1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
|
# 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 regsub
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_REUSEPORT, 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 = eval(regsub.gsub('\.', ',', 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', grpaddr, ifaddr)
#
# Add group membership
s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
#
return s
main()
|
