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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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,

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 *

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package com.sun.jndi.ldap.spi;

import javax.naming.Context;

import javax.naming.NamingException;

import java.util.Map;

import java.util.Optional;

/**

 * Service-provider class for DNS lookups when performing LDAP operations.

 *

 * <p> An LDAP DNS provider is a concrete subclass of this class that

 * has a zero-argument constructor. LDAP DNS providers are located using the

 * ServiceLoader facility, as specified by

 * {@linkplain javax.naming.directory.InitialDirContext InitialDirectContext}.

 *

 * The

 * {@link java.util.ServiceLoader ServiceLoader} is used to create and register

 * implementations of {@code LdapDnsProvider}.

 *

 * <p> An LDAP DNS provider can be used in environments where the default

 * DNS resolution mechanism is not sufficient to accurately pinpoint the

 * correct LDAP servers needed to perform LDAP operations. For example, in an

 * environment containing a mix of {@code ldap} and {@code ldaps} servers

 * you may want the {@linkplain javax.naming.ldap.LdapContext LdapContext}

 * to query {@code ldaps} servers only.

 *

 * @since 12

 */

public abstract class LdapDnsProvider {

    // The {@code RuntimePermission("ldapDnsProvider")} is

    // necessary to subclass and instantiate the {@code LdapDnsProvider} class.

    private static final RuntimePermission DNSPROVIDER_PERMISSION =

            new RuntimePermission("ldapDnsProvider");

    /**

     * Creates a new instance of {@code LdapDnsProvider}.

     *

     * @throws SecurityException if a security manager is present and its

     *                           {@code checkPermission} method doesn't allow

     *                           the {@code RuntimePermission("ldapDnsProvider")}.

     */

    protected LdapDnsProvider() {

        this(checkPermission());

    }

    private LdapDnsProvider(Void unused) {

        // nothing to do.

    }

    private static Void checkPermission() {

        final SecurityManager sm = System.getSecurityManager();

        if (sm != null) {

            sm.checkPermission(DNSPROVIDER_PERMISSION);

        }

        return null;

    }

    /**

     * Lookup the endpoints and domain name for the given {@link Context}

     * {@link Context#PROVIDER_URL provider URL} and environment. The resolved

     * endpoints and domain name are returned as an

     * {@link LdapDnsProviderResult}.

     *

     * <p> An endpoint is a {@code String} representation of an LDAP URL which

     * points to an LDAP server to be used for LDAP operations. The syntax of

     * an LDAP URL is defined by <a href="http://www.ietf.org/rfc/rfc2255.txt">

     * <i>RFC&nbsp;2255: The LDAP URL Format</i></a>.

     *

     * @param url   The {@link Context} {@link Context#PROVIDER_URL provider URL}

     * @param env   The {@link Context} environment.

     *

     * @return  an {@link LdapDnsProviderResult} or empty {@code Optional}

     *          if the lookup fails.

     *

     * @throws NamingException      if the {@code url} is not valid or an error

     *                              occurred while performing the lookup.

     * @throws NullPointerException if either {@code url} or {@code env} are

     *                              {@code null}.

     */

    public abstract Optional<LdapDnsProviderResult> lookupEndpoints(

            String url, Map<?,?> env) throws NamingException;

}