Node Server receive XmlHttpRequest

I'm using the following code to send a session description (tiny JSON code - http://www.ietf.org/rfc/rfc2327.txt).

function sendMessage(message) {
  var msgString = JSON.stringify(message);
  console.log('C->S: ' + msgString);
  path = '/message?r=67987409' + '&u=57188688';
  var xhr = new XMLHttpRequest();
  xhr.open('POST', path, true);
  xhr.send(msgString);
}

I'm not sure how to go about retreiving the JSON on my Node.js server.

Here's a code that can handle POST request in node.js .

var http = require('http');

var server = http.createServer(function (request, response) {
    if (request.method == 'POST') {
        var body = '';
        request.on('data', function (data) {
            body += data;
        });
        request.on('end', function () {

            var POST = JSON.parse(body);
            // POST is the post data

        });
    }
});
server.listen(80);

Hope this can help you.