mcast.py :  » Language-Interface » ChinesePython » chinesepython2.1.3-0.4 » Demo » sockets » Python Open Source

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Python Open Source » Language Interface » ChinesePython 
ChinesePython » chinesepython2.1.3 0.4 » Demo » sockets » mcast.py
# Send/receive UDP multicast packets.
# Requires that your OS kernel supports IP multicast.
# This is built-in on SGI, still optional for most other vendors.
#
# Usage:
#   mcast -s (sender)
#   mcast -b (sender, using broadcast instead multicast)
#   mcast    (receivers)

MYPORT = 8123
MYGROUP = '225.0.0.250'

import sys
import time
import struct
import regsub
from socket import *


# Main program
def main():
  flags = sys.argv[1:]
  #
  if flags:
    sender(flags[0])
  else:
    receiver()


# Sender subroutine (only one per local area network)
def sender(flag):
  s = socket(AF_INET, SOCK_DGRAM)
  if flag == '-b':
    s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
    mygroup = '<broadcast>'
  else:
    mygroup = MYGROUP
    ttl = struct.pack('b', 1)    # Time-to-live
    s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
  while 1:
    data = `time.time()`
##    data = data + (1400 - len(data)) * '\0'
    s.sendto(data, (mygroup, MYPORT))
    time.sleep(1)


# Receiver subroutine (as many as you like)
def receiver():
  # Open and initialize the socket
  s = openmcastsock(MYGROUP, MYPORT)
  #
  # Loop, printing any data we receive
  while 1:
    data, sender = s.recvfrom(1500)
    while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
    print sender, ':', `data`


# Open a UDP socket, bind it to a port and select a multicast group
def openmcastsock(group, port):
  # Import modules used only here
  import string
  import struct
  #
  # Create a socket
  s = socket(AF_INET, SOCK_DGRAM)
  #
  # Allow multiple copies of this program on one machine
  # (not strictly needed)
  s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
  #
  # Bind it to the port
  s.bind(('', port))
  #
  # Look up multicast group address in name server
  # (doesn't hurt if it is already in ddd.ddd.ddd.ddd format)
  group = gethostbyname(group)
  #
  # Construct binary group address
  bytes = map(int, string.split(group, "."))
  grpaddr = 0
  for byte in bytes: grpaddr = (grpaddr << 8) | byte
  #
  # Construct struct mreq from grpaddr and ifaddr
  ifaddr = INADDR_ANY
  mreq = struct.pack('ll', htonl(grpaddr), htonl(ifaddr))
  #
  # Add group membership
  s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
  #
  return s


main()
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