How to handle which child process gets a socket.io socket handle

Question

I am using Socket.io and clustering. What I need to do is be able to make multiple child processes and send specific [socket.io] sockets to each one as I see fit. Currently (see code below) when I attempt to send the [socket.io] socket as a handle I get an exception.

My code below doesn't have it (as I am trying to get the most basic example to work) but what I want to do is allow a client to connect and tell it what process to go to upon some message. So a client will send an 'init' message with some data and based on that data I forward the [socket.io] socket to a specific process. This was my original plan.

I know I can have socket.io listen from every child process however when a client connects only one of those processes receive it.

My two questions are:

Is there a way to send a socket.io socket to a child process?
If not, is there another way to decide which process gets the handle? (Could you use a different authorization function in each process and if one process doesn't accept the socket another process could?)

var cluster = require('cluster');

if (cluster.isMaster) {
    var io = require('socket.io').listen(80);
    var cpuCount = require('os').cpus().length;
    var children = [];

    for (var i = 0; i < cpuCount; i += 1) {
        children.push(cluster.fork());
    }

    //Master Process is listening for all connections
    io.sockets.on('connection', function (socket) {

        //upon a connection, send the 'handle' to a worker.
        children[0].send('server', socket);
    });
} else {
    process.on('message', function (m, handle) {
        //worker receives it here.
        console.log('here');
    });
}

Console output with stack trace:

C:\Users\randy>node "C:\Users\randy\Documents\Visual Studio 2012\Projects\tesselconnect-server\tesselconnect-server\server.js"
   info  - socket.io started
   debug - client authorized
   info  - handshake authorized bZCM2CVpFFdU9eU1zYwx
   debug - setting request GET /socket.io/1/websocket/bZCM2CVpFFdU9eU1zYwx
   debug - set heartbeat interval for client bZCM2CVpFFdU9eU1zYwx
   debug - client authorized for
   debug - websocket writing 1::

child_process.js:427
        throw new TypeError("This handle type can't be sent");
              ^
TypeError: This handle type can't be sent
    at ChildProcess.target.send (child_process.js:427:15)
    at Worker.send (cluster.js:401:21)
    at SocketNamespace.<anonymous> (C:\Users\randy\Documents\Visual Studio 2012\Projects\tesselconnect-server\tesselconnect-server\server.js:16:15)
    at SocketNamespace.EventEmitter.emit [as $emit] (events.js:117:20)
    at connect (C:\Users\randy\node_modules\socket.io\lib\namespace.js:292:10)
    at C:\Users\randy\node_modules\socket.io\lib\namespace.js:308:13
    at SocketNamespace.authorize (C:\Users\randy\node_modules\socket.io\lib\namespace.js:252:5)
    at SocketNamespace.handlePacket (C:\Users\randy\node_modules\socket.io\lib\namespace.js:302:14)
    at Manager.handleClient (C:\Users\randy\node_modules\socket.io\lib\manager.js:698:32)
    at Manager.handleUpgrade (C:\Users\randy\node_modules\socket.io\lib\manager.js:618:8)

Line 16:

children[0].send('server', socket);

Also like to note that I can send a socket which was created by net.createServer(function (socket) { });. So, I am going to assume that this is not possible using socket.io. — Randy
– Randy, Commented Sep 12, 2013 at 5:12

hexacyanide · Accepted Answer · 2013-09-12 13:13:49Z

3

You should not structure your application in this manner as it will not work. Cluster is generally used for handling high load, and if you wanted to spread load you could then use Cluster and a Redis store.

Aside from that, you can't send a Socket.IO socket object to a worker, because it will fail this check:

if (handle instanceof net.Socket) {
  message.type = 'net.Socket';
} else if (handle instanceof net.Server) {
  message.type = 'net.Server';
} else if (handle instanceof process.binding('tcp_wrap').TCP ||
           handle instanceof process.binding('pipe_wrap').Pipe) {
  message.type = 'net.Native';
} else if (handle instanceof dgram.Socket) {
  message.type = 'dgram.Socket';
} else if (handle instanceof process.binding('udp_wrap').UDP) {
  message.type = 'dgram.Native';
} else {
  throw new TypeError("This handle type can't be sent");
}

You can't really choose which worker to send the process to, so you should think about restructuring your application. Even if one worker rejected a socket using authentication, the client would have to just keep randomly reconnecting to find its intended worker.

If you need different sockets to receive different data, you should look into rooms or namespaces. This is how namespacing works:

var nsp = io.of('/nsp');

nsp.on('connection', function(socket) {
  // use socket here as you would with the global namespace
});

And this is how rooms work:

io.sockets.on('connection', function(socket) {
  socket.join('room');
});

// emit to clients in that room
io.sockets.in('room').emit('event_name', data);

edited Sep 12, 2013 at 13:13

answered Sep 12, 2013 at 4:07

hexacyanide

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2 Comments

Randy Over a year ago

But you can send handles to child processeslink. Node doesn't attempt to stringify a handle (must use 2nd param rather than 1st, see link). Also note, the reason I am wishing to structure it this way is because I was hoping to run untrusted code in a new context AND in a new process. And I wanted the context to have as direct communication with the socket as possible. I was just hoping someone ran into this before.

hexacyanide Over a year ago

Ah, I didn't do adequate research. Modified the answer. Also, why not run all sockets from a main process and send the code rather than the socket to the child processes?

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