Unwanted multiple messages when using redis for pub-sub

Question

The following code works just fine, when I do pub/sub using socket.io.

Basically, I send a chat message from browser. At the server, I listen to this message and emit it back to all, the same message from the server. So, I expect 1 message to be returned/printed for every message I send.

With the below, I can login from multiple browsers, and when I send a chat message, it gets returned/printed as a single chat message as expected.

io.use(socketHandshake({store: sessionStore, key:'jsessionid', secret:'secret', parser:cookieParser()}));
io.on('connection', function (socket) {
    socket.on('chat', function (message) {
        io.emit('chat', "hello world");
    });
});

However, when I try to do pub/sub using redis, there is a problem.

From first browser: 1 chat message results in printing out 1 chat message

From second browser: 1 chat message results in printing out 2 chat messages

From third browser: 1 chat message results in printing out 3 chat message

var sub = redis.createClient();
var pub = redis.createClient();
sub.subscribe('chat');
io.use(socketHandshake({store: sessionStore, key:'jsessionid', secret:'secret', parser:cookieParser()}));
io.on('connection', function (socket) {
    socket.on('chat', function (message) {
        // io.emit('chat', "hello world");
        pub.publish('chat', "hello world");
    });
    sub.on('message', function (channel, message) {
        io.emit(channel, message);
    });
});

What am I missing ? I'm a beginner and I'm trying out this example http://blog.cloudfoundry.org/2013/01/24/scaling-real-time-apps-on-cloud-foundry-using-node-js-and-redis/ using latest versions of express, socket.io, socket.io-handshake and redis.

I'm getting stumped at this redis pub/sub. Please help.

Answer 1

You're adding a new 'message' handler for every connection. So that is why you start seeing more and more duplicates with more and more connections. Try moving your sub.on('message', ...); outside of your socket.io connection handler.