import socket
import struct
import sys


def get_udp_header_bytes(payload):
    sport = 15843
    dport = 42849
    length = 8 + len(payload)
    checksum = 0
    udp_header = struct.pack('!HHHH', sport, dport, length, checksum)
    return udp_header


def get_payload_bytes():
    return b"moo"


def say_moo(ip):
    payload = get_payload_bytes()
    udp_header = get_udp_header_bytes(payload)

    # Concatenate the bytes of all the layers
    packet = udp_header + payload

    s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_UDP)
    s.sendto(packet, (ip, 0))
    s.close()


if __name__ == "__main__":
    if len(sys.argv) < 2:
        print("Usage: cow.py ip", file=sys.stderr)
        sys.exit(1)
    ip = sys.argv[1]
    say_moo(ip)