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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.util;
  
  import com.oracle.svm.core.annotate.Alias;
  import com.oracle.svm.core.annotate.InjectAccessors;
  import com.oracle.svm.core.annotate.TargetClass;
  
  import java.net.Inet4Address;
  import java.net.Inet6Address;
  import java.net.InetAddress;
  import java.net.NetworkInterface;
  import java.util.Collection;
  
  @TargetClass(NetUtil.class)
  final class NetUtilSubstitutions {
      private NetUtilSubstitutions() {
      }
  
      @Alias
      @InjectAccessors(NetUtilLocalhost4Accessor.class)
      public static Inet4Address LOCALHOST4;
  
      @Alias
      @InjectAccessors(NetUtilLocalhost6Accessor.class)
      public static Inet6Address LOCALHOST6;
  
      @Alias
      @InjectAccessors(NetUtilLocalhostAccessor.class)
      public static InetAddress LOCALHOST;
  
      @Alias
      @InjectAccessors(NetUtilNetworkInterfacesAccessor.class)
      public static Collection<NetworkInterface> NETWORK_INTERFACES;
  
      private static final class NetUtilLocalhost4Accessor {
          static Inet4Address get() {
              // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
              return NetUtilLocalhost4LazyHolder.LOCALHOST4;
          }
  
          static void set(Inet4Address ignored) {
              // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
          }
      }
  
      private static final class NetUtilLocalhost4LazyHolder {
          private static final Inet4Address LOCALHOST4 = NetUtilInitializations.createLocalhost4();
      }
  
      private static final class NetUtilLocalhost6Accessor {
          static Inet6Address get() {
              // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
              return NetUtilLocalhost6LazyHolder.LOCALHOST6;
          }
  
          static void set(Inet6Address ignored) {
              // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
          }
      }
  
      private static final class NetUtilLocalhost6LazyHolder {
          private static final Inet6Address LOCALHOST6 = NetUtilInitializations.createLocalhost6();
      }
  
      private static final class NetUtilLocalhostAccessor {
          static InetAddress get() {
              // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
              return NetUtilLocalhostLazyHolder.LOCALHOST;
          }
  
          static void set(InetAddress ignored) {
              // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
          }
      }
  
      private static final class NetUtilLocalhostLazyHolder {
          private static final InetAddress LOCALHOST = NetUtilInitializations
                  .determineLoopback(NetUtilNetworkInterfacesLazyHolder.NETWORK_INTERFACES,
                          NetUtilLocalhost4LazyHolder.LOCALHOST4, NetUtilLocalhost6LazyHolder.LOCALHOST6)
                  .address();
      }
  
      private static final class NetUtilNetworkInterfacesAccessor {
          static Collection<NetworkInterface> get() {
              // using https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
             return NetUtilNetworkInterfacesLazyHolder.NETWORK_INTERFACES;
         }
 
         static void set(Collection<NetworkInterface> ignored) {
             // a no-op setter to avoid exceptions when NetUtil is initialized at run-time
         }
     }
 
     private static final class NetUtilNetworkInterfacesLazyHolder {
         private static final Collection<NetworkInterface> NETWORK_INTERFACES =
                 NetUtilInitializations.networkInterfaces();
     }
 }