[ipv6]: 8224014: Don't run test/jdk/java/net/NetworkInterface/IPv4Only.java in IPv6 only environment

[Arthur Eubanks]

*From: *Chris Hegarty <chris.hegarty at oracle.com>
*Date: *Thu, May 16, 2019 at 3:52 AM
*To: *Arthur Eubanks
*Cc: *OpenJDK Network Dev list

Arthur,
>
> On 16 May 2019, at 00:24, Arthur Eubanks <aeubanks at google.com> wrote:
>
> webrev: http://cr.openjdk.java.net/~aeubanks/8224014/webrev.00/
> bug: https://bugs.openjdk.java.net/browse/JDK-8224014
>
> In https://bugs.openjdk.java.net/browse/JDK-8220673, I missed
> skipping test/jdk/java/net/NetworkInterface/IPv4Only.java when running in
> an IPv6 only environment. It should have a call to
> IPSupport.throwSkippedExceptionIfNonOperational().
>
>
> After the change for 8223532 in NetworkInterface.c, it is no longer
> required that AF_INET sockets be able to be created, coupled with
> -Djava.net.preferIPv4Stack=true, enumInterfaces may return NULL, which
> in turn bubbles up to the Java layer, in this case getNetworkInterfaces,
> as null ( rather than a collection containing the interfaces ).
>
> The specification for NetworkInterface::getNetworkInterfaces guarantees
> that there be at least one element in the returned collection, but there
> cannot be since the system is mis-configured ( the underlying platform
> is IPv6-only coupled with -Djava.net.preferIPv4Stack=true ). The only
> sensible thing for the NetworkInterface implementation to do is to throw
> an exception ( which is perfectly fine as per its specification,
> "java.net.SocketException: No network interfaces configured" ).
>
> Rather than skipping the test, which will clearly work, an alternative
> is to ensure that an exception is thrown for this case, e.g.
>
>     if (IPSupport.hasIPv4()) {
>         out.println("Testing IPv4");
>         Enumeration<NetworkInterface> nifs =
> NetworkInterface.getNetworkInterfaces();
>         while (nifs.hasMoreElements()) {
>             NetworkInterface nif = nifs.nextElement();
>             Enumeration<InetAddress> addrs = nif.getInetAddresses();
>             while (addrs.hasMoreElements()) {
>                InetAddress hostAddr = addrs.nextElement();
>                if ( hostAddr instanceof Inet6Address ){
>                     throw new RuntimeException( "NetworkInterfaceV6List
> failed - found v6 address " + hostAddr.getHostAddress() );
>                }
>             }
>         }
>     } else {
>         // No platform IPv4 support & -Djava.net.preferIPv4Stack=true
>         out.println("Testing without IPv4 support");
>         try {
>             NetworkInterface.getNetworkInterfaces();
>         } catch (SocketException expected) {
>             out.println("caught expected exception: " + expected);
>         }
>
>         try {
>             NetworkInterface.networkInterfaces();
>         } catch (SocketException expected) {
>             out.println("caught expected exception: " + expected);
>         }
>     }
>
> -Chris.
>
>
Good idea, done. PTAL. Tested with and without IPv4 support.
http://cr.openjdk.java.net/~aeubanks/8224014/webrev.01/index.html
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