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1   /*
2    * Copyright 2018 The Netty Project
3    *
4    * The Netty Project licenses this file to you under the Apache License,
5    * version 2.0 (the "License"); you may not use this file except in compliance
6    * with the License. You may obtain a copy of the License at:
7    *
8    *   https://www.apache.org/licenses/LICENSE-2.0
9    *
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
12   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
13   * License for the specific language governing permissions and limitations
14   * under the License.
15   */
16  package io.netty.resolver.dns;
17  
18  import io.netty.util.internal.ObjectUtil;
19  
20  import java.io.Serializable;
21  import java.net.InetAddress;
22  import java.net.InetSocketAddress;
23  import java.util.Comparator;
24  import java.util.List;
25  
26  /**
27   * Special {@link Comparator} implementation to sort the nameservers to use when follow redirects.
28   *
29   * This implementation follows all the semantics listed in the
30   * <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html">Comparator apidocs</a>
31   * with the limitation that {@link InetSocketAddress#equals(Object)} will not result in the same return value as
32   * {@link #compare(InetSocketAddress, InetSocketAddress)}. This is completely fine as this should only be used
33   * to sort {@link List}s.
34   */
35  public final class NameServerComparator implements Comparator<InetSocketAddress>, Serializable {
36  
37      private static final long serialVersionUID = 8372151874317596185L;
38  
39      private final Class<? extends InetAddress> preferredAddressType;
40  
41      public NameServerComparator(Class<? extends InetAddress> preferredAddressType) {
42          this.preferredAddressType = ObjectUtil.checkNotNull(preferredAddressType, "preferredAddressType");
43      }
44  
45      @Override
46      public int compare(InetSocketAddress addr1, InetSocketAddress addr2) {
47          if (addr1.equals(addr2)) {
48              return 0;
49          }
50          if (!addr1.isUnresolved() && !addr2.isUnresolved()) {
51              if (addr1.getAddress().getClass() == addr2.getAddress().getClass()) {
52                  return 0;
53              }
54              return preferredAddressType.isAssignableFrom(addr1.getAddress().getClass()) ? -1 : 1;
55          }
56          if (addr1.isUnresolved() && addr2.isUnresolved()) {
57              return 0;
58          }
59          return addr1.isUnresolved() ? 1 : -1;
60      }
61  }