1#!/usr/bin/env python
2#
3# Send/receive UDP multicast packets.
4# Requires that your OS kernel supports IP multicast.
5#
6# Usage:
7#   mcast -s (sender, IPv4)
8#   mcast -s -6 (sender, IPv6)
9#   mcast    (receivers, IPv4)
10#   mcast  -6  (receivers, IPv6)
11
12MYPORT = 8123
13MYGROUP_4 = '225.0.0.250'
14MYGROUP_6 = 'ff15:7079:7468:6f6e:6465:6d6f:6d63:6173'
15MYTTL = 1 # Increase to reach other networks
16
17import time
18import struct
19import socket
20import sys
21
22def main():
23    group = MYGROUP_6 if "-6" in sys.argv[1:] else MYGROUP_4
24
25    if "-s" in sys.argv[1:]:
26        sender(group)
27    else:
28        receiver(group)
29
30
31def sender(group):
32    addrinfo = socket.getaddrinfo(group, None)[0]
33
34    s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)
35
36    # Set Time-to-live (optional)
37    ttl_bin = struct.pack('@i', MYTTL)
38    if addrinfo[0] == socket.AF_INET: # IPv4
39        s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl_bin)
40    else:
41        s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, ttl_bin)
42
43    while True:
44        data = repr(time.time())
45        s.sendto(data + '\0', (addrinfo[4][0], MYPORT))
46        time.sleep(1)
47
48
49def receiver(group):
50    # Look up multicast group address in name server and find out IP version
51    addrinfo = socket.getaddrinfo(group, None)[0]
52
53    # Create a socket
54    s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)
55
56    # Allow multiple copies of this program on one machine
57    # (not strictly needed)
58    s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
59
60    # Bind it to the port
61    s.bind(('', MYPORT))
62
63    group_bin = socket.inet_pton(addrinfo[0], addrinfo[4][0])
64    # Join group
65    if addrinfo[0] == socket.AF_INET: # IPv4
66        mreq = group_bin + struct.pack('=I', socket.INADDR_ANY)
67        s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
68    else:
69        mreq = group_bin + struct.pack('@I', 0)
70        s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)
71
72    # Loop, printing any data we receive
73    while True:
74        data, sender = s.recvfrom(1500)
75        while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
76        print (str(sender) + '  ' + repr(data))
77
78
79if __name__ == '__main__':
80    main()
81