Question

I need some help about my node.js+socket.io implementation.

This service expose a server that connects to an ActiveMQ broker over the STOMP protocol, using the stomp-js node.js module to receive events; that then are displayed in a web front end through websockets using socket.io.

So, everything was fine until I started use the Filters feature of ActiveMQ, but this was not the failure point because of my and my team researching, we found the way to ensure the implementation was fine, the problem comes with the connections: So here’s the thing, I receive the filters to subscribe, I successfully subscribe to but when I receive a new set of filters is when comes the duplicated, triplicated and more and more messages depending the number of times that I subscribe-unsubscribe to.

So making some debug, I cannot see what’s the problem but I’m almost sure that is some bad implementation of the callbacks or the program flow, I’ll attach my code to read your comments about it.

Thanks a lot!

var sys = require('util');
var stomp = require('stomp');
var io = require('socket.io').listen(3000);

var socket = io.sockets.on('connection', function (socket) {

var stomp_args = {
    port: 61616,
    host: 'IP.ADDRESS',
    debug: true,
    };

var headers;
var client = new stomp.Stomp(stomp_args);
var setFilters = false; 

socket.on('filtros', function (message) {

    console.log('DEBUG: Getting filters');

    if(setFilters){
            client.unsubscribe(headers);
        }
    else{
            client.connect();
        }

    var selector = '';
    headers = '';

    for(var attributename in message){
        console.log(attributename+" : " + message[attributename]);
        if(message[attributename] != ''){
            selector += ' ' + attributename + '=\'' + message[attributename] + '\' AND ';
        }
    }

    selector = selector.substring(0, selector.length - 4)
    console.log('DEBUG: Selector String: ' + selector);

    headers = {
        destination: '/topic/virtualtopic',
        ack: 'client',
        selector: selector
    };

    if(setFilters)
        client.subscribe(headers);

    client.on('connected', function() {
        client.subscribe(headers);
        console.log('DEBUG: Client Connected');
        setFilters = true;
    });
});
var bufferMessage;
client.on('message', function(message) {
    console.log("Got message: " + message.headers['message-id']);
    var jsonMessage = JSON.parse(message.body);
    if(bufferMessage === jsonMessage){
        console.log('DEBUG: recibo un mensaje repetido');
        return 0;
        }
    else{
        console.log('DEBUG: Cool');
        socket.emit('eventoCajero', jsonMessage);
        }           
    client.ack(message.headers['message-id']);
    bufferMessage = jsonMessage;
});

socket.on('disconnect', function(){
        console.log('DEBUG: Client disconnected');
        if(setFilters){
            console.log('DEBUG: Consumer disconnected');
            client.disconnect();
            }
        });
client.on('error', function(error_frame) {
    console.log(error_frame.body);
});

});

Answer 1

Looking in the Socket.IO documentation, I’ve found that this is a known issue (I think critical known issue) and they have not fixed it yet. So, to correct this is necessary to reconnect to the socket in the client side to avoid duplicate messages, using:

socket.socket.reconnect();

function to force reconnection explicitly.