How to setsockopt under node.js?

I think this is what you want: https://www.npmjs.org/package/raw-socket

Take a look at the official node.js documentation for net and see if there's something that will do what you want. node's socket interface isn't a simple clone of the C api, unlike some other languages.

This is my getsockopt:

var ffi = require('ffi');
var net = require('net');
var StructType = require('ref-struct');
var ref = require('ref');

var current = ffi.Library(null, {
  'getsockopt': [ 'int', [ 'int', 'int', 'int', 'pointer', 'pointer']],
  'ntohs': ['uint16', ['uint16']],
//    const char *inet_ntop(int af, const void *src, char *dst, socklen_t size);

});

var SOL_IP = 0;
var SO_ORIGINAL_DST = 80;
var AF_INET = 2;

var sockaddr_in = StructType([
    ['int16', 'sin_family'],
    ['uint16', 'sin_port'],
    ['uint32', 'sin_addr'],
    ['uint32', 'trash1'],
    ['uint32', 'trash2'],
]);

function get_original_dst(client) {
    var dst = new sockaddr_in;
    var dstlen = ref.alloc(ref.types.int, sockaddr_in.size);
    var r = current.getsockopt(client._handle.fd, SOL_IP, SO_ORIGINAL_DST, dst.ref(), dstlen);
    if (r === -1)
        throw new Error("getsockopt(SO_ORIGINAL_DST) error");
    if (dst.sin_family !== AF_INET)
        throw new Error("getsockopt(SO_ORIGINAL_DST) returns unknown family: " + dst.sin_family );

    // TODO: inet_ntop. inet_ntoa is _UNSAFE_
    var ipaddr = dst.ref(); ipaddr = ipaddr[4] + "." + ipaddr[5] + "." + ipaddr[6] + "." + ipaddr[7];

    return [ipaddr, current.ntohs(dst.sin_port)];
}

module.exports.get_original_dst = get_original_dst;