Initial revision

Demo/sockets/mcast.py

+# Send/receive UDP multicast packets (SGI)
+# After /usr/people/4Dgifts/examples/network/mcast.c
+# Usage:
+#   mcast -s (sender)
+#   mcast    (receivers)
+
+MYPORT = 8123
+MYGROUP_BYTES = 225, 0, 0, 250
+
+import sys
+import time
+import struct
+from socket import *
+from SOCKET import *
+from IN import *
+
+sender = (sys.argv[1:2] == ['-s'])
+
+s = socket(AF_INET, SOCK_DGRAM)
+
+if sender:
+	# Ugly: construct decimal IP address string from MYGROUP_BYTES
+	mygroup = ''
+	for byte in MYGROUP_BYTES: mygroup = mygroup + '.' + `byte`
+	mygroup = mygroup[1:]
+	ttl = struct.pack('b', 1)		# Time-to-live
+	s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
+	while 1:
+		data = `time.time()` + '\n'
+		s.sendto(data, (mygroup, MYPORT))
+		time.sleep(5)
+else:
+	# Bind the socket to my port
+	s.bind('', MYPORT)
+
+	# Allow multiple copies of this program on one machine
+	s.setsockopt(SOL_SOCKET, SO_REUSEPORT, 1) # (Not strictly needed)
+
+	# Ugly: construct binary group address from MYGROUP_BYTES
+	grpaddr = 0
+	for byte in MYGROUP_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)
+
+	# 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`