passing socket from master to worker causes a timeout issue where socket is null.

[japrescott]

node: 8
npm: 5.0.2
linux Ubuntu 1604 -> 4.8.0-51

Setup:
When using node with the cluster module while using socket.io, connections are passed from the master to the children by emitting. This is needed for "sticky-sessions" to work. This worked with node v7.10.

Since node8, I am getting following error;

worker process 3583 got 'uncaughtException', shutdown gracefully! TypeError: Cannot read property 'emit' of null
    at Socket.socketOnTimeout (_http_server.js:386:34)
    at emitNone (events.js:105:13)
    at Socket.emit (events.js:207:7)
    at Socket._onTimeout (net.js:401:8)
    at ontimeout (timers.js:488:11)
    at tryOnTimeout (timers.js:323:5)
    at Timer.listOnTimeout (timers.js:283:5) 'TypeError: Cannot read property \'emit\' of null\n    at Socket.socketOnTimeout (_http_server.js:386:34)\n    at emitNone (events.js:105:13)\n    at Socket.emit (events.js:207:7)\n
    at Socket._onTimeout (net.js:401:8)\n    at ontimeout (timers.js:488:11)\n    at tryOnTimeout (timers.js:323:5)\n    at Timer.listOnTimeout (timers.js:283:5)'

This is particularly strange as I have a domain wrapping the worker code which should prevent an uncaughtException.

I have my suspicion, this is related to #13348

[gavinaiken]

I have this problem too. I have a simple repro for the bug - use the script from https://github.com/elad/node-cluster-socket.io, i.e. this:

var express = require('express'),
    cluster = require('cluster'),
    net = require('net'),
    sio = require('socket.io'),
    sio_redis = require('socket.io-redis');

var port = 3000,
    num_processes = require('os').cpus().length;

if (cluster.isMaster) {
	// This stores our workers. We need to keep them to be able to reference
	// them based on source IP address. It's also useful for auto-restart,
	// for example.
	var workers = [];

	// Helper function for spawning worker at index 'i'.
	var spawn = function(i) {
		workers[i] = cluster.fork();

		// Optional: Restart worker on exit
		workers[i].on('exit', function(code, signal) {
			console.log('respawning worker', i);
			spawn(i);
		});
    };

    // Spawn workers.
	for (var i = 0; i < num_processes; i++) {
		spawn(i);
	}

	// Helper function for getting a worker index based on IP address.
	// This is a hot path so it should be really fast. The way it works
	// is by converting the IP address to a number by removing non numeric
  // characters, then compressing it to the number of slots we have.
	//
	// Compared against "real" hashing (from the sticky-session code) and
	// "real" IP number conversion, this function is on par in terms of
	// worker index distribution only much faster.
	var worker_index = function(ip, len) {
		var s = '';
		for (var i = 0, _len = ip.length; i < _len; i++) {
			if (!isNaN(ip[i])) {
				s += ip[i];
			}
		}

		return Number(s) % len;
	};

	// Create the outside facing server listening on our port.
	var server = net.createServer({ pauseOnConnect: true }, function(connection) {
		// We received a connection and need to pass it to the appropriate
		// worker. Get the worker for this connection's source IP and pass
		// it the connection.
		var worker = workers[worker_index(connection.remoteAddress, num_processes)];
		worker.send('sticky-session:connection', connection);
	}).listen(port);
} else {
    // Note we don't use a port here because the master listens on it for us.
	var app = new express();

	// Here you might use middleware, attach routes, etc.

	// Don't expose our internal server to the outside.
	var server = app.listen(0, 'localhost'),
	    io = sio(server);

	// Tell Socket.IO to use the redis adapter. By default, the redis
	// server is assumed to be on localhost:6379. You don't have to
	// specify them explicitly unless you want to change them.
	io.adapter(sio_redis({ host: 'localhost', port: 6379 }));

	// Here you might use Socket.IO middleware for authorization etc.

	// Listen to messages sent from the master. Ignore everything else.
	process.on('message', function(message, connection) {
		if (message !== 'sticky-session:connection') {
			return;
		}

		// Emulate a connection event on the server by emitting the
		// event with the connection the master sent us.
		server.emit('connection', connection);

		connection.resume();
	});
}

Run that script with node, and hit the server with Chrome (should see an error Cannot GET / returned). With node 7.10.0 the server keeps running fine. With node 8.0.0 I get this error 5s after making the request in the browser:

_http_server.js:386
  var serverTimeout = this.server.emit('timeout', this);
                                 ^

TypeError: Cannot read property 'emit' of null
    at Socket.socketOnTimeout (_http_server.js:386:34)
    at emitNone (events.js:105:13)
    at Socket.emit (events.js:207:7)
    at Socket._onTimeout (net.js:401:8)
    at ontimeout (timers.js:488:11)
    at tryOnTimeout (timers.js:323:5)
    at Timer.listOnTimeout (timers.js:283:5)
respawning worker 4

[Tjommel]

Same here! worked with 7.x now wiht 8.x i get the same error message as @gavinaiken get.

[lpinca]

This is probably my fault. In #11926 I wrongly assumed that socket.server is always set but in this case the 'connection' event is emitted manually with a socket argument whose server property is null.

Can you build node with this patch and see if it fixes the issue?

diff --git a/lib/_http_server.js b/lib/_http_server.js
index 357400e350..aae55a5282 100644
--- a/lib/_http_server.js
+++ b/lib/_http_server.js
@@ -292,6 +292,9 @@ Server.prototype.setTimeout = function setTimeout(msecs, callback) {
 function connectionListener(socket) {
   debug('SERVER new http connection');
 
+  if (socket.server === null)
+    socket.server = this;
+
   httpSocketSetup(socket);
 
   // If the user has added a listener to the server,

[gavinaiken]

Just tested, was able to recreate the bug with node built from master, and that patch does seem to fix it 👍

[lpinca]

I'm working on a PR, almost done.