/*

 * 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 com.sun.jndi.dns;

import javax.naming.*;

/**

 * The Resolver class performs DNS client operations in support of DnsContext.

 *

 * <p> Every DnsName instance passed to or returned from a method of

 * this class should be fully-qualified and contain a root label (an

 * empty component at position 0).

 *

 * @author Scott Seligman

 */

class Resolver {

    private DnsClient dnsClient;

    private int timeout;                // initial timeout on UDP queries in ms

    private int retries;                // number of UDP retries

    /*

     * Constructs a new Resolver given its servers and timeout parameters.

     * Each server is of the form "server[:port]".

     * IPv6 literal host names include delimiting brackets.

     * There must be at least one server.

     * "timeout" is the initial timeout interval (in ms) for UDP queries,

     * and "retries" gives the number of retries per server.

     */

    Resolver(String[] servers, int timeout, int retries)

            throws NamingException {

        this.timeout = timeout;

        this.retries = retries;

        dnsClient = new DnsClient(servers, timeout, retries);

    }

    public void close() {

        dnsClient.close();

        dnsClient = null;

    }

    /*

     * Queries resource records of a particular class and type for a

     * given domain name.

     * Useful values of rrclass are ResourceRecord.[Q]CLASS_xxx.

     * Useful values of rrtype are ResourceRecord.[Q]TYPE_xxx.

     * If recursion is true, recursion is requested on the query.

     * If auth is true, only authoritative responses are accepted.

     */

    ResourceRecords query(DnsName fqdn, int rrclass, int rrtype,

                          boolean recursion, boolean auth)

            throws NamingException {

        return dnsClient.query(fqdn, rrclass, rrtype, recursion, auth);

    }

    /*

     * Queries all resource records of a zone given its domain name and class.

     * If recursion is true, recursion is requested on the query to find

     * the name server (and also on the zone transfer, but it won't matter).

     */

    ResourceRecords queryZone(DnsName zone, int rrclass, boolean recursion)

            throws NamingException {

        DnsClient cl =

            new DnsClient(findNameServers(zone, recursion), timeout, retries);

        try {

            return cl.queryZone(zone, rrclass, recursion);

        } finally {

            cl.close();

        }

    }

    /*

     * Finds the zone of a given domain name.  The method is to look

     * for the first SOA record on the path from the given domain to

     * the root.  This search may be partially bypassed if the zone's

     * SOA record is received in the authority section of a response.

     * If recursion is true, recursion is requested on any queries.

     */

    DnsName findZoneName(DnsName fqdn, int rrclass, boolean recursion)

            throws NamingException {

        fqdn = (DnsName) fqdn.clone();

        while (fqdn.size() > 1) {       // while below root

            ResourceRecords rrs = null;

            try {

                rrs = query(fqdn, rrclass, ResourceRecord.TYPE_SOA,

                            recursion, false);

            } catch (NameNotFoundException e) {

                throw e;

            } catch (NamingException e) {

                // Ignore error and keep searching up the tree.

            }

            if (rrs != null) {

                if (rrs.answer.size() > 0) {    // found zone's SOA

                    return fqdn;

                }

                // Look for an SOA record giving the zone's top node.

                for (int i = 0; i < rrs.authority.size(); i++) {

                    ResourceRecord rr = (ResourceRecord)

                        rrs.authority.elementAt(i);

                    if (rr.getType() == ResourceRecord.TYPE_SOA) {

                        DnsName zone = rr.getName();

                        if (fqdn.endsWith(zone)) {

                            return zone;

                        }

                    }

                }

            }

            fqdn.remove(fqdn.size() - 1);       // one step rootward

        }

        return fqdn;                    // no SOA found below root, so

                                        // return root

    }

    /*

     * Finds a zone's SOA record.  Returns null if no SOA is found (in

     * which case "zone" is not actually a zone).

     * If recursion is true, recursion is requested on the query.

     */

     ResourceRecord findSoa(DnsName zone, int rrclass, boolean recursion)

            throws NamingException {

        ResourceRecords rrs = query(zone, rrclass, ResourceRecord.TYPE_SOA,

                                    recursion, false);

        for (int i = 0; i < rrs.answer.size(); i++) {

            ResourceRecord rr = (ResourceRecord) rrs.answer.elementAt(i);

            if (rr.getType() == ResourceRecord.TYPE_SOA) {

                return rr;

            }

        }

        return null;

    }

    /*

     * Finds the name servers of a zone.  <tt>zone</tt> is a fully-qualified

     * domain name at the top of a zone.

     * If recursion is true, recursion is requested on the query.

     */

    private String[] findNameServers(DnsName zone, boolean recursion)

            throws NamingException {

        // %%% As an optimization, could look in authority section of

        // findZoneName() response first.

        ResourceRecords rrs =

            query(zone, ResourceRecord.CLASS_INTERNET, ResourceRecord.TYPE_NS,

                  recursion, false);

        String[] ns = new String[rrs.answer.size()];

        for (int i = 0; i < ns.length; i++) {

            ResourceRecord rr = (ResourceRecord)

                rrs.answer.elementAt(i);

            if (rr.getType() != ResourceRecord.TYPE_NS) {

                throw new CommunicationException("Corrupted DNS message");

            }

            ns[i] = (String) rr.getRdata();

            // Server name will be passed to InetAddress.getByName(), which

            // may not be able to handle a trailing dot.

            // assert ns[i].endsWith(".");

            ns[i] = ns[i].substring(0, ns[i].length() - 1);

        }

        return ns;

    }

}