Issue 5379 - applies patch supplied by philipp hagemeister to fix

many problems with the ancient mcast.py demo code.

Demo/sockets/README

@@ -5,17 +5,10 @@ echosvr.py		About the simplest TCP server possible.
 finger.py		Client for the 'finger' protocol.
 ftp.py			A very simple ftp client.
 gopher.py		A simple gopher client.
+mcast.py		IPv4/v6 multicast example
 radio.py		Receive time broadcasts from broadcast.py.
 telnet.py		Client for the 'telnet' protocol.
 throughput.py		Client and server to measure TCP throughput.
 unixclient.py		Unix socket example, client side
 unixserver.py		Unix socket example, server side
 udpecho.py		Client and server for the UDP echo protocol.
-
-The following file is only relevant on SGI machines (or other systems
-that support multicast):
-
-mcast.py		A Python translation of
-			/usr/people/4Dgifts/examples/network/mcast.c
-			(Note that IN.py is in ../../lib/sgi.)
-

Demo/sockets/mcast.py

+#!/usr/bin/env python
+#
 # 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)
+#   mcast -s (sender, IPv4)
+#   mcast -s -6 (sender, IPv6)
+#   mcast    (receivers, IPv4)
+#   mcast  -6  (receivers, IPv6)
 
 MYPORT = 8123
-MYGROUP = '225.0.0.250'
+MYGROUP_4 = '225.0.0.250'
+MYGROUP_6 = 'ff15:7079:7468:6f6e:6465:6d6f:6d63:6173'
+MYTTL = 1 # Increase to reach other networks
 
-import sys
+import ipaddr
 import time
 import struct
-from socket import *
-
+import socket
+import sys
 
-# Main program
 def main():
-    flags = sys.argv[1:]
-    #
-    if flags:
-        sender(flags[0])
+    group = MYGROUP_6 if "-6" in sys.argv[1:] else MYGROUP_4
+
+    if "-s" in sys.argv[1:]:
+        sender(group)
+    else:
+        receiver(group)
+
+def _sockfam(ip):
+    """Returns the family argument of socket.socket"""
+    if ip.version == 4:
+        return socket.AF_INET
+    elif ip.version == 6:
+        return socket.AF_INET6
     else:
-        receiver()
+        raise ValueError('IPv' + ip.version + ' is not supported')
+
+def sender(group):
+    group_ip = ipaddr.IP(group)
 
+    s = socket.socket(_sockfam(group_ip), socket.SOCK_DGRAM)
 
-# 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>'
+    # Set Time-to-live (optional)
+    ttl_bin = struct.pack('@i', MYTTL)
+    if group_ip.version == 4:
+        s.setsockopt(socket.IPPROTO_IP, socket.IP_MULTICAST_TTL, ttl_bin)
     else:
-        mygroup = MYGROUP
-        ttl = struct.pack('b', 1)               # Time-to-live
-        s.setsockopt(IPPROTO_IP, IP_MULTICAST_TTL, ttl)
-    while 1:
+        s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_MULTICAST_HOPS, ttl_bin)
+
+    while True:
         data = repr(time.time())
-##              data = data + (1400 - len(data)) * '\0'
-        s.sendto(data, (mygroup, MYPORT))
+        s.sendto(data + '\0', (group_ip.ip_ext_full, 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)
+def receiver(group):
+    group_ip = ipaddr.IP(group)
 
-
-# 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)
-    #
+    s = socket.socket(_sockfam(group_ip), socket.SOCK_DGRAM)
+
     # Allow multiple copies of this program on one machine
     # (not strictly needed)
-    s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
-    #
+    s.setsockopt(socket.SOL_SOCKET, 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 = 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()
+    s.bind(('', MYPORT))
+
+    # Join group
+    if group_ip.version == 4: # IPv4
+        mreq = group_ip.packed + struct.pack('=I', socket.INADDR_ANY)
+        s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
+    else:
+        mreq = group_ip.packed + struct.pack('@I', 0)
+        s.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_JOIN_GROUP, mreq)
+
+    # Loop, printing any data we receive
+    while True:
+        data, sender = s.recvfrom(1500)
+        while data[-1:] == '\0': data = data[:-1] # Strip trailing \0's
+        print (str(sender) + '  ' + repr(data))
+
+
+if __name__ == '__main__':
+    main()