[jboss-jira] [JBoss JIRA] Created: (JGRP-777) Revisit multicast socket creation code

[Bela Ban (JIRA)]

Revisit multicast socket creation code
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                 Key: JGRP-777
                 URL: http://jira.jboss.com/jira/browse/JGRP-777
             Project: JGroups
          Issue Type: Task
            Reporter: Bela Ban
         Assigned To: Bela Ban
             Fix For: 2.7


[Dieter Cailliau]

I looked into the UDP class (trunk) and found out that the MulticastSocket(port) constructor is used.
This doesn't work well on many linux systems: http://forum.java.sun.com/thread.jspa?threadID=5216130&messageID=9875372 It's not entirely clear who's 'fault' this is, but i have a workaround below.

I experienced this problem in jgroups when i tried to set up 2 distinct processes on the same machine, that use a different stack with different UDP mcast_addr. Still the one process would complain about the other: discard msg from different group.
java 1.5.0_10-b03, jgroups 2.5.0.GA.

The code i use for making MulticastSockets is below. In combination with a default gateway and preferIPv4 this was the only way to make sure that my socket only received datagrams for the group it actually joined. Using the constructor with only a port results in a sokcet receiving ALL datagrams that are multicasted to that port (regardless of the group address it joined!).

Can someone please give some feedback on this, and consider if this is a fix for UDP?

        public static MulticastSocket createMulticastSocket(int TIMEOUT_MS, InetAddress group, int port) {
                MulticastSocket socket = null;
                try {
                        socket = new MulticastSocket(new InetSocketAddress(group, port));
                } catch (BindException e1) {
                        String warn = null == System.getProperty("java.net.preferIPv4Stack") ? "-Djava.net.preferIPv4Stack != true ??" : "java.net.preferIPv4Stack=true";
                        log.warn("Unable to create the multicast socket at address " + group + ":" + port + "; I'll fall back to the windows solution (create the socket with port only) " + warn,e1);
                        // Windows fallback
                        try {
                                socket = new MulticastSocket(new InetSocketAddress(port));
                        } catch (IOException e) {
                                throw new RuntimeException(e1);
                        }
                } catch (Exception e1) {
                        throw new RuntimeException(e1);
                }
                try {
                        socket.setSoTimeout(TIMEOUT_MS);
                        socket.joinGroup(group);
                } catch (Exception e1) {
                        byte[] address = group.getAddress();
                        String ad = address[0] + "." + address[1] + "." + address[2] + "." + address[3] + ":" + port + " " + e1.toString();
                        try {
                                socket.close();
                        } catch(Exception c){
                                log.warn("Ignore exception while closing bad multicast socket: " + c);
                        }
                        throw new RuntimeException(ad,e1);
                }
                return socket;
        }


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