Facebook XMPP Chat API send Message PHP

I am currently messing about with the Facebook Chat API. I want to send chat messages to my facebook contacts via an App.

Using the example provided by facebook I was able to connect to the facebook chat server. But that had more of an trial and error thing here. I could only vaguely understand how requests and responses are sent and received. It would be great if someone could provide further explanation or further reading.

My actual question is: How can I send messages after connecting to the chat server?

<?php

// Copyright 2004-present Facebook. All Rights Reserved.

$STREAM_XML = '<stream:stream '.
  'xmlns:stream="http://etherx.jabber.org/streams" '.
  'version="1.0" xmlns="jabber:client" to="chat.facebook.com" '.
  'xml:lang="en" xmlns:xml="http://www.w3.org/XML/1998/namespace">';

$AUTH_XML = '<auth xmlns="urn:ietf:params:xml:ns:xmpp-sasl" '.
  'mechanism="X-FACEBOOK-PLATFORM"></auth>';

$CLOSE_XML = '</stream:stream>';

$RESOURCE_XML = '<iq type="set" id="3">'.
  '<bind xmlns="urn:ietf:params:xml:ns:xmpp-bind">'.
  '<resource>fb_xmpp_script</resource></bind></iq>';

$SESSION_XML = '<iq type="set" id="4" to="chat.facebook.com">'.
  '<session xmlns="urn:ietf:params:xml:ns:xmpp-session"/></iq>';

$START_TLS = '<starttls xmlns="urn:ietf:params:xml:ns:xmpp-tls"/>';


function open_connection($server) {
  print "[INFO] Opening connection... ";

  $fp = fsockopen($server, 5222, $errno, $errstr);
  if (!$fp) {
    print "$errstr ($errno)<br>";
  } else {
    print "connnection open<br>";
  }

  return $fp;
}

function send_xml($fp, $xml) {
  fwrite($fp, $xml);
}

function recv_xml($fp,  $size=4096) {
  $xml = fread($fp, $size);
  if ($xml === "") {
     return null;
  }

  // parses xml
  $xml_parser = xml_parser_create();
  xml_parse_into_struct($xml_parser, $xml, $val, $index);
  xml_parser_free($xml_parser);

  return array($val,