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94 lines
2.1 KiB
Python
Executable file
94 lines
2.1 KiB
Python
Executable file
# Send/receive UDP multicast packets.
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# Requires that your OS kernel supports IP multicast.
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# This is built-in on SGI, still optional for most other vendors.
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#
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# Usage:
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# mcast -s (sender)
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# mcast -b (sender, using broadcast instead multicast)
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# mcast (receivers)
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MYPORT = 8123
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MYGROUP = '225.0.0.250'
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import sys
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import time
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import struct
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import regsub
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from socket import *
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# Main program
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def main():
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flags = sys.argv[1:]
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#
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if flags:
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sender(flags[0])
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else:
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receiver()
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# Sender subroutine (only one per local area network)
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def sender(flag):
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s = socket(AF_INET, SOCK_DGRAM)
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if flag == '-b':
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s.setsockopt(SOL_SOCKET, SO_BROADCAST, 1)
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mygroup = '<broadcast>'
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else:
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mygroup = MYGROUP
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ttl = struct.pack('b', 1) # Time-to-live
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s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
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while 1:
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data = `time.time()`
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## 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)
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def receiver():
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# Open and initialize the socket
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s = openmcastsock(MYGROUP, MYPORT)
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#
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# Loop, printing any data we receive
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while 1:
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data, sender = s.recvfrom(1500)
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while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
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print sender, ':', `data`
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# Open a UDP socket, bind it to a port and select a multicast group
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def openmcastsock(group, port):
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# Import modules used only here
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import string
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import struct
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#
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# Create a socket
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s = socket(AF_INET, SOCK_DGRAM)
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#
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# Allow multiple copies of this program on one machine
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# (not strictly needed)
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s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
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#
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# Bind it to the port
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s.bind(('', port))
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#
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# Look up multicast group address in name server
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# (doesn't hurt if it is already in ddd.ddd.ddd.ddd format)
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group = gethostbyname(group)
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#
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# Construct binary group address
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bytes = map(int, string.split(group, "."))
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grpaddr = 0
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for byte in bytes: grpaddr = (grpaddr << 8) | byte
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#
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# Construct struct mreq from grpaddr and ifaddr
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ifaddr = INADDR_ANY
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mreq = struct.pack('ll', htonl(grpaddr), htonl(ifaddr))
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#
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# Add group membership
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s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
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#
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return s
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main()
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