Valheim / Valve Game Networking Sockets server online checker

server_online_check.py

#!/usr/bin/env python3

# Valheim/Valve Game Networking Sockets server online checker
# Zini, 2021

# Usage:
# ./server_online_check.py hostname_or_ip port
# Hostname defaults to localhost, port defaults to 2456

import socket
import sys

def is_server_online(server_addr) -> bool:
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

    # Create k_ESteamNetworkingUDPMsg_ConnectionClosed packet with zero "to_connection_id".
    # 24 05 00 25 00 00 00 00
    # ^  ^---^ ^  ^---------^
    # |  |     |  |
    # |  |     |  32-bit "to_connection_id"
    # |  |     |
    # |  |     Protobuf field ID (0 0100 101)
    # |  |                          ^    ^
    # |  |                          |    |
    # |  |                          |    Wire type (5, 32-bit (fixed32))
    # |  |                          Field number (4)
    # |  Message length (Little endian)
    # Message ID (ConnectionClosed)

    connclosed_pkt = b"\x24\x05\x00\x25\x00\x00\x00\x00"
    # Pad the packet to be 512 bytes
    padded = connclosed_pkt + (b"\x00" * (512 - len(connclosed_pkt)))

    # Send to the server
    sock.sendto(padded, server_addr)
    sock.settimeout(3.0)
    try:
        resp, _ = sock.recvfrom(1)
    except:
        return False

    if resp == b"\x25":
        # Server using Valve Game Networking Sockets is alive at this address.
        # The server responded with k_ESteamNetworkingUDPMsg_NoConnection, indicating
        # that there is no connection to close. The server doesn't want a reply to this message.
        return True

    # Server responded, but with something else
    # There is something online, but it most likely isn't using Valve Game Networking Sockets
    return False

if __name__ == "__main__":
    server_addr = ("localhost", 2456)

    if len(sys.argv) == 2:
        server_addr = (sys.argv[1], server_addr[1])
    elif len(sys.argv) > 2:
        server_addr = (sys.argv[1], int(sys.argv[2]))

    if is_server_online(server_addr):
        print("Server online")
        sys.exit(0)
    else:
        print("Server offline")
        sys.exit(1)