/*
 * Copyright (C) 2008 The Guava Authors
 *
 * Licensed 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
 *
 * http://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 com.google.common.net;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.base.CharMatcher;
import com.google.common.base.MoreObjects;
import com.google.common.hash.Hashing;
import com.google.common.io.ByteStreams;
import com.google.common.primitives.Ints;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.math.BigInteger;
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 javax.annotation.CheckForNull;

/**
 * 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:
 *
 * <dl>
 *   <dt>The IPv4 loopback address, {@code "127.0.0.1"}.
 *   <dd>{@code 7f 00 00 01}
 *   <dt>The IPv6 loopback address, {@code "::1"}.
 *   <dd>{@code 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 01}
 *   <dt>From the IPv6 reserved documentation prefix ({@code 2001:db8::/32}), {@code "2001:db8::1"}.
 *   <dd>{@code 20 01 0d b8 00 00 00 00 00 00 00 00 00 00 00 01}
 *   <dt>An IPv6 "IPv4 compatible" (or "compat") address, {@code "::192.168.0.1"}.
 *   <dd>{@code 00 00 00 00 00 00 00 00 00 00 00 00 c0 a8 00 01}
 *   <dt>An IPv6 "IPv4 mapped" address, {@code "::ffff:192.168.0.1"}.
 *   <dd>{@code 00 00 00 00 00 00 00 00 00 00 ff ff c0 a8 00 01}
 * </dl>
 *
 * <p>A few notes about IPv6 "IPv4 mapped" addresses and their observed use in Java.
 *
 * <p>"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>
 *
 * @author Erik Kline
 * @since 5.0
 */
@J2ktIncompatible
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public final class InetAddresses {
  private static final int IPV4_PART_COUNT = 4;
  private static final int IPV6_PART_COUNT = 8;
  private static final char IPV4_DELIMITER = '.';
  private static final char IPV6_DELIMITER = ':';
  private static final CharMatcher IPV4_DELIMITER_MATCHER = CharMatcher.is(IPV4_DELIMITER);
  private static final CharMatcher IPV6_DELIMITER_MATCHER = CharMatcher.is(IPV6_DELIMITER);
  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) {
    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).
   *
   * <p>Anything after a {@code %} in an IPv6 address is ignored (assumed to be a Scope ID).
   *
   * <p>This method accepts non-ASCII digits, for example {@code "１９２.１６８.０.１"} (those are fullwidth
   * characters). That is consistent with {@link InetAddress}, but not with various RFCs. If you
   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * @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
   */
  @CanIgnoreReturnValue // TODO(b/219820829): consider removing
  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.
   *
   * <p>This method accepts non-ASCII digits, for example {@code "１９２.１６８.０.１"} (those are fullwidth
   * characters). That is consistent with {@link InetAddress}, but not with various RFCs. If you
   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * @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;
  }

  /** Returns {@code null} if unable to parse into a {@code byte[]}. */
  @CheckForNull
  private static byte[] ipStringToBytes(String ipStringParam) {
    String ipString = ipStringParam;
    // Make a first pass to categorize the characters in this string.
    boolean hasColon = false;
    boolean hasDot = false;
    int percentIndex = -1;
    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 (c == '%') {
        percentIndex = i;
        break; // everything after a '%' is ignored (it's a Scope ID): http://superuser.com/a/99753
      } 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;
        }
      }
      if (percentIndex != -1) {
        ipString = ipString.substring(0, percentIndex);
      }
      return textToNumericFormatV6(ipString);
    } else if (hasDot) {
      if (percentIndex != -1) {
        return null; // Scope IDs are not supported for IPV4
      }
      return textToNumericFormatV4(ipString);
    }
    return null;
  }

  @CheckForNull
  private static byte[] textToNumericFormatV4(String ipString) {
    if (IPV4_DELIMITER_MATCHER.countIn(ipString) + 1 != IPV4_PART_COUNT) {
      return null; // Wrong number of parts
    }

    byte[] bytes = new byte[IPV4_PART_COUNT];
    int start = 0;
    // Iterate through the parts of the ip string.
    // Invariant: start is always the beginning of an octet.
    for (int i = 0; i < IPV4_PART_COUNT; i++) {
      int end = ipString.indexOf(IPV4_DELIMITER, start);
      if (end == -1) {
        end = ipString.length();
      }
      try {
        bytes[i] = parseOctet(ipString, start, end);
      } catch (NumberFormatException ex) {
        return null;
      }
      start = end + 1;
    }

    return bytes;
  }

  @CheckForNull
  private static byte[] textToNumericFormatV6(String ipString) {
    // An address can have [2..8] colons.
    int delimiterCount = IPV6_DELIMITER_MATCHER.countIn(ipString);
    if (delimiterCount < 2 || delimiterCount > IPV6_PART_COUNT) {
      return null;
    }
    int partsSkipped = IPV6_PART_COUNT - (delimiterCount + 1); // estimate; may be modified later
    boolean hasSkip = false;
    // Scan for the appearance of ::, to mark a skip-format IPV6 string and adjust the partsSkipped
    // estimate.
    for (int i = 0; i < ipString.length() - 1; i++) {
      if (ipString.charAt(i) == IPV6_DELIMITER && ipString.charAt(i + 1) == IPV6_DELIMITER) {
        if (hasSkip) {
          return null; // Can't have more than one ::
        }
        hasSkip = true;
        partsSkipped++; // :: means we skipped an extra part in between the two delimiters.
        if (i == 0) {
          partsSkipped++; // Begins with ::, so we skipped the part preceding the first :
        }
        if (i == ipString.length() - 2) {
          partsSkipped++; // Ends with ::, so we skipped the part after the last :
        }
      }
    }
    if (ipString.charAt(0) == IPV6_DELIMITER && ipString.charAt(1) != IPV6_DELIMITER) {
      return null; // ^: requires ^::
    }
    if (ipString.charAt(ipString.length() - 1) == IPV6_DELIMITER
        && ipString.charAt(ipString.length() - 2) != IPV6_DELIMITER) {
      return null; // :$ requires ::$
    }
    if (hasSkip && partsSkipped <= 0) {
      return null; // :: must expand to at least one '0'
    }
    if (!hasSkip && delimiterCount + 1 != IPV6_PART_COUNT) {
      return null; // Incorrect number of parts
    }

    ByteBuffer rawBytes = ByteBuffer.allocate(2 * IPV6_PART_COUNT);
    try {
      // Iterate through the parts of the ip string.
      // Invariant: start is always the beginning of a hextet, or the second ':' of the skip
      // sequence "::"
      int start = 0;
      if (ipString.charAt(0) == IPV6_DELIMITER) {
        start = 1;
      }
      while (start < ipString.length()) {
        int end = ipString.indexOf(IPV6_DELIMITER, start);
        if (end == -1) {
          end = ipString.length();
        }
        if (ipString.charAt(start) == IPV6_DELIMITER) {
          // expand zeroes
          for (int i = 0; i < partsSkipped; i++) {
            rawBytes.putShort((short) 0);
          }

        } else {
          rawBytes.putShort(parseHextet(ipString, start, end));
        }
        start = end + 1;
      }
    } catch (NumberFormatException ex) {
      return null;
    }
    return rawBytes.array();
  }

  @CheckForNull
  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 ipString, int start, int end) {
    // Note: we already verified that this string contains only hex digits, but the string may still
    // contain non-decimal characters.
    int length = end - start;
    if (length <= 0 || length > 3) {
      throw new NumberFormatException();
    }
    // Disallow leading zeroes, because no clear standard exists on
    // whether these should be interpreted as decimal or octal.
    if (length > 1 && ipString.charAt(start) == '0') {
      throw new NumberFormatException();
    }
    int octet = 0;
    for (int i = start; i < end; i++) {
      octet *= 10;
      int digit = Character.digit(ipString.charAt(i), 10);
      if (digit < 0) {
        throw new NumberFormatException();
      }
      octet += digit;
    }
    if (octet > 255) {
      throw new NumberFormatException();
    }
    return (byte) octet;
  }

  // Parse a hextet out of the ipString from start (inclusive) to end (exclusive)
  private static short parseHextet(String ipString, int start, int end) {
    // Note: we already verified that this string contains only hex digits.
    int length = end - start;
    if (length <= 0 || length > 4) {
      throw new NumberFormatException();
    }
    int hextet = 0;
    for (int i = start; i < end; i++) {
      hextet = hextet << 4;
      hextet |= Character.digit(ipString.charAt(i), 16);
    }
    return (short) hextet;
  }

  /**
   * Convert a byte array into an InetAddress.
   *
   * <p>{@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) {
    checkNotNull(ip);
    if (ip instanceof Inet4Address) {
      // For IPv4, Java's formatting is good enough.
      return ip.getHostAddress();
    }
    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] = Ints.fromBytes((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">RFC 3986</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 method is similar to {@link InetAddresses#forString(String)}, however, it requires that
   * IPv6 addresses are surrounded by square brackets.
   *
   * <p>This method is the inverse of {@link InetAddresses#toUriString(java.net.InetAddress)}.
   *
   * <p>This method accepts non-ASCII digits, for example {@code "１９２.１６８.０.１"} (those are fullwidth
   * characters). That is consistent with {@link InetAddress}, but not with various RFCs. If you
   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * @param hostAddr an 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) {
    InetAddress addr = forUriStringNoThrow(hostAddr);
    if (addr == null) {
      throw formatIllegalArgumentException("Not a valid URI IP literal: '%s'", hostAddr);
    }

    return addr;
  }

  @CheckForNull
  private static InetAddress forUriStringNoThrow(String hostAddr) {
    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) {
      return null;
    }

    return bytesToInetAddress(addr);
  }

  /**
   * Returns {@code true} if the supplied string is a valid URI IP string literal, {@code false}
   * otherwise.
   *
   * <p>This method accepts non-ASCII digits, for example {@code "１９２.１６８.０.１"} (those are fullwidth
   * characters). That is consistent with {@link InetAddress}, but not with various RFCs. If you
   * want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * @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) {
    return forUriStringNoThrow(ipString) != null;
  }

  /**
   * 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">RFC 4291</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) {
    checkArgument(
        isCompatIPv4Address(ip), "Address '%s' is not IPv4-compatible.", toAddrString(ip));

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

  /**
   * Evaluates whether the argument is a 6to4 address.
   *
   * <p>6to4 addresses begin with the {@code "2002::/16"} prefix. The next 32 bits are the IPv4
   * address of the host to which IPv6-in-IPv4 tunneled packets should be routed.
   *
   * <p>For more on 6to4 addresses see section 2 of <a target="_parent"
   * href="http://tools.ietf.org/html/rfc3056#section-2">RFC 3056</a>.
   *
   * @param ip {@link Inet6Address} to be examined for 6to4 address format
   * @return {@code true} if the argument is a 6to4 address
   */
  public static boolean is6to4Address(Inet6Address ip) {
    byte[] bytes = ip.getAddress();
    return (bytes[0] == (byte) 0x20) && (bytes[1] == (byte) 0x02);
  }

  /**
   * Returns the IPv4 address embedded in a 6to4 address.
   *
   * @param ip {@link Inet6Address} to be examined for embedded IPv4 in 6to4 address
   * @return {@link Inet4Address} of embedded IPv4 in 6to4 address
   * @throws IllegalArgumentException if the argument is not a valid IPv6 6to4 address
   */
  public static Inet4Address get6to4IPv4Address(Inet6Address ip) {
    checkArgument(is6to4Address(ip), "Address '%s' is not a 6to4 address.", toAddrString(ip));

    return getInet4Address(Arrays.copyOfRange(ip.getAddress(), 2, 6));
  }

  /**
   * A simple immutable data class to encapsulate the information to be found in a Teredo address.
   *
   * <p>All of the fields in this class are encoded in various portions of the IPv6 address as part
   * of the protocol. More protocols details can be found at: <a target="_parent"
   * href="http://en.wikipedia.org/wiki/Teredo_tunneling">http://en.wikipedia.
   * org/wiki/Teredo_tunneling</a>.
   *
   * <p>The RFC can be found here: <a target="_parent" href="http://tools.ietf.org/html/rfc4380">RFC
   * 4380</a>.
   *
   * @since 5.0
   */
  public static final class TeredoInfo {
    private final Inet4Address server;
    private final Inet4Address client;
    private final int port;
    private final int flags;

    /**
     * Constructs a TeredoInfo instance.
     *
     * <p>Both server and client can be {@code null}, in which case the value {@code "0.0.0.0"} will
     * be assumed.
     *
     * @throws IllegalArgumentException if either of the {@code port} or the {@code flags} arguments
     *     are out of range of an unsigned short
     */
    // TODO: why is this public?
    public TeredoInfo(
        @CheckForNull Inet4Address server, @CheckForNull Inet4Address client, int port, int flags) {
      checkArgument(
          (port >= 0) && (port <= 0xffff), "port '%s' is out of range (0 <= port <= 0xffff)", port);
      checkArgument(
          (flags >= 0) && (flags <= 0xffff),
          "flags '%s' is out of range (0 <= flags <= 0xffff)",
          flags);

      this.server = MoreObjects.firstNonNull(server, ANY4);
      this.client = MoreObjects.firstNonNull(client, ANY4);
      this.port = port;
      this.flags = flags;
    }

    public Inet4Address getServer() {
      return server;
    }

    public Inet4Address getClient() {
      return client;
    }

    public int getPort() {
      return port;
    }

    public int getFlags() {
      return flags;
    }
  }

  /**
   * Evaluates whether the argument is a Teredo address.
   *
   * <p>Teredo addresses begin with the {@code "2001::/32"} prefix.
   *
   * @param ip {@link Inet6Address} to be examined for Teredo address format
   * @return {@code true} if the argument is a Teredo address
   */
  public static boolean isTeredoAddress(Inet6Address ip) {
    byte[] bytes = ip.getAddress();
    return (bytes[0] == (byte) 0x20)
        && (bytes[1] == (byte) 0x01)
        && (bytes[2] == 0)
        && (bytes[3] == 0);
  }

  /**
   * Returns the Teredo information embedded in a Teredo address.
   *
   * @param ip {@link Inet6Address} to be examined for embedded Teredo information
   * @return extracted {@code TeredoInfo}
   * @throws IllegalArgumentException if the argument is not a valid IPv6 Teredo address
   */
  public static TeredoInfo getTeredoInfo(Inet6Address ip) {
    checkArgument(isTeredoAddress(ip), "Address '%s' is not a Teredo address.", toAddrString(ip));

    byte[] bytes = ip.getAddress();
    Inet4Address server = getInet4Address(Arrays.copyOfRange(bytes, 4, 8));

    int flags = ByteStreams.newDataInput(bytes, 8).readShort() & 0xffff;

    // Teredo obfuscates the mapped client port, per section 4 of the RFC.
    int port = ~ByteStreams.newDataInput(bytes, 10).readShort() & 0xffff;

    byte[] clientBytes = Arrays.copyOfRange(bytes, 12, 16);
    for (int i = 0; i < clientBytes.length; i++) {
      // Teredo obfuscates the mapped client IP, per section 4 of the RFC.
      clientBytes[i] = (byte) ~clientBytes[i];
    }
    Inet4Address client = getInet4Address(clientBytes);

    return new TeredoInfo(server, client, port, flags);
  }

  /**
   * Evaluates whether the argument is an ISATAP address.
   *
   * <p>From RFC 5214: "ISATAP interface identifiers are constructed in Modified EUI-64 format [...]
   * by concatenating the 24-bit IANA OUI (00-00-5E), the 8-bit hexadecimal value 0xFE, and a 32-bit
   * IPv4 address in network byte order [...]"
   *
   * <p>For more on ISATAP addresses see section 6.1 of <a target="_parent"
   * href="http://tools.ietf.org/html/rfc5214#section-6.1">RFC 5214</a>.
   *
   * @param ip {@link Inet6Address} to be examined for ISATAP address format
   * @return {@code true} if the argument is an ISATAP address
   */
  public static boolean isIsatapAddress(Inet6Address ip) {

    // If it's a Teredo address with the right port (41217, or 0xa101)
    // which would be encoded as 0x5efe then it can't be an ISATAP address.
    if (isTeredoAddress(ip)) {
      return false;
    }

    byte[] bytes = ip.getAddress();

    if ((bytes[8] | (byte) 0x03) != (byte) 0x03) {

      // Verify that high byte of the 64 bit identifier is zero, modulo
      // the U/L and G bits, with which we are not concerned.
      return false;
    }

    return (bytes[9] == (byte) 0x00) && (bytes[10] == (byte) 0x5e) && (bytes[11] == (byte) 0xfe);
  }

  /**
   * Returns the IPv4 address embedded in an ISATAP address.
   *
   * @param ip {@link Inet6Address} to be examined for embedded IPv4 in ISATAP address
   * @return {@link Inet4Address} of embedded IPv4 in an ISATAP address
   * @throws IllegalArgumentException if the argument is not a valid IPv6 ISATAP address
   */
  public static Inet4Address getIsatapIPv4Address(Inet6Address ip) {
    checkArgument(isIsatapAddress(ip), "Address '%s' is not an ISATAP address.", toAddrString(ip));

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

  /**
   * Examines the Inet6Address to determine if it is an IPv6 address of one of the specified address
   * types that contain an embedded IPv4 address.
   *
   * <p>NOTE: ISATAP addresses are explicitly excluded from this method due to their trivial
   * spoofability. With other transition addresses spoofing involves (at least) infection of one's
   * BGP routing table.
   *
   * @param ip {@link Inet6Address} to be examined for embedded IPv4 client address
   * @return {@code true} if there is an embedded IPv4 client address
   * @since 7.0
   */
  public static boolean hasEmbeddedIPv4ClientAddress(Inet6Address ip) {
    return isCompatIPv4Address(ip) || is6to4Address(ip) || isTeredoAddress(ip);
  }

  /**
   * Examines the Inet6Address to extract the embedded IPv4 client address if the InetAddress is an
   * IPv6 address of one of the specified address types that contain an embedded IPv4 address.
   *
   * <p>NOTE: ISATAP addresses are explicitly excluded from this method due to their trivial
   * spoofability. With other transition addresses spoofing involves (at least) infection of one's
   * BGP routing table.
   *
   * @param ip {@link Inet6Address} to be examined for embedded IPv4 client address
   * @return {@link Inet4Address} of embedded IPv4 client address
   * @throws IllegalArgumentException if the argument does not have a valid embedded IPv4 address
   */
  public static Inet4Address getEmbeddedIPv4ClientAddress(Inet6Address ip) {
    if (isCompatIPv4Address(ip)) {
      return getCompatIPv4Address(ip);
    }

    if (is6to4Address(ip)) {
      return get6to4IPv4Address(ip);
    }

    if (isTeredoAddress(ip)) {
      return getTeredoInfo(ip).getClient();
    }

    throw formatIllegalArgumentException("'%s' has no embedded IPv4 address.", toAddrString(ip));
  }

  /**
   * Evaluates whether the argument is an "IPv4 mapped" IPv6 address.
   *
   * <p>An "IPv4 mapped" address is anything in the range ::ffff:0:0/96 (sometimes written as
   * ::ffff:0.0.0.0/96), with the last 32 bits interpreted as an IPv4 address.
   *
   * <p>For more on IPv4 mapped addresses see section 2.5.5.2 of <a target="_parent"
   * href="http://tools.ietf.org/html/rfc4291#section-2.5.5.2">RFC 4291</a>.
   *
   * <p>Note: This method takes a {@code String} argument because {@link InetAddress} automatically
   * collapses mapped addresses to IPv4. (It is actually possible to avoid this using one of the
   * obscure {@link Inet6Address} methods, but it would be unwise to depend on such a
   * poorly-documented feature.)
   *
   * <p>This method accepts non-ASCII digits. That is consistent with {@link InetAddress}, but not
   * with various RFCs. If you want to accept ASCII digits only, you can use something like {@code
   * CharMatcher.ascii().matchesAllOf(ipString)}.
   *
   * @param ipString {@code String} to be examined for embedded IPv4-mapped IPv6 address format
   * @return {@code true} if the argument is a valid "mapped" address
   * @since 10.0
   */
  public static boolean isMappedIPv4Address(String ipString) {
    byte[] bytes = ipStringToBytes(ipString);
    if (bytes != null && bytes.length == 16) {
      for (int i = 0; i < 10; i++) {
        if (bytes[i] != 0) {
          return false;
        }
      }
      for (int i = 10; i < 12; i++) {
        if (bytes[i] != (byte) 0xff) {
          return false;
        }
      }
      return true;
    }
    return false;
  }

  /**
   * Coerces an IPv6 address into an IPv4 address.
   *
   * <p>HACK: As long as applications continue to use IPv4 addresses for indexing into tables,
   * accounting, et cetera, it may be necessary to <b>coerce</b> IPv6 addresses into IPv4 addresses.
   * This method does so by hashing 64 bits of the IPv6 address into {@code 224.0.0.0/3} (64 bits
   * into 29 bits):
   *
   * <ul>
   *   <li>If the IPv6 address contains an embedded IPv4 address, the function hashes that.
   *   <li>Otherwise, it hashes the upper 64 bits of the IPv6 address.
   * </ul>
   *
   * <p>A "coerced" IPv4 address is equivalent to itself.
   *
   * <p>NOTE: This method is failsafe for security purposes: ALL IPv6 addresses (except localhost
   * (::1)) are hashed to avoid the security risk associated with extracting an embedded IPv4
   * address that might permit elevated privileges.
   *
   * @param ip {@link InetAddress} to "coerce"
   * @return {@link Inet4Address} represented "coerced" address
   * @since 7.0
   */
  public static Inet4Address getCoercedIPv4Address(InetAddress ip) {
    if (ip instanceof Inet4Address) {
      return (Inet4Address) ip;
    }

    // Special cases:
    byte[] bytes = ip.getAddress();
    boolean leadingBytesOfZero = true;
    for (int i = 0; i < 15; ++i) {
      if (bytes[i] != 0) {
        leadingBytesOfZero = false;
        break;
      }
    }
    if (leadingBytesOfZero && (bytes[15] == 1)) {
      return LOOPBACK4; // ::1
    } else if (leadingBytesOfZero && (bytes[15] == 0)) {
      return ANY4; // ::0
    }

    Inet6Address ip6 = (Inet6Address) ip;
    long addressAsLong = 0;
    if (hasEmbeddedIPv4ClientAddress(ip6)) {
      addressAsLong = getEmbeddedIPv4ClientAddress(ip6).hashCode();
    } else {
      // Just extract the high 64 bits (assuming the rest is user-modifiable).
      addressAsLong = ByteBuffer.wrap(ip6.getAddress(), 0, 8).getLong();
    }

    // Many strategies for hashing are possible. This might suffice for now.
    int coercedHash = Hashing.murmur3_32_fixed().hashLong(addressAsLong).asInt();

    // Squash into 224/4 Multicast and 240/4 Reserved space (i.e. 224/3).
    coercedHash |= 0xe0000000;

    // Fixup to avoid some "illegal" values. Currently the only potential
    // illegal value is 255.255.255.255.
    if (coercedHash == 0xffffffff) {
      coercedHash = 0xfffffffe;
    }

    return getInet4Address(Ints.toByteArray(coercedHash));
  }

  /**
   * Returns an integer representing an IPv4 address regardless of whether the supplied argument is
   * an IPv4 address or not.
   *
   * <p>IPv6 addresses are <b>coerced</b> to IPv4 addresses before being converted to integers.
   *
   * <p>As long as there are applications that assume that all IP addresses are IPv4 addresses and
   * can therefore be converted safely to integers (for whatever purpose) this function can be used
   * to handle IPv6 addresses as well until the application is suitably fixed.
   *
   * <p>NOTE: an IPv6 address coerced to an IPv4 address can only be used for such purposes as
   * rudimentary identification or indexing into a collection of real {@link InetAddress}es. They
   * cannot be used as real addresses for the purposes of network communication.
   *
   * @param ip {@link InetAddress} to convert
   * @return {@code int}, "coerced" if ip is not an IPv4 address
   * @since 7.0
   */
  public static int coerceToInteger(InetAddress ip) {
    return ByteStreams.newDataInput(getCoercedIPv4Address(ip).getAddress()).readInt();
  }

  /**
   * Returns a BigInteger representing the address.
   *
   * <p>Unlike {@code coerceToInteger}, IPv6 addresses are not coerced to IPv4 addresses.
   *
   * @param address {@link InetAddress} to convert
   * @return {@code BigInteger} representation of the address
   * @since 28.2
   */
  public static BigInteger toBigInteger(InetAddress address) {
    return new BigInteger(1, address.getAddress());
  }

  /**
   * Returns an Inet4Address having the integer value specified by the argument.
   *
   * @param address {@code int}, the 32bit integer address to be converted
   * @return {@link Inet4Address} equivalent of the argument
   */
  public static Inet4Address fromInteger(int address) {
    return getInet4Address(Ints.toByteArray(address));
  }

  /**
   * Returns the {@code Inet4Address} corresponding to a given {@code BigInteger}.
   *
   * @param address BigInteger representing the IPv4 address
   * @return Inet4Address representation of the given BigInteger
   * @throws IllegalArgumentException if the BigInteger is not between 0 and 2^32-1
   * @since 28.2
   */
  public static Inet4Address fromIPv4BigInteger(BigInteger address) {
    return (Inet4Address) fromBigInteger(address, false);
  }
  /**
   * Returns the {@code Inet6Address} corresponding to a given {@code BigInteger}.
   *
   * @param address BigInteger representing the IPv6 address
   * @return Inet6Address representation of the given BigInteger
   * @throws IllegalArgumentException if the BigInteger is not between 0 and 2^128-1
   * @since 28.2
   */
  public static Inet6Address fromIPv6BigInteger(BigInteger address) {
    return (Inet6Address) fromBigInteger(address, true);
  }

  /**
   * Converts a BigInteger to either an IPv4 or IPv6 address. If the IP is IPv4, it must be
   * constrained to 32 bits, otherwise it is constrained to 128 bits.
   *
   * @param address the address represented as a big integer
   * @param isIpv6 whether the created address should be IPv4 or IPv6
   * @return the BigInteger converted to an address
   * @throws IllegalArgumentException if the BigInteger is not between 0 and maximum value for IPv4
   *     or IPv6 respectively
   */
  private static InetAddress fromBigInteger(BigInteger address, boolean isIpv6) {
    checkArgument(address.signum() >= 0, "BigInteger must be greater than or equal to 0");

    int numBytes = isIpv6 ? 16 : 4;

    byte[] addressBytes = address.toByteArray();
    byte[] targetCopyArray = new byte[numBytes];

    int srcPos = Math.max(0, addressBytes.length - numBytes);
    int copyLength = addressBytes.length - srcPos;
    int destPos = numBytes - copyLength;

    // Check the extra bytes in the BigInteger are all zero.
    for (int i = 0; i < srcPos; i++) {
      if (addressBytes[i] != 0x00) {
        throw formatIllegalArgumentException(
            "BigInteger cannot be converted to InetAddress because it has more than %d"
                + " bytes: %s",
            numBytes, address);
      }
    }

    // Copy the bytes into the least significant positions.
    System.arraycopy(addressBytes, srcPos, targetCopyArray, destPos, copyLength);

    try {
      return InetAddress.getByAddress(targetCopyArray);
    } catch (UnknownHostException impossible) {
      throw new AssertionError(impossible);
    }
  }

  /**
   * Returns an address from a <b>little-endian ordered</b> byte array (the opposite of what {@link
   * InetAddress#getByAddress} expects).
   *
   * <p>IPv4 address byte array must be 4 bytes long and IPv6 byte array must be 16 bytes long.
   *
   * @param addr the raw IP address in little-endian byte order
   * @return an InetAddress object created from the raw IP address
   * @throws UnknownHostException if IP address is of illegal length
   */
  public static InetAddress fromLittleEndianByteArray(byte[] addr) throws UnknownHostException {
    byte[] reversed = new byte[addr.length];
    for (int i = 0; i < addr.length; i++) {
      reversed[i] = addr[addr.length - i - 1];
    }
    return InetAddress.getByAddress(reversed);
  }

  /**
   * Returns a new InetAddress that is one less than the passed in address. This method works for
   * both IPv4 and IPv6 addresses.
   *
   * @param address the InetAddress to decrement
   * @return a new InetAddress that is one less than the passed in address
   * @throws IllegalArgumentException if InetAddress is at the beginning of its range
   * @since 18.0
   */
  public static InetAddress decrement(InetAddress address) {
    byte[] addr = address.getAddress();
    int i = addr.length - 1;
    while (i >= 0 && addr[i] == (byte) 0x00) {
      addr[i] = (byte) 0xff;
      i--;
    }

    checkArgument(i >= 0, "Decrementing %s would wrap.", address);

    addr[i]--;
    return bytesToInetAddress(addr);
  }

  /**
   * Returns a new InetAddress that is one more than the passed in address. This method works for
   * both IPv4 and IPv6 addresses.
   *
   * @param address the InetAddress to increment
   * @return a new InetAddress that is one more than the passed in address
   * @throws IllegalArgumentException if InetAddress is at the end of its range
   * @since 10.0
   */
  public static InetAddress increment(InetAddress address) {
    byte[] addr = address.getAddress();
    int i = addr.length - 1;
    while (i >= 0 && addr[i] == (byte) 0xff) {
      addr[i] = 0;
      i--;
    }

    checkArgument(i >= 0, "Incrementing %s would wrap.", address);

    addr[i]++;
    return bytesToInetAddress(addr);
  }

  /**
   * Returns true if the InetAddress is either 255.255.255.255 for IPv4 or
   * ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff for IPv6.
   *
   * @return true if the InetAddress is either 255.255.255.255 for IPv4 or
   *     ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff for IPv6
   * @since 10.0
   */
  public static boolean isMaximum(InetAddress address) {
    byte[] addr = address.getAddress();
    for (byte b : addr) {
      if (b != (byte) 0xff) {
        return false;
      }
    }
    return true;
  }

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