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   /*
    * Copyright 2016 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.internal;
  
  import io.netty.util.NetUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.net.InetAddress;
  import java.net.NetworkInterface;
  import java.net.SocketException;
  import java.util.Arrays;
  import java.util.Enumeration;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Map.Entry;
  
  import static io.netty.util.internal.EmptyArrays.EMPTY_BYTES;
  
  public final class MacAddressUtil {
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(MacAddressUtil.class);
  
      private static final int EUI64_MAC_ADDRESS_LENGTH = 8;
      private static final int EUI48_MAC_ADDRESS_LENGTH = 6;
  
      /**
       * Obtains the best MAC address found on local network interfaces.
       * Generally speaking, an active network interface used on public
       * networks is better than a local network interface.
       *
       * @return byte array containing a MAC. null if no MAC can be found.
       */
      public static byte[] bestAvailableMac() {
          // Find the best MAC address available.
          byte[] bestMacAddr = EMPTY_BYTES;
          InetAddress bestInetAddr = NetUtil.LOCALHOST4;
  
          // Retrieve the list of available network interfaces.
          Map<NetworkInterface, InetAddress> ifaces = new LinkedHashMap<NetworkInterface, InetAddress>();
          for (NetworkInterface iface: NetUtil.NETWORK_INTERFACES) {
              // Use the interface with proper INET addresses only.
              Enumeration<InetAddress> addrs = SocketUtils.addressesFromNetworkInterface(iface);
              if (addrs.hasMoreElements()) {
                  InetAddress a = addrs.nextElement();
                  if (!a.isLoopbackAddress()) {
                      ifaces.put(iface, a);
                  }
              }
          }
  
          for (Entry<NetworkInterface, InetAddress> entry: ifaces.entrySet()) {
              NetworkInterface iface = entry.getKey();
              InetAddress inetAddr = entry.getValue();
              if (iface.isVirtual()) {
                  continue;
              }
  
              byte[] macAddr;
              try {
                  macAddr = SocketUtils.hardwareAddressFromNetworkInterface(iface);
              } catch (SocketException e) {
                  logger.debug("Failed to get the hardware address of a network interface: {}", iface, e);
                  continue;
              }
  
              boolean replace = false;
              int res = compareAddresses(bestMacAddr, macAddr);
              if (res < 0) {
                  // Found a better MAC address.
                  replace = true;
              } else if (res == 0) {
                  // Two MAC addresses are of pretty much same quality.
                  res = compareAddresses(bestInetAddr, inetAddr);
                  if (res < 0) {
                      // Found a MAC address with better INET address.
                      replace = true;
                  } else if (res == 0) {
                      // Cannot tell the difference.  Choose the longer one.
                      if (bestMacAddr.length < macAddr.length) {
                          replace = true;
                      }
                  }
              }
  
              if (replace) {
                 bestMacAddr = macAddr;
                 bestInetAddr = inetAddr;
             }
         }
 
         if (bestMacAddr == EMPTY_BYTES) {
             return null;
         }
 
         if (bestMacAddr.length == EUI48_MAC_ADDRESS_LENGTH) { // EUI-48 - convert to EUI-64
             byte[] newAddr = new byte[EUI64_MAC_ADDRESS_LENGTH];
             System.arraycopy(bestMacAddr, 0, newAddr, 0, 3);
             newAddr[3] = (byte) 0xFF;
             newAddr[4] = (byte) 0xFE;
             System.arraycopy(bestMacAddr, 3, newAddr, 5, 3);
             bestMacAddr = newAddr;
         } else {
             // Unknown
             bestMacAddr = Arrays.copyOf(bestMacAddr, EUI64_MAC_ADDRESS_LENGTH);
         }
 
         return bestMacAddr;
     }
 
     /**
      * Returns the result of {@link #bestAvailableMac()} if non-{@code null} otherwise returns a random EUI-64 MAC
      * address.
      */
     public static byte[] defaultMachineId() {
         byte[] bestMacAddr = bestAvailableMac();
         if (bestMacAddr == null) {
             bestMacAddr = new byte[EUI64_MAC_ADDRESS_LENGTH];
             PlatformDependent.threadLocalRandom().nextBytes(bestMacAddr);
             logger.warn(
                     "Failed to find a usable hardware address from the network interfaces; using random bytes: {}",
                     formatAddress(bestMacAddr));
         }
         return bestMacAddr;
     }
 
     /**
      * Parse a EUI-48, MAC-48, or EUI-64 MAC address from a {@link String} and return it as a {@code byte[]}.
      * @param value The string representation of the MAC address.
      * @return The byte representation of the MAC address.
      */
     public static byte[] parseMAC(String value) {
         final byte[] machineId;
         final char separator;
         switch (value.length()) {
             case 17:
                 separator = value.charAt(2);
                 validateMacSeparator(separator);
                 machineId = new byte[EUI48_MAC_ADDRESS_LENGTH];
                 break;
             case 23:
                 separator = value.charAt(2);
                 validateMacSeparator(separator);
                 machineId = new byte[EUI64_MAC_ADDRESS_LENGTH];
                 break;
             default:
                 throw new IllegalArgumentException("value is not supported [MAC-48, EUI-48, EUI-64]");
         }
 
         final int end = machineId.length - 1;
         int j = 0;
         for (int i = 0; i < end; ++i, j += 3) {
             final int sIndex = j + 2;
             machineId[i] = StringUtil.decodeHexByte(value, j);
             if (value.charAt(sIndex) != separator) {
                 throw new IllegalArgumentException("expected separator '" + separator + " but got '" +
                         value.charAt(sIndex) + "' at index: " + sIndex);
             }
         }
 
         machineId[end] = StringUtil.decodeHexByte(value, j);
 
         return machineId;
     }
 
     private static void validateMacSeparator(char separator) {
         if (separator != ':' && separator != '-') {
             throw new IllegalArgumentException("unsupported separator: " + separator + " (expected: [:-])");
         }
     }
 
     /**
      * @param addr byte array of a MAC address.
      * @return hex formatted MAC address.
      */
     public static String formatAddress(byte[] addr) {
         StringBuilder buf = new StringBuilder(24);
         for (byte b: addr) {
             buf.append(String.format("%02x:", b & 0xff));
         }
         return buf.substring(0, buf.length() - 1);
     }
 
     /**
      * @return positive - current is better, 0 - cannot tell from MAC addr, negative - candidate is better.
      */
     // visible for testing
     static int compareAddresses(byte[] current, byte[] candidate) {
         if (candidate == null || candidate.length < EUI48_MAC_ADDRESS_LENGTH) {
             return 1;
         }
 
         // Must not be filled with only 0 and 1.
         boolean onlyZeroAndOne = true;
         for (byte b: candidate) {
             if (b != 0 && b != 1) {
                 onlyZeroAndOne = false;
                 break;
             }
         }
 
         if (onlyZeroAndOne) {
             return 1;
         }
 
         // Must not be a multicast address
         if ((candidate[0] & 1) != 0) {
             return 1;
         }
 
         // Prefer globally unique address.
         if ((candidate[0] & 2) == 0) {
             if (current.length != 0 && (current[0] & 2) == 0) {
                 // Both current and candidate are globally unique addresses.
                 return 0;
             } else {
                 // Only candidate is globally unique.
                 return -1;
             }
         } else {
             if (current.length != 0 && (current[0] & 2) == 0) {
                 // Only current is globally unique.
                 return 1;
             } else {
                 // Both current and candidate are non-unique.
                 return 0;
             }
         }
     }
 
     /**
      * @return positive - current is better, 0 - cannot tell, negative - candidate is better
      */
     private static int compareAddresses(InetAddress current, InetAddress candidate) {
         return scoreAddress(current) - scoreAddress(candidate);
     }
 
     private static int scoreAddress(InetAddress addr) {
         if (addr.isAnyLocalAddress() || addr.isLoopbackAddress()) {
             return 0;
         }
         if (addr.isMulticastAddress()) {
             return 1;
         }
         if (addr.isLinkLocalAddress()) {
             return 2;
         }
         if (addr.isSiteLocalAddress()) {
             return 3;
         }
 
         return 4;
     }
 
     private MacAddressUtil() { }
 }