Disconnect event is not fired if socket disconnects before middleware is finished

You want to:

• report a bug
• request a feature

It’s possible this is intended behavior, in which case it would be nice if the documentation explained this clearly.

Current behaviour

If a disconnect listener is bound on a socket from middleware, the callback is not fired if the socket disconnects before the middleware completes.

My use case for this is along the lines of:

io.use((socket, next) => {
    const foo = allocSomeResource(socket);
    socket.once('disconnect', () => free(foo));
    authorize(socket, next);
})

Where authorize is a call that completes asynchronously

Steps to reproduce (if the current behaviour is a bug)

server;js:

const express = require('express');
const app = express();
const server = require('http').createServer(app);
const io = require('socket.io')(server);
const port = process.env.PORT || 3000;

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

io.on('connect', onConnect);
io.use(function (socket, next) {
    console.log('waiting for ' + socket.id);
    setTimeout(next, 1000);
});
server.listen(port, () => console.log('server listening on port ' + port));

function onConnect(socket){
  console.log('connect ' + socket.id);

  socket.on('disconnect', () => console.log('disconnect ' + socket.id));
}

client.js

const socket = require('socket.io-client')('http://localhost:3000');

socket.on('connect', onConnect);

function onConnect(){
  console.log('connect ' + socket.id);
}

setTimeout(() => socket.disconnect(), 500);

Expected behaviour

disconnect event is fired when the socket is closed OR the documentation clearly states whether/which events are supported during the middleware phase.

Setup

• OS: Linux
• browser: N/A, reproduced with node.js client
• socket.io version: socket.io@2.0.4

Other information (e.g. stacktraces, related issues, suggestions how to fix)

[TroyKomodo]

how is this still a thing?

[RoDmitry]

@TobiasWehrum thank you for idea. I tried to use ping function:

socket.conn.on('packet', packet => {
  if (packet.type === 'ping' && socket.id in clients) {
    clients[socket.id].seen = Math.trunc(Date.now() / 1000);
  }
});

But I noticed that’s actually overkill, because socket.io disconnects all of the not pingable clients itself. And others left are not found in connected, so my workaround is:

setInterval(() => {
  const socket_ids = Object.keys(clients);
  socket_ids.forEach(socket_id => {
    if (!(socket_id in io.sockets.connected)) {
      delete clients[socket_id];
    }
  });
}, 900000);