Question

I’m trying pubsub with redis and socketio in nodejs.

My server-side code is:

var io = require('socket.io').listen(server);
var pub = redis.createClient();

io.sockets.on("connection", function(socket) {
    console.log('connecteed');

    var sub = redis.createClient();

    sub.subscribe("messages");
    sub.on("message", function(channel, message) {
      console.log('message',message);
      socket.emit(channel,message);
    });

    socket.on("disconnect", function() {
      sub.unsubscribe("messages");
      sub.quit();
    });
});
pub.publish("messages", JSON.stringify({type: "foo", content: "bar"}));

My html page index.html contains the following script:

var host = window.location.host.split(':')[0];
var socket = io.connect('http://' + host);
socket.on('messages',function(msg){
    console.log(msg);
})

but in index.html console.log is never executed.

It is elementary, but i don’t find the error in my code. Where is it?

Answer 1

That probably because you don’t have any clients connected when you publish the message (hint io.socket.on connect function is executed after pub.publish). Try to replace

pub.publish("messages", JSON.stringify({type: "foo", content: "bar"}));

with

setIntervall(function(){
    pub.publish("messages", JSON.stringify({type: "foo", content: "bar"}));
},1000);

This will send the message each second and will give you plenty of time to verify your setup.