[Python] Receving a strange packets from client to cs1.6 server (HLDS)

I was trying to emulate a CS 1.6 server but got stuck handling a mysterious packet: b'\xff\xff\xff\xffX'.

Observed raw bytes: FF FF FF FF 58 (header FF FF FF FF + single byte X/0x58), but it's not a part of standard A2S protocol (A2S_INFO=0x54, A2S_PLAYER=0x55, etc.). Sent repeatedly by the client if ignored, but no response observed from real servers.

I checked traffic to other servers. Same packet FF FF FF FF 58 appears, but servers ignore it (no reply). I tried ignoring it, but client spams it every time when tries to connect. I haven't found anything in Valve’s Server Query Protocol or GoldSrc specs.

Source code

import socket
import struct
import time
import threading
from random import randint
import os

FAKE_SERVER_IP = "0.0.0.0"
FAKE_SERVER_PORT_START = 27015
FAKE_SERVER_PORT_END = 27115
REDIRECT_IP = "185.97.255.43"
REDIRECT_PORT = 27017

challenge_token = os.urandom(4)
steam_challenge_token = os.urandom(8).hex().encode()

SERVER_ANSWER = f'\xFF\xFF\xFF\xFFS2C_CONNECTION {REDIRECT_IP} {REDIRECT_PORT} {randint(100, 9999999)}'
SERVER_TOKEN_A2S = b'\xFF\xFF\xFF\xFF\x41' + challenge_token
SERVER_TOKEN_STEAM = b'\xFF\xFF\xFF\xFFchallenge ' + steam_challenge_token + b'\n'
SERVER_NAME = "Мой Фейковый Сервер (Редирект)"
MAP_NAME = "de_dust2"
GAME_FOLDER = "cstrike"
GAME_NAME = "Counter-Strike 1.6"
APP_ID = 10
MAX_PLAYERS = 32
BOTS = 0
SERVER_TYPE = b'd'
ENVIRONMENT = b'w'
VISIBILITY = 0
VAC = 1

HEADER_INFO = b'\xFF\xFF\xFF\xFF\x49'
HEADER_CHALLENGE = b'\xFE\xFD\x09'
HEADER_REDIRECT = b'\xFF\xFF\xFF\xFF\x09redirect '
INFO_QUERIES = (
b'\xFF\xFF\xFF\xFFTSource Engine Query\x00',
b'\xFF\xFF\xFF\xFF\x54'
)

redirect_packet = (
b'\xFF\xFF\xFF\xFF' # Заголовок
+ b'redirect\x00' # Команда
+ b'185.97.255.43:27017\00' # Новый адрес
)


def create_info_response():
response = b'\xFF\xFF\xFF\xFF\x49' # Заголовок ответа
response += struct.pack('<b', 17) # Protocol version
response += SERVER_NAME.encode('utf-8') + b'\x00'
response += MAP_NAME.encode('utf-8') + b'\x00'
response += GAME_FOLDER.encode('utf-8') + b'\x00'
response += GAME_NAME.encode('utf-8') + b'\x00'
response += struct.pack('<h', APP_ID)
response += struct.pack('<bbbb', 0, MAX_PLAYERS, BOTS, SERVER_TYPE[0])
response += struct.pack('<bb', ENVIRONMENT[0], VISIBILITY)
response += struct.pack('<b', VAC)
response += b'\x00' # No ETV
return response


def handle_redirect():
# return HEADER_REDIRECT + f"{REDIRECT_IP}:{REDIRECT_PORT}".encode()
pass


def run_fake_server(FAKE_SERVER_PORT):
with socket.socket(socket.AF_INET, socket.SOCK_DGRAM) as sock:
try:
sock.bind((FAKE_SERVER_IP, FAKE_SERVER_PORT))
print(f"Сервер запущен на {FAKE_SERVER_IP}:{FAKE_SERVER_PORT}")

while True:
data, addr = sock.recvfrom(1024)
print(f"Пакет от {addr[0]}:{addr[1]} [{len(data)} байт]")

print(data)

if data in INFO_QUERIES:
sock.sendto(create_info_response(), addr)
print(f"Ответил на A2S_INFO {addr[0]}")
elif b'getchallenge' in data:
if b'steam' in data:
sock.sendto(SERVER_TOKEN_STEAM, addr)
print("Отправляю токен для стим")
else:
sock.sendto(SERVER_TOKEN_A2S, addr)
print("Отправляю токен для A2C")

if b'\xff\xff\xff\xffX' in data:
# sock.sendto(b'\xff\xff\xff\xffInvalid query', addr)
print("Мистический пакет, ignore")
sock.sendto(b'\xff\xff\xff\xff', addr)

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