1 /*
   2  * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package com.sun.jndi.ldap;
  27 
  28 import java.security.AccessController;
  29 import java.security.PrivilegedAction;
  30 import java.util.*;
  31 import javax.naming.NamingException;
  32 import javax.naming.ldap.spi.LdapDnsProvider;
  33 import javax.naming.ldap.spi.LdapDnsProviderResult;
  34 import sun.security.util.SecurityConstants;
  35 
  36 /**
  37  * The {@code LdapDnsProviderService} is responsible for creating and providing
  38  * access to the registered {@code LdapDnsProvider}s. The {@link ServiceLoader}
  39  * is used to find and register any implementations of {@link LdapDnsProvider}.
  40  *
  41  * <p> Instances of this class are safe for use by multiple threads.
  42  */
  43 final class LdapDnsProviderService {
  44 
  45     private static volatile LdapDnsProviderService service;
  46     private static final Object LOCK = new int[0];
  47     private final ServiceLoader<LdapDnsProvider> providers;
  48 
  49     /**
  50      * Creates a new instance of LdapDnsProviderService
  51      */
  52     private LdapDnsProviderService() {
  53         SecurityManager sm = System.getSecurityManager();
  54         if (sm == null) {
  55             providers = ServiceLoader.load(
  56                     LdapDnsProvider.class,
  57                     ClassLoader.getSystemClassLoader());
  58         } else {
  59             final PrivilegedAction<ServiceLoader<LdapDnsProvider>> pa =
  60                     () -> ServiceLoader.load(
  61                             LdapDnsProvider.class,
  62                             ClassLoader.getSystemClassLoader());
  63 
  64             providers = AccessController.doPrivileged(
  65                 pa,
  66                 null,
  67                 new RuntimePermission("ldapDnsProvider"),
  68                 SecurityConstants.GET_CLASSLOADER_PERMISSION);
  69         }
  70     }
  71 
  72     /**
  73      * Retrieves the singleton instance of LdapDnsProviderService.
  74      */
  75     static LdapDnsProviderService getInstance() {
  76         if (service != null) return service;
  77         synchronized (LOCK) {
  78             if (service != null) return service;
  79             service = new LdapDnsProviderService();
  80         }
  81         return service;
  82     }
  83 
  84     /**
  85      * Retrieves result from the first provider that successfully resolves
  86      * the endpoints. If no results are found when calling installed
  87      * subclasses of {@code LdapDnsProvider} then this method will fall back
  88      * to the {@code DefaultLdapDnsProvider}.
  89      *
  90      * @throws NamingException if the {@code url} in not valid or an error
  91      *                         occurred while performing the lookup.
  92      */
  93     LdapDnsProviderResult lookupEndpoints(String url, Hashtable<?,?> env)
  94         throws NamingException
  95     {
  96         LdapDnsProviderResult result = null;
  97         Hashtable<?, ?> envCopy = new Hashtable<>(env);
  98         synchronized (LOCK) {
  99             Iterator<LdapDnsProvider> iterator = providers.iterator();
 100             while (result == null && iterator.hasNext()) {
 101                 result = iterator.next().lookupEndpoints(url, envCopy)
 102                         .filter(r -> !r.getEndpoints().isEmpty())
 103                         .orElse(null);
 104             }
 105         }
 106 
 107         if (result == null) {
 108             return new DefaultLdapDnsProvider().lookupEndpoints(url, env)
 109                 .orElse(new LdapDnsProviderResult("", List.of()));
 110         }
 111         return result;
 112     }
 113 
 114 }