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   /*
    * Copyright 2015 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.util.internal.PlatformDependent;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.UnstableApi;
  
  import java.net.IDN;
  
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  /**
   * A skeletal implementation of {@link DnsRecord}.
   */
  @UnstableApi
  public abstract class AbstractDnsRecord implements DnsRecord {
  
      private final String name;
      private final DnsRecordType type;
      private final short dnsClass;
      private final long timeToLive;
      private int hashCode;
  
      /**
       * Creates a new {@link #CLASS_IN IN-class} record.
       *
       * @param name the domain name
       * @param type the type of the record
       * @param timeToLive the TTL value of the record
       */
      protected AbstractDnsRecord(String name, DnsRecordType type, long timeToLive) {
          this(name, type, CLASS_IN, timeToLive);
      }
  
      /**
       * Creates a new record.
       *
       * @param name the domain name
       * @param type the type of the record
       * @param dnsClass the class of the record, usually one of the following:
       *                 <ul>
       *                     <li>{@link #CLASS_IN}</li>
       *                     <li>{@link #CLASS_CSNET}</li>
       *                     <li>{@link #CLASS_CHAOS}</li>
       *                     <li>{@link #CLASS_HESIOD}</li>
       *                     <li>{@link #CLASS_NONE}</li>
       *                     <li>{@link #CLASS_ANY}</li>
       *                 </ul>
       * @param timeToLive the TTL value of the record
       */
      protected AbstractDnsRecord(String name, DnsRecordType type, int dnsClass, long timeToLive) {
          checkPositiveOrZero(timeToLive, "timeToLive");
          // Convert to ASCII which will also check that the length is not too big.
          // See:
          //   - https://github.com/netty/netty/issues/4937
          //   - https://github.com/netty/netty/issues/4935
          this.name = appendTrailingDot(IDNtoASCII(name));
          this.type = checkNotNull(type, "type");
          this.dnsClass = (short) dnsClass;
          this.timeToLive = timeToLive;
      }
  
      private static String IDNtoASCII(String name) {
          checkNotNull(name, "name");
          if (PlatformDependent.isAndroid() && DefaultDnsRecordDecoder.ROOT.equals(name)) {
              // Prior Android 10 there was a bug that did not correctly parse ".".
              //
              // See https://github.com/netty/netty/issues/10034
              return name;
          }
          return IDN.toASCII(name);
      }
  
      private static String appendTrailingDot(String name) {
          if (name.length() > 0 && name.charAt(name.length() - 1) != '.') {
              return name + '.';
          }
          return name;
      }
  
      @Override
      public String name() {
          return name;
      }
 
     @Override
     public DnsRecordType type() {
         return type;
     }
 
     @Override
     public int dnsClass() {
         return dnsClass & 0xFFFF;
     }
 
     @Override
     public long timeToLive() {
         return timeToLive;
     }
 
     @Override
     public boolean equals(Object obj) {
         if (this == obj) {
             return true;
         }
 
         if (!(obj instanceof DnsRecord)) {
             return false;
         }
 
         final DnsRecord that = (DnsRecord) obj;
         final int hashCode = this.hashCode;
         if (hashCode != 0 && hashCode != that.hashCode()) {
             return false;
         }
 
         return type().intValue() == that.type().intValue() &&
                dnsClass() == that.dnsClass() &&
                name().equals(that.name());
     }
 
     @Override
     public int hashCode() {
         final int hashCode = this.hashCode;
         if (hashCode != 0) {
             return hashCode;
         }
 
         return this.hashCode = name.hashCode() * 31 + type().intValue() * 31 + dnsClass();
     }
 
     @Override
     public String toString() {
         StringBuilder buf = new StringBuilder(64);
 
         buf.append(StringUtil.simpleClassName(this))
            .append('(')
            .append(name())
            .append(' ')
            .append(timeToLive())
            .append(' ');
 
         DnsMessageUtil.appendRecordClass(buf, dnsClass())
                       .append(' ')
                       .append(type().name())
                       .append(')');
 
         return buf.toString();
     }
 }