cpython/Demo/sockets/mcast.py

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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.
#
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# Usage:
# mcast -s (sender)
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# mcast -b (sender, using broadcast instead multicast)
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# mcast (receivers)
MYPORT = 8123
MYGROUP = '225.0.0.250'
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import sys
import time
import struct
import regsub
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from socket import *
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# Main program
def main():
flags = sys.argv[1:]
#
if flags:
sender(flags[0])
else:
receiver()
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# Sender subroutine (only one per local area network)
def sender(flag):
s = socket(AF_INET, SOCK_DGRAM)
if flag == '-b':
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s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
mygroup = '<broadcast>'
else:
mygroup = MYGROUP
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ttl = struct.pack('b', 1) # Time-to-live
s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
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while 1:
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data = `time.time()`
## data = data + (1400 - len(data)) * '\0'
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s.sendto(data, (mygroup, MYPORT))
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time.sleep(1)
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# 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 regsub
import struct
#
# Create a socket
s = socket(AF_INET, SOCK_DGRAM)
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#
# Allow multiple copies of this program on one machine
# (not strictly needed)
s.setsockopt(SOL_SOCKET, SO_REUSEPORT, 1)
#
# Bind it to the port
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s.bind(('', port))
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#
# Look up multicast group address in name server
# (doesn't hurt if it is already in ddd.ddd.ddd.ddd format)
group = gethostbyname(group)
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#
# Construct binary group address
bytes = eval(regsub.gsub('\.', ',', group))
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grpaddr = 0
for byte in bytes: grpaddr = (grpaddr << 8) | byte
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#
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# Construct struct mreq from grpaddr and ifaddr
ifaddr = INADDR_ANY
mreq = struct.pack('ll', grpaddr, ifaddr)
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#
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# Add group membership
s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
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#
return s
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main()