#!/usr/bin/env python
     # encoding: utf-8
     #
     # Copyright (c) 2010 Doug Hellmann.  All rights reserved.
     #
     """Receive multicast messages.
     """
     #end_pymotw_header
     
     import socket
     import struct
     import sys
     
     multicast_group = '224.3.29.71'
     server_address = ('', 10000)
     
     # Create the socket
     sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
     
     # Bind to the server address
     sock.bind(server_address)
     
     # Tell the operating system to add the socket to the multicast group
     # on all interfaces.
     group = socket.inet_aton(multicast_group)
     mreq = struct.pack('4sL', group, socket.INADDR_ANY)
     sock.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
     
     # Receive/respond loop
     while True:
         print >>sys.stderr, '\nwaiting to receive message'
         data, address = sock.recvfrom(1024)
         
         print >>sys.stderr, 'received %s bytes from %s' % (len(data), address)
         print >>sys.stderr, data
     
         print >>sys.stderr, 'sending acknowledgement to', address
         sock.sendto('ack', address)