Okay, as of 0.7.7 this is available, but not in the manner that lubar describes. I ended up needing to parse through some commit logs on git hub to figure this one out, but the following code does actually work for me now:

var io = require('socket.io').listen(server);

io.sockets.on('connection', function (socket) {
  var address = socket.handshake.address;
  console.log('New connection from ' + address.address + ':' + address.port);
});

for 1.0.4:

io.sockets.on('connection', function (socket) {
  var socketId = socket.id;
  var clientIp = socket.request.connection.remoteAddress;

  console.log(clientIp);
});

If you use an other server as reverse proxy all of the mentioned fields will contain localhost. The easiest workaround is to add headers for ip/port in the proxy server.

Example for nginx: add this after your proxy_pass:

proxy_set_header  X-Real-IP $remote_addr;
proxy_set_header  X-Real-Port $remote_port;

This will make the headers available in the socket.io node server:

var ip = socket.handshake.headers["x-real-ip"];
var port = socket.handshake.headers["x-real-port"];

Note that the header is internally converted to lower case.

If you are connecting the node server directly to the client,

var ip = socket.conn.remoteAddress;

works with socket.io version 1.4.6 for me.

For latest socket.io version use

socket.request.connection.remoteAddress

For example:

var socket = io.listen(server);
socket.on('connection', function (client) {
  var client_ip_address = socket.request.connection.remoteAddress;
}

beware that the code below returns the Server's IP, not the Client's IP

var address = socket.handshake.address;
console.log('New connection from ' + address.address + ':' + address.port);

Using the latest 1.0.6 version of Socket.IO and have my app deployed on Heroku, I get the client IP and port using the headers into the socket handshake:

var socketio = require('socket.io').listen(server);

socketio.on('connection', function(socket) {

  var sHeaders = socket.handshake.headers;
  console.info('[%s:%s] CONNECT', sHeaders['x-forwarded-for'], sHeaders['x-forwarded-port']);

}

This seems to work:

var io = require('socket.io').listen(80);
io.sockets.on('connection', function (socket) {
  var endpoint = socket.manager.handshaken[socket.id].address;
  console.log('Client connected from: ' + endpoint.address + ":" + endpoint.port);
});

Since socket.io 1.1.0, I use :

io.on('connection', function (socket) {
  console.log('connection :', socket.request.connection._peername);
  // connection : { address: '192.168.1.86', family: 'IPv4', port: 52837 }
}

Edit : Note that this is not part of the official API, and therefore not guaranteed to work in future releases of socket.io.

Also see this relevant link : engine.io issue

Version 0.7.7 of Socket.IO now claims to return the client's IP address. I've had success with:

var socket = io.listen(server);
socket.on('connection', function (client) {
  var ip_address = client.connection.remoteAddress;
}

Very easy. First put

io.sockets.on('connection', function (socket) {

console.log(socket);

You will see all fields of socket. then use CTRL+F and search the word address. Finally, when you find the field remoteAddress use dots to filter data. in my case it is

console.log(socket.conn.remoteAddress);

From reading the socket.io source code it looks like the "listen" method takes arguments (server, options, fn) and if "server" is an instance of an HTTP/S server it will simply wrap it for you.

So you could presumably give it an empty server which listens for the 'connection' event and handles the socket remoteAddress; however, things might be very difficult if you need to associate that address with an actual socket.io Socket object.

var http = require('http')
  , io = require('socket.io');
io.listen(new http.Server().on('connection', function(sock) {
  console.log('Client connected from: ' + sock.remoteAddress);
}).listen(80));

Might be easier to submit a patch to socket.io wherein their own Socket object is extended with the remoteAddress property assigned at connection time...

Latest version works with:

console.log(socket.handshake.address);

on socket.io 1.3.4 you have the following possibilities.

socket.handshake.address,

socket.conn.remoteAddress or

socket.request.client._peername.address

I have found that within the socket.handshake.headers there is a forwarded for address which doesn't appear on my local machine. And I was able to get the remote address using:

socket.handshake.headers['x-forwarded-for']

This is in the server side and not client side.

In socket.io 2.0: you can use:

socket.conn.transport.socket._socket.remoteAddress

works with transports: ['websocket']

In 1.3.5 :

var clientIP = socket.handshake.headers.host;

socket.handshake.headers['x-forwarded-for'].split(",")[0]

As of socket 3.1.2