comment.txt

Notice that neither can receive any message on sender. It stops receiving messages, when I pass an IP address to bind().

However, I am required to pass an IP address to bind() to make the Mac use it's non-default gw.

So here, I am also showing my work around, which is having two sockets with different configuration.

default-inet.output

This is Linux, 192.168.178.45, on default inet.

RECEIVER received from  192.168.178.22  :  [sender] pid: 32651
RECEIVER received from  192.168.178.45  :  [sender] pid: 1996
RECEIVER received from  192.168.178.45  :  [receiver] pid: 1996

multicast.js

var dgram = require('dgram');
var sender = dgram.createSocket('udp4');
var receiver = dgram.createSocket('udp4');

var testSender = new Buffer('[sender] pid: ' + process.pid);
var testReceiver = new Buffer('[receiver] pid: ' + process.pid);

var multicastAddress = '239.1.2.3';
var multicastPort = 5554;

var wlan = require('os').networkInterfaces().wlan0;

// Mac interface is en1
if (!wlan) {
    wlan = require('os').networkInterfaces().en1;
}

if (wlan) {
    wlan = wlan.filter(function(inet) { return inet.family === 'IPv4' })[0];
}


sender.bind(multicastPort, wlan.address);
sender.addMembership(multicastAddress, wlan.address);

receiver.bind(multicastPort);
receiver.addMembership(multicastAddress, wlan.address);


receiver.on('message', function ( data, rinfo ) {
    console.log('RECEIVER received from ', rinfo.address, ' : ', data.toString());
});

sender.on('message', function ( data, rinfo ) {
    console.log('SENDER received from ', rinfo.address, ' : ', data.toString());
});

setInterval(function () {
    receiver.send(testReceiver, 0, testReceiver.length, multicastPort, multicastAddress);
    sender.send(testSender, 0, testSender.length, multicastPort, multicastAddress);
}, 1000);

non-default-inet.output

This is a Mac, 192.168.178.22, where this is the non-default inet:

RECEIVER received from  192.168.178.22  :  [sender] pid: 32651
RECEIVER received from  192.168.178.45  :  [sender] pid: 1996
RECEIVER received from  192.168.178.45  :  [receiver] pid: 1996

And here is the output, when the Mac is on default gw (same output for both machines again):

RECEIVER received from 192.168.178.22 : [sender] pid: 32735
RECEIVER received from 192.168.178.22 : [receiver] pid: 32735
RECEIVER received from 192.168.178.45 : [sender] pid: 2002
RECEIVER received from 192.168.178.45 : [receiver] pid: 2002