JavaScript | // Returns the local machine's - Anonymous - f764a0303

// Returns the local machine's IP address as a dotted-quad string, by
// sending myself a UDP packet with a unique string.  This function
// UDP-broadcasts, otherwise the remote address of a received packet
// is 127.0.0.1.
function findMyIP() {
  var sock = new java.net.DatagramSocket();
  var sendSock = new java.net.DatagramSocket();
  var secret = java.util.UUID.randomUUID().toString();
  var place = new java.util.Hashtable(1); // thread-safe
  // Receive UDP packet with secret in looping background thread.
  spawn(function() {
    var sb = new java.lang.StringBuffer();
    sb.setLength(secret.length);
    while(true) {
      var p = new java.net.DatagramPacket(new java.lang.String(sb.toString()).getBytes(), secret.length);
      sock.receive(p);
      if (new java.lang.String(p.getData()) == secret) {
        place.put("ip", p.getAddress().getHostAddress());
        break;
      }
    }
  });
  // Send packets with secret until receiver thread puts IP into table.
  while(true) {
    var p = new java.net.DatagramPacket(new java.lang.String(secret).getBytes(),
                                        secret.length,
                                        java.net.InetAddress.getByName("255.255.255.255"),
                                        sock.getLocalPort());
    sendSock.send(p);
    app.log("Waiting for my IP...");
    java.lang.Thread.sleep(500);
    var myIP = place.get("ip");
    if (myIP != null) {
      return myIP;
    }
  }
}