Demo/sockets/mcast.py

   1 # Send/receive UDP multicast packets.
   2 # Requires that your OS kernel supports IP multicast.
   3 # This is built-in on SGI, still optional for most other vendors.
   4 #
   5 # Usage:
   6 #   mcast -s (sender)
   7 #   mcast -b (sender, using broadcast instead multicast)
   8 #   mcast    (receivers)
   9
  10 MYPORT = 8123
  11 MYGROUP = '225.0.0.250'
  12
  13 import sys
  14 import time
  15 import struct
  16 import regsub
  17 from socket import *
  18
  19
  20 # Main program
  21 def main():
  22         flags = sys.argv[1:]
  23         #
  24         if flags:
  25                 sender(flags[0])
  26         else:
  27                 receiver()
  28
  29
  30 # Sender subroutine (only one per local area network)
  31 def sender(flag):
  32         s = socket(AF_INET, SOCK_DGRAM)
  33         if flag == '-b':
  34                 s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
  35                 mygroup = '<broadcast>'
  36         else:
  37                 mygroup = MYGROUP
  38                 ttl = struct.pack('b', 1)               # Time-to-live
  39                 s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
  40         while 1:
  41                 data = `time.time()`
  42 ##              data = data + (1400 - len(data)) * '\0'
  43                 s.sendto(data, (mygroup, MYPORT))
  44                 time.sleep(1)
  45
  46
  47 # Receiver subroutine (as many as you like)
  48 def receiver():
  49         # Open and initialize the socket
  50         s = openmcastsock(MYGROUP, MYPORT)
  51         #
  52         # Loop, printing any data we receive
  53         while 1:
  54                 data, sender = s.recvfrom(1500)
  55                 while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
  56                 print sender, ':', `data`
  57
  58
  59 # Open a UDP socket, bind it to a port and select a multicast group
  60 def openmcastsock(group, port):
  61         # Import modules used only here
  62         import regsub
  63         import struct
  64         #
  65         # Create a socket
  66         s = socket(AF_INET, SOCK_DGRAM)
  67         #
  68         # Allow multiple copies of this program on one machine
  69         # (not strictly needed)
  70         s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
  71         #
  72         # Bind it to the port
  73         s.bind(('', port))
  74         #
  75         # Look up multicast group address in name server
  76         # (doesn't hurt if it is already in ddd.ddd.ddd.ddd format)
  77         group = gethostbyname(group)
  78         #
  79         # Construct binary group address
  80         bytes = eval(regsub.gsub('\.', ',', group))
  81         grpaddr = 0
  82         for byte in bytes: grpaddr = (grpaddr << 8) | byte
  83         #
  84         # Construct struct mreq from grpaddr and ifaddr
  85         ifaddr = INADDR_ANY
  86         mreq = struct.pack('ll', grpaddr, ifaddr)
  87         #
  88         # Add group membership
  89         s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
  90         #
  91         return s
  92
  93
  94 main()