1  #!/usr/bin/env python3
       2  
       3  """
       4  Send/receive UDP multicast packets.
       5  Requires that your OS kernel supports IP multicast.
       6  
       7  Usage:
       8    mcast -s (sender, IPv4)
       9    mcast -s -6 (sender, IPv6)
      10    mcast    (receivers, IPv4)
      11    mcast  -6  (receivers, IPv6)
      12  """
      13  
      14  MYPORT = 8123
      15  MYGROUP_4 = '225.0.0.250'
      16  MYGROUP_6 = 'ff15:7079:7468:6f6e:6465:6d6f:6d63:6173'
      17  MYTTL = 1 # Increase to reach other networks
      18  
      19  import time
      20  import struct
      21  import socket
      22  import sys
      23  
      24  def main():
      25      group = MYGROUP_6 if "-6" in sys.argv[1:] else MYGROUP_4
      26  
      27      if "-s" in sys.argv[1:]:
      28          sender(group)
      29      else:
      30          receiver(group)
      31  
      32  
      33  def sender(group):
      34      addrinfo = socket.getaddrinfo(group, None)[0]
      35  
      36      s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)
      37  
      38      # Set Time-to-live (optional)
      39      ttl_bin = struct.pack('@i', MYTTL)
      40      if addrinfo[0] == socket.AF_INET: # IPv4
      41          s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl_bin)
      42      else:
      43          s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, ttl_bin)
      44  
      45      while True:
      46          data = repr(time.time()).encode('utf-8') + b'\0'
      47          s.sendto(data, (addrinfo[4][0], MYPORT))
      48          time.sleep(1)
      49  
      50  
      51  def receiver(group):
      52      # Look up multicast group address in name server and find out IP version
      53      addrinfo = socket.getaddrinfo(group, None)[0]
      54  
      55      # Create a socket
      56      s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)
      57  
      58      # Allow multiple copies of this program on one machine
      59      # (not strictly needed)
      60      s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
      61  
      62      # Bind it to the port
      63      s.bind(('', MYPORT))
      64  
      65      group_bin = socket.inet_pton(addrinfo[0], addrinfo[4][0])
      66      # Join group
      67      if addrinfo[0] == socket.AF_INET: # IPv4
      68          mreq = group_bin + struct.pack('=I', socket.INADDR_ANY)
      69          s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
      70      else:
      71          mreq = group_bin + struct.pack('@I', 0)
      72          s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)
      73  
      74      # Loop, printing any data we receive
      75      while True:
      76          data, sender = s.recvfrom(1500)
      77          while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
      78          print(str(sender) + '  ' + repr(data))
      79  
      80  
      81  if __name__ == '__main__':
      82      main()