenines on Freenode
• @lhoguin on Twitter

Questions?