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   /*
    * Copyright 2014 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.ChannelFactory;
  import io.netty.channel.EventLoop;
  import io.netty.channel.socket.DatagramChannel;
  import io.netty.resolver.AddressResolver;
  import io.netty.resolver.AddressResolverGroup;
  import io.netty.resolver.InetSocketAddressResolver;
  import io.netty.resolver.NameResolver;
  import io.netty.util.concurrent.EventExecutor;
  import io.netty.util.concurrent.Promise;
  import io.netty.util.internal.StringUtil;
  
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.util.List;
  import java.util.concurrent.ConcurrentMap;
  
  import static io.netty.util.internal.PlatformDependent.newConcurrentHashMap;
  
  /**
   * A {@link AddressResolverGroup} of {@link DnsNameResolver}s.
   */
  public class DnsAddressResolverGroup extends AddressResolverGroup<InetSocketAddress> {
  
      private final DnsNameResolverBuilder dnsResolverBuilder;
  
      private final ConcurrentMap<String, Promise<InetAddress>> resolvesInProgress = newConcurrentHashMap();
      private final ConcurrentMap<String, Promise<List<InetAddress>>> resolveAllsInProgress = newConcurrentHashMap();
  
      public DnsAddressResolverGroup(DnsNameResolverBuilder dnsResolverBuilder) {
          this.dnsResolverBuilder = dnsResolverBuilder.copy();
      }
  
      public DnsAddressResolverGroup(
              Class<? extends DatagramChannel> channelType,
              DnsServerAddressStreamProvider nameServerProvider) {
          this.dnsResolverBuilder = new DnsNameResolverBuilder();
          dnsResolverBuilder.channelType(channelType).nameServerProvider(nameServerProvider);
      }
  
      public DnsAddressResolverGroup(
              ChannelFactory<? extends DatagramChannel> channelFactory,
              DnsServerAddressStreamProvider nameServerProvider) {
          this.dnsResolverBuilder = new DnsNameResolverBuilder();
          dnsResolverBuilder.channelFactory(channelFactory).nameServerProvider(nameServerProvider);
      }
  
      @SuppressWarnings("deprecation")
      @Override
      protected final AddressResolver<InetSocketAddress> newResolver(EventExecutor executor) throws Exception {
          if (!(executor instanceof EventLoop)) {
              throw new IllegalStateException(
                      "unsupported executor type: " + StringUtil.simpleClassName(executor) +
                      " (expected: " + StringUtil.simpleClassName(EventLoop.class));
          }
  
          // we don't really need to pass channelFactory and nameServerProvider separately,
          // but still keep this to ensure backward compatibility with (potentially) override methods
          EventLoop loop = dnsResolverBuilder.eventLoop;
          return newResolver(loop == null ? (EventLoop) executor : loop,
                  dnsResolverBuilder.channelFactory(),
                  dnsResolverBuilder.nameServerProvider());
      }
  
      /**
       * @deprecated Override {@link #newNameResolver(EventLoop, ChannelFactory, DnsServerAddressStreamProvider)}.
       */
      @Deprecated
      protected AddressResolver<InetSocketAddress> newResolver(
              EventLoop eventLoop, ChannelFactory<? extends DatagramChannel> channelFactory,
              DnsServerAddressStreamProvider nameServerProvider) throws Exception {
  
          final NameResolver<InetAddress> resolver = new InflightNameResolver<InetAddress>(
                  eventLoop,
                  newNameResolver(eventLoop, channelFactory, nameServerProvider),
                  resolvesInProgress,
                  resolveAllsInProgress);
  
          return newAddressResolver(eventLoop, resolver);
      }
  
      /**
      * Creates a new {@link NameResolver}. Override this method to create an alternative {@link NameResolver}
      * implementation or override the default configuration.
      */
     protected NameResolver<InetAddress> newNameResolver(EventLoop eventLoop,
                                                         ChannelFactory<? extends DatagramChannel> channelFactory,
                                                         DnsServerAddressStreamProvider nameServerProvider)
             throws Exception {
         DnsNameResolverBuilder builder = dnsResolverBuilder.copy();
 
         // once again, channelFactory and nameServerProvider are most probably set in builder already,
         // but I do reassign them again to avoid corner cases with override methods
         return builder.eventLoop(eventLoop)
                 .channelFactory(channelFactory)
                 .nameServerProvider(nameServerProvider)
                 .build();
     }
 
     /**
      * Creates a new {@link AddressResolver}. Override this method to create an alternative {@link AddressResolver}
      * implementation or override the default configuration.
      */
     protected AddressResolver<InetSocketAddress> newAddressResolver(EventLoop eventLoop,
                                                                     NameResolver<InetAddress> resolver)
             throws Exception {
         return new InetSocketAddressResolver(eventLoop, resolver);
     }
 }