/*

 * 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;

import java.io.BufferedReader;

import java.io.FileReader;

import java.io.IOException;

/*

 * An implementation of ResolverConfiguration for Solaris

 * and Linux.

 */

public class ResolverConfigurationImpl

    extends ResolverConfiguration

{

    // Lock helds whilst loading configuration or checking

    private static Object lock = new Object();

    // Time of last refresh.

    private static long lastRefresh = -1;

    // Cache timeout (300 seconds) - should be converted into property

    // or configured as preference in the future.

    private static final int TIMEOUT = 300000;

    // Resolver options

    private final Options opts;

    // Parse /etc/resolv.conf to get the values for a particular

    // keyword.

    //

    private LinkedList<String> resolvconf(String keyword,

                                          int maxperkeyword,

                                          int maxkeywords)

    {

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

        try {

            BufferedReader in =

                new BufferedReader(new FileReader("/etc/resolv.conf"));

            String line;

            while ((line = in.readLine()) != null) {

                int maxvalues = maxperkeyword;

                if (line.length() == 0)

                   continue;

                if (line.charAt(0) == '#' || line.charAt(0) == ';')

                    continue;

                if (!line.startsWith(keyword))

                    continue;

                String value = line.substring(keyword.length());

                if (value.length() == 0)

                    continue;

                if (value.charAt(0) != ' ' && value.charAt(0) != '\t')

                    continue;

                StringTokenizer st = new StringTokenizer(value, " \t");

                while (st.hasMoreTokens()) {

                    String val = st.nextToken();

                    if (val.charAt(0) == '#' || val.charAt(0) == ';') {

                        break;

                    }

                    ll.add(val);

                    if (--maxvalues == 0) {

                        break;

                    }

                }

                if (--maxkeywords == 0) {

                    break;

                }

            }

            in.close();

        } catch (IOException ioe) {

            // problem reading value

        }

        return ll;

    }

    private LinkedList<String> searchlist;

    private LinkedList<String> nameservers;

    // Load DNS configuration from OS

    private void loadConfig() {

        assert Thread.holdsLock(lock);

        // check if cached settings have expired.

        if (lastRefresh >= 0) {

            long currTime = System.currentTimeMillis();

            if ((currTime - lastRefresh) < TIMEOUT) {

                return;

            }

        }

        // get the name servers from /etc/resolv.conf

        nameservers =

            java.security.AccessController.doPrivileged(

                new java.security.PrivilegedAction<LinkedList<String>>() {

                    public LinkedList<String> run() {

                        // typically MAXNS is 3 but we've picked 5 here

                        // to allow for additional servers if required.

                        return resolvconf("nameserver", 1, 5);

                    } /* run */

                });

        // get the search list (or domain)

        searchlist = getSearchList();

        // update the timestamp on the configuration

        lastRefresh = System.currentTimeMillis();

    }

    // obtain search list or local domain

    private LinkedList<String> getSearchList() {

        LinkedList<String> sl;

        // first try the search keyword in /etc/resolv.conf

        sl = java.security.AccessController.doPrivileged(

                 new java.security.PrivilegedAction<LinkedList<String>>() {

                    public LinkedList<String> run() {

                        // first try search keyword (max 6 domains)

                        ll = resolvconf("search", 6, 1);

                        if (ll.size() > 0) {

                            return ll;

                        }

                        return null;

                    } /* run */

                });

        if (sl != null) {

            return sl;

        }

        // No search keyword so use local domain

        // LOCALDOMAIN has absolute priority on Solaris

        String localDomain = localDomain0();

        if (localDomain != null && localDomain.length() > 0) {

            sl.add(localDomain);

            return sl;

        }

        // try domain keyword in /etc/resolv.conf

        sl = java.security.AccessController.doPrivileged(

                 new java.security.PrivilegedAction<LinkedList<String>>() {

                    public LinkedList<String> run() {

                        LinkedList<String> ll;

                        ll = resolvconf("domain", 1, 1);

                        if (ll.size() > 0) {

                            return ll;

                        }

                        return null;

                    } /* run */

                });

        if (sl != null) {

            return sl;

        }

        // no local domain so try fallback (RPC) domain or

        sl = new LinkedList<>();

        String domain = fallbackDomain0();

        if (domain != null && domain.length() > 0) {

            sl.add(domain);

        }

        return sl;

    }

    // ----

    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;

    }

    // --- Native methods --

    static native String localDomain0();

    static native String fallbackDomain0();

    static {

        java.security.AccessController.doPrivileged(

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

    }

}

/**

 * Implementation of {@link ResolverConfiguration.Options}

 */

class OptionsImpl extends ResolverConfiguration.Options {

}