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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 java.net.IDN;
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.ByteBufHolder;
  import io.netty.handler.codec.dns.DnsRawRecord;
  import io.netty.handler.codec.dns.DnsRecord;
  
  /**
   * Decodes an {@link InetAddress} from an A or AAAA {@link DnsRawRecord}.
   */
  final class DnsAddressDecoder {
  
      private static final int INADDRSZ4 = 4;
      private static final int INADDRSZ6 = 16;
  
      /**
       * Decodes an {@link InetAddress} from an A or AAAA {@link DnsRawRecord}.
       *
       * @param record the {@link DnsRecord}, most likely a {@link DnsRawRecord}
       * @param name the host name of the decoded address
       * @param decodeIdn whether to convert {@code name} to a unicode host name
       *
       * @return the {@link InetAddress}, or {@code null} if {@code record} is not a {@link DnsRawRecord} or
       *         its content is malformed
       */
      static InetAddress decodeAddress(DnsRecord record, String name, boolean decodeIdn) {
          if (!(record instanceof DnsRawRecord)) {
              return null;
          }
          final ByteBuf content = ((ByteBufHolder) record).content();
          final int contentLen = content.readableBytes();
          if (contentLen != INADDRSZ4 && contentLen != INADDRSZ6) {
              return null;
          }
  
          final byte[] addrBytes = new byte[contentLen];
          content.getBytes(content.readerIndex(), addrBytes);
  
          try {
              return InetAddress.getByAddress(decodeIdn ? IDN.toUnicode(name) : name, addrBytes);
          } catch (UnknownHostException e) {
              // Should never reach here.
              throw new Error(e);
          }
      }
  
      private DnsAddressDecoder() { }
  }