added a small php example

doc/protocol.txt

@@ -44,3 +44,27 @@ Initialization:
 		u8 type = TYPE_CONTROL = 0
 		u8 controltype = CONTROLTYPE_DISCO = 2
 
+- Here's a quick untested connect-disconnect done in PHP:
+# host: ip of server (use gethostbyname(hostname) to get from a dns name)
+# port: port of server
+function check_if_minetestserver_up($host, $port)
+	$socket = socket_create(AF_INET, SOCK_DGRAM, SOL_UDP);
+	$timeout = array("sec" => 1, "usec" => 0);
+	socket_set_option($socket, SOL_SOCKET, SO_RCVTIMEO, $timeout);
+	$buf = "\x4f\x45\x74\x03\x00\x00\x00\x03\xff\xdc\x01";
+	socket_sendto($socket, $buf, strlen($buf), 0, $host, $port);
+	$buf = socket_read($socket, 1000);
+	if($buf != "")
+	{
+		# We got a reply! read the peer id from it.
+		$peer_id = substr($buf, 9, 2);
+		
+		# Disconnect
+		$buf = "\x4f\x45\x74\x03".$peer_id."\x00\x00\x02";
+		socket_sendto($socket, $buf, strlen($buf), 0, $host, $port);
+		socket_close($socket);
+		
+		return true;
+	}
+	return false;
+