EventEmitter memory leak from function within socket.io handler

Question

I have a server that requires a dynamic value that's continuously updating from a spawned process. I tried to make a custom listener outside of the scope of the server because I was receiving potential memory leaks errors but I'm still receiving these messages after several connect/disconnects occur on the server. Why arn't the listeners that were added after the initial connect being removed during the disconnect event listener?

var express = require('express');
var http = require('http');
var spawn = require('child_process').spawn;
var util = require('util');
var fs = require('fs');
var EventEmitter = require('events').EventEmitter;
var sys = require('sys');

var app     = express(),
    server  = http.createServer(app),
    io      = require('socket.io').listen(server);

function Looper(req)  {
    this.req = req;
    EventEmitter.call(this);
}
sys.inherits(Looper, EventEmitter);

Looper.prototype.run = function() {
    var self = this;
    var cmd = spawn('./flow',[this.req]); // <-- script that outputs req every second
    cmd.stdout.setEncoding('utf8');
    cmd.stdout.on('data', function(data) {
        self.emit('output',data);
    });
}

Looper.prototype.output = function(callback) {
    this.on('output', function(data) {
        return callback(data.trim());
    });
}

var looper = new Looper('blah');
looper.run();

app.use(express.static(__dirname + '/public'));

app.get('/', function(req, res) {
    res.send(
        "<script src='/socket.io/socket.io.js'></script>\n"+
        "<script>\n"+
        "\tvar socket=io.connect('http://127.0.0.1:3000');\n"+
        "\tsocket.on('stream', function(data) {\n"+
        "\t\tconsole.log(data);\n"+
        "\t});\n"+
        "</script>\n"
    );
});
server.listen(3000);

io.sockets.on('connection', function(webSocket) {
    looper.output(function(res) {
        webSocket.emit('stream',res);
    });

    webSocket.on('disconnect', function() {
        looper.removeListener('output',looper.output); // <- not remove listener added when connection was made
    });
});

Answer 1

You add(!) an extra callback function every time you call looper.output to the event 'output'. I don't know what you want to achieve, but to get this call only once use this.once('output', ...) or move the callback setting to the object or remove the old function first...