gistfile1.js

var client = bayeux.getClient()
  , channelKeyPrefix = "room:";

bayeux.bind('subscribe', function(clientId, channel){
  redisClient.incr(channelKeyPrefix + channel, function(error, value){
    client.publish(channel, {
      event: 'user-change',
      params: {
        onlineUsers: value
      }
    });
  });
});

bayeux.bind('unsubscribe', function(clientId, channel){
  redisClient.decr(channelKeyPrefix + channel, function(error, value){
    client.publish(channel, {
      event: 'user-change',
      params: {
        onlineUsers: value
      }
    });
  });
});