/*
* Copyright (c) 2011, 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
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package java.net;
/**
* Choose a network inteface to be the default for
* outgoing IPv6 traffic that does not specify a scope_id (and which needs one).
* We choose the first interface that is up and is (in order of preference):
* 1. neither loopback nor point to point
* 2. point to point
* 3. loopback
* 4. none.
* Platforms that do not require a default interface implement a dummy
* that returns null.
*/
import java.util.Enumeration;
import java.io.IOException;
class DefaultInterface {
private final static NetworkInterface defaultInterface =
chooseDefaultInterface();
static NetworkInterface getDefault() {
return defaultInterface;
}
/**
* Choose a default interface. This method returns an interface that is
* both "up" and supports multicast. This method choses an interface in
* order of preference:
* 1. neither loopback nor point to point
* 2. point to point
* 3. loopback
*
* @return the chosen interface or {@code null} if there isn't a suitable
* default
*/
private static NetworkInterface chooseDefaultInterface() {
Enumeration<NetworkInterface> nifs;
try {
nifs = NetworkInterface.getNetworkInterfaces();
} catch (IOException ignore) {
// unable to enumate network interfaces
return null;
}
NetworkInterface ppp = null;
NetworkInterface loopback = null;
while (nifs.hasMoreElements()) {
NetworkInterface ni = nifs.nextElement();
try {
if (ni.isUp() && ni.supportsMulticast()) {
boolean isLoopback = ni.isLoopback();
boolean isPPP = ni.isPointToPoint();
if (!isLoopback && !isPPP) {
// found an interface that is not the loopback or a
// point-to-point interface
return ni;
}
if (ppp == null && isPPP)
ppp = ni;
if (loopback == null && isLoopback)
loopback = ni;
}
} catch (IOException skip) { }
}
return (ppp != null) ? ppp : loopback;
}
}