/*

 * 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

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

 *

 * 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.

 *

 */

package java.net;

import java.security.AccessController;

import java.security.PrivilegedAction;

/**

 * This class defines a factory for creating DatagramSocketImpls. It defaults

 * to creating plain DatagramSocketImpls, but may create other DatagramSocketImpls

 * by setting the impl.prefix system property.

 *

 * For Windows versions lower than Windows Vista a TwoStacksPlainDatagramSocketImpl

 * is always created. This impl supports IPv6 on these platform where available.

 *

 * On Windows platforms greater than Vista that support a dual layer TCP/IP stack

 * a DualStackPlainDatagramSocketImpl is created for DatagramSockets. For MulticastSockets

 * a TwoStacksPlainDatagramSocketImpl is always created. This is to overcome the lack

 * of behavior defined for multicasting over a dual layer socket by the RFC.

 *

 * @author Chris Hegarty

 */

class DefaultDatagramSocketImplFactory

{

    static Class prefixImplClass = null;

    /* the windows version. */

    private static float version;

    /* java.net.preferIPv4Stack */

    private static boolean preferIPv4Stack = false;

    /* If the version supports a dual stack TCP implementation */

    private static boolean useDualStackImpl = false;

    static {

        // Determine Windows Version.

        java.security.AccessController.doPrivileged( new PrivilegedAction<Object>() {

                public Object run() {

                    version = 0;

                    try {

                        version = Float.parseFloat(System.getProperties().getProperty("os.version"));

                        preferIPv4Stack = Boolean.parseBoolean(

                                          System.getProperties().getProperty("java.net.preferIPv4Stack"));

                    } catch (NumberFormatException e ) {

                        assert false : e;

                    }

                    return null; // nothing to return

                } });

        // (version >= 6.0) implies Vista or greater.

        if (version >= 6.0 && !preferIPv4Stack) {

            useDualStackImpl = true;

        }

        // impl.prefix

        String prefix = null;

        try {

            prefix = AccessController.doPrivileged(

                new sun.security.action.GetPropertyAction("impl.prefix", null));

            if (prefix != null)

                prefixImplClass = Class.forName("java.net."+prefix+"DatagramSocketImpl");

        } catch (Exception e) {

            System.err.println("Can't find class: java.net." +

                                prefix +

                                "DatagramSocketImpl: check impl.prefix property");

        }

    }

    /**

     * Creates a new <code>DatagramSocketImpl</code> instance.

     *

     * @param   isMulticast true if this impl is to be used for a MutlicastSocket

     * @return  a new instance of <code>PlainDatagramSocketImpl</code>.

     */

    static DatagramSocketImpl createDatagramSocketImpl(boolean isMulticast)

        throws SocketException {

        if (prefixImplClass != null) {

            try {

                return (DatagramSocketImpl) prefixImplClass.newInstance();

            } catch (Exception e) {

                throw new SocketException("can't instantiate DatagramSocketImpl");

            }

        } else {

            if (useDualStackImpl && !isMulticast)

                return new DualStackPlainDatagramSocketImpl();

            else

                return new TwoStacksPlainDatagramSocketImpl();

        }

    }

}