使用connect-form，socket.io和express在node.js上的行为确实很奇怪

Question

the following code:

req.form.on('progress', function(bytesReceived, bytesExpected){
    var percent = (bytesReceived / bytesExpected * 100) | 0;
    // progressEvent.download(percent);

    io.sockets.on('connection', function (socket) {        
      socket.emit('progress', { percent: percent});
      client = socket;
      });        
  });

written on an http post handler (express.js) sends socket messages to the client js, but it obviously creates a huge amount of listeners, in fact it warns me saying: "node) warning: possible EventEmitter memory leak detected. 11 listeners added. Use emitter.setMaxListeners() to increase limit."

on the other hand this code:

io.sockets.on('connection', function (socket) {
    progressEvent.on('progress', function(percentage) {
    console.log(percentage);
    socket.emit('progress', { percent: percentage});
    });
});

Doesn't send any message back to the client, the ProgressEvent is:

var util = require('util'),
    events = require('events');

function ProgressEvent() {
    if(false === (this instanceof ProgressEvent)) {
        return new ProgressEvent();
    }

    events.EventEmitter.call(this);
}

util.inherits(ProgressEvent, events.EventEmitter);

ProgressEvent.prototype.download = function(percentage) {
    var self = this;  
    self.emit('progress', percentage);    
}

exports.ProgressEvent = ProgressEvent;

I've been a good day on this strange problem I can't really see why socket.io doesn't send the socket message to the client.

the whole project is here: https://github.com/aterreno/superuploader

Thanks for your attention & help

Answer 1

You shouldn't listen to socket.io connections inside of the progress event. It looks like you're trying to get socket.io to connect when a user uploads a file, but that will not do that. Instead it will listen for a new connection each time the progress event fires on the upload, which I'm guessing is pretty often and it's why you're getting the warning about too many listeners.

What you want to do instead is on the client side, when you initialize an upload, tell the server through socket.io. Then the server links up that socket.io client with their upload through their session, http://www.danielbaulig.de/socket-ioexpress/

Something like this should do it

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

  socket.on('initUpload', function() {
    session.socket = socket;
  });

  socket.on('disconnect', function() {
    session.socket = null;
  });
});

And then in your route

req.form.on('progress', function(bytesReceived, bytesExpected){
  var percent = (bytesReceived / bytesExpected * 100) | 0;
  if (req.session.socket) {
    socket.emit('progress', percent);
  }
});

This only works with one upload per session, but you get the idea.