1 /*

     2  * Copyright (c) 2011, 2013, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 

    26 package java.net;

    27 

    28 /**

    29  * Choose a network interface to be the default for

    30  * outgoing IPv6 traffic that does not specify a scope_id (and which needs one).

    31  * We choose the first interface that is up and is (in order of preference):

    32  * 1. neither loopback nor point to point

    33  * 2. point to point

    34  * 3. loopback

    35  * 4. none.

    36  * Platforms that do not require a default interface implement a dummy

    37  * that returns null.

    38  */

    39 

    40 import java.util.Enumeration;

    41 import java.io.IOException;

    42 

    43 class DefaultInterface {

    44 

    45     private static final NetworkInterface defaultInterface =

    46         chooseDefaultInterface();

    47 

    48     static NetworkInterface getDefault() {

    49         return defaultInterface;

    50     }

    51 

    52     /**

    53      * Choose a default interface. This method returns the first interface that

    54      * is both "up" and supports multicast. This method chooses an interface in

    55      * order of preference:

    56      * 1. neither loopback nor point to point

    57      *    ( prefer interfaces with dual IP support )

    58      * 2. point to point

    59      * 3. loopback

    60      *

    61      * @return  the chosen interface or {@code null} if there isn't a suitable

    62      *          default

    63      */

    64     private static NetworkInterface chooseDefaultInterface() {

    65         Enumeration<NetworkInterface> nifs;

    66 

    67         try {

    68            nifs = NetworkInterface.getNetworkInterfaces();

    69         } catch (IOException ignore) {

    70             // unable to enumerate network interfaces

    71             return null;

    72         }

    73 

    74         NetworkInterface preferred = null;

    75         NetworkInterface ppp = null;

    76         NetworkInterface loopback = null;

    77 

    78         while (nifs.hasMoreElements()) {

    79             NetworkInterface ni = nifs.nextElement();

    80             try {

    81                 if (!ni.isUp() || !ni.supportsMulticast())

    82                     continue;

    83 

    84                 boolean ip4 = false, ip6 = false;

    85                 Enumeration<InetAddress> addrs = ni.getInetAddresses();

    86                 while (addrs.hasMoreElements()) {

    87                     InetAddress addr = addrs.nextElement();

    88                     if (!addr.isAnyLocalAddress()) {

    89                         if (addr instanceof Inet4Address) {

    90                             ip4 = true;

    91                         } else if (addr instanceof Inet6Address) {

    92                             ip6 = true;

    93                         }

    94                     }

    95                 }

    96 

    97                 boolean isLoopback = ni.isLoopback();

    98                 boolean isPPP = ni.isPointToPoint();

    99                 if (!isLoopback && !isPPP) {

   100                     // found an interface that is not the loopback or a

   101                     // point-to-point interface

   102                     if (preferred == null) {

   103                         preferred = ni;

   104                     } else if (ip4 && ip6){

   105                         return ni;

   106                     }

   107                 }

   108                 if (ppp == null && isPPP)

   109                     ppp = ni;

   110                 if (loopback == null && isLoopback)

   111                     loopback = ni;

   112 

   113             } catch (IOException skip) { }

   114         }

   115 

   116         if (preferred != null) {

   117             return preferred;

   118         } else {

   119             return (ppp != null) ? ppp : loopback;

   120         }

   121     }

   122 }