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   /*
    * Copyright 2018 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.net.InetSocketAddress;
  import java.util.ArrayList;
  import java.util.List;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * {@link AuthoritativeDnsServerCache} implementation which delegates all operations to a wrapped {@link DnsCache}.
   * This implementation is only present to preserve a upgrade story.
   */
  final class AuthoritativeDnsServerCacheAdapter implements AuthoritativeDnsServerCache {
  
      private static final DnsRecord[] EMPTY = new DnsRecord[0];
      private final DnsCache cache;
  
      AuthoritativeDnsServerCacheAdapter(DnsCache cache) {
          this.cache = checkNotNull(cache, "cache");
      }
  
      @Override
      public DnsServerAddressStream get(String hostname) {
          List<? extends DnsCacheEntry> entries = cache.get(hostname, EMPTY);
          if (entries == null || entries.isEmpty()) {
              return null;
          }
          if (entries.get(0).cause() != null) {
              return null;
          }
  
          List<InetSocketAddress> addresses = new ArrayList<InetSocketAddress>(entries.size());
  
          int i = 0;
          do {
              InetAddress addr = entries.get(i).address();
              addresses.add(new InetSocketAddress(addr, DefaultDnsServerAddressStreamProvider.DNS_PORT));
          } while (++i < entries.size());
          return new SequentialDnsServerAddressStream(addresses, 0);
      }
  
      @Override
      public void cache(String hostname, InetSocketAddress address, long originalTtl, EventLoop loop) {
          // We only cache resolved addresses.
          if (!address.isUnresolved()) {
              cache.cache(hostname, EMPTY, address.getAddress(), originalTtl, loop);
          }
      }
  
      @Override
      public void clear() {
          cache.clear();
      }
  
      @Override
      public boolean clear(String hostname) {
          return cache.clear(hostname);
      }
  }