#!/usr/bin/env python3

#
# @RDE_HEADER@
# $Id$
# $HeadURL$
# $Author$
# Created by Christian Fröbel, NLE, 2019-08-08
#

import socket
import struct
from contextlib import contextmanager
from argparse import ArgumentParser, RawDescriptionHelpFormatter
import sys

# struct in_addr
# {
#     uint32_t       s_addr;     /* address in network byte order */
# };

# struct ip_mreqn
# {
#     struct in_addr imr_multiaddr; /* IP multicast group address */
#     struct in_addr imr_address;   /* IP address of local interface */
#     int            imr_ifindex;   /* interface index */
# };

def _createBoundSocket(multicastGroup, multicastPort, interface):
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    
    s.bind((multicastGroup, multicastPort))
    
    mreqn = struct.pack('4s4si', socket.inet_aton(multicastGroup), socket.inet_aton(interface), 0)
    s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreqn)
    
    return s


def _receive(s):
    while True:
        buf, address = s.recvfrom(4096)
        print('received {} bytes from {}'.format(len(buf), address))


def _main():
    args = _parseCmdLine()
    with autoClose(_createBoundSocket(args.group, args.port, args.interface)) as s:
        _receive(s)

    
@contextmanager
def autoClose(resource):
    try:
        yield resource
    finally:
        resource.close()

def _parseCmdLine():
    parser = ArgumentParser(description='Tool to receive multicast traffic', formatter_class=RawDescriptionHelpFormatter)
    parser.add_argument('--group', '-g', required=True, help='multicast group')
    parser.add_argument('--port', '-p', type=int, required=True, help='port')
    parser.add_argument('--interface', '-i', default='0.0.0.0', help='address of interface to listen on; default 0.0.0.0')
    return parser.parse_args()

if __name__ == '__main__':
    _main()