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   /*
    * Copyright 2019 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.codec.dns;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
  import io.netty.util.internal.UnstableApi;
  
  import java.net.SocketAddress;
  
  @UnstableApi
  public final class TcpDnsResponseDecoder extends LengthFieldBasedFrameDecoder {
  
      private final DnsResponseDecoder<SocketAddress> responseDecoder;
  
      /**
       * Creates a new decoder with {@linkplain DnsRecordDecoder#DEFAULT the default record decoder}.
       */
      public TcpDnsResponseDecoder() {
          this(DnsRecordDecoder.DEFAULT, 64 * 1024);
      }
  
      /**
       * Creates a new decoder with the specified {@code recordDecoder} and {@code maxFrameLength}
       */
      public TcpDnsResponseDecoder(DnsRecordDecoder recordDecoder, int maxFrameLength) {
          // Length is two octets as defined by RFC-7766
          // See https://tools.ietf.org/html/rfc7766#section-8
          super(maxFrameLength, 0, 2, 0, 2);
  
          this.responseDecoder = new DnsResponseDecoder<SocketAddress>(recordDecoder) {
              @Override
              protected DnsResponse newResponse(SocketAddress sender, SocketAddress recipient,
                                                int id, DnsOpCode opCode, DnsResponseCode responseCode) {
                  return new DefaultDnsResponse(id, opCode, responseCode);
              }
          };
      }
  
      @Override
      protected Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
          ByteBuf frame = (ByteBuf) super.decode(ctx, in);
          if (frame == null) {
              return null;
          }
  
          try {
              return responseDecoder.decode(ctx.channel().remoteAddress(), ctx.channel().localAddress(), frame.slice());
          } finally {
              frame.release();
          }
      }
  
      @Override
      protected ByteBuf extractFrame(ChannelHandlerContext ctx, ByteBuf buffer, int index, int length) {
          return buffer.copy(index, length);
      }
  }