/*

 * 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

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 */

package sun.net.dns;

import java.util.List;

/**

 * The configuration of the client resolver.

 *

 * <p>A ResolverConfiguration is a singleton that represents the

 * configuration of the client resolver. The ResolverConfiguration

 * is opened by invoking the {@link #open() open} method.

 *

 * @since 1.4

 */

public abstract class ResolverConfiguration {

    private static final Object lock = new Object();

    private static ResolverConfiguration provider;

    protected ResolverConfiguration() { }

    /**

     * Opens the resolver configuration.

     *

     * @return the resolver configuration

     */

    public static ResolverConfiguration open() {

        synchronized (lock) {

            if (provider == null) {

                provider = new sun.net.dns.ResolverConfigurationImpl();

            }

            return provider;

        }

    }

    /**

     * Returns a list corresponding to the domain search path. The

     * list is ordered by the search order used for host name lookup.

     * Each element in the list returns a {@link java.lang.String}

     * containing a domain name or suffix.

     *

     * @return list of domain names

     */

    public abstract List<String> searchlist();

    /**

     * Returns a list of name servers used for host name lookup.

     * Each element in the list returns a {@link java.lang.String}

     * containing the textual representation of the IP address of

     * the name server.

     *

     * @return list of the name servers

     */

    public abstract List<String> nameservers();

    /**

     * Options representing certain resolver variables of

     * a {@link ResolverConfiguration}.

     */

    public static abstract class Options {

        /**

         * Returns the maximum number of attempts the resolver

         * will connect to each name server before giving up

         * and returning an error.

         *

         * @return the resolver attempts value or -1 is unknown

         */

        public int attempts() {

            return -1;

        }

        /**

         * Returns the basic retransmit timeout, in milliseconds,

         * used by the resolver. The resolver will typically use

         * an exponential backoff algorithm where the timeout is

         * doubled for every retransmit attempt. The basic

         * retransmit timeout, returned here, is the initial

         * timeout for the exponential backoff algorithm.

         *

         * @return the basic retransmit timeout value or -1

         *         if unknown

         */

        public int retrans() {

            return -1;

        }

    }

    /**

     * Returns the {@link #Options} for the resolver.

     *

     * @return options for the resolver

     */

    public abstract Options options();

}