Index: README
===================================================================
--- README	(revision 70006)
+++ README	(working copy)
@@ -5,17 +5,10 @@
 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.)
-
Index: mcast.py
===================================================================
--- mcast.py	(revision 70006)
+++ mcast.py	(working copy)
@@ -1,14 +1,16 @@
 # 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 time
@@ -18,76 +20,64 @@
 
 # Main program
 def main():
-    flags = sys.argv[1:]
+    group = MYGROUP_6 if "-6" in sys.argv[1:] else MYGROUP_4
     #
-    if flags:
-        sender(flags[0])
+    if "-s" in sys.argv[1:]:
+        sender(group)
     else:
-        receiver()
+        receiver(group)
 
 
-# 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>'
+# Sender subroutine (typically one per local area network)
+def sender(group):
+    addrinfo = getaddrinfo(group, None)[0]
+    #
+    s = socket(addrinfo[0], SOCK_DGRAM)
+    #
+    # Set Time-to-live (optional)
+    ttl_bin = struct.pack('@i', MYTTL)
+    if addrinfo[0] == AF_INET: # IPv4
+        s.setsockopt(IPPROTO_IP, 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(IPPROTO_IPV6, 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', (addrinfo[4][0], MYPORT))
         time.sleep(1)
 
 
 # Receiver subroutine (as many as you like)
-def receiver():
-    # Open and initialize the socket
-    s = openmcastsock(MYGROUP, MYPORT)
+def receiver(group):
+    # Look up multicast group address in name server and find out IP version
+    addrinfo = getaddrinfo(group, None)[0]
     #
-    # 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)
-
-
-# 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(addrinfo[0], SOCK_DGRAM)
     #
     # Allow multiple copies of this program on one machine
     # (not strictly needed)
     s.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1)
     #
     # Bind it to the port
-    s.bind(('', port))
+    s.bind(('', MYPORT))
     #
-    # Look up multicast group address in name server
-    # (doesn't hurt if it is already in ddd.ddd.ddd.ddd format)
-    group = gethostbyname(group)
+    group_bin = inet_pton(addrinfo[0], addrinfo[4][0])
+    # Join group
+    if addrinfo[0] == AF_INET: # IPv4
+        mreq = group_bin + struct.pack('!I', INADDR_ANY)
+        s.setsockopt(IPPROTO_IP, IP_ADD_MEMBERSHIP, mreq)
+    else: # IPv6
+        mreq = group_bin + struct.pack('@I', 0)
+        s.setsockopt(IPPROTO_IPV6, IPV6_JOIN_GROUP, mreq)
     #
-    # 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
+    # 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))
 
 
 main()