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   /*
    * Copyright 2016 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.resolver.dns;
  
  import io.netty.channel.EventLoop;
  import io.netty.handler.codec.dns.DnsRecord;
  
  import java.net.InetAddress;
  import java.util.Collections;
  import java.util.List;
  
  /**
   * A noop DNS cache that actually never caches anything.
   */
  public final class NoopDnsCache implements DnsCache {
  
      public static final NoopDnsCache INSTANCE = new NoopDnsCache();
  
      /**
       * Private singleton constructor.
       */
      private NoopDnsCache() {
      }
  
      @Override
      public void clear() {
      }
  
      @Override
      public boolean clear(String hostname) {
          return false;
      }
  
      @Override
      public List<? extends DnsCacheEntry> get(String hostname, DnsRecord[] additionals) {
          return Collections.emptyList();
      }
  
      @Override
      public DnsCacheEntry cache(String hostname, DnsRecord[] additional,
                                 InetAddress address, long originalTtl, EventLoop loop) {
          return new NoopDnsCacheEntry(address);
      }
  
      @Override
      public DnsCacheEntry cache(String hostname, DnsRecord[] additional, Throwable cause, EventLoop loop) {
          return null;
      }
  
      @Override
      public String toString() {
          return NoopDnsCache.class.getSimpleName();
      }
  
      private static final class NoopDnsCacheEntry implements DnsCacheEntry {
          private final InetAddress address;
  
          NoopDnsCacheEntry(InetAddress address) {
              this.address = address;
          }
  
          @Override
          public InetAddress address() {
              return address;
          }
  
          @Override
          public Throwable cause() {
              return null;
          }
  
          @Override
          public String toString() {
              return address.toString();
          }
      }
  }