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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.channel.EventLoop;
19  import io.netty.util.AsciiString;
20  
21  import java.util.List;
22  
23  import static io.netty.util.internal.ObjectUtil.*;
24  
25  /**
26   * Default implementation of a {@link DnsCnameCache}.
27   */
28  public final class DefaultDnsCnameCache implements DnsCnameCache {
29      private final int minTtl;
30      private final int maxTtl;
31  
32      private final Cache<String> cache = new Cache<String>() {
33          @Override
34          protected boolean shouldReplaceAll(String entry) {
35              // Only one 1:1 mapping is supported as specified in the RFC.
36              return true;
37          }
38  
39          @Override
40          protected boolean equals(String entry, String otherEntry) {
41              return AsciiString.contentEqualsIgnoreCase(entry, otherEntry);
42          }
43      };
44  
45      /**
46       * Create a cache that respects the TTL returned by the DNS server.
47       */
48      public DefaultDnsCnameCache() {
49          this(0, Cache.MAX_SUPPORTED_TTL_SECS);
50      }
51  
52      /**
53       * Create a cache.
54       *
55       * @param minTtl the minimum TTL
56       * @param maxTtl the maximum TTL
57       */
58      public DefaultDnsCnameCache(int minTtl, int maxTtl) {
59          this.minTtl = Math.min(Cache.MAX_SUPPORTED_TTL_SECS, checkPositiveOrZero(minTtl, "minTtl"));
60          this.maxTtl = Math.min(Cache.MAX_SUPPORTED_TTL_SECS, checkPositive(maxTtl, "maxTtl"));
61          if (minTtl > maxTtl) {
62              throw new IllegalArgumentException(
63                      "minTtl: " + minTtl + ", maxTtl: " + maxTtl + " (expected: 0 <= minTtl <= maxTtl)");
64          }
65      }
66  
67      @SuppressWarnings("unchecked")
68      @Override
69      public String get(String hostname) {
70          List<? extends String> cached =  cache.get(checkNotNull(hostname, "hostname"));
71          if (cached == null || cached.isEmpty()) {
72              return null;
73          }
74          // We can never have more then one record.
75          return cached.get(0);
76      }
77  
78      @Override
79      public void cache(String hostname, String cname, long originalTtl, EventLoop loop) {
80          checkNotNull(hostname, "hostname");
81          checkNotNull(cname, "cname");
82          checkNotNull(loop, "loop");
83          cache.cache(hostname, cname, Math.max(minTtl, (int) Math.min(maxTtl, originalTtl)), loop);
84      }
85  
86      @Override
87      public void clear() {
88          cache.clear();
89      }
90  
91      @Override
92      public boolean clear(String hostname) {
93          return cache.clear(checkNotNull(hostname, "hostname"));
94      }
95  }