Node: http.get option localAddress not working

[k1tzu]

Hello! The binding to Local interface option is not working at all.
The case: Arch Linux system with two different ethernet interfaces.
eth0: 192.168.0.173/24
eth1: 192.168.0.182/24
routing table is
default via 192.168.0.1 dev eth0 metric 280
default via 192.168.0.1 dev eth1 metric 281

Every interface has a listening http server on other end with the address: 192.168.0.1
So I'm trying to send a request to each of them with nodejs.
Sample code:

var http = require('http');
var options = {};
options.port = 80;
options.host = "192.168.0.1";
options.path = '/index.html';
options.headers = {'Referer': 'http://' + options.host + ':' + options.port + '/index.html'};

options.localAddress = '192.168.0.182'; //NOT WORKING!! - REQUEST GOING FROM 192.168.0.173!

var creq = http.get(options);
creq.on('response', function (res) {
    res.on('data', function (chunk) {
        console.log(chunk);
    });
});

I've even tried creating a socket for that request with new net.Socket({ handle: net._createServerHandle( '192.168.0.182')}); and requests kept going from the wrong address.
There's workaround with 'curl --interface eth1 ...' that works, but it's not a good solution.

[mscdex]

IIRC routing on Linux uses the route with the _lowest_ metric value when multiple routes match, which in this case would agree with what you're experiencing.

[k1tzu]

Of cause it uses the route with the lowest metric! But that's the question!
I need to send packets to _both_ interfaces with nodejs.

In C language it is a simplest question to resolve with SO_BINDTODEVICE socket option. And I thought nodejs do this also in some intellectual way like

 //convert localAddress to the Interface name
#ifdef __linux__
     //SO_BINDTODEVICE to the interface
#elif __APPLE__
     //IP_BOUND_IF  to the interface
#endif

No problemo

[bnoordhuis]

Perhaps it's stating the obvious but the .localAddress option binds to an address, not an interface. There is no direct support for SO_BINDTODEVICE in node.js but you can jury-rig it with socat(1):

# so-bindtodevice needs root
$ socat TCP4:<address>:80,so-bindtodevice=<dev> EXEC:'node script.js',nofork,fdin=3,fdout=3

With script.js looking something like this:

var socket = require('net').Socket({ fd: 3, readable: true, writable: true });
var req = require('http').get({
  createConnection: () => socket,
  headers: { Host: 'example.com' },
}, res => res.pipe(process.stdout));

[k1tzu]

I've found another workaround that works. Using ffi and call to setsockopt. But I wish I could do that with nodejs only.

var http = require('http'),
    net = require('net'),
    util = require('util'),
    ffi = require('ffi');

var SOL_SOCKET = 1;
var SO_BINDTODEVICE = 25;
var current = ffi.Library(null, {
    'setsockopt': ['int', ['int', 'int', 'int', 'string', 'int']]
});

var remoteIp = "192.168.0.1";
var ourIp = "192.168.0.182";
var ourInterface = "eth1";

function bindingAgent(options) {
    http.Agent.call(this, options);
    this.createConnection = bindingCreateConnection;
}

util.inherits(bindingAgent, http.Agent);

function bindingCreateConnection(port, host, options) {
    var socket;
    socket = new net.Socket({handle: net._createServerHandle(ourIp)});
    var iface = ourInterface;
    var r = current.setsockopt(socket._handle.fd, SOL_SOCKET, SO_BINDTODEVICE, iface, 6);
    if (r === -1)
        throw new Error("getsockopt(SO_BINDTODEVICE) error");

    socket.connect(port, host);

    return socket;
}

var optionsAgent = {};
var ourBindingAgent = new bindingAgent(optionsAgent);

var httpReq = {};
httpReq.port = 80;
httpReq.host = remoteIp;
httpReq.path = '/index.html';
httpReq.headers = {'Referer': 'http://' + remoteIp + ':' + httpReq.port + '/index.html'};
httpReq.agent = ourBindingAgent;

var body = '';
var creq = http.get(httpReq);
creq.on('response', function (res) {
    res.setEncoding('utf8');
    res.on('data', function (chunk) {
        console.log(chunk);
    });
});