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   /*
    * Copyright 2020 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.handler.address;
  
  import io.netty.channel.ChannelHandler.Sharable;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelOutboundHandlerAdapter;
  import io.netty.channel.ChannelPromise;
  import io.netty.resolver.AddressResolver;
  import io.netty.resolver.AddressResolverGroup;
  import io.netty.util.concurrent.Future;
  import io.netty.util.concurrent.FutureListener;
  import io.netty.util.internal.ObjectUtil;
  
  import java.net.SocketAddress;
  
  /**
   * {@link ChannelOutboundHandlerAdapter} which will resolve the {@link SocketAddress} that is passed to
   * {@link #connect(ChannelHandlerContext, SocketAddress, SocketAddress, ChannelPromise)} if it is not already resolved
   * and the {@link AddressResolver} supports the type of {@link SocketAddress}.
   */
  @Sharable
  public class ResolveAddressHandler extends ChannelOutboundHandlerAdapter {
  
      private final AddressResolverGroup<? extends SocketAddress> resolverGroup;
  
      public ResolveAddressHandler(AddressResolverGroup<? extends SocketAddress> resolverGroup) {
          this.resolverGroup = ObjectUtil.checkNotNull(resolverGroup, "resolverGroup");
      }
  
      @Override
      public void connect(final ChannelHandlerContext ctx, SocketAddress remoteAddress,
                          final SocketAddress localAddress, final ChannelPromise promise)  {
          AddressResolver<? extends SocketAddress> resolver = resolverGroup.getResolver(ctx.executor());
          if (resolver.isSupported(remoteAddress) && !resolver.isResolved(remoteAddress)) {
              resolver.resolve(remoteAddress).addListener(new FutureListener<SocketAddress>() {
                  @Override
                  public void operationComplete(Future<SocketAddress> future) {
                      Throwable cause = future.cause();
                      if (cause != null) {
                          promise.setFailure(cause);
                      } else {
                          ctx.connect(future.getNow(), localAddress, promise);
                      }
                      ctx.pipeline().remove(ResolveAddressHandler.this);
                  }
              });
          } else {
              ctx.connect(remoteAddress, localAddress, promise);
              ctx.pipeline().remove(this);
          }
      }
  }