/*
 * Copyright 2007 Sun Microsystems, Inc.  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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */
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.
 *
 * @version 1.2, 06/11/07
 * @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 = (String) 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();
	}
    }
}