Initial Jack import.

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+/*
+ * 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 com.google.common.annotations.Beta;
+import com.google.common.base.Objects;
+import com.google.common.base.Preconditions;
+import com.google.common.hash.Hashing;
+import com.google.common.io.ByteStreams;
+import com.google.common.primitives.Ints;
+
+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 javax.annotation.Nullable;
+
+/**
+ * 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>
+ *
+ * @author Erik Kline
+ * @since 5.0
+ */
+@Beta
+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 new IllegalArgumentException(
+          String.format("'%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 if 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] = 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"
+   *  >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 new IllegalArgumentException(
+          String.format("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));
+  }
+
+  /**
+   * 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"
+   *    >http://tools.ietf.org/html/rfc3056</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) {
+    Preconditions.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"
+   *    >http://tools.ietf.org/html/rfc4380</a>.
+   *
+   * @since 5.0
+   */
+  @Beta
+  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(
+        @Nullable Inet4Address server, @Nullable Inet4Address client, int port, int flags) {
+      Preconditions.checkArgument((port >= 0) && (port <= 0xffff),
+          "port '%s' is out of range (0 <= port <= 0xffff)", port);
+      Preconditions.checkArgument((flags >= 0) && (flags <= 0xffff),
+          "flags '%s' is out of range (0 <= flags <= 0xffff)", flags);
+      
+      this.server = Objects.firstNonNull(server, ANY4);
+      this.client = Objects.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) {
+    Preconditions.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"
+   *    >http://tools.ietf.org/html/rfc5214</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) {
+    Preconditions.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 new IllegalArgumentException(
+        String.format("'%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"
+   *    >http://tools.ietf.org/html/rfc4291</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.)
+   *
+   * @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 function does
+   * so by hashing the upper 64 bits into {@code 224.0.0.0/3}
+   * (64 bits into 29 bits).
+   *
+   * <p>A "coerced" IPv4 address is equivalent to itself.
+   *
+   * <p>NOTE: This function 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().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 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 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 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--;
+    }
+
+    Preconditions.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 (int i = 0; i < addr.length; i++) {
+      if (addr[i] != (byte) 0xff) {
+        return false;
+      }
+    }
+    return true;
+  }
+}