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# 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
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 = repr(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, ':', repr(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 = list(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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