import socket
import struct

def start_server(ip, port):
    server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM, socket.IPPROTO_UDP)
    server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)  # Enable port reusage
    server_socket.bind(('', port))  # Bind to the port, not the multicast IP
    print(f"UDP server listening on {ip}:{port}")
    
    # Join the multicast group
    mreq = struct.pack("4sl", socket.inet_aton(ip), socket.INADDR_ANY)
    server_socket.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)

    while True:
        data, addr = server_socket.recvfrom(1024)  # buffer size is 1024 bytes
        print(f"received message: {data} from {addr}")

if __name__ == "__main__":
    start_server("239.1.2.3", 1234)