/*

 * Copyright (c) 2002, 2010, 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

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

 * questions.

 */

package sun.net.dns;

import java.util.List;

import java.util.LinkedList;

import java.util.StringTokenizer;

/*

 * An implementation of sun.net.ResolverConfiguration for Windows.

 */

public class ResolverConfigurationImpl

    extends ResolverConfiguration

{

    // Lock helds whilst loading configuration or checking

    private static Object lock = new Object();

    // Resolver options

    private final Options opts;

    // Addreses have changed

    private static boolean changed = false;

    // Time of last refresh.

    private static long lastRefresh = -1;

    // Cache timeout (120 seconds) - should be converted into property

    // or configured as preference in the future.

    private static final int TIMEOUT = 120000;

    // DNS suffix list and name servers populated by native method

    private static String os_searchlist;

    private static String os_nameservers;

    // Cached lists

    // Parse string that consists of token delimited by space or commas

    // and return LinkedHashMap

    private LinkedList<String> stringToList(String str) {

        LinkedList<String> ll = new LinkedList<>();

        // comma and space are valid delimites

        StringTokenizer st = new StringTokenizer(str, ", ");

        while (st.hasMoreTokens()) {

            String s = st.nextToken();

            if (!ll.contains(s)) {

                ll.add(s);

            }

        }

        return ll;

    }

    // Load DNS configuration from OS

    private void loadConfig() {

        assert Thread.holdsLock(lock);

        // if address have changed then DNS probably changed aswell;

        // otherwise check if cached settings have expired.

        //

        if (changed) {

            changed = false;

        } else {

            if (lastRefresh >= 0) {

                long currTime = System.currentTimeMillis();

                if ((currTime - lastRefresh) < TIMEOUT) {

                    return;

                }

            }

        }

        // load DNS configuration, update timestamp, create

        // new HashMaps from the loaded configuration

        //

        loadDNSconfig0();

        lastRefresh = System.currentTimeMillis();

        searchlist = stringToList(os_searchlist);

        nameservers = stringToList(os_nameservers);

        os_searchlist = null;                       // can be GC'ed

        os_nameservers = null;

    }

    ResolverConfigurationImpl() {

        opts = new OptionsImpl();

    }

    public List<String> searchlist() {

        synchronized (lock) {

            loadConfig();

            // List is mutable so return a shallow copy

        }

    }

    public List<String> nameservers() {

        synchronized (lock) {

            loadConfig();

            // List is mutable so return a shallow copy

         }

    }

    public Options options() {

        return opts;

    }

    // --- Address Change Listener

    static class AddressChangeListener extends Thread {

        public void run() {

            for (;;) {

                // wait for configuration to change

                if (notifyAddrChange0() != 0)

                    return;

                synchronized (lock) {

                    changed = true;

                }

            }

        }

    }

    // --- Native methods --

    static native void init0();

    static native void loadDNSconfig0();

    static native int notifyAddrChange0();

    static {

        java.security.AccessController.doPrivileged(

            new sun.security.action.LoadLibraryAction("net"));

        init0();

        // start the address listener thread

        AddressChangeListener thr = new AddressChangeListener();

        thr.setDaemon(true);

        thr.start();

    }

}

/**

 * Implementation of {@link ResolverConfiguration.Options}

 */

class OptionsImpl extends ResolverConfiguration.Options {

}