#!/usr/bin/env python3

"""
Send/receive UDP multicast packets.
Requires that your OS kernel supports IP multicast.

Usage:
 mcast -s (sender, IPv4)
 mcast -s -6 (sender, IPv6)
 mcast (receivers, IPv4)
 mcast -6 (receivers, IPv6)
"""

MYPORT = 8123
MYGROUP_4 = '225.0.0.250'
MYGROUP_6 = 'ff15:7079:7468:6f6e:6465:6d6f:6d63:6173'
MYTTL = 1 # Increase to reach other networks

import time
import struct
import socket
import sys

def main():
 group = MYGROUP_6 if "-6" in sys.argv[1:] else MYGROUP_4

 if "-s" in sys.argv[1:]:
 sender(group)
 else:
 receiver(group)


def sender(group):
 addrinfo = socket.getaddrinfo(group, None)[0]

 s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)

 # Set Time-to-live (optional)
 ttl_bin = struct.pack('@i', MYTTL)
 if addrinfo[0] == socket.AF_INET: # IPv4
 s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl_bin)
 else:
 s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, ttl_bin)

 while True:
 data = repr(time.time()).encode('utf-8') + b'0円'
 s.sendto(data, (addrinfo[4][0], MYPORT))
 time.sleep(1)


def receiver(group):
 # Look up multicast group address in name server and find out IP version
 addrinfo = socket.getaddrinfo(group, None)[0]

 # Create a socket
 s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)

 # Allow multiple copies of this program on one machine
 # (not strictly needed)
 s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

 # Bind it to the port
 s.bind(('', MYPORT))

 group_bin = socket.inet_pton(addrinfo[0], addrinfo[4][0])
 # Join group
 if addrinfo[0] == socket.AF_INET: # IPv4
 mreq = group_bin + struct.pack('=I', socket.INADDR_ANY)
 s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
 else:
 mreq = group_bin + struct.pack('@I', 0)
 s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)

 # Loop, printing any data we receive
 while True:
 data, sender = s.recvfrom(1500)
 while data[-1:] == '0円': data = data[:-1] # Strip trailing 0円's
 print(str(sender) + ' ' + repr(data))


if __name__ == '__main__':
 main()