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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.channel.unix;
  
  import java.net.Inet6Address;
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.net.UnknownHostException;
  
  /**
   * <strong>Internal usage only!</strong>
   */
  public final class NativeInetAddress {
      private static final byte[] IPV4_MAPPED_IPV6_PREFIX = {
              0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, (byte) 0xff, (byte) 0xff };
      final byte[] address;
      final int scopeId;
  
      public static NativeInetAddress newInstance(InetAddress addr) {
          byte[] bytes = addr.getAddress();
          if (addr instanceof Inet6Address) {
              return new NativeInetAddress(bytes, ((Inet6Address) addr).getScopeId());
          } else {
              // convert to ipv4 mapped ipv6 address;
              return new NativeInetAddress(ipv4MappedIpv6Address(bytes));
          }
      }
  
      public NativeInetAddress(byte[] address, int scopeId) {
          this.address = address;
          this.scopeId = scopeId;
      }
  
      public NativeInetAddress(byte[] address) {
          this(address, 0);
      }
  
      public byte[] address() {
          return address;
      }
  
      public int scopeId() {
          return scopeId;
      }
  
      public static byte[] ipv4MappedIpv6Address(byte[] ipv4) {
          byte[] address = new byte[16];
          copyIpv4MappedIpv6Address(ipv4, address);
          return address;
      }
  
      public static void copyIpv4MappedIpv6Address(byte[] ipv4, byte[] ipv6) {
          System.arraycopy(IPV4_MAPPED_IPV6_PREFIX, 0, ipv6, 0, IPV4_MAPPED_IPV6_PREFIX.length);
          System.arraycopy(ipv4, 0, ipv6, 12, ipv4.length);
      }
  
      public static InetSocketAddress address(byte[] addr, int offset, int len) {
          // The last 4 bytes are always the port
          final int port = decodeInt(addr, offset + len - 4);
          final InetAddress address;
  
          try {
              switch (len) {
                  // 8 bytes:
                  // - 4  == ipaddress
                  // - 4  == port
                  case 8:
                      byte[] ipv4 = new byte[4];
                      System.arraycopy(addr, offset, ipv4, 0, 4);
                      address = InetAddress.getByAddress(ipv4);
                      break;
  
                  // 24 bytes:
                  // - 16  == ipaddress
                  // - 4   == scopeId
                  // - 4   == port
                  case 24:
                      byte[] ipv6 = new byte[16];
                      System.arraycopy(addr, offset, ipv6, 0, 16);
                      int scopeId = decodeInt(addr, offset + len  - 8);
                      address = Inet6Address.getByAddress(null, ipv6, scopeId);
                      break;
                  default:
                      throw new Error();
              }
              return new InetSocketAddress(address, port);
         } catch (UnknownHostException e) {
             throw new Error("Should never happen", e);
         }
     }
 
     static int decodeInt(byte[] addr, int index) {
         return  (addr[index]     & 0xff) << 24 |
                 (addr[index + 1] & 0xff) << 16 |
                 (addr[index + 2] & 0xff) <<  8 |
                 addr[index + 3] & 0xff;
     }
 }