8241786: Improve heuristic to determine default network interface on …

…macOS

DefaultInetrface.getDefault is updated to prefer interfaces that have non link-local addresses. NetworkConfiguration is updated to skip interface that have only link-local addresses, whether IPv4 or IPv6, for multicasting.

Reviewed-by: chegar, alanb

src/java.base/macosx/classes/java/net/DefaultInterface.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -54,11 +54,30 @@ static NetworkInterface getDefault() {
     /**
      * Choose a default interface. This method returns the first interface that
      * is both "up" and supports multicast. This method chooses an interface in
-     * order of preference:
-     * 1. neither loopback nor point to point
-     *    ( prefer interfaces with dual IP support )
-     * 2. point to point
-     * 3. loopback
+     * order of preference, using the following algorithm:
+     *
+     * <pre>
+     * Interfaces that are down, or don't support multicasting, are skipped.
+     * In steps 1-4 below, PPP and loopback interfaces are skipped.
+     *
+     * 1. The first interface that has at least an IPv4 address, and an IPv6 address,
+     *    and a non link-local IP address, is picked.
+     *
+     * 2. If none is found, then the first interface that has at least an
+     *    IPv4 address, and an IPv6 address is picked.
+     *
+     * 3. If none is found, then the first interface that has at least a
+     *    non link local IP address is picked.
+     *
+     * 4. If none is found, then the first non loopback and non PPP interface
+     *    is picked.
+     *
+     * 5. If none is found then first PPP interface is picked.
+     *
+     * 6. If none is found, then the first loopback interface is picked.
+     *
+     * 7. If none is found, then null is returned.
+     * </pre>
      *
      * @return  the chosen interface or {@code null} if there isn't a suitable
      *          default
@@ -74,6 +93,8 @@ private static NetworkInterface chooseDefaultInterface() {
         }
 
         NetworkInterface preferred = null;
+        NetworkInterface dual = null;
+        NetworkInterface nonLinkLocal = null;
         NetworkInterface ppp = null;
         NetworkInterface loopback = null;
 
@@ -83,7 +104,7 @@ private static NetworkInterface chooseDefaultInterface() {
                 if (!ni.isUp() || !ni.supportsMulticast())
                     continue;
 
-                boolean ip4 = false, ip6 = false;
+                boolean ip4 = false, ip6 = false, isNonLinkLocal = false;
                 PrivilegedAction<Enumeration<InetAddress>> pa = ni::getInetAddresses;
                 Enumeration<InetAddress> addrs = AccessController.doPrivileged(pa);
                 while (addrs.hasMoreElements()) {
@@ -94,6 +115,9 @@ private static NetworkInterface chooseDefaultInterface() {
                         } else if (addr instanceof Inet6Address) {
                             ip6 = true;
                         }
+                        if (!addr.isLinkLocalAddress()) {
+                            isNonLinkLocal = true;
+                        }
                     }
                 }
 
@@ -104,8 +128,13 @@ private static NetworkInterface chooseDefaultInterface() {
                     // point-to-point interface
                     if (preferred == null) {
                         preferred = ni;
-                    } else if (ip4 && ip6){
-                        return ni;
+                    }
+                    if (ip4 && ip6) {
+                        if (isNonLinkLocal) return ni;
+                        if (dual == null) dual = ni;
+                    }
+                    if (nonLinkLocal == null) {
+                        if (isNonLinkLocal) nonLinkLocal = ni;
                     }
                 }
                 if (ppp == null && isPPP)
@@ -116,7 +145,11 @@ private static NetworkInterface chooseDefaultInterface() {
             } catch (IOException skip) { }
         }
 
-        if (preferred != null) {
+        if (dual != null) {
+            return dual;
+        } else if (nonLinkLocal != null) {
+            return nonLinkLocal;
+        } else if (preferred != null) {
             return preferred;
         } else {
             return (ppp != null) ? ppp : loopback;

test/jdk/java/net/MulticastSocket/SetLoopbackMode.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2002, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -26,11 +26,14 @@
  * @bug 4686717
  * @summary Test MulticastSocket.setLoopbackMode
  * @library /test/lib
+ * @modules java.base/java.net:+open
  * @build jdk.test.lib.NetworkConfiguration
  *        jdk.test.lib.Platform
  * @run main/othervm SetLoopbackMode
  */
 
+import java.lang.reflect.Method;
+import java.lang.reflect.UndeclaredThrowableException;
 import java.net.*;
 import java.io.IOException;
 import jdk.test.lib.NetworkConfiguration;
@@ -99,38 +102,75 @@ public static void main (String args[]) throws Exception {
         int failures = 0;
         NetworkConfiguration nc = NetworkConfiguration.probe();
 
-        MulticastSocket mc = new MulticastSocket();
-        InetAddress grp = InetAddress.getByName("224.80.80.80");
+        try (MulticastSocket mc = new MulticastSocket()) {
+            InetAddress grp = InetAddress.getByName("224.80.80.80");
 
 
-        /*
-         * If IPv6 is available then use IPv6 multicast group - needed
-         * to workaround Linux IPv6 bug whereby !IPV6_MULTICAST_LOOP
-         * doesn't prevent loopback of IPv4 multicast packets.
-         */
+            /*
+             * If IPv6 is available then use IPv6 multicast group - needed
+             * to workaround Linux IPv6 bug whereby !IPV6_MULTICAST_LOOP
+             * doesn't prevent loopback of IPv4 multicast packets.
+             */
 
-        if (canUseIPv6(nc)) {
-            grp = InetAddress.getByName("ff01::1");
-        }
+            if (canUseIPv6(nc)) {
+                System.out.println("IPv6 can be used");
+                grp = InetAddress.getByName("ff01::1");
+            } else {
+                System.out.println("IPv6 cannot be used: using IPv4");
+            }
+            System.out.println("Default network interface: " + DefaultInterface.getDefaultName());
+            System.out.println("\nTest will use multicast group: " + grp);
+            try {
+                System.out.println("NetworkInterface.getByInetAddress(grp): "
+                        + getName(NetworkInterface.getByInetAddress(grp)));
+            } catch (Exception x) {
+                // OK
+            }
+            mc.joinGroup(grp);
 
-        //mc.setNetworkInterface(NetworkInterface.getByInetAddress(lb));
-        System.out.println("\nTest will use multicast group: " + grp);
-        mc.joinGroup(grp);
+            System.out.println("\n******************\n");
 
-        System.out.println("\n******************\n");
+            mc.setLoopbackMode(true);
+            if (test(mc, grp) == FAILED) failures++;
 
-        mc.setLoopbackMode(true);
-        if (test(mc, grp) == FAILED) failures++;
+            System.out.println("\n******************\n");
 
-        System.out.println("\n******************\n");
+            mc.setLoopbackMode(false);
+            if (test(mc, grp) == FAILED) failures++;
 
-        mc.setLoopbackMode(false);
-        if (test(mc, grp) == FAILED) failures++;
+            System.out.println("\n******************\n");
+
+            if (failures > 0) {
+                throw new RuntimeException("Test failed");
+            }
+        }
+    }
 
-        System.out.println("\n******************\n");
+    static String getName(NetworkInterface nif) {
+        return nif == null ? null : nif.getName();
+    }
 
-        if (failures > 0) {
-            throw new RuntimeException("Test failed");
+    static class DefaultInterface {
+        static final Method GET_DEFAULT;
+        static {
+            try {
+                GET_DEFAULT = Class.forName("java.net.DefaultInterface")
+                        .getDeclaredMethod("getDefault");
+                GET_DEFAULT.setAccessible(true);
+            } catch (Exception x) {
+                throw new ExceptionInInitializerError(x);
+            }
+        }
+        static NetworkInterface getDefault() {
+            try {
+                return (NetworkInterface) GET_DEFAULT
+                        .invoke(null);
+            } catch (Exception x) {
+                throw new UndeclaredThrowableException(x);
+            }
+        }
+        static String getDefaultName() {
+            return getName(getDefault());
         }
     }
 }

test/jdk/java/net/MulticastSocket/SetLoopbackModeIPv4.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -23,9 +23,10 @@
 
 /*
  * @test
- * @bug 4686717
+ * @bug 4686717 8241786
  * @summary Test MulticastSocket.setLoopbackMode with IPv4 addresses
  * @library /test/lib
+ * @modules java.base/java.net:+open
  * @build jdk.test.lib.NetworkConfiguration
  *        jdk.test.lib.Platform
  *        SetLoopbackMode