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1   /*
2    * ====================================================================
3    * Licensed to the Apache Software Foundation (ASF) under one
4    * or more contributor license agreements.  See the NOTICE file
5    * distributed with this work for additional information
6    * regarding copyright ownership.  The ASF licenses this file
7    * to you under the Apache License, Version 2.0 (the
8    * "License"); you may not use this file except in compliance
9    * with the License.  You may obtain a copy of the License at
10   *
11   *   http://www.apache.org/licenses/LICENSE-2.0
12   *
13   * Unless required by applicable law or agreed to in writing,
14   * software distributed under the License is distributed on an
15   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
16   * KIND, either express or implied.  See the License for the
17   * specific language governing permissions and limitations
18   * under the License.
19   * ====================================================================
20   *
21   * This software consists of voluntary contributions made by many
22   * individuals on behalf of the Apache Software Foundation.  For more
23   * information on the Apache Software Foundation, please see
24   * <http://www.apache.org/>.
25   *
26   */
27  package org.apache.hc.client5.http;
28  
29  import java.net.InetAddress;
30  import java.net.InetSocketAddress;
31  import java.net.UnknownHostException;
32  import java.util.Arrays;
33  import java.util.Collections;
34  import java.util.List;
35  import java.util.stream.Collectors;
36  
37  import org.apache.hc.core5.annotation.Contract;
38  import org.apache.hc.core5.annotation.ThreadingBehavior;
39  
40  /**
41   * Users may implement this interface to override the normal DNS lookup offered
42   * by the OS.
43   *
44   * @since 4.2
45   */
46  @Contract(threading = ThreadingBehavior.STATELESS)
47  public interface DnsResolver {
48  
49      /**
50       * Returns the IP address for the specified host name, or null if the given
51       * host is not recognized or the associated IP address cannot be used to
52       * build an InetAddress instance.
53       *
54       * @see InetAddress
55       *
56       * @param host
57       *            The host name to be resolved by this resolver.
58       * @return The IP address associated to the given host name, or null if the
59       *         host name is not known by the implementation class.
60       */
61      InetAddress[] resolve(String host) throws UnknownHostException;
62  
63      /**
64       * Gets the fully qualified domain name for given host name.
65       * @since 5.0
66       */
67      String resolveCanonicalHostname(String host) throws UnknownHostException;
68  
69      /**
70       * Returns a list of {@link InetSocketAddress} for the given host with the given port.
71       *
72       * @see InetSocketAddress
73       *
74       * @since 5.5
75       */
76      default List<InetSocketAddress> resolve(String host, int port) throws UnknownHostException {
77          final InetAddress[] inetAddresses = resolve(host);
78          if (inetAddresses == null) {
79              return Collections.singletonList(InetSocketAddress.createUnresolved(host, port));
80          }
81          return Arrays.stream(inetAddresses)
82                  .map(e -> new InetSocketAddress(e, port))
83                  .collect(Collectors.toList());
84      }
85  }