This is the repository for the socket.io server used in @TooTallNate's talk for the Automattic VIP Workshop 2015.

Basically it's a demonstration of how you can add realtime capabilities to your WordPress VIP installation, by having the web browser connect to a Node.js socket.io server hosted somewhere on your infrastructure.

In this particular example, we add realtime "presence" capabilities. That is:

How many other people are viewing this post?

The solution? Socket.IO and Redis.

Socket.IO is a realtime application server, written in JavaScript for Node.js. It allows bi-directional event-based message passing between connected clients and the server. Similar in concept to WebSockets, but Socket.IO offers features common to realtime applications like reconnection and packet buffering.

Hash that contains all sessions as keys, and their last known post being viewed at the value.

Used when a session is expired/deleted to look up the last known post that the user was viewing, so that the corresponding viewers:<post-id> Set can have its entry removed.

127.0.0.1:6379> HGETALL viewers
1) "mXbcRrQtsjpdKbmsAAAX"
2) "13"

Set that contains all the session IDs that are currently viewing post-id.

Used to get the overall "presence" count for a given post.

127.0.0.1:6379> SMEMBERS viewers:13
1) "mXbcRrQtsjpdKbmsAAAX"

String with an 11 minute expiration time (TTL, configurable in ./config.js). The contents of the string are not actually used, instead the existence of the key is enough to signify that the session is still "alive".

Used to create and destroy "session" instances. Redis' EXPIRES command is leveraged to have the database expire the keys automatically.

127.0.0.1:6379> GET session:mXbcRrQtsjpdKbmsAAAX
"13"

Redis and Node.js are required to be in your $PATH on the server that will run this Socket.IO application code.

$ git clone git://github.com/TooTallNate/vip-workshop-2015-realtime.git
$ cd vip-workshop-2015-realtime
$ npm install
$ node app &   # spawn application server
$ node gc &    # spawn "garbage collection" server

The first piece of this example is the "application server", which is the actual Socket.IO server.

When a new Socket.IO connection is established, the client side sends a "