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   /*
    * Copyright 2012 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 io.netty.util.NetUtilInitializations.NetworkIfaceAndInetAddress;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.net.Inet4Address;
  import java.net.Inet6Address;
  import java.net.InetAddress;
  import java.net.InetSocketAddress;
  import java.net.NetworkInterface;
  import java.net.UnknownHostException;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.Arrays;
  import java.util.Collection;
  
  import static io.netty.util.AsciiString.indexOf;
  
  /**
   * A class that holds a number of network-related constants.
   * <p/>
   * This class borrowed some of its methods from a  modified fork of the
   * <a href="https://svn.apache.org/repos/asf/harmony/enhanced/java/branches/java6/classlib/modules/luni/
   * src/main/java/org/apache/harmony/luni/util/Inet6Util.java">Inet6Util class</a> which was part of Apache Harmony.
   */
  public final class NetUtil {
  
      /**
       * The {@link Inet4Address} that represents the IPv4 loopback address '127.0.0.1'
       */
      public static final Inet4Address LOCALHOST4;
  
      /**
       * The {@link Inet6Address} that represents the IPv6 loopback address '::1'
       */
      public static final Inet6Address LOCALHOST6;
  
      /**
       * The {@link InetAddress} that represents the loopback address. If IPv6 stack is available, it will refer to
       * {@link #LOCALHOST6}.  Otherwise, {@link #LOCALHOST4}.
       */
      public static final InetAddress LOCALHOST;
  
      /**
       * The loopback {@link NetworkInterface} of the current machine
       */
      public static final NetworkInterface LOOPBACK_IF;
  
      /**
       * An unmodifiable Collection of all the interfaces on this machine.
       */
      public static final Collection<NetworkInterface> NETWORK_INTERFACES;
  
      /**
       * The SOMAXCONN value of the current machine.  If failed to get the value,  {@code 200} is used as a
       * default value for Windows and {@code 128} for others.
       */
      public static final int SOMAXCONN;
  
      /**
       * This defines how many words (represented as ints) are needed to represent an IPv6 address
       */
      private static final int IPV6_WORD_COUNT = 8;
  
      /**
       * The maximum number of characters for an IPV6 string with no scope
       */
      private static final int IPV6_MAX_CHAR_COUNT = 39;
  
      /**
       * Number of bytes needed to represent an IPV6 value
       */
      private static final int IPV6_BYTE_COUNT = 16;
  
     /**
      * Maximum amount of value adding characters in between IPV6 separators
      */
     private static final int IPV6_MAX_CHAR_BETWEEN_SEPARATOR = 4;
 
     /**
      * Minimum number of separators that must be present in an IPv6 string
      */
     private static final int IPV6_MIN_SEPARATORS = 2;
 
     /**
      * Maximum number of separators that must be present in an IPv6 string
      */
     private static final int IPV6_MAX_SEPARATORS = 8;
 
     /**
      * Maximum amount of value adding characters in between IPV4 separators
      */
     private static final int IPV4_MAX_CHAR_BETWEEN_SEPARATOR = 3;
 
     /**
      * Number of separators that must be present in an IPv4 string
      */
     private static final int IPV4_SEPARATORS = 3;
 
     /**
      * {@code true} if IPv4 should be used even if the system supports both IPv4 and IPv6.
      */
     private static final boolean IPV4_PREFERRED = SystemPropertyUtil.getBoolean("java.net.preferIPv4Stack", false);
 
     /**
      * {@code true} if an IPv6 address should be preferred when a host has both an IPv4 address and an IPv6 address.
      */
     private static final boolean IPV6_ADDRESSES_PREFERRED;
 
     /**
      * The logger being used by this class
      */
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(NetUtil.class);
 
     static {
         String prefer = SystemPropertyUtil.get("java.net.preferIPv6Addresses", "false");
         if ("true".equalsIgnoreCase(prefer.trim())) {
             IPV6_ADDRESSES_PREFERRED = true;
         } else {
             // Let's just use false in this case as only true is "forcing" ipv6.
             IPV6_ADDRESSES_PREFERRED = false;
         }
         logger.debug("-Djava.net.preferIPv4Stack: {}", IPV4_PREFERRED);
         logger.debug("-Djava.net.preferIPv6Addresses: {}", prefer);
 
         NETWORK_INTERFACES = NetUtilInitializations.networkInterfaces();
 
         // Create IPv4 loopback address.
         LOCALHOST4 = NetUtilInitializations.createLocalhost4();
 
         // Create IPv6 loopback address.
         LOCALHOST6 = NetUtilInitializations.createLocalhost6();
 
         NetworkIfaceAndInetAddress loopback =
                 NetUtilInitializations.determineLoopback(NETWORK_INTERFACES, LOCALHOST4, LOCALHOST6);
         LOOPBACK_IF = loopback.iface();
         LOCALHOST = loopback.address();
 
         // As a SecurityManager may prevent reading the somaxconn file we wrap this in a privileged block.
         //
         // See https://github.com/netty/netty/issues/3680
         SOMAXCONN = AccessController.doPrivileged(new SoMaxConnAction());
     }
 
     private static final class SoMaxConnAction implements PrivilegedAction<Integer> {
         @Override
         public Integer run() {
             // Determine the default somaxconn (server socket backlog) value of the platform.
             // The known defaults:
             // - Windows NT Server 4.0+: 200
             // - Linux and Mac OS X: 128
             int somaxconn = PlatformDependent.isWindows() ? 200 : 128;
             File file = new File("/proc/sys/net/core/somaxconn");
             BufferedReader in = null;
             try {
                 // file.exists() may throw a SecurityException if a SecurityManager is used, so execute it in the
                 // try / catch block.
                 // See https://github.com/netty/netty/issues/4936
                 if (file.exists()) {
                     in = new BufferedReader(new FileReader(file));
                     somaxconn = Integer.parseInt(in.readLine());
                     if (logger.isDebugEnabled()) {
                         logger.debug("{}: {}", file, somaxconn);
                     }
                 } else {
                     // Try to get from sysctl
                     Integer tmp = null;
                     if (SystemPropertyUtil.getBoolean("io.netty.net.somaxconn.trySysctl", false)) {
                         tmp = sysctlGetInt("kern.ipc.somaxconn");
                         if (tmp == null) {
                             tmp = sysctlGetInt("kern.ipc.soacceptqueue");
                             if (tmp != null) {
                                 somaxconn = tmp;
                             }
                         } else {
                             somaxconn = tmp;
                         }
                     }
 
                     if (tmp == null) {
                         logger.debug("Failed to get SOMAXCONN from sysctl and file {}. Default: {}", file,
                                 somaxconn);
                     }
                 }
             } catch (Exception e) {
                 if (logger.isDebugEnabled()) {
                     logger.debug("Failed to get SOMAXCONN from sysctl and file {}. Default: {}",
                             file, somaxconn, e);
                 }
             } finally {
                 if (in != null) {
                     try {
                         in.close();
                     } catch (Exception e) {
                         // Ignored.
                     }
                 }
             }
             return somaxconn;
         }
     }
     /**
      * This will execute <a href ="https://www.freebsd.org/cgi/man.cgi?sysctl(8)">sysctl</a> with the {@code sysctlKey}
      * which is expected to return the numeric value for for {@code sysctlKey}.
      * @param sysctlKey The key which the return value corresponds to.
      * @return The <a href ="https://www.freebsd.org/cgi/man.cgi?sysctl(8)">sysctl</a> value for {@code sysctlKey}.
      */
     private static Integer sysctlGetInt(String sysctlKey) throws IOException {
         Process process = new ProcessBuilder("sysctl", sysctlKey).start();
         try {
             // Suppress warnings about resource leaks since the buffered reader is closed below
             InputStream is = process.getInputStream();
             InputStreamReader isr = new InputStreamReader(is);
             BufferedReader br = new BufferedReader(isr);
             try {
                 String line = br.readLine();
                 if (line != null && line.startsWith(sysctlKey)) {
                     for (int i = line.length() - 1; i > sysctlKey.length(); --i) {
                         if (!Character.isDigit(line.charAt(i))) {
                             return Integer.valueOf(line.substring(i + 1));
                         }
                     }
                 }
                 return null;
             } finally {
                 br.close();
             }
         } finally {
             // No need of 'null' check because we're initializing
             // the Process instance in first line. Any exception
             // raised will directly lead to throwable.
             process.destroy();
         }
     }
 
     /**
      * Returns {@code true} if IPv4 should be used even if the system supports both IPv4 and IPv6. Setting this
      * property to {@code true} will disable IPv6 support. The default value of this property is {@code false}.
      *
      * @see <a href="https://docs.oracle.com/javase/8/docs/api/java/net/doc-files/net-properties.html">Java SE
      *      networking properties</a>
      */
     public static boolean isIpV4StackPreferred() {
         return IPV4_PREFERRED;
     }
 
     /**
      * Returns {@code true} if an IPv6 address should be preferred when a host has both an IPv4 address and an IPv6
      * address. The default value of this property is {@code false}.
      *
      * @see <a href="https://docs.oracle.com/javase/8/docs/api/java/net/doc-files/net-properties.html">Java SE
      *      networking properties</a>
      */
     public static boolean isIpV6AddressesPreferred() {
         return IPV6_ADDRESSES_PREFERRED;
     }
 
     /**
      * Creates an byte[] based on an ipAddressString. No error handling is performed here.
      */
     public static byte[] createByteArrayFromIpAddressString(String ipAddressString) {
 
         if (isValidIpV4Address(ipAddressString)) {
             return validIpV4ToBytes(ipAddressString);
         }
 
         if (isValidIpV6Address(ipAddressString)) {
             if (ipAddressString.charAt(0) == '[') {
                 ipAddressString = ipAddressString.substring(1, ipAddressString.length() - 1);
             }
 
             int percentPos = ipAddressString.indexOf('%');
             if (percentPos >= 0) {
                 ipAddressString = ipAddressString.substring(0, percentPos);
             }
 
             return getIPv6ByName(ipAddressString, true);
         }
         return null;
     }
 
     /**
      * Creates an {@link InetAddress} based on an ipAddressString or might return null if it can't be parsed.
      * No error handling is performed here.
      */
     public static InetAddress createInetAddressFromIpAddressString(String ipAddressString) {
         if (isValidIpV4Address(ipAddressString)) {
             byte[] bytes = validIpV4ToBytes(ipAddressString);
             try {
                 return InetAddress.getByAddress(bytes);
             } catch (UnknownHostException e) {
                 // Should never happen!
                 throw new IllegalStateException(e);
             }
         }
 
         if (isValidIpV6Address(ipAddressString)) {
             if (ipAddressString.charAt(0) == '[') {
                 ipAddressString = ipAddressString.substring(1, ipAddressString.length() - 1);
             }
 
             int percentPos = ipAddressString.indexOf('%');
             if (percentPos >= 0) {
                 try {
                     int scopeId = Integer.parseInt(ipAddressString.substring(percentPos + 1));
                     ipAddressString = ipAddressString.substring(0, percentPos);
                     byte[] bytes = getIPv6ByName(ipAddressString, true);
                     if (bytes == null) {
                         return null;
                     }
                     try {
                         return Inet6Address.getByAddress(null, bytes, scopeId);
                     } catch (UnknownHostException e) {
                         // Should never happen!
                         throw new IllegalStateException(e);
                     }
                 } catch (NumberFormatException e) {
                     return null;
                 }
             }
             byte[] bytes = getIPv6ByName(ipAddressString, true);
             if (bytes == null) {
                 return null;
             }
             try {
                 return InetAddress.getByAddress(bytes);
             } catch (UnknownHostException e) {
                 // Should never happen!
                 throw new IllegalStateException(e);
             }
         }
         return null;
     }
 
     private static int decimalDigit(String str, int pos) {
         return str.charAt(pos) - '0';
     }
 
     private static byte ipv4WordToByte(String ip, int from, int toExclusive) {
         int ret = decimalDigit(ip, from);
         from++;
         if (from == toExclusive) {
             return (byte) ret;
         }
         ret = ret * 10 + decimalDigit(ip, from);
         from++;
         if (from == toExclusive) {
             return (byte) ret;
         }
         return (byte) (ret * 10 + decimalDigit(ip, from));
     }
 
     // visible for tests
     static byte[] validIpV4ToBytes(String ip) {
         int i;
         return new byte[] {
                 ipv4WordToByte(ip, 0, i = ip.indexOf('.', 1)),
                 ipv4WordToByte(ip, i + 1, i = ip.indexOf('.', i + 2)),
                 ipv4WordToByte(ip, i + 1, i = ip.indexOf('.', i + 2)),
                 ipv4WordToByte(ip, i + 1, ip.length())
         };
     }
 
     /**
      * Convert {@link Inet4Address} into {@code int}
      */
     public static int ipv4AddressToInt(Inet4Address ipAddress) {
         byte[] octets = ipAddress.getAddress();
 
         return  (octets[0] & 0xff) << 24 |
                 (octets[1] & 0xff) << 16 |
                 (octets[2] & 0xff) << 8 |
                  octets[3] & 0xff;
     }
 
     /**
      * Converts a 32-bit integer into an IPv4 address.
      */
     public static String intToIpAddress(int i) {
         StringBuilder buf = new StringBuilder(15);
         buf.append(i >> 24 & 0xff);
         buf.append('.');
         buf.append(i >> 16 & 0xff);
         buf.append('.');
         buf.append(i >> 8 & 0xff);
         buf.append('.');
         buf.append(i & 0xff);
         return buf.toString();
     }
 
     /**
      * Converts 4-byte or 16-byte data into an IPv4 or IPv6 string respectively.
      *
      * @throws IllegalArgumentException
      *         if {@code length} is not {@code 4} nor {@code 16}
      */
     public static String bytesToIpAddress(byte[] bytes) {
         return bytesToIpAddress(bytes, 0, bytes.length);
     }
 
     /**
      * Converts 4-byte or 16-byte data into an IPv4 or IPv6 string respectively.
      *
      * @throws IllegalArgumentException
      *         if {@code length} is not {@code 4} nor {@code 16}
      */
     public static String bytesToIpAddress(byte[] bytes, int offset, int length) {
         switch (length) {
             case 4: {
                 return new StringBuilder(15)
                         .append(bytes[offset] & 0xff)
                         .append('.')
                         .append(bytes[offset + 1] & 0xff)
                         .append('.')
                         .append(bytes[offset + 2] & 0xff)
                         .append('.')
                         .append(bytes[offset + 3] & 0xff).toString();
             }
             case 16:
                 return toAddressString(bytes, offset, false);
             default:
                 throw new IllegalArgumentException("length: " + length + " (expected: 4 or 16)");
         }
     }
 
     public static boolean isValidIpV6Address(String ip) {
         return isValidIpV6Address((CharSequence) ip);
     }
 
     public static boolean isValidIpV6Address(CharSequence ip) {
         int end = ip.length();
         if (end < 2) {
             return false;
         }
 
         // strip "[]"
         int start;
         char c = ip.charAt(0);
         if (c == '[') {
             end--;
             if (ip.charAt(end) != ']') {
                 // must have a close ]
                 return false;
             }
             start = 1;
             c = ip.charAt(1);
         } else {
             start = 0;
         }
 
         int colons;
         int compressBegin;
         if (c == ':') {
             // an IPv6 address can start with "::" or with a number
             if (ip.charAt(start + 1) != ':') {
                 return false;
             }
             colons = 2;
             compressBegin = start;
             start += 2;
         } else {
             colons = 0;
             compressBegin = -1;
         }
 
         int wordLen = 0;
         loop:
         for (int i = start; i < end; i++) {
             c = ip.charAt(i);
             if (isValidHexChar(c)) {
                 if (wordLen < 4) {
                     wordLen++;
                     continue;
                 }
                 return false;
             }
 
             switch (c) {
             case ':':
                 if (colons > 7) {
                     return false;
                 }
                 if (ip.charAt(i - 1) == ':') {
                     if (compressBegin >= 0) {
                         return false;
                     }
                     compressBegin = i - 1;
                 } else {
                     wordLen = 0;
                 }
                 colons++;
                 break;
             case '.':
                 // case for the last 32-bits represented as IPv4 x:x:x:x:x:x:d.d.d.d
 
                 // check a normal case (6 single colons)
                 if (compressBegin < 0 && colons != 6 ||
                     // a special case ::1:2:3:4:5:d.d.d.d allows 7 colons with an
                     // IPv4 ending, otherwise 7 :'s is bad
                     (colons == 7 && compressBegin >= start || colons > 7)) {
                     return false;
                 }
 
                 // Verify this address is of the correct structure to contain an IPv4 address.
                 // It must be IPv4-Mapped or IPv4-Compatible
                 // (see https://tools.ietf.org/html/rfc4291#section-2.5.5).
                 int ipv4Start = i - wordLen;
                 int j = ipv4Start - 2; // index of character before the previous ':'.
                 if (isValidIPv4MappedChar(ip.charAt(j))) {
                     if (!isValidIPv4MappedChar(ip.charAt(j - 1)) ||
                         !isValidIPv4MappedChar(ip.charAt(j - 2)) ||
                         !isValidIPv4MappedChar(ip.charAt(j - 3))) {
                         return false;
                     }
                     j -= 5;
                 }
 
                 for (; j >= start; --j) {
                     char tmpChar = ip.charAt(j);
                     if (tmpChar != '0' && tmpChar != ':') {
                         return false;
                     }
                 }
 
                 // 7 - is minimum IPv4 address length
                 int ipv4End = indexOf(ip, '%', ipv4Start + 7);
                 if (ipv4End < 0) {
                     ipv4End = end;
                 }
                 return isValidIpV4Address(ip, ipv4Start, ipv4End);
             case '%':
                 // strip the interface name/index after the percent sign
                 end = i;
                 break loop;
             default:
                 return false;
             }
         }
 
         // normal case without compression
         if (compressBegin < 0) {
             return colons == 7 && wordLen > 0;
         }
 
         return compressBegin + 2 == end ||
                // 8 colons is valid only if compression in start or end
                wordLen > 0 && (colons < 8 || compressBegin <= start);
     }
 
     private static boolean isValidIpV4Word(CharSequence word, int from, int toExclusive) {
         int len = toExclusive - from;
         char c0, c1, c2;
         if (len < 1 || len > 3 || (c0 = word.charAt(from)) < '0') {
             return false;
         }
         if (len == 3) {
             return (c1 = word.charAt(from + 1)) >= '0' &&
                    (c2 = word.charAt(from + 2)) >= '0' &&
                    (c0 <= '1' && c1 <= '9' && c2 <= '9' ||
                     c0 == '2' && c1 <= '5' && (c2 <= '5' || c1 < '5' && c2 <= '9'));
         }
         return c0 <= '9' && (len == 1 || isValidNumericChar(word.charAt(from + 1)));
     }
 
     private static boolean isValidHexChar(char c) {
         return c >= '0' && c <= '9' || c >= 'A' && c <= 'F' || c >= 'a' && c <= 'f';
     }
 
     private static boolean isValidNumericChar(char c) {
         return c >= '0' && c <= '9';
     }
 
     private static boolean isValidIPv4MappedChar(char c) {
         return c == 'f' || c == 'F';
     }
 
     private static boolean isValidIPv4MappedSeparators(byte b0, byte b1, boolean mustBeZero) {
         // We allow IPv4 Mapped (https://tools.ietf.org/html/rfc4291#section-2.5.5.1)
         // and IPv4 compatible (https://tools.ietf.org/html/rfc4291#section-2.5.5.1).
         // The IPv4 compatible is deprecated, but it allows parsing of plain IPv4 addressed into IPv6-Mapped addresses.
         return b0 == b1 && (b0 == 0 || !mustBeZero && b1 == -1);
     }
 
     private static boolean isValidIPv4Mapped(byte[] bytes, int currentIndex, int compressBegin, int compressLength) {
         final boolean mustBeZero = compressBegin + compressLength >= 14;
         return currentIndex <= 12 && currentIndex >= 2 && (!mustBeZero || compressBegin < 12) &&
                 isValidIPv4MappedSeparators(bytes[currentIndex - 1], bytes[currentIndex - 2], mustBeZero) &&
                 PlatformDependent.isZero(bytes, 0, currentIndex - 3);
     }
 
     /**
      * Takes a {@link CharSequence} and parses it to see if it is a valid IPV4 address.
      *
      * @return true, if the string represents an IPV4 address in dotted
      *         notation, false otherwise
      */
     public static boolean isValidIpV4Address(CharSequence ip) {
         return isValidIpV4Address(ip, 0, ip.length());
     }
 
     /**
      * Takes a {@link String} and parses it to see if it is a valid IPV4 address.
      *
      * @return true, if the string represents an IPV4 address in dotted
      *         notation, false otherwise
      */
     public static boolean isValidIpV4Address(String ip) {
         return isValidIpV4Address(ip, 0, ip.length());
     }
 
     private static boolean isValidIpV4Address(CharSequence ip, int from, int toExcluded) {
         return ip instanceof String ? isValidIpV4Address((String) ip, from, toExcluded) :
                 ip instanceof AsciiString ? isValidIpV4Address((AsciiString) ip, from, toExcluded) :
                         isValidIpV4Address0(ip, from, toExcluded);
     }
 
     @SuppressWarnings("DuplicateBooleanBranch")
     private static boolean isValidIpV4Address(String ip, int from, int toExcluded) {
         int len = toExcluded - from;
         int i;
         return len <= 15 && len >= 7 &&
                 (i = ip.indexOf('.', from + 1)) > 0 && isValidIpV4Word(ip, from, i) &&
                 (i =  ip.indexOf('.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 (i =  ip.indexOf('.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 isValidIpV4Word(ip, i + 1, toExcluded);
     }
 
     @SuppressWarnings("DuplicateBooleanBranch")
     private static boolean isValidIpV4Address(AsciiString ip, int from, int toExcluded) {
         int len = toExcluded - from;
         int i;
         return len <= 15 && len >= 7 &&
                 (i = ip.indexOf('.', from + 1)) > 0 && isValidIpV4Word(ip, from, i) &&
                 (i =  ip.indexOf('.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 (i =  ip.indexOf('.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 isValidIpV4Word(ip, i + 1, toExcluded);
     }
 
     @SuppressWarnings("DuplicateBooleanBranch")
     private static boolean isValidIpV4Address0(CharSequence ip, int from, int toExcluded) {
         int len = toExcluded - from;
         int i;
         return len <= 15 && len >= 7 &&
                 (i = indexOf(ip, '.', from + 1)) > 0 && isValidIpV4Word(ip, from, i) &&
                 (i =  indexOf(ip, '.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 (i =  indexOf(ip, '.', from = i + 2)) > 0 && isValidIpV4Word(ip, from - 1, i) &&
                 isValidIpV4Word(ip, i + 1, toExcluded);
     }
 
     /**
      * Returns the {@link Inet6Address} representation of a {@link CharSequence} IP address.
      * <p>
      * This method will treat all IPv4 type addresses as "IPv4 mapped" (see {@link #getByName(CharSequence, boolean)})
      * @param ip {@link CharSequence} IP address to be converted to a {@link Inet6Address}
      * @return {@link Inet6Address} representation of the {@code ip} or {@code null} if not a valid IP address.
      */
     public static Inet6Address getByName(CharSequence ip) {
         return getByName(ip, true);
     }
 
     /**
      * Returns the {@link Inet6Address} representation of a {@link CharSequence} IP address.
      * <p>
      * The {@code ipv4Mapped} parameter specifies how IPv4 addresses should be treated.
      * "IPv4 mapped" format as
      * defined in <a href="https://tools.ietf.org/html/rfc4291#section-2.5.5">rfc 4291 section 2</a> is supported.
      * @param ip {@link CharSequence} IP address to be converted to a {@link Inet6Address}
      * @param ipv4Mapped
      * <ul>
      * <li>{@code true} To allow IPv4 mapped inputs to be translated into {@link Inet6Address}</li>
      * <li>{@code false} Consider IPv4 mapped addresses as invalid.</li>
      * </ul>
      * @return {@link Inet6Address} representation of the {@code ip} or {@code null} if not a valid IP address.
      */
     public static Inet6Address getByName(CharSequence ip, boolean ipv4Mapped) {
         byte[] bytes = getIPv6ByName(ip, ipv4Mapped);
         if (bytes == null) {
             return null;
         }
         try {
             return Inet6Address.getByAddress(null, bytes, -1);
         } catch (UnknownHostException e) {
             throw new RuntimeException(e); // Should never happen
         }
     }
 
     /**
      * Returns the byte array representation of a {@link CharSequence} IP address.
      * <p>
      * The {@code ipv4Mapped} parameter specifies how IPv4 addresses should be treated.
      * "IPv4 mapped" format as
      * defined in <a href="https://tools.ietf.org/html/rfc4291#section-2.5.5">rfc 4291 section 2</a> is supported.
      * @param ip {@link CharSequence} IP address to be converted to a {@link Inet6Address}
      * @param ipv4Mapped
      * <ul>
      * <li>{@code true} To allow IPv4 mapped inputs to be translated into {@link Inet6Address}</li>
      * <li>{@code false} Consider IPv4 mapped addresses as invalid.</li>
      * </ul>
      * @return byte array representation of the {@code ip} or {@code null} if not a valid IP address.
      */
      // visible for test
     static byte[] getIPv6ByName(CharSequence ip, boolean ipv4Mapped) {
         final byte[] bytes = new byte[IPV6_BYTE_COUNT];
         final int ipLength = ip.length();
         int compressBegin = 0;
         int compressLength = 0;
         int currentIndex = 0;
         int value = 0;
         int begin = -1;
         int i = 0;
         int ipv6Separators = 0;
         int ipv4Separators = 0;
         int tmp;
         for (; i < ipLength; ++i) {
             final char c = ip.charAt(i);
             switch (c) {
             case ':':
                 ++ipv6Separators;
                 if (i - begin > IPV6_MAX_CHAR_BETWEEN_SEPARATOR ||
                         ipv4Separators > 0 || ipv6Separators > IPV6_MAX_SEPARATORS ||
                         currentIndex + 1 >= bytes.length) {
                     return null;
                 }
                 value <<= (IPV6_MAX_CHAR_BETWEEN_SEPARATOR - (i - begin)) << 2;
 
                 if (compressLength > 0) {
                     compressLength -= 2;
                 }
 
                 // The value integer holds at most 4 bytes from right (most significant) to left (least significant).
                 // The following bit shifting is used to extract and re-order the individual bytes to achieve a
                 // left (most significant) to right (least significant) ordering.
                 bytes[currentIndex++] = (byte) (((value & 0xf) << 4) | ((value >> 4) & 0xf));
                 bytes[currentIndex++] = (byte) ((((value >> 8) & 0xf) << 4) | ((value >> 12) & 0xf));
                 tmp = i + 1;
                 if (tmp < ipLength && ip.charAt(tmp) == ':') {
                     ++tmp;
                     if (compressBegin != 0 || (tmp < ipLength && ip.charAt(tmp) == ':')) {
                         return null;
                     }
                     ++ipv6Separators;
                     compressBegin = currentIndex;
                     compressLength = bytes.length - compressBegin - 2;
                     ++i;
                 }
                 value = 0;
                 begin = -1;
                 break;
             case '.':
                 ++ipv4Separators;
                 tmp = i - begin; // tmp is the length of the current segment.
                 if (tmp > IPV4_MAX_CHAR_BETWEEN_SEPARATOR
                         || begin < 0
                         || ipv4Separators > IPV4_SEPARATORS
                         || (ipv6Separators > 0 && (currentIndex + compressLength < 12))
                         || i + 1 >= ipLength
                         || currentIndex >= bytes.length
                         || ipv4Separators == 1 &&
                             // We also parse pure IPv4 addresses as IPv4-Mapped for ease of use.
                             ((!ipv4Mapped || currentIndex != 0 && !isValidIPv4Mapped(bytes, currentIndex,
                                                                                      compressBegin, compressLength)) ||
                                 (tmp == 3 && (!isValidNumericChar(ip.charAt(i - 1)) ||
                                               !isValidNumericChar(ip.charAt(i - 2)) ||
                                               !isValidNumericChar(ip.charAt(i - 3))) ||
                                  tmp == 2 && (!isValidNumericChar(ip.charAt(i - 1)) ||
                                               !isValidNumericChar(ip.charAt(i - 2))) ||
                                  tmp == 1 && !isValidNumericChar(ip.charAt(i - 1))))) {
                     return null;
                 }
                 value <<= (IPV4_MAX_CHAR_BETWEEN_SEPARATOR - tmp) << 2;
 
                 // The value integer holds at most 3 bytes from right (most significant) to left (least significant).
                 // The following bit shifting is to restructure the bytes to be left (most significant) to
                 // right (least significant) while also accounting for each IPv4 digit is base 10.
                 begin = (value & 0xf) * 100 + ((value >> 4) & 0xf) * 10 + ((value >> 8) & 0xf);
                 if (begin > 255) {
                     return null;
                 }
                 bytes[currentIndex++] = (byte) begin;
                 value = 0;
                 begin = -1;
                 break;
             default:
                 if (!isValidHexChar(c) || (ipv4Separators > 0 && !isValidNumericChar(c))) {
                     return null;
                 }
                 if (begin < 0) {
                     begin = i;
                 } else if (i - begin > IPV6_MAX_CHAR_BETWEEN_SEPARATOR) {
                     return null;
                 }
                 // The value is treated as a sort of array of numbers because we are dealing with
                 // at most 4 consecutive bytes we can use bit shifting to accomplish this.
                 // The most significant byte will be encountered first, and reside in the right most
                 // position of the following integer
                 value += StringUtil.decodeHexNibble(c) << ((i - begin) << 2);
                 break;
             }
         }
 
         final boolean isCompressed = compressBegin > 0;
         // Finish up last set of data that was accumulated in the loop (or before the loop)
         if (ipv4Separators > 0) {
             if (begin > 0 && i - begin > IPV4_MAX_CHAR_BETWEEN_SEPARATOR ||
                     ipv4Separators != IPV4_SEPARATORS ||
                     currentIndex >= bytes.length) {
                 return null;
             }
             if (!(ipv6Separators == 0 || ipv6Separators >= IPV6_MIN_SEPARATORS &&
                            (!isCompressed && (ipv6Separators == 6 && ip.charAt(0) != ':') ||
                             isCompressed && (ipv6Separators < IPV6_MAX_SEPARATORS &&
                                              (ip.charAt(0) != ':' || compressBegin <= 2))))) {
                 return null;
             }
             value <<= (IPV4_MAX_CHAR_BETWEEN_SEPARATOR - (i - begin)) << 2;
 
             // The value integer holds at most 3 bytes from right (most significant) to left (least significant).
             // The following bit shifting is to restructure the bytes to be left (most significant) to
             // right (least significant) while also accounting for each IPv4 digit is base 10.
             begin = (value & 0xf) * 100 + ((value >> 4) & 0xf) * 10 + ((value >> 8) & 0xf);
             if (begin > 255) {
                 return null;
             }
             bytes[currentIndex++] = (byte) begin;
         } else {
             tmp = ipLength - 1;
             if (begin > 0 && i - begin > IPV6_MAX_CHAR_BETWEEN_SEPARATOR ||
                     ipv6Separators < IPV6_MIN_SEPARATORS ||
                     !isCompressed && (ipv6Separators + 1 != IPV6_MAX_SEPARATORS  ||
                                       ip.charAt(0) == ':' || ip.charAt(tmp) == ':') ||
                     isCompressed && (ipv6Separators > IPV6_MAX_SEPARATORS ||
                         (ipv6Separators == IPV6_MAX_SEPARATORS &&
                           (compressBegin <= 2 && ip.charAt(0) != ':' ||
                            compressBegin >= 14 && ip.charAt(tmp) != ':'))) ||
                     currentIndex + 1 >= bytes.length ||
                     begin < 0 && ip.charAt(tmp - 1) != ':' ||
                     compressBegin > 2 && ip.charAt(0) == ':') {
                 return null;
             }
             if (begin >= 0 && i - begin <= IPV6_MAX_CHAR_BETWEEN_SEPARATOR) {
                 value <<= (IPV6_MAX_CHAR_BETWEEN_SEPARATOR - (i - begin)) << 2;
             }
             // The value integer holds at most 4 bytes from right (most significant) to left (least significant).
             // The following bit shifting is used to extract and re-order the individual bytes to achieve a
             // left (most significant) to right (least significant) ordering.
             bytes[currentIndex++] = (byte) (((value & 0xf) << 4) | ((value >> 4) & 0xf));
             bytes[currentIndex++] = (byte) ((((value >> 8) & 0xf) << 4) | ((value >> 12) & 0xf));
         }
 
         if (currentIndex < bytes.length) {
             int toBeCopiedLength = currentIndex - compressBegin;
             int targetIndex = bytes.length - toBeCopiedLength;
             System.arraycopy(bytes, compressBegin, bytes, targetIndex, toBeCopiedLength);
             // targetIndex is also the `toIndex` to fill 0
             Arrays.fill(bytes, compressBegin, targetIndex, (byte) 0);
         }
 
         if (ipv4Separators > 0) {
             // We only support IPv4-Mapped addresses [1] because IPv4-Compatible addresses are deprecated [2].
             // [1] https://tools.ietf.org/html/rfc4291#section-2.5.5.2
             // [2] https://tools.ietf.org/html/rfc4291#section-2.5.5.1
             bytes[10] = bytes[11] = (byte) 0xff;
         }
 
         return bytes;
     }
 
     /**
      * Returns the {@link String} representation of an {@link InetSocketAddress}.
      * <p>
      * The output does not include Scope ID.
      * @param addr {@link InetSocketAddress} to be converted to an address string
      * @return {@code String} containing the text-formatted IP address
      */
     public static String toSocketAddressString(InetSocketAddress addr) {
         String port = String.valueOf(addr.getPort());
         final StringBuilder sb;
 
         if (addr.isUnresolved()) {
             String hostname = getHostname(addr);
             sb = newSocketAddressStringBuilder(hostname, port, !isValidIpV6Address(hostname));
         } else {
             InetAddress address = addr.getAddress();
             String hostString = toAddressString(address);
             sb = newSocketAddressStringBuilder(hostString, port, address instanceof Inet4Address);
         }
         return sb.append(':').append(port).toString();
     }
 
     /**
      * Returns the {@link String} representation of a host port combo.
      */
     public static String toSocketAddressString(String host, int port) {
         String portStr = String.valueOf(port);
         return newSocketAddressStringBuilder(
                 host, portStr, !isValidIpV6Address(host)).append(':').append(portStr).toString();
     }
 
     private static StringBuilder newSocketAddressStringBuilder(String host, String port, boolean ipv4) {
         int hostLen = host.length();
         if (ipv4) {
             // Need to include enough space for hostString:port.
             return new StringBuilder(hostLen + 1 + port.length()).append(host);
         }
         // Need to include enough space for [hostString]:port.
         StringBuilder stringBuilder = new StringBuilder(hostLen + 3 + port.length());
         if (hostLen > 1 && host.charAt(0) == '[' && host.charAt(hostLen - 1) == ']') {
             return stringBuilder.append(host);
         }
         return stringBuilder.append('[').append(host).append(']');
     }
 
     /**
      * Returns the {@link String} representation of an {@link InetAddress}.
      * <ul>
      * <li>Inet4Address results are identical to {@link InetAddress#getHostAddress()}</li>
      * <li>Inet6Address results adhere to
      * <a href="https://tools.ietf.org/html/rfc5952#section-4">rfc 5952 section 4</a></li>
      * </ul>
      * <p>
      * The output does not include Scope ID.
      * @param ip {@link InetAddress} to be converted to an address string
      * @return {@code String} containing the text-formatted IP address
      */
     public static String toAddressString(InetAddress ip) {
         return toAddressString(ip, false);
     }
 
     /**
      * Returns the {@link String} representation of an {@link InetAddress}.
      * <ul>
      * <li>Inet4Address results are identical to {@link InetAddress#getHostAddress()}</li>
      * <li>Inet6Address results adhere to
      * <a href="https://tools.ietf.org/html/rfc5952#section-4">rfc 5952 section 4</a> if
      * {@code ipv4Mapped} is false.  If {@code ipv4Mapped} is true then "IPv4 mapped" format
      * from <a href="https://tools.ietf.org/html/rfc4291#section-2.5.5">rfc 4291 section 2</a> will be supported.
      * The compressed result will always obey the compression rules defined in
      * <a href="https://tools.ietf.org/html/rfc5952#section-4">rfc 5952 section 4</a></li>
      * </ul>
      * <p>
      * The output does not include Scope ID.
      * @param ip {@link InetAddress} to be converted to an address string
      * @param ipv4Mapped
      * <ul>
      * <li>{@code true} to stray from strict rfc 5952 and support the "IPv4 mapped" format
      * defined in <a href="https://tools.ietf.org/html/rfc4291#section-2.5.5">rfc 4291 section 2</a> while still
      * following the updated guidelines in
      * <a href="https://tools.ietf.org/html/rfc5952#section-4">rfc 5952 section 4</a></li>
      * <li>{@code false} to strictly follow rfc 5952</li>
      * </ul>
      * @return {@code String} containing the text-formatted IP address
      */
     public static String toAddressString(InetAddress ip, boolean ipv4Mapped) {
         if (ip instanceof Inet4Address) {
             return ip.getHostAddress();
         }
         if (!(ip instanceof Inet6Address)) {
             throw new IllegalArgumentException("Unhandled type: " + ip);
         }
 
         return toAddressString(ip.getAddress(), 0, ipv4Mapped);
     }
 
     private static String toAddressString(byte[] bytes, int offset, boolean ipv4Mapped) {
         final int[] words = new int[IPV6_WORD_COUNT];
         for (int i = 0; i < words.length; ++i) {
             int idx = (i << 1) + offset;
             words[i] = ((bytes[idx] & 0xff) << 8) | (bytes[idx + 1] & 0xff);
         }
 
         // Find longest run of 0s, tie goes to first found instance
         int currentStart = -1;
         int currentLength;
         int shortestStart = -1;
         int shortestLength = 0;
         for (int i = 0; i < words.length; ++i) {
             if (words[i] == 0) {
                 if (currentStart < 0) {
                     currentStart = i;
                 }
             } else if (currentStart >= 0) {
                 currentLength = i - currentStart;
                 if (currentLength > shortestLength) {
                     shortestStart = currentStart;
                     shortestLength = currentLength;
                 }
                 currentStart = -1;
             }
         }
         // If the array ends on a streak of zeros, make sure we account for it
         if (currentStart >= 0) {
             currentLength = words.length - currentStart;
             if (currentLength > shortestLength) {
                 shortestStart = currentStart;
                 shortestLength = currentLength;
             }
         }
         // Ignore the longest streak if it is only 1 long
         if (shortestLength == 1) {
             shortestLength = 0;
             shortestStart = -1;
         }
 
         // Translate to string taking into account longest consecutive 0s
         final int shortestEnd = shortestStart + shortestLength;
         final StringBuilder b = new StringBuilder(IPV6_MAX_CHAR_COUNT);
         if (shortestEnd < 0) { // Optimization when there is no compressing needed
             b.append(Integer.toHexString(words[0]));
             for (int i = 1; i < words.length; ++i) {
                 b.append(':');
                 b.append(Integer.toHexString(words[i]));
             }
         } else { // General case that can handle compressing (and not compressing)
             // Loop unroll the first index (so we don't constantly check i==0 cases in loop)
             final boolean isIpv4Mapped;
             if (inRangeEndExclusive(0, shortestStart, shortestEnd)) {
                 b.append("::");
                 isIpv4Mapped = ipv4Mapped && (shortestEnd == 5 && words[5] == 0xffff);
             } else {
                 b.append(Integer.toHexString(words[0]));
                 isIpv4Mapped = false;
             }
             for (int i = 1; i < words.length; ++i) {
                 if (!inRangeEndExclusive(i, shortestStart, shortestEnd)) {
                     if (!inRangeEndExclusive(i - 1, shortestStart, shortestEnd)) {
                         // If the last index was not part of the shortened sequence
                         if (!isIpv4Mapped || i == 6) {
                             b.append(':');
                         } else {
                             b.append('.');
                         }
                     }
                     if (isIpv4Mapped && i > 5) {
                         b.append(words[i] >> 8);
                         b.append('.');
                         b.append(words[i] & 0xff);
                     } else {
                         b.append(Integer.toHexString(words[i]));
                     }
                 } else if (!inRangeEndExclusive(i - 1, shortestStart, shortestEnd)) {
                     // If we are in the shortened sequence and the last index was not
                     b.append("::");
                 }
             }
         }
 
         return b.toString();
     }
 
     /**
      * Returns {@link InetSocketAddress#getHostString()} if Java >= 7,
      * or {@link InetSocketAddress#getHostName()} otherwise.
      * @param addr The address
      * @return the host string
      */
     public static String getHostname(InetSocketAddress addr) {
         return PlatformDependent.javaVersion() >= 7 ? addr.getHostString() : addr.getHostName();
     }
 
     /**
      * Does a range check on {@code value} if is within {@code start} (inclusive) and {@code end} (exclusive).
      * @param value The value to checked if is within {@code start} (inclusive) and {@code end} (exclusive)
      * @param start The start of the range (inclusive)
      * @param end The end of the range (exclusive)
      * @return
      * <ul>
      * <li>{@code true} if {@code value} if is within {@code start} (inclusive) and {@code end} (exclusive)</li>
      * <li>{@code false} otherwise</li>
      * </ul>
      */
     private static boolean inRangeEndExclusive(int value, int start, int end) {
         return value >= start && value < end;
     }
 
     /**
      * A constructor to stop this class being constructed.
      */
     private NetUtil() {
         // Unused
     }
 }