artemis-commons/src/main/java/org/apache/activemq/artemis/utils/InetAddresses.java - activemq-artemis - Git at Google

 /**
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements. See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF 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
  * <p>
  * http://www.apache.org/licenses/LICENSE-2.0
  * <p>
  * 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 org.apache.activemq.artemis.utils;

 import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 import java.util.Locale;

 import static org.apache.activemq.artemis.utils.ByteUtil.intFromBytes;

 /**
  * Static utility methods pertaining to {@link InetAddress} instances.
  *
  * <p><b>Important note:</b> Unlike {@code InetAddress.getByName()}, the
  * methods of this class never cause DNS services to be accessed. For
  * this reason, you should prefer these methods as much as possible over
  * their JDK equivalents whenever you are expecting to handle only
  * IP address string literals -- there is no blocking DNS penalty for a
  * malformed string.
  *
  * <p>When dealing with {@link Inet4Address} and {@link Inet6Address}
  * objects as byte arrays (vis. {@code InetAddress.getAddress()}) they
  * are 4 and 16 bytes in length, respectively, and represent the address
  * in network byte order.
  *
  * <p>Examples of IP addresses and their byte representations:
  * <ul>
  * <li>The IPv4 loopback address, {@code "127.0.0.1"}.<br>
  *   {@code 7f 00 00 01}
  *
  * <li>The IPv6 loopback address, {@code "::1"}.<br>
  *   {@code 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01}
  *
  * <li>From the IPv6 reserved documentation prefix ({@code 2001:db8::/32}),
  *   {@code "2001:db8::1"}.<br>
  *   {@code 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01}
  *
  * <li>An IPv6 "IPv4 compatible" (or "compat") address,
  *   {@code "::192.168.0.1"}.<br>
  *   {@code 00 00 00 00 00 00 00 00 00 00 00 00 c0 a8 00 01}
  *
  * <li>An IPv6 "IPv4 mapped" address, {@code "::ffff:192.168.0.1"}.<br>
  *   {@code 00 00 00 00 00 00 00 00 00 00 ff ff c0 a8 00 01}
  * </ul>
  *
  * <p>A few notes about IPv6 "IPv4 mapped" addresses and their observed
  * use in Java.
  * <br><br>
  * "IPv4 mapped" addresses were originally a representation of IPv4
  * addresses for use on an IPv6 socket that could receive both IPv4
  * and IPv6 connections (by disabling the {@code IPV6_V6ONLY} socket
  * option on an IPv6 socket).  Yes, it's confusing.  Nevertheless,
  * these "mapped" addresses were never supposed to be seen on the
  * wire.  That assumption was dropped, some say mistakenly, in later
  * RFCs with the apparent aim of making IPv4-to-IPv6 transition simpler.
  *
  * <p>Technically one <i>can</i> create a 128bit IPv6 address with the wire
  * format of a "mapped" address, as shown above, and transmit it in an
  * IPv6 packet header.  However, Java's InetAddress creation methods
  * appear to adhere doggedly to the original intent of the "mapped"
  * address: all "mapped" addresses return {@link Inet4Address} objects.
  *
  * <p>For added safety, it is common for IPv6 network operators to filter
  * all packets where either the source or destination address appears to
  * be a "compat" or "mapped" address.  Filtering suggestions usually
  * recommend discarding any packets with source or destination addresses
  * in the invalid range {@code ::/3}, which includes both of these bizarre
  * address formats.  For more information on "bogons", including lists
  * of IPv6 bogon space, see:
  *
  * <ul>
  * <li><a target="_parent"
  *     href="http://en.wikipedia.org/wiki/Bogon_filtering"
  *     >http://en.wikipedia.org/wiki/Bogon_filtering</a>
  * <li><a target="_parent"
  *     href="http://www.cymru.com/Bogons/ipv6.txt"
  *     >http://www.cymru.com/Bogons/ipv6.txt</a>
  * <li><a target="_parent"
  *     href="http://www.cymru.com/Bogons/v6bogon.html"
  *     >http://www.cymru.com/Bogons/v6bogon.html</a>
  * <li><a target="_parent"
  *     href="http://www.space.net/~gert/RIPE/ipv6-filters.html"
  *     >http://www.space.net/~gert/RIPE/ipv6-filters.html</a>
  * </ul>
  *
  */
 public final class InetAddresses {
    private static final int IPV4_PART_COUNT = 4;
    private static final int IPV6_PART_COUNT = 8;
    private static final Inet4Address LOOPBACK4 = (Inet4Address) forString("127.0.0.1");
    private static final Inet4Address ANY4 = (Inet4Address) forString("0.0.0.0");

    private InetAddresses() {
    }

    /**
     * Returns an {@link Inet4Address}, given a byte array representation of the IPv4 address.
     *
     * @param bytes byte array representing an IPv4 address (should be of length 4)
     * @return {@link Inet4Address} corresponding to the supplied byte array
     * @throws IllegalArgumentException if a valid {@link Inet4Address} can not be created
     */
    private static Inet4Address getInet4Address(byte[] bytes) {
       Preconditions.checkArgument(bytes.length == 4,
             "Byte array has invalid length for an IPv4 address: %s != 4.",
             bytes.length);

       // Given a 4-byte array, this cast should always succeed.
       return (Inet4Address) bytesToInetAddress(bytes);
    }

    /**
     * Returns the {@link InetAddress} having the given string representation.
     *
     * <p>This deliberately avoids all nameservice lookups (e.g. no DNS).
     *
     * @param ipString {@code String} containing an IPv4 or IPv6 string literal, e.g.
     *   {@code "192.168.0.1"} or {@code "2001:db8::1"}
     * @return {@link InetAddress} representing the argument
     * @throws IllegalArgumentException if the argument is not a valid IP string literal
     */
    public static InetAddress forString(String ipString) {
       byte[] addr = ipStringToBytes(ipString);

       // The argument was malformed, i.e. not an IP string literal.
       if (addr == null) {
          throw formatIllegalArgumentException("'%s' is not an IP string literal.", ipString);
       }

       return bytesToInetAddress(addr);
    }

    /**
     * Returns {@code true} if the supplied string is a valid IP string
     * literal, {@code false} otherwise.
     *
     * @param ipString {@code String} to evaluated as an IP string literal
     * @return {@code true} if the argument is a valid IP string literal
     */
    public static boolean isInetAddress(String ipString) {
       return ipStringToBytes(ipString) != null;
    }

    private static byte[] ipStringToBytes(String ipString) {
       // Make a first pass to categorize the characters in this string.
       boolean hasColon = false;
       boolean hasDot = false;
       for (int i = 0; i < ipString.length(); i++) {
          char c = ipString.charAt(i);
          if (c == '.') {
             hasDot = true;
          } else if (c == ':') {
             if (hasDot) {
                return null;  // Colons must not appear after dots.
             }
             hasColon = true;
          } else if (Character.digit(c, 16) == -1) {
             return null;  // Everything else must be a decimal or hex digit.
          }
       }

       // Now decide which address family to parse.
       if (hasColon) {
          if (hasDot) {
             ipString = convertDottedQuadToHex(ipString);
             if (ipString == null) {
                return null;
             }
          }
          return textToNumericFormatV6(ipString);
       } else if (hasDot) {
          return textToNumericFormatV4(ipString);
       }
       return null;
    }

    private static byte[] textToNumericFormatV4(String ipString) {
       String[] address = ipString.split("\\.", IPV4_PART_COUNT + 1);
       if (address.length != IPV4_PART_COUNT) {
          return null;
       }

       byte[] bytes = new byte[IPV4_PART_COUNT];
       try {
          for (int i = 0; i < bytes.length; i++) {
             bytes[i] = parseOctet(address[i]);
          }
       } catch (NumberFormatException ex) {
          return null;
       }

       return bytes;
    }

    private static byte[] textToNumericFormatV6(String ipString) {
       // An address can have [2..8] colons, and N colons make N+1 parts.
       String[] parts = ipString.split(":", IPV6_PART_COUNT + 2);
       if (parts.length < 3 || parts.length > IPV6_PART_COUNT + 1) {
          return null;
       }

       // Disregarding the endpoints, find "::" with nothing in between.
       // This indicates that a run of zeroes has been skipped.
       int skipIndex = -1;
       for (int i = 1; i < parts.length - 1; i++) {
          if (parts[i].length() == 0) {
             if (skipIndex >= 0) {
                return null;  // Can't have more than one ::
             }
             skipIndex = i;
          }
       }

       int partsHi;  // Number of parts to copy from above/before the "::"
       int partsLo;  // Number of parts to copy from below/after the "::"
       if (skipIndex >= 0) {
          // If we found a "::", then check if it also covers the endpoints.
          partsHi = skipIndex;
          partsLo = parts.length - skipIndex - 1;
          if (parts[0].length() == 0 && --partsHi != 0) {
             return null;  // ^: requires ^::
          }
          if (parts[parts.length - 1].length() == 0 && --partsLo != 0) {
             return null;  // :$ requires ::$
          }
       } else {
          // Otherwise, allocate the entire address to partsHi.  The endpoints
          // could still be empty, but parseHextet() will check for that.
          partsHi = parts.length;
          partsLo = 0;
       }

       // If we found a ::, then we must have skipped at least one part.
       // Otherwise, we must have exactly the right number of parts.
       int partsSkipped = IPV6_PART_COUNT - (partsHi + partsLo);
       if (!(skipIndex >= 0 ? partsSkipped >= 1 : partsSkipped == 0)) {
          return null;
       }

       // Now parse the hextets into a byte array.
       ByteBuffer rawBytes = ByteBuffer.allocate(2 * IPV6_PART_COUNT);
       try {
          for (int i = 0; i < partsHi; i++) {
             rawBytes.putShort(parseHextet(parts[i]));
          }
          for (int i = 0; i < partsSkipped; i++) {
             rawBytes.putShort((short) 0);
          }
          for (int i = partsLo; i > 0; i--) {
             rawBytes.putShort(parseHextet(parts[parts.length - i]));
          }
       } catch (NumberFormatException ex) {
          return null;
       }
       return rawBytes.array();
    }

    private static String convertDottedQuadToHex(String ipString) {
       int lastColon = ipString.lastIndexOf(':');
       String initialPart = ipString.substring(0, lastColon + 1);
       String dottedQuad = ipString.substring(lastColon + 1);
       byte[] quad = textToNumericFormatV4(dottedQuad);
       if (quad == null) {
          return null;
       }
       String penultimate = Integer.toHexString(((quad[0] & 0xff) << 8) | (quad[1] & 0xff));
       String ultimate = Integer.toHexString(((quad[2] & 0xff) << 8) | (quad[3] & 0xff));
       return initialPart + penultimate + ":" + ultimate;
    }

    private static byte parseOctet(String ipPart) {
       // Note: we already verified that this string contains only hex digits.
       int octet = Integer.parseInt(ipPart);
       // Disallow leading zeroes, because no clear standard exists on
       // whether these should be interpreted as decimal or octal.
       if (octet > 255 || (ipPart.startsWith("0") && ipPart.length() > 1)) {
          throw new NumberFormatException();
       }
       return (byte) octet;
    }

    private static short parseHextet(String ipPart) {
       // Note: we already verified that this string contains only hex digits.
       int hextet = Integer.parseInt(ipPart, 16);
       if (hextet > 0xffff) {
          throw new NumberFormatException();
       }
       return (short) hextet;
    }

    /**
     * Convert a byte array into an InetAddress.
     *
     * {@link InetAddress#getByAddress} is documented as throwing a checked
     * exception "if IP address is of illegal length."  We replace it with
     * an unchecked exception, for use by callers who already know that addr
     * is an array of length 4 or 16.
     *
     * @param addr the raw 4-byte or 16-byte IP address in big-endian order
     * @return an InetAddress object created from the raw IP address
     */
    private static InetAddress bytesToInetAddress(byte[] addr) {
       try {
          return InetAddress.getByAddress(addr);
       } catch (UnknownHostException e) {
          throw new AssertionError(e);
       }
    }

    /**
     * Returns the string representation of an {@link InetAddress}.
     *
     * <p>For IPv4 addresses, this is identical to
     * {@link InetAddress#getHostAddress()}, but for IPv6 addresses, the output
     * follows <a href="http://tools.ietf.org/html/rfc5952">RFC 5952</a>
     * section 4.  The main difference is that this method uses "::" for zero
     * compression, while Java's version uses the uncompressed form.
     *
     * <p>This method uses hexadecimal for all IPv6 addresses, including
     * IPv4-mapped IPv6 addresses such as "::c000:201".  The output does not
     * include a Scope ID.
     *
     * @param ip {@link InetAddress} to be converted to an address string
     * @return {@code String} containing the text-formatted IP address
     * @since 10.0
     */
    public static String toAddrString(InetAddress ip) {
       Preconditions.checkNotNull(ip);
       if (ip instanceof Inet4Address) {
          // For IPv4, Java's formatting is good enough.
          return ip.getHostAddress();
       }
       Preconditions.checkArgument(ip instanceof Inet6Address);
       byte[] bytes = ip.getAddress();
       int[] hextets = new int[IPV6_PART_COUNT];
       for (int i = 0; i < hextets.length; i++) {
          hextets[i] = intFromBytes((byte) 0, (byte) 0, bytes[2 * i], bytes[2 * i + 1]);
       }
       compressLongestRunOfZeroes(hextets);
       return hextetsToIPv6String(hextets);
    }

    /**
     * Identify and mark the longest run of zeroes in an IPv6 address.
     *
     * <p>Only runs of two or more hextets are considered.  In case of a tie, the
     * leftmost run wins.  If a qualifying run is found, its hextets are replaced
     * by the sentinel value -1.
     *
     * @param hextets {@code int[]} mutable array of eight 16-bit hextets
     */
    private static void compressLongestRunOfZeroes(int[] hextets) {
       int bestRunStart = -1;
       int bestRunLength = -1;
       int runStart = -1;
       for (int i = 0; i < hextets.length + 1; i++) {
          if (i < hextets.length && hextets[i] == 0) {
             if (runStart < 0) {
                runStart = i;
             }
          } else if (runStart >= 0) {
             int runLength = i - runStart;
             if (runLength > bestRunLength) {
                bestRunStart = runStart;
                bestRunLength = runLength;
             }
             runStart = -1;
          }
       }
       if (bestRunLength >= 2) {
          Arrays.fill(hextets, bestRunStart, bestRunStart + bestRunLength, -1);
       }
    }

    /**
     * Convert a list of hextets into a human-readable IPv6 address.
     *
     * <p>In order for "::" compression to work, the input should contain negative
     * sentinel values in place of the elided zeroes.
     *
     * @param hextets {@code int[]} array of eight 16-bit hextets, or -1s
     */
    private static String hextetsToIPv6String(int[] hextets) {
       /*
        * While scanning the array, handle these state transitions:
        *   start->num => "num"   start->gap => "::"
        *   num->num   => ":num"   num->gap   => "::"
        *   gap->num   => "num"   gap->gap   => ""
        */
       StringBuilder buf = new StringBuilder(39);
       boolean lastWasNumber = false;
       for (int i = 0; i < hextets.length; i++) {
          boolean thisIsNumber = hextets[i] >= 0;
          if (thisIsNumber) {
             if (lastWasNumber) {
                buf.append(':');
             }
             buf.append(Integer.toHexString(hextets[i]));
          } else {
             if (i == 0 || lastWasNumber) {
                buf.append("::");
             }
          }
          lastWasNumber = thisIsNumber;
       }
       return buf.toString();
    }

    /**
     * Returns the string representation of an {@link InetAddress} suitable
     * for inclusion in a URI.
     *
     * <p>For IPv4 addresses, this is identical to
     * {@link InetAddress#getHostAddress()}, but for IPv6 addresses it
     * compresses zeroes and surrounds the text with square brackets; for example
     * {@code "[2001:db8::1]"}.
     *
     * <p>Per section 3.2.2 of
     * <a target="_parent"
     *   href="http://tools.ietf.org/html/rfc3986#section-3.2.2"
     *  >http://tools.ietf.org/html/rfc3986</a>,
     * a URI containing an IPv6 string literal is of the form
     * {@code "http://[2001:db8::1]:8888/index.html"}.
     *
     * <p>Use of either {@link InetAddresses#toAddrString},
     * {@link InetAddress#getHostAddress()}, or this method is recommended over
     * {@link InetAddress#toString()} when an IP address string literal is
     * desired.  This is because {@link InetAddress#toString()} prints the
     * hostname and the IP address string joined by a "/".
     *
     * @param ip {@link InetAddress} to be converted to URI string literal
     * @return {@code String} containing URI-safe string literal
     */
    public static String toUriString(InetAddress ip) {
       if (ip instanceof Inet6Address) {
          return "[" + toAddrString(ip) + "]";
       }
       return toAddrString(ip);
    }

    /**
     * Returns an InetAddress representing the literal IPv4 or IPv6 host
     * portion of a URL, encoded in the format specified by RFC 3986 section 3.2.2.
     *
     * <p>This function is similar to {@link InetAddresses#forString(String)},
     * however, it requires that IPv6 addresses are surrounded by square brackets.
     *
     * <p>This function is the inverse of
     * {@link InetAddresses#toUriString(java.net.InetAddress)}.
     *
     * @param hostAddr A RFC 3986 section 3.2.2 encoded IPv4 or IPv6 address
     * @return an InetAddress representing the address in {@code hostAddr}
     * @throws IllegalArgumentException if {@code hostAddr} is not a valid
     *   IPv4 address, or IPv6 address surrounded by square brackets
     */
    public static InetAddress forUriString(String hostAddr) {
       Preconditions.checkNotNull(hostAddr);

       // Decide if this should be an IPv6 or IPv4 address.
       String ipString;
       int expectBytes;
       if (hostAddr.startsWith("[") && hostAddr.endsWith("]")) {
          ipString = hostAddr.substring(1, hostAddr.length() - 1);
          expectBytes = 16;
       } else {
          ipString = hostAddr;
          expectBytes = 4;
       }

       // Parse the address, and make sure the length/version is correct.
       byte[] addr = ipStringToBytes(ipString);
       if (addr == null || addr.length != expectBytes) {
          throw formatIllegalArgumentException("Not a valid URI IP literal: '%s'", hostAddr);
       }

       return bytesToInetAddress(addr);
    }

    /**
     * Returns {@code true} if the supplied string is a valid URI IP string
     * literal, {@code false} otherwise.
     *
     * @param ipString {@code String} to evaluated as an IP URI host string literal
     * @return {@code true} if the argument is a valid IP URI host
     */
    public static boolean isUriInetAddress(String ipString) {
       try {
          forUriString(ipString);
          return true;
       } catch (IllegalArgumentException e) {
          return false;
       }
    }

    /**
     * Evaluates whether the argument is an IPv6 "compat" address.
     *
     * <p>An "IPv4 compatible", or "compat", address is one with 96 leading
     * bits of zero, with the remaining 32 bits interpreted as an
     * IPv4 address.  These are conventionally represented in string
     * literals as {@code "::192.168.0.1"}, though {@code "::c0a8:1"} is
     * also considered an IPv4 compatible address (and equivalent to
     * {@code "::192.168.0.1"}).
     *
     * <p>For more on IPv4 compatible addresses see section 2.5.5.1 of
     * <a target="_parent"
     *   href="http://tools.ietf.org/html/rfc4291#section-2.5.5.1"
     *   >http://tools.ietf.org/html/rfc4291</a>
     *
     * <p>NOTE: This method is different from
     * {@link Inet6Address#isIPv4CompatibleAddress} in that it more
     * correctly classifies {@code "::"} and {@code "::1"} as
     * proper IPv6 addresses (which they are), NOT IPv4 compatible
     * addresses (which they are generally NOT considered to be).
     *
     * @param ip {@link Inet6Address} to be examined for embedded IPv4 compatible address format
     * @return {@code true} if the argument is a valid "compat" address
     */
    public static boolean isCompatIPv4Address(Inet6Address ip) {
       if (!ip.isIPv4CompatibleAddress()) {
          return false;
       }

       byte[] bytes = ip.getAddress();
       if ((bytes[12] == 0) && (bytes[13] == 0) && (bytes[14] == 0)
             && ((bytes[15] == 0) || (bytes[15] == 1))) {
          return false;
       }

       return true;
    }

    /**
     * Returns the IPv4 address embedded in an IPv4 compatible address.
     *
     * @param ip {@link Inet6Address} to be examined for an embedded IPv4 address
     * @return {@link Inet4Address} of the embedded IPv4 address
     * @throws IllegalArgumentException if the argument is not a valid IPv4 compatible address
     */
    public static Inet4Address getCompatIPv4Address(Inet6Address ip) {
       Preconditions.checkArgument(isCompatIPv4Address(ip),
             "Address '%s' is not IPv4-compatible.", toAddrString(ip));

       return getInet4Address(Arrays.copyOfRange(ip.getAddress(), 12, 16));
    }

    private static IllegalArgumentException formatIllegalArgumentException(
          String format, Object... args) {
       return new IllegalArgumentException(String.format(Locale.ROOT, format, args));
    }

 }
	/**
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF 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
	* <p>
	* http://www.apache.org/licenses/LICENSE-2.0
	* <p>
	* 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 org.apache.activemq.artemis.utils;

	import java.net.Inet4Address;
	import java.net.Inet6Address;
	import java.net.InetAddress;
	import java.net.UnknownHostException;
	import java.nio.ByteBuffer;
	import java.util.Arrays;
	import java.util.Locale;

	import static org.apache.activemq.artemis.utils.ByteUtil.intFromBytes;

	/**
	* Static utility methods pertaining to {@link InetAddress} instances.
	*
	* <p><b>Important note:</b> Unlike {@code InetAddress.getByName()}, the
	* methods of this class never cause DNS services to be accessed. For
	* this reason, you should prefer these methods as much as possible over
	* their JDK equivalents whenever you are expecting to handle only
	* IP address string literals -- there is no blocking DNS penalty for a
	* malformed string.
	*
	* <p>When dealing with {@link Inet4Address} and {@link Inet6Address}
	* objects as byte arrays (vis. {@code InetAddress.getAddress()}) they
	* are 4 and 16 bytes in length, respectively, and represent the address
	* in network byte order.
	*
	* <p>Examples of IP addresses and their byte representations:
	* <ul>
	* <li>The IPv4 loopback address, {@code "127.0.0.1"}.<br>
	* {@code 7f 00 00 01}
	*
	* <li>The IPv6 loopback address, {@code "::1"}.<br>
	* {@code 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01}
	*
	* <li>From the IPv6 reserved documentation prefix ({@code 2001:db8::/32}),
	* {@code "2001:db8::1"}.<br>
	* {@code 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01}
	*
	* <li>An IPv6 "IPv4 compatible" (or "compat") address,
	* {@code "::192.168.0.1"}.<br>
	* {@code 00 00 00 00 00 00 00 00 00 00 00 00 c0 a8 00 01}
	*
	* <li>An IPv6 "IPv4 mapped" address, {@code "::ffff:192.168.0.1"}.<br>
	* {@code 00 00 00 00 00 00 00 00 00 00 ff ff c0 a8 00 01}
	* </ul>
	*
	* <p>A few notes about IPv6 "IPv4 mapped" addresses and their observed
	* use in Java.
	* <br><br>
	* "IPv4 mapped" addresses were originally a representation of IPv4
	* addresses for use on an IPv6 socket that could receive both IPv4
	* and IPv6 connections (by disabling the {@code IPV6_V6ONLY} socket
	* option on an IPv6 socket). Yes, it's confusing. Nevertheless,
	* these "mapped" addresses were never supposed to be seen on the
	* wire. That assumption was dropped, some say mistakenly, in later
	* RFCs with the apparent aim of making IPv4-to-IPv6 transition simpler.
	*
	* <p>Technically one <i>can</i> create a 128bit IPv6 address with the wire
	* format of a "mapped" address, as shown above, and transmit it in an
	* IPv6 packet header. However, Java's InetAddress creation methods
	* appear to adhere doggedly to the original intent of the "mapped"
	* address: all "mapped" addresses return {@link Inet4Address} objects.
	*
	* <p>For added safety, it is common for IPv6 network operators to filter
	* all packets where either the source or destination address appears to
	* be a "compat" or "mapped" address. Filtering suggestions usually
	* recommend discarding any packets with source or destination addresses
	* in the invalid range {@code ::/3}, which includes both of these bizarre
	* address formats. For more information on "bogons", including lists
	* of IPv6 bogon space, see:
	*
	* <ul>
	* <li><a target="_parent"
	* href="http://en.wikipedia.org/wiki/Bogon_filtering"
	* >http://en.wikipedia.org/wiki/Bogon_filtering</a>
	* <li><a target="_parent"
	* href="http://www.cymru.com/Bogons/ipv6.txt"
	* >http://www.cymru.com/Bogons/ipv6.txt</a>
	* <li><a target="_parent"
	* href="http://www.cymru.com/Bogons/v6bogon.html"
	* >http://www.cymru.com/Bogons/v6bogon.html</a>
	* <li><a target="_parent"
	* href="http://www.space.net/~gert/RIPE/ipv6-filters.html"
	* >http://www.space.net/~gert/RIPE/ipv6-filters.html</a>
	* </ul>
	*
	*/
	public final class InetAddresses {
	private static final int IPV4_PART_COUNT = 4;
	private static final int IPV6_PART_COUNT = 8;
	private static final Inet4Address LOOPBACK4 = (Inet4Address) forString("127.0.0.1");
	private static final Inet4Address ANY4 = (Inet4Address) forString("0.0.0.0");

	private InetAddresses() {
	}

	/**
	* Returns an {@link Inet4Address}, given a byte array representation of the IPv4 address.
	*
	* @param bytes byte array representing an IPv4 address (should be of length 4)
	* @return {@link Inet4Address} corresponding to the supplied byte array
	* @throws IllegalArgumentException if a valid {@link Inet4Address} can not be created
	*/
	private static Inet4Address getInet4Address(byte[] bytes) {
	Preconditions.checkArgument(bytes.length == 4,
	"Byte array has invalid length for an IPv4 address: %s != 4.",
	bytes.length);

	// Given a 4-byte array, this cast should always succeed.
	return (Inet4Address) bytesToInetAddress(bytes);
	}

	/**
	* Returns the {@link InetAddress} having the given string representation.
	*
	* <p>This deliberately avoids all nameservice lookups (e.g. no DNS).
	*
	* @param ipString {@code String} containing an IPv4 or IPv6 string literal, e.g.
	* {@code "192.168.0.1"} or {@code "2001:db8::1"}
	* @return {@link InetAddress} representing the argument
	* @throws IllegalArgumentException if the argument is not a valid IP string literal
	*/
	public static InetAddress forString(String ipString) {
	byte[] addr = ipStringToBytes(ipString);

	// The argument was malformed, i.e. not an IP string literal.
	if (addr == null) {
	throw formatIllegalArgumentException("'%s' is not an IP string literal.", ipString);
	}

	return bytesToInetAddress(addr);
	}

	/**
	* Returns {@code true} if the supplied string is a valid IP string
	* literal, {@code false} otherwise.
	*
	* @param ipString {@code String} to evaluated as an IP string literal
	* @return {@code true} if the argument is a valid IP string literal
	*/
	public static boolean isInetAddress(String ipString) {
	return ipStringToBytes(ipString) != null;
	}

	private static byte[] ipStringToBytes(String ipString) {
	// Make a first pass to categorize the characters in this string.
	boolean hasColon = false;
	boolean hasDot = false;
	for (int i = 0; i < ipString.length(); i++) {
	char c = ipString.charAt(i);
	if (c == '.') {
	hasDot = true;
	} else if (c == ':') {
	if (hasDot) {
	return null; // Colons must not appear after dots.
	}
	hasColon = true;
	} else if (Character.digit(c, 16) == -1) {
	return null; // Everything else must be a decimal or hex digit.
	}
	}

	// Now decide which address family to parse.
	if (hasColon) {
	if (hasDot) {
	ipString = convertDottedQuadToHex(ipString);
	if (ipString == null) {
	return null;
	}
	}
	return textToNumericFormatV6(ipString);
	} else if (hasDot) {
	return textToNumericFormatV4(ipString);
	}
	return null;
	}

	private static byte[] textToNumericFormatV4(String ipString) {
	String[] address = ipString.split("\\.", IPV4_PART_COUNT + 1);
	if (address.length != IPV4_PART_COUNT) {
	return null;
	}

	byte[] bytes = new byte[IPV4_PART_COUNT];
	try {
	for (int i = 0; i < bytes.length; i++) {
	bytes[i] = parseOctet(address[i]);
	}
	} catch (NumberFormatException ex) {
	return null;
	}

	return bytes;
	}

	private static byte[] textToNumericFormatV6(String ipString) {
	// An address can have [2..8] colons, and N colons make N+1 parts.
	String[] parts = ipString.split(":", IPV6_PART_COUNT + 2);
	if (parts.length < 3 \|\| parts.length > IPV6_PART_COUNT + 1) {
	return null;
	}

	// Disregarding the endpoints, find "::" with nothing in between.
	// This indicates that a run of zeroes has been skipped.
	int skipIndex = -1;
	for (int i = 1; i < parts.length - 1; i++) {
	if (parts[i].length() == 0) {
	if (skipIndex >= 0) {
	return null; // Can't have more than one ::
	}
	skipIndex = i;
	}
	}

	int partsHi; // Number of parts to copy from above/before the "::"
	int partsLo; // Number of parts to copy from below/after the "::"
	if (skipIndex >= 0) {
	// If we found a "::", then check if it also covers the endpoints.
	partsHi = skipIndex;
	partsLo = parts.length - skipIndex - 1;
	if (parts[0].length() == 0 && --partsHi != 0) {
	return null; // ^: requires ^::
	}
	if (parts[parts.length - 1].length() == 0 && --partsLo != 0) {
	return null; // :$ requires ::$
	}
	} else {
	// Otherwise, allocate the entire address to partsHi. The endpoints
	// could still be empty, but parseHextet() will check for that.
	partsHi = parts.length;
	partsLo = 0;
	}

	// If we found a ::, then we must have skipped at least one part.
	// Otherwise, we must have exactly the right number of parts.
	int partsSkipped = IPV6_PART_COUNT - (partsHi + partsLo);
	if (!(skipIndex >= 0 ? partsSkipped >= 1 : partsSkipped == 0)) {
	return null;
	}

	// Now parse the hextets into a byte array.
	ByteBuffer rawBytes = ByteBuffer.allocate(2 * IPV6_PART_COUNT);
	try {
	for (int i = 0; i < partsHi; i++) {
	rawBytes.putShort(parseHextet(parts[i]));
	}
	for (int i = 0; i < partsSkipped; i++) {
	rawBytes.putShort((short) 0);
	}
	for (int i = partsLo; i > 0; i--) {
	rawBytes.putShort(parseHextet(parts[parts.length - i]));
	}
	} catch (NumberFormatException ex) {
	return null;
	}
	return rawBytes.array();
	}

	private static String convertDottedQuadToHex(String ipString) {
	int lastColon = ipString.lastIndexOf(':');
	String initialPart = ipString.substring(0, lastColon + 1);
	String dottedQuad = ipString.substring(lastColon + 1);
	byte[] quad = textToNumericFormatV4(dottedQuad);
	if (quad == null) {
	return null;
	}
	String penultimate = Integer.toHexString(((quad[0] & 0xff) << 8) \| (quad[1] & 0xff));
	String ultimate = Integer.toHexString(((quad[2] & 0xff) << 8) \| (quad[3] & 0xff));
	return initialPart + penultimate + ":" + ultimate;
	}

	private static byte parseOctet(String ipPart) {
	// Note: we already verified that this string contains only hex digits.
	int octet = Integer.parseInt(ipPart);
	// Disallow leading zeroes, because no clear standard exists on
	// whether these should be interpreted as decimal or octal.
	if (octet > 255 \|\| (ipPart.startsWith("0") && ipPart.length() > 1)) {
	throw new NumberFormatException();
	}
	return (byte) octet;
	}

	private static short parseHextet(String ipPart) {
	// Note: we already verified that this string contains only hex digits.
	int hextet = Integer.parseInt(ipPart, 16);
	if (hextet > 0xffff) {
	throw new NumberFormatException();
	}
	return (short) hextet;
	}

	/**
	* Convert a byte array into an InetAddress.
	*
	* {@link InetAddress#getByAddress} is documented as throwing a checked
	* exception "if IP address is of illegal length." We replace it with
	* an unchecked exception, for use by callers who already know that addr
	* is an array of length 4 or 16.
	*
	* @param addr the raw 4-byte or 16-byte IP address in big-endian order
	* @return an InetAddress object created from the raw IP address
	*/
	private static InetAddress bytesToInetAddress(byte[] addr) {
	try {
	return InetAddress.getByAddress(addr);
	} catch (UnknownHostException e) {
	throw new AssertionError(e);
	}
	}

	/**
	* Returns the string representation of an {@link InetAddress}.
	*
	* <p>For IPv4 addresses, this is identical to
	* {@link InetAddress#getHostAddress()}, but for IPv6 addresses, the output
	* follows <a href="http://tools.ietf.org/html/rfc5952">RFC 5952</a>
	* section 4. The main difference is that this method uses "::" for zero
	* compression, while Java's version uses the uncompressed form.
	*
	* <p>This method uses hexadecimal for all IPv6 addresses, including
	* IPv4-mapped IPv6 addresses such as "::c000:201". The output does not
	* include a Scope ID.
	*
	* @param ip {@link InetAddress} to be converted to an address string
	* @return {@code String} containing the text-formatted IP address
	* @since 10.0
	*/
	public static String toAddrString(InetAddress ip) {
	Preconditions.checkNotNull(ip);
	if (ip instanceof Inet4Address) {
	// For IPv4, Java's formatting is good enough.
	return ip.getHostAddress();
	}
	Preconditions.checkArgument(ip instanceof Inet6Address);
	byte[] bytes = ip.getAddress();
	int[] hextets = new int[IPV6_PART_COUNT];
	for (int i = 0; i < hextets.length; i++) {
	hextets[i] = intFromBytes((byte) 0, (byte) 0, bytes[2 * i], bytes[2 * i + 1]);
	}
	compressLongestRunOfZeroes(hextets);
	return hextetsToIPv6String(hextets);
	}

	/**
	* Identify and mark the longest run of zeroes in an IPv6 address.
	*
	* <p>Only runs of two or more hextets are considered. In case of a tie, the
	* leftmost run wins. If a qualifying run is found, its hextets are replaced
	* by the sentinel value -1.
	*
	* @param hextets {@code int[]} mutable array of eight 16-bit hextets
	*/
	private static void compressLongestRunOfZeroes(int[] hextets) {
	int bestRunStart = -1;
	int bestRunLength = -1;
	int runStart = -1;
	for (int i = 0; i < hextets.length + 1; i++) {
	if (i < hextets.length && hextets[i] == 0) {
	if (runStart < 0) {
	runStart = i;
	}
	} else if (runStart >= 0) {
	int runLength = i - runStart;
	if (runLength > bestRunLength) {
	bestRunStart = runStart;
	bestRunLength = runLength;
	}
	runStart = -1;
	}
	}
	if (bestRunLength >= 2) {
	Arrays.fill(hextets, bestRunStart, bestRunStart + bestRunLength, -1);
	}
	}

	/**
	* Convert a list of hextets into a human-readable IPv6 address.
	*
	* <p>In order for "::" compression to work, the input should contain negative
	* sentinel values in place of the elided zeroes.
	*
	* @param hextets {@code int[]} array of eight 16-bit hextets, or -1s
	*/
	private static String hextetsToIPv6String(int[] hextets) {
	/*
	* While scanning the array, handle these state transitions:
	* start->num => "num" start->gap => "::"
	* num->num => ":num" num->gap => "::"
	* gap->num => "num" gap->gap => ""
	*/
	StringBuilder buf = new StringBuilder(39);
	boolean lastWasNumber = false;
	for (int i = 0; i < hextets.length; i++) {
	boolean thisIsNumber = hextets[i] >= 0;
	if (thisIsNumber) {
	if (lastWasNumber) {
	buf.append(':');
	}
	buf.append(Integer.toHexString(hextets[i]));
	} else {
	if (i == 0 \|\| lastWasNumber) {
	buf.append("::");
	}
	}
	lastWasNumber = thisIsNumber;
	}
	return buf.toString();
	}

	/**
	* Returns the string representation of an {@link InetAddress} suitable
	* for inclusion in a URI.
	*
	* <p>For IPv4 addresses, this is identical to
	* {@link InetAddress#getHostAddress()}, but for IPv6 addresses it
	* compresses zeroes and surrounds the text with square brackets; for example
	* {@code "[2001:db8::1]"}.
	*
	* <p>Per section 3.2.2 of
	* <a target="_parent"
	* href="http://tools.ietf.org/html/rfc3986#section-3.2.2"
	* >http://tools.ietf.org/html/rfc3986</a>,
	* a URI containing an IPv6 string literal is of the form
	* {@code "http://[2001:db8::1]:8888/index.html"}.
	*
	* <p>Use of either {@link InetAddresses#toAddrString},
	* {@link InetAddress#getHostAddress()}, or this method is recommended over
	* {@link InetAddress#toString()} when an IP address string literal is
	* desired. This is because {@link InetAddress#toString()} prints the
	* hostname and the IP address string joined by a "/".
	*
	* @param ip {@link InetAddress} to be converted to URI string literal
	* @return {@code String} containing URI-safe string literal
	*/
	public static String toUriString(InetAddress ip) {
	if (ip instanceof Inet6Address) {
	return "[" + toAddrString(ip) + "]";
	}
	return toAddrString(ip);
	}

	/**
	* Returns an InetAddress representing the literal IPv4 or IPv6 host
	* portion of a URL, encoded in the format specified by RFC 3986 section 3.2.2.
	*
	* <p>This function is similar to {@link InetAddresses#forString(String)},
	* however, it requires that IPv6 addresses are surrounded by square brackets.
	*
	* <p>This function is the inverse of
	* {@link InetAddresses#toUriString(java.net.InetAddress)}.
	*
	* @param hostAddr A RFC 3986 section 3.2.2 encoded IPv4 or IPv6 address
	* @return an InetAddress representing the address in {@code hostAddr}
	* @throws IllegalArgumentException if {@code hostAddr} is not a valid
	* IPv4 address, or IPv6 address surrounded by square brackets
	*/
	public static InetAddress forUriString(String hostAddr) {
	Preconditions.checkNotNull(hostAddr);

	// Decide if this should be an IPv6 or IPv4 address.
	String ipString;
	int expectBytes;
	if (hostAddr.startsWith("[") && hostAddr.endsWith("]")) {
	ipString = hostAddr.substring(1, hostAddr.length() - 1);
	expectBytes = 16;
	} else {
	ipString = hostAddr;
	expectBytes = 4;
	}

	// Parse the address, and make sure the length/version is correct.
	byte[] addr = ipStringToBytes(ipString);
	if (addr == null \|\| addr.length != expectBytes) {
	throw formatIllegalArgumentException("Not a valid URI IP literal: '%s'", hostAddr);
	}

	return bytesToInetAddress(addr);
	}

	/**
	* Returns {@code true} if the supplied string is a valid URI IP string
	* literal, {@code false} otherwise.
	*
	* @param ipString {@code String} to evaluated as an IP URI host string literal
	* @return {@code true} if the argument is a valid IP URI host
	*/
	public static boolean isUriInetAddress(String ipString) {
	try {
	forUriString(ipString);
	return true;
	} catch (IllegalArgumentException e) {
	return false;
	}
	}

	/**
	* Evaluates whether the argument is an IPv6 "compat" address.
	*
	* <p>An "IPv4 compatible", or "compat", address is one with 96 leading
	* bits of zero, with the remaining 32 bits interpreted as an
	* IPv4 address. These are conventionally represented in string
	* literals as {@code "::192.168.0.1"}, though {@code "::c0a8:1"} is
	* also considered an IPv4 compatible address (and equivalent to
	* {@code "::192.168.0.1"}).
	*
	* <p>For more on IPv4 compatible addresses see section 2.5.5.1 of
	* <a target="_parent"
	* href="http://tools.ietf.org/html/rfc4291#section-2.5.5.1"
	* >http://tools.ietf.org/html/rfc4291</a>
	*
	* <p>NOTE: This method is different from
	* {@link Inet6Address#isIPv4CompatibleAddress} in that it more
	* correctly classifies {@code "::"} and {@code "::1"} as
	* proper IPv6 addresses (which they are), NOT IPv4 compatible
	* addresses (which they are generally NOT considered to be).
	*
	* @param ip {@link Inet6Address} to be examined for embedded IPv4 compatible address format
	* @return {@code true} if the argument is a valid "compat" address
	*/
	public static boolean isCompatIPv4Address(Inet6Address ip) {
	if (!ip.isIPv4CompatibleAddress()) {
	return false;
	}

	byte[] bytes = ip.getAddress();
	if ((bytes[12] == 0) && (bytes[13] == 0) && (bytes[14] == 0)
	&& ((bytes[15] == 0) \|\| (bytes[15] == 1))) {
	return false;
	}

	return true;
	}

	/**
	* Returns the IPv4 address embedded in an IPv4 compatible address.
	*
	* @param ip {@link Inet6Address} to be examined for an embedded IPv4 address
	* @return {@link Inet4Address} of the embedded IPv4 address
	* @throws IllegalArgumentException if the argument is not a valid IPv4 compatible address
	*/
	public static Inet4Address getCompatIPv4Address(Inet6Address ip) {
	Preconditions.checkArgument(isCompatIPv4Address(ip),
	"Address '%s' is not IPv4-compatible.", toAddrString(ip));

	return getInet4Address(Arrays.copyOfRange(ip.getAddress(), 12, 16));
	}

	private static IllegalArgumentException formatIllegalArgumentException(
	String format, Object... args) {
	return new IllegalArgumentException(String.format(Locale.ROOT, format, args));
	}

	}