1 /*
   2  * Copyright (c) 1995, 2021, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.net;
  27 
  28 import java.util.List;
  29 import java.util.NavigableSet;
  30 import java.util.ArrayList;
  31 import java.util.Objects;
  32 import java.util.Scanner;
  33 import java.io.File;
  34 import java.io.ObjectStreamException;
  35 import java.io.ObjectStreamField;
  36 import java.io.IOException;
  37 import java.io.InvalidObjectException;
  38 import java.io.ObjectInputStream;
  39 import java.io.ObjectInputStream.GetField;
  40 import java.io.ObjectOutputStream;
  41 import java.io.ObjectOutputStream.PutField;
  42 import java.lang.annotation.Native;
  43 import java.util.concurrent.ConcurrentHashMap;
  44 import java.util.concurrent.ConcurrentMap;
  45 import java.util.concurrent.ConcurrentSkipListSet;
  46 import java.util.concurrent.atomic.AtomicLong;
  47 import java.util.Arrays;
  48 
  49 import jdk.internal.access.JavaNetInetAddressAccess;
  50 import jdk.internal.access.SharedSecrets;
  51 import sun.security.action.*;
  52 import sun.net.InetAddressCachePolicy;
  53 import sun.net.util.IPAddressUtil;
  54 import sun.nio.cs.UTF_8;
  55 
  56 /**
  57  * This class represents an Internet Protocol (IP) address.
  58  *
  59  * <p> An IP address is either a 32-bit or 128-bit unsigned number
  60  * used by IP, a lower-level protocol on which protocols like UDP and
  61  * TCP are built. The IP address architecture is defined by <a
  62  * href="http://www.ietf.org/rfc/rfc790.txt"><i>RFC&nbsp;790:
  63  * Assigned Numbers</i></a>, <a
  64  * href="http://www.ietf.org/rfc/rfc1918.txt"> <i>RFC&nbsp;1918:
  65  * Address Allocation for Private Internets</i></a>, <a
  66  * href="http://www.ietf.org/rfc/rfc2365.txt"><i>RFC&nbsp;2365:
  67  * Administratively Scoped IP Multicast</i></a>, and <a
  68  * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IP
  69  * Version 6 Addressing Architecture</i></a>. An instance of an
  70  * InetAddress consists of an IP address and possibly its
  71  * corresponding host name (depending on whether it is constructed
  72  * with a host name or whether it has already done reverse host name
  73  * resolution).
  74  *
  75  * <h2> Address types </h2>
  76  *
  77  * <table class="striped" style="margin-left:2em">
  78  *   <caption style="display:none">Description of unicast and multicast address types</caption>
  79  *   <thead>
  80  *   <tr><th scope="col">Address Type</th><th scope="col">Description</th></tr>
  81  *   </thead>
  82  *   <tbody>
  83  *   <tr><th scope="row" style="vertical-align:top">unicast</th>
  84  *       <td>An identifier for a single interface. A packet sent to
  85  *         a unicast address is delivered to the interface identified by
  86  *         that address.
  87  *
  88  *         <p> The Unspecified Address -- Also called anylocal or wildcard
  89  *         address. It must never be assigned to any node. It indicates the
  90  *         absence of an address. One example of its use is as the target of
  91  *         bind, which allows a server to accept a client connection on any
  92  *         interface, in case the server host has multiple interfaces.
  93  *
  94  *         <p> The <i>unspecified</i> address must not be used as
  95  *         the destination address of an IP packet.
  96  *
  97  *         <p> The <i>Loopback</i> Addresses -- This is the address
  98  *         assigned to the loopback interface. Anything sent to this
  99  *         IP address loops around and becomes IP input on the local
 100  *         host. This address is often used when testing a
 101  *         client.</td></tr>
 102  *   <tr><th scope="row" style="vertical-align:top">multicast</th>
 103  *       <td>An identifier for a set of interfaces (typically belonging
 104  *         to different nodes). A packet sent to a multicast address is
 105  *         delivered to all interfaces identified by that address.</td></tr>
 106  * </tbody>
 107  * </table>
 108  *
 109  * <h3> IP address scope </h3>
 110  *
 111  * <p> <i>Link-local</i> addresses are designed to be used for addressing
 112  * on a single link for purposes such as auto-address configuration,
 113  * neighbor discovery, or when no routers are present.
 114  *
 115  * <p> <i>Site-local</i> addresses are designed to be used for addressing
 116  * inside of a site without the need for a global prefix.
 117  *
 118  * <p> <i>Global</i> addresses are unique across the internet.
 119  *
 120  * <h3> Textual representation of IP addresses </h3>
 121  *
 122  * The textual representation of an IP address is address family specific.
 123  *
 124  * <p>
 125  *
 126  * For IPv4 address format, please refer to <A
 127  * HREF="Inet4Address.html#format">Inet4Address#format</A>; For IPv6
 128  * address format, please refer to <A
 129  * HREF="Inet6Address.html#format">Inet6Address#format</A>.
 130  *
 131  * <P>There is a <a href="doc-files/net-properties.html#Ipv4IPv6">couple of
 132  * System Properties</a> affecting how IPv4 and IPv6 addresses are used.</P>
 133  *
 134  * <h3> Host Name Resolution </h3>
 135  *
 136  * Host name-to-IP address <i>resolution</i> is accomplished through
 137  * the use of a combination of local machine configuration information
 138  * and network naming services such as the Domain Name System (DNS)
 139  * and Network Information Service(NIS). The particular naming
 140  * services(s) being used is by default the local machine configured
 141  * one. For any host name, its corresponding IP address is returned.
 142  *
 143  * <p> <i>Reverse name resolution</i> means that for any IP address,
 144  * the host associated with the IP address is returned.
 145  *
 146  * <p> The InetAddress class provides methods to resolve host names to
 147  * their IP addresses and vice versa.
 148  *
 149  * <h3> InetAddress Caching </h3>
 150  *
 151  * The InetAddress class has a cache to store successful as well as
 152  * unsuccessful host name resolutions.
 153  *
 154  * <p> By default, when a security manager is installed, in order to
 155  * protect against DNS spoofing attacks,
 156  * the result of positive host name resolutions are
 157  * cached forever. When a security manager is not installed, the default
 158  * behavior is to cache entries for a finite (implementation dependent)
 159  * period of time. The result of unsuccessful host
 160  * name resolution is cached for a very short period of time (10
 161  * seconds) to improve performance.
 162  *
 163  * <p> If the default behavior is not desired, then a Java security property
 164  * can be set to a different Time-to-live (TTL) value for positive
 165  * caching. Likewise, a system admin can configure a different
 166  * negative caching TTL value when needed.
 167  *
 168  * <p> Two Java security properties control the TTL values used for
 169  *  positive and negative host name resolution caching:
 170  *
 171  * <dl style="margin-left:2em">
 172  * <dt><b>networkaddress.cache.ttl</b></dt>
 173  * <dd>Indicates the caching policy for successful name lookups from
 174  * the name service. The value is specified as an integer to indicate
 175  * the number of seconds to cache the successful lookup. The default
 176  * setting is to cache for an implementation specific period of time.
 177  * <p>
 178  * A value of -1 indicates "cache forever".
 179  * </dd>
 180  * <dt><b>networkaddress.cache.negative.ttl</b> (default: 10)</dt>
 181  * <dd>Indicates the caching policy for un-successful name lookups
 182  * from the name service. The value is specified as an integer to
 183  * indicate the number of seconds to cache the failure for
 184  * un-successful lookups.
 185  * <p>
 186  * A value of 0 indicates "never cache".
 187  * A value of -1 indicates "cache forever".
 188  * </dd>
 189  * </dl>
 190  *
 191  * @author  Chris Warth
 192  * @see     java.net.InetAddress#getByAddress(byte[])
 193  * @see     java.net.InetAddress#getByAddress(java.lang.String, byte[])
 194  * @see     java.net.InetAddress#getAllByName(java.lang.String)
 195  * @see     java.net.InetAddress#getByName(java.lang.String)
 196  * @see     java.net.InetAddress#getLocalHost()
 197  * @since 1.0
 198  */
 199 public class InetAddress implements java.io.Serializable {
 200 
 201     @Native static final int PREFER_IPV4_VALUE = 0;
 202     @Native static final int PREFER_IPV6_VALUE = 1;
 203     @Native static final int PREFER_SYSTEM_VALUE = 2;
 204 
 205     /**
 206      * Specify the address family: Internet Protocol, Version 4
 207      * @since 1.4
 208      */
 209     @Native static final int IPv4 = 1;
 210 
 211     /**
 212      * Specify the address family: Internet Protocol, Version 6
 213      * @since 1.4
 214      */
 215     @Native static final int IPv6 = 2;
 216 
 217     /* Specify address family preference */
 218     static transient final int preferIPv6Address;
 219 
 220     static class InetAddressHolder {
 221         /**
 222          * Reserve the original application specified hostname.
 223          *
 224          * The original hostname is useful for domain-based endpoint
 225          * identification (see RFC 2818 and RFC 6125).  If an address
 226          * was created with a raw IP address, a reverse name lookup
 227          * may introduce endpoint identification security issue via
 228          * DNS forging.
 229          *
 230          * Oracle JSSE provider is using this original hostname, via
 231          * jdk.internal.misc.JavaNetAccess, for SSL/TLS endpoint identification.
 232          *
 233          * Note: May define a new public method in the future if necessary.
 234          */
 235         String originalHostName;
 236 
 237         InetAddressHolder() {}
 238 
 239         InetAddressHolder(String hostName, int address, int family) {
 240             this.originalHostName = hostName;
 241             this.hostName = hostName;
 242             this.address = address;
 243             this.family = family;
 244         }
 245 
 246         void init(String hostName, int family) {
 247             this.originalHostName = hostName;
 248             this.hostName = hostName;
 249             if (family != -1) {
 250                 this.family = family;
 251             }
 252         }
 253 
 254         String hostName;
 255 
 256         String getHostName() {
 257             return hostName;
 258         }
 259 
 260         String getOriginalHostName() {
 261             return originalHostName;
 262         }
 263 
 264         /**
 265          * Holds a 32-bit IPv4 address.
 266          */
 267         int address;
 268 
 269         int getAddress() {
 270             return address;
 271         }
 272 
 273         /**
 274          * Specifies the address family type, for instance, '1' for IPv4
 275          * addresses, and '2' for IPv6 addresses.
 276          */
 277         int family;
 278 
 279         int getFamily() {
 280             return family;
 281         }
 282     }
 283 
 284     /* Used to store the serializable fields of InetAddress */
 285     final transient InetAddressHolder holder;
 286 
 287     InetAddressHolder holder() {
 288         return holder;
 289     }
 290 
 291     /* Used to store the name service provider */
 292     private static transient NameService nameService;
 293 
 294     /**
 295      * Used to store the best available hostname.
 296      * Lazily initialized via a data race; safe because Strings are immutable.
 297      */
 298     private transient String canonicalHostName = null;
 299 
 300     /** use serialVersionUID from JDK 1.0.2 for interoperability */
 301     @java.io.Serial
 302     private static final long serialVersionUID = 3286316764910316507L;
 303 
 304     /*
 305      * Load net library into runtime, and perform initializations.
 306      */
 307     static {
 308         String str = GetPropertyAction.privilegedGetProperty("java.net.preferIPv6Addresses");
 309         if (str == null) {
 310             preferIPv6Address = PREFER_IPV4_VALUE;
 311         } else if (str.equalsIgnoreCase("true")) {
 312             preferIPv6Address = PREFER_IPV6_VALUE;
 313         } else if (str.equalsIgnoreCase("false")) {
 314             preferIPv6Address = PREFER_IPV4_VALUE;
 315         } else if (str.equalsIgnoreCase("system")) {
 316             preferIPv6Address = PREFER_SYSTEM_VALUE;
 317         } else {
 318             preferIPv6Address = PREFER_IPV4_VALUE;
 319         }
 320         jdk.internal.loader.BootLoader.loadLibrary("net");
 321         SharedSecrets.setJavaNetInetAddressAccess(
 322                 new JavaNetInetAddressAccess() {
 323                     public String getOriginalHostName(InetAddress ia) {
 324                         return ia.holder.getOriginalHostName();
 325                     }
 326 
 327                     public InetAddress getByName(String hostName,
 328                                                  InetAddress hostAddress)
 329                         throws UnknownHostException
 330                     {
 331                         return InetAddress.getByName(hostName, hostAddress);
 332                     }
 333 
 334                     public int addressValue(Inet4Address inet4Address) {
 335                         return inet4Address.addressValue();
 336                     }
 337 
 338                     public byte[] addressBytes(Inet6Address inet6Address) {
 339                         return inet6Address.addressBytes();
 340                     }
 341                 }
 342         );
 343         init();
 344     }
 345 
 346     /**
 347      * Constructor for the Socket.accept() method.
 348      * This creates an empty InetAddress, which is filled in by
 349      * the accept() method.  This InetAddress, however, is not
 350      * put in the address cache, since it is not created by name.
 351      */
 352     InetAddress() {
 353         holder = new InetAddressHolder();
 354     }
 355 
 356     /**
 357      * Replaces the de-serialized object with an Inet4Address object.
 358      *
 359      * @return the alternate object to the de-serialized object.
 360      *
 361      * @throws ObjectStreamException if a new object replacing this
 362      * object could not be created
 363      */
 364     @java.io.Serial
 365     private Object readResolve() throws ObjectStreamException {
 366         // will replace the deserialized 'this' object
 367         return new Inet4Address(holder().getHostName(), holder().getAddress());
 368     }
 369 
 370     /**
 371      * Utility routine to check if the InetAddress is an
 372      * IP multicast address.
 373      * @return a {@code boolean} indicating if the InetAddress is
 374      * an IP multicast address
 375      * @since   1.1
 376      */
 377     public boolean isMulticastAddress() {
 378         return false;
 379     }
 380 
 381     /**
 382      * Utility routine to check if the InetAddress is a wildcard address.
 383      * @return a {@code boolean} indicating if the InetAddress is
 384      *         a wildcard address.
 385      * @since 1.4
 386      */
 387     public boolean isAnyLocalAddress() {
 388         return false;
 389     }
 390 
 391     /**
 392      * Utility routine to check if the InetAddress is a loopback address.
 393      *
 394      * @return a {@code boolean} indicating if the InetAddress is
 395      * a loopback address; or false otherwise.
 396      * @since 1.4
 397      */
 398     public boolean isLoopbackAddress() {
 399         return false;
 400     }
 401 
 402     /**
 403      * Utility routine to check if the InetAddress is a link local address.
 404      *
 405      * @return a {@code boolean} indicating if the InetAddress is
 406      * a link local address; or false if address is not a link local unicast address.
 407      * @since 1.4
 408      */
 409     public boolean isLinkLocalAddress() {
 410         return false;
 411     }
 412 
 413     /**
 414      * Utility routine to check if the InetAddress is a site local address.
 415      *
 416      * @return a {@code boolean} indicating if the InetAddress is
 417      * a site local address; or false if address is not a site local unicast address.
 418      * @since 1.4
 419      */
 420     public boolean isSiteLocalAddress() {
 421         return false;
 422     }
 423 
 424     /**
 425      * Utility routine to check if the multicast address has global scope.
 426      *
 427      * @return a {@code boolean} indicating if the address has
 428      *         is a multicast address of global scope, false if it is not
 429      *         of global scope or it is not a multicast address
 430      * @since 1.4
 431      */
 432     public boolean isMCGlobal() {
 433         return false;
 434     }
 435 
 436     /**
 437      * Utility routine to check if the multicast address has node scope.
 438      *
 439      * @return a {@code boolean} indicating if the address has
 440      *         is a multicast address of node-local scope, false if it is not
 441      *         of node-local scope or it is not a multicast address
 442      * @since 1.4
 443      */
 444     public boolean isMCNodeLocal() {
 445         return false;
 446     }
 447 
 448     /**
 449      * Utility routine to check if the multicast address has link scope.
 450      *
 451      * @return a {@code boolean} indicating if the address has
 452      *         is a multicast address of link-local scope, false if it is not
 453      *         of link-local scope or it is not a multicast address
 454      * @since 1.4
 455      */
 456     public boolean isMCLinkLocal() {
 457         return false;
 458     }
 459 
 460     /**
 461      * Utility routine to check if the multicast address has site scope.
 462      *
 463      * @return a {@code boolean} indicating if the address has
 464      *         is a multicast address of site-local scope, false if it is not
 465      *         of site-local scope or it is not a multicast address
 466      * @since 1.4
 467      */
 468     public boolean isMCSiteLocal() {
 469         return false;
 470     }
 471 
 472     /**
 473      * Utility routine to check if the multicast address has organization scope.
 474      *
 475      * @return a {@code boolean} indicating if the address has
 476      *         is a multicast address of organization-local scope,
 477      *         false if it is not of organization-local scope
 478      *         or it is not a multicast address
 479      * @since 1.4
 480      */
 481     public boolean isMCOrgLocal() {
 482         return false;
 483     }
 484 
 485 
 486     /**
 487      * Test whether that address is reachable. Best effort is made by the
 488      * implementation to try to reach the host, but firewalls and server
 489      * configuration may block requests resulting in an unreachable status
 490      * while some specific ports may be accessible.
 491      * A typical implementation will use ICMP ECHO REQUESTs if the
 492      * privilege can be obtained, otherwise it will try to establish
 493      * a TCP connection on port 7 (Echo) of the destination host.
 494      * <p>
 495      * The timeout value, in milliseconds, indicates the maximum amount of time
 496      * the try should take. If the operation times out before getting an
 497      * answer, the host is deemed unreachable. A negative value will result
 498      * in an IllegalArgumentException being thrown.
 499      *
 500      * @param   timeout the time, in milliseconds, before the call aborts
 501      * @return a {@code boolean} indicating if the address is reachable.
 502      * @throws IOException if a network error occurs
 503      * @throws  IllegalArgumentException if {@code timeout} is negative.
 504      * @since 1.5
 505      */
 506     public boolean isReachable(int timeout) throws IOException {
 507         return isReachable(null, 0 , timeout);
 508     }
 509 
 510     /**
 511      * Test whether that address is reachable. Best effort is made by the
 512      * implementation to try to reach the host, but firewalls and server
 513      * configuration may block requests resulting in a unreachable status
 514      * while some specific ports may be accessible.
 515      * A typical implementation will use ICMP ECHO REQUESTs if the
 516      * privilege can be obtained, otherwise it will try to establish
 517      * a TCP connection on port 7 (Echo) of the destination host.
 518      * <p>
 519      * The {@code network interface} and {@code ttl} parameters
 520      * let the caller specify which network interface the test will go through
 521      * and the maximum number of hops the packets should go through.
 522      * A negative value for the {@code ttl} will result in an
 523      * IllegalArgumentException being thrown.
 524      * <p>
 525      * The timeout value, in milliseconds, indicates the maximum amount of time
 526      * the try should take. If the operation times out before getting an
 527      * answer, the host is deemed unreachable. A negative value will result
 528      * in an IllegalArgumentException being thrown.
 529      *
 530      * @param   netif   the NetworkInterface through which the
 531      *                    test will be done, or null for any interface
 532      * @param   ttl     the maximum numbers of hops to try or 0 for the
 533      *                  default
 534      * @param   timeout the time, in milliseconds, before the call aborts
 535      * @throws  IllegalArgumentException if either {@code timeout}
 536      *                          or {@code ttl} are negative.
 537      * @return a {@code boolean} indicating if the address is reachable.
 538      * @throws IOException if a network error occurs
 539      * @since 1.5
 540      */
 541     public boolean isReachable(NetworkInterface netif, int ttl,
 542                                int timeout) throws IOException {
 543         if (ttl < 0)
 544             throw new IllegalArgumentException("ttl can't be negative");
 545         if (timeout < 0)
 546             throw new IllegalArgumentException("timeout can't be negative");
 547 
 548         return impl.isReachable(this, timeout, netif, ttl);
 549     }
 550 
 551     /**
 552      * Gets the host name for this IP address.
 553      *
 554      * <p>If this InetAddress was created with a host name,
 555      * this host name will be remembered and returned;
 556      * otherwise, a reverse name lookup will be performed
 557      * and the result will be returned based on the system
 558      * configured name lookup service. If a lookup of the name service
 559      * is required, call
 560      * {@link #getCanonicalHostName() getCanonicalHostName}.
 561      *
 562      * <p>If there is a security manager, its
 563      * {@code checkConnect} method is first called
 564      * with the hostname and {@code -1}
 565      * as its arguments to see if the operation is allowed.
 566      * If the operation is not allowed, it will return
 567      * the textual representation of the IP address.
 568      *
 569      * @return  the host name for this IP address, or if the operation
 570      *    is not allowed by the security check, the textual
 571      *    representation of the IP address.
 572      *
 573      * @see InetAddress#getCanonicalHostName
 574      * @see SecurityManager#checkConnect
 575      */
 576     public String getHostName() {
 577         return getHostName(true);
 578     }
 579 
 580     /**
 581      * Returns the hostname for this address.
 582      * If the host is equal to null, then this address refers to any
 583      * of the local machine's available network addresses.
 584      * this is package private so SocketPermission can make calls into
 585      * here without a security check.
 586      *
 587      * <p>If there is a security manager, this method first
 588      * calls its {@code checkConnect} method
 589      * with the hostname and {@code -1}
 590      * as its arguments to see if the calling code is allowed to know
 591      * the hostname for this IP address, i.e., to connect to the host.
 592      * If the operation is not allowed, it will return
 593      * the textual representation of the IP address.
 594      *
 595      * @return  the host name for this IP address, or if the operation
 596      *    is not allowed by the security check, the textual
 597      *    representation of the IP address.
 598      *
 599      * @param check make security check if true
 600      *
 601      * @see SecurityManager#checkConnect
 602      */
 603     String getHostName(boolean check) {
 604         if (holder().getHostName() == null) {
 605             holder().hostName = InetAddress.getHostFromNameService(this, check);
 606         }
 607         return holder().getHostName();
 608     }
 609 
 610     /**
 611      * Gets the fully qualified domain name for this IP address.
 612      * Best effort method, meaning we may not be able to return
 613      * the FQDN depending on the underlying system configuration.
 614      *
 615      * <p>If there is a security manager, this method first
 616      * calls its {@code checkConnect} method
 617      * with the hostname and {@code -1}
 618      * as its arguments to see if the calling code is allowed to know
 619      * the hostname for this IP address, i.e., to connect to the host.
 620      * If the operation is not allowed, it will return
 621      * the textual representation of the IP address.
 622      *
 623      * @return  the fully qualified domain name for this IP address,
 624      *    or if the operation is not allowed by the security check,
 625      *    the textual representation of the IP address.
 626      *
 627      * @see SecurityManager#checkConnect
 628      *
 629      * @since 1.4
 630      */
 631     public String getCanonicalHostName() {
 632         String value = canonicalHostName;
 633         if (value == null)
 634             canonicalHostName = value =
 635                 InetAddress.getHostFromNameService(this, true);
 636         return value;
 637     }
 638 
 639     /**
 640      * Returns the hostname for this address.
 641      *
 642      * <p>If there is a security manager, this method first
 643      * calls its {@code checkConnect} method
 644      * with the hostname and {@code -1}
 645      * as its arguments to see if the calling code is allowed to know
 646      * the hostname for this IP address, i.e., to connect to the host.
 647      * If the operation is not allowed, it will return
 648      * the textual representation of the IP address.
 649      *
 650      * @return  the host name for this IP address, or if the operation
 651      *    is not allowed by the security check, the textual
 652      *    representation of the IP address.
 653      *
 654      * @param check make security check if true
 655      *
 656      * @see SecurityManager#checkConnect
 657      */
 658     private static String getHostFromNameService(InetAddress addr, boolean check) {
 659         String host = null;
 660         try {
 661             // first lookup the hostname
 662             host = nameService.getHostByAddr(addr.getAddress());
 663 
 664             /* check to see if calling code is allowed to know
 665              * the hostname for this IP address, ie, connect to the host
 666              */
 667             if (check) {
 668                 @SuppressWarnings("removal")
 669                 SecurityManager sec = System.getSecurityManager();
 670                 if (sec != null) {
 671                     sec.checkConnect(host, -1);
 672                 }
 673             }
 674 
 675             /* now get all the IP addresses for this hostname,
 676              * and make sure one of them matches the original IP
 677              * address. We do this to try and prevent spoofing.
 678              */
 679 
 680             InetAddress[] arr = InetAddress.getAllByName0(host, check);
 681             boolean ok = false;
 682 
 683             if (arr != null) {
 684                 for (int i = 0; !ok && i < arr.length; i++) {
 685                     ok = addr.equals(arr[i]);
 686                 }
 687             }
 688 
 689             //XXX: if it looks like a spoof just return the address?
 690             if (!ok) {
 691                 host = addr.getHostAddress();
 692                 return host;
 693             }
 694         } catch (SecurityException e) {
 695             host = addr.getHostAddress();
 696         } catch (UnknownHostException e) {
 697             host = addr.getHostAddress();
 698             // let next provider resolve the hostname
 699         }
 700         return host;
 701     }
 702 
 703     /**
 704      * Returns the raw IP address of this {@code InetAddress}
 705      * object. The result is in network byte order: the highest order
 706      * byte of the address is in {@code getAddress()[0]}.
 707      *
 708      * @return  the raw IP address of this object.
 709      */
 710     public byte[] getAddress() {
 711         return null;
 712     }
 713 
 714     /**
 715      * Returns the IP address string in textual presentation.
 716      *
 717      * @return  the raw IP address in a string format.
 718      * @since   1.0.2
 719      */
 720     public String getHostAddress() {
 721         return null;
 722      }
 723 
 724     /**
 725      * Returns a hashcode for this IP address.
 726      *
 727      * @return  a hash code value for this IP address.
 728      */
 729     public int hashCode() {
 730         return -1;
 731     }
 732 
 733     /**
 734      * Compares this object against the specified object.
 735      * The result is {@code true} if and only if the argument is
 736      * not {@code null} and it represents the same IP address as
 737      * this object.
 738      * <p>
 739      * Two instances of {@code InetAddress} represent the same IP
 740      * address if the length of the byte arrays returned by
 741      * {@code getAddress} is the same for both, and each of the
 742      * array components is the same for the byte arrays.
 743      *
 744      * @param   obj   the object to compare against.
 745      * @return  {@code true} if the objects are the same;
 746      *          {@code false} otherwise.
 747      * @see     java.net.InetAddress#getAddress()
 748      */
 749     public boolean equals(Object obj) {
 750         return false;
 751     }
 752 
 753     /**
 754      * Converts this IP address to a {@code String}. The
 755      * string returned is of the form: hostname / literal IP
 756      * address.
 757      *
 758      * If the host name is unresolved, no reverse name service lookup
 759      * is performed. The hostname part will be represented by an empty string.
 760      *
 761      * @return  a string representation of this IP address.
 762      */
 763     public String toString() {
 764         String hostName = holder().getHostName();
 765         return Objects.toString(hostName, "")
 766             + "/" + getHostAddress();
 767     }
 768 
 769     // mapping from host name to Addresses - either NameServiceAddresses (while
 770     // still being looked-up by NameService(s)) or CachedAddresses when cached
 771     private static final ConcurrentMap<String, Addresses> cache =
 772         new ConcurrentHashMap<>();
 773 
 774     // CachedAddresses that have to expire are kept ordered in this NavigableSet
 775     // which is scanned on each access
 776     private static final NavigableSet<CachedAddresses> expirySet =
 777         new ConcurrentSkipListSet<>();
 778 
 779     // common interface
 780     private interface Addresses {
 781         InetAddress[] get() throws UnknownHostException;
 782     }
 783 
 784     // a holder for cached addresses with required metadata
 785     private static final class CachedAddresses  implements Addresses, Comparable<CachedAddresses> {
 786         private static final AtomicLong seq = new AtomicLong();
 787         final String host;
 788         final InetAddress[] inetAddresses;
 789         final long expiryTime; // time of expiry (in terms of System.nanoTime())
 790         final long id = seq.incrementAndGet(); // each instance is unique
 791 
 792         CachedAddresses(String host, InetAddress[] inetAddresses, long expiryTime) {
 793             this.host = host;
 794             this.inetAddresses = inetAddresses;
 795             this.expiryTime = expiryTime;
 796         }
 797 
 798         @Override
 799         public InetAddress[] get() throws UnknownHostException {
 800             if (inetAddresses == null) {
 801                 throw new UnknownHostException(host);
 802             }
 803             return inetAddresses;
 804         }
 805 
 806         @Override
 807         public int compareTo(CachedAddresses other) {
 808             // natural order is expiry time -
 809             // compare difference of expiry times rather than
 810             // expiry times directly, to avoid possible overflow.
 811             // (see System.nanoTime() recommendations...)
 812             long diff = this.expiryTime - other.expiryTime;
 813             if (diff < 0L) return -1;
 814             if (diff > 0L) return 1;
 815             // ties are broken using unique id
 816             return Long.compare(this.id, other.id);
 817         }
 818     }
 819 
 820     // a name service lookup based Addresses implementation which replaces itself
 821     // in cache when the result is obtained
 822     private static final class NameServiceAddresses implements Addresses {
 823         private final String host;
 824         private final InetAddress reqAddr;
 825 
 826         NameServiceAddresses(String host, InetAddress reqAddr) {
 827             this.host = host;
 828             this.reqAddr = reqAddr;
 829         }
 830 
 831         @Override
 832         public InetAddress[] get() throws UnknownHostException {
 833             Addresses addresses;
 834             // only one thread is doing lookup to name service
 835             // for particular host at any time.
 836             synchronized (this) {
 837                 // re-check that we are still us + re-install us if slot empty
 838                 addresses = cache.putIfAbsent(host, this);
 839                 if (addresses == null) {
 840                     // this can happen when we were replaced by CachedAddresses in
 841                     // some other thread, then CachedAddresses expired and were
 842                     // removed from cache while we were waiting for lock...
 843                     addresses = this;
 844                 }
 845                 // still us ?
 846                 if (addresses == this) {
 847                     // lookup name services
 848                     InetAddress[] inetAddresses;
 849                     UnknownHostException ex;
 850                     int cachePolicy;
 851                     try {
 852                         inetAddresses = getAddressesFromNameService(host, reqAddr);
 853                         ex = null;
 854                         cachePolicy = InetAddressCachePolicy.get();
 855                     } catch (UnknownHostException uhe) {
 856                         inetAddresses = null;
 857                         ex = uhe;
 858                         cachePolicy = InetAddressCachePolicy.getNegative();
 859                     }
 860                     // remove or replace us with cached addresses according to cachePolicy
 861                     if (cachePolicy == InetAddressCachePolicy.NEVER) {
 862                         cache.remove(host, this);
 863                     } else {
 864                         CachedAddresses cachedAddresses = new CachedAddresses(
 865                             host,
 866                             inetAddresses,
 867                             cachePolicy == InetAddressCachePolicy.FOREVER
 868                             ? 0L
 869                             // cachePolicy is in [s] - we need [ns]
 870                             : System.nanoTime() + 1000_000_000L * cachePolicy
 871                         );
 872                         if (cache.replace(host, this, cachedAddresses) &&
 873                             cachePolicy != InetAddressCachePolicy.FOREVER) {
 874                             // schedule expiry
 875                             expirySet.add(cachedAddresses);
 876                         }
 877                     }
 878                     if (inetAddresses == null) {
 879                         throw ex == null ? new UnknownHostException(host) : ex;
 880                     }
 881                     return inetAddresses;
 882                 }
 883                 // else addresses != this
 884             }
 885             // delegate to different addresses when we are already replaced
 886             // but outside of synchronized block to avoid any chance of dead-locking
 887             return addresses.get();
 888         }
 889     }
 890 
 891     /**
 892      * NameService provides host and address lookup service
 893      *
 894      * @since 9
 895      */
 896     private interface NameService {
 897 
 898         /**
 899          * Lookup a host mapping by name. Retrieve the IP addresses
 900          * associated with a host
 901          *
 902          * @param host the specified hostname
 903          * @return array of IP addresses for the requested host
 904          * @throws UnknownHostException
 905          *             if no IP address for the {@code host} could be found
 906          */
 907         InetAddress[] lookupAllHostAddr(String host)
 908                 throws UnknownHostException;
 909 
 910         /**
 911          * Lookup the host corresponding to the IP address provided
 912          *
 913          * @param addr byte array representing an IP address
 914          * @return {@code String} representing the host name mapping
 915          * @throws UnknownHostException
 916          *             if no host found for the specified IP address
 917          */
 918         String getHostByAddr(byte[] addr) throws UnknownHostException;
 919 
 920     }
 921 
 922     /**
 923      * The default NameService implementation, which delegates to the underlying
 924      * OS network libraries to resolve host address mappings.
 925      *
 926      * @since 9
 927      */
 928     private static final class PlatformNameService implements NameService {
 929 
 930         public InetAddress[] lookupAllHostAddr(String host)
 931             throws UnknownHostException
 932         {
 933             return impl.lookupAllHostAddr(host);
 934         }
 935 
 936         public String getHostByAddr(byte[] addr)
 937             throws UnknownHostException
 938         {
 939             return impl.getHostByAddr(addr);
 940         }
 941     }
 942 
 943     /**
 944      * The HostsFileNameService provides host address mapping
 945      * by reading the entries in a hosts file, which is specified by
 946      * {@code jdk.net.hosts.file} system property
 947      *
 948      * <p>The file format is that which corresponds with the /etc/hosts file
 949      * IP Address host alias list.
 950      *
 951      * <p>When the file lookup is enabled it replaces the default NameService
 952      * implementation
 953      *
 954      * @since 9
 955      */
 956     private static final class HostsFileNameService implements NameService {
 957 
 958         private static final InetAddress[] EMPTY_ARRAY = new InetAddress[0];
 959 
 960         // Specify if only IPv4 addresses should be returned by HostsFileService implementation
 961         private static final boolean preferIPv4Stack = Boolean.parseBoolean(
 962                 GetPropertyAction.privilegedGetProperty("java.net.preferIPv4Stack"));
 963 
 964         private final String hostsFile;
 965 
 966         public HostsFileNameService(String hostsFileName) {
 967             this.hostsFile = hostsFileName;
 968         }
 969 
 970         /**
 971          * Lookup the host name  corresponding to the IP address provided.
 972          * Search the configured host file a host name corresponding to
 973          * the specified IP address.
 974          *
 975          * @param addr byte array representing an IP address
 976          * @return {@code String} representing the host name mapping
 977          * @throws UnknownHostException
 978          *             if no host found for the specified IP address
 979          */
 980         @Override
 981         public String getHostByAddr(byte[] addr) throws UnknownHostException {
 982             String hostEntry;
 983             String host = null;
 984 
 985             try (Scanner hostsFileScanner = new Scanner(new File(hostsFile),
 986                                                         UTF_8.INSTANCE))
 987             {
 988                 while (hostsFileScanner.hasNextLine()) {
 989                     hostEntry = hostsFileScanner.nextLine();
 990                     if (!hostEntry.startsWith("#")) {
 991                         hostEntry = removeComments(hostEntry);
 992                         String[] mapping = hostEntry.split("\\s+");
 993                         if (mapping.length >= 2 &&
 994                             Arrays.equals(addr, createAddressByteArray(mapping[0]))) {
 995                             host = mapping[1];
 996                             break;
 997                         }
 998                     }
 999                 }
1000             } catch (IOException e) {
1001                 throw new UnknownHostException("Unable to resolve address "
1002                         + Arrays.toString(addr) + " as hosts file " + hostsFile
1003                         + " not found ");
1004             }
1005 
1006             if ((host == null) || (host.isEmpty()) || (host.equals(" "))) {
1007                 throw new UnknownHostException("Requested address "
1008                         + Arrays.toString(addr)
1009                         + " resolves to an invalid entry in hosts file "
1010                         + hostsFile);
1011             }
1012             return host;
1013         }
1014 
1015         /**
1016          * <p>Lookup a host mapping by name. Retrieve the IP addresses
1017          * associated with a host.
1018          *
1019          * <p>Search the configured hosts file for the addresses associated
1020          * with the specified host name.
1021          *
1022          * @param host the specified hostname
1023          * @return array of IP addresses for the requested host
1024          * @throws UnknownHostException
1025          *             if no IP address for the {@code host} could be found
1026          */
1027         public InetAddress[] lookupAllHostAddr(String host)
1028                 throws UnknownHostException {
1029             String hostEntry;
1030             String addrStr;
1031             byte addr[];
1032             List<InetAddress> inetAddresses = new ArrayList<>();
1033             List<InetAddress> inet4Addresses = new ArrayList<>();
1034             List<InetAddress> inet6Addresses = new ArrayList<>();
1035 
1036             // lookup the file and create a list InetAddress for the specified host
1037             try (Scanner hostsFileScanner = new Scanner(new File(hostsFile),
1038                                                         UTF_8.INSTANCE)) {
1039                 while (hostsFileScanner.hasNextLine()) {
1040                     hostEntry = hostsFileScanner.nextLine();
1041                     if (!hostEntry.startsWith("#")) {
1042                         hostEntry = removeComments(hostEntry);
1043                         if (hostEntry.contains(host)) {
1044                             addrStr = extractHostAddr(hostEntry, host);
1045                             if ((addrStr != null) && (!addrStr.isEmpty())) {
1046                                 addr = createAddressByteArray(addrStr);
1047                                 if (addr != null) {
1048                                     InetAddress address = InetAddress.getByAddress(host, addr);
1049                                     inetAddresses.add(address);
1050                                     if (address instanceof Inet4Address) {
1051                                         inet4Addresses.add(address);
1052                                     }
1053                                     if (address instanceof Inet6Address) {
1054                                         inet6Addresses.add(address);
1055                                     }
1056                                 }
1057                             }
1058                         }
1059                     }
1060                 }
1061             } catch (IOException e) {
1062                 throw new UnknownHostException("Unable to resolve host " + host
1063                         + " as hosts file " + hostsFile + " not found ");
1064             }
1065 
1066             List<InetAddress> res;
1067             // If "preferIPv4Stack" system property is set to "true" then return
1068             // only IPv4 addresses
1069             if (preferIPv4Stack) {
1070                 res = inet4Addresses;
1071             } else {
1072                 // Otherwise, analyse "preferIPv6Addresses" value
1073                 res = switch (preferIPv6Address) {
1074                     case PREFER_IPV4_VALUE -> concatAddresses(inet4Addresses, inet6Addresses);
1075                     case PREFER_IPV6_VALUE -> concatAddresses(inet6Addresses, inet4Addresses);
1076                     default -> inetAddresses;
1077                 };
1078             }
1079 
1080             if (res.isEmpty()) {
1081                 throw new UnknownHostException("Unable to resolve host " + host
1082                         + " in hosts file " + hostsFile);
1083             }
1084             return res.toArray(EMPTY_ARRAY);
1085         }
1086 
1087         private static List<InetAddress> concatAddresses(List<InetAddress> firstPart,
1088                                                          List<InetAddress> secondPart) {
1089             List<InetAddress> result = new ArrayList<>(firstPart);
1090             result.addAll(secondPart);
1091             return result;
1092         }
1093 
1094         private String removeComments(String hostsEntry) {
1095             String filteredEntry = hostsEntry;
1096             int hashIndex;
1097 
1098             if ((hashIndex = hostsEntry.indexOf("#")) != -1) {
1099                 filteredEntry = hostsEntry.substring(0, hashIndex);
1100             }
1101             return filteredEntry;
1102         }
1103 
1104         private byte [] createAddressByteArray(String addrStr) {
1105             byte[] addrArray;
1106             // check if IPV4 address - most likely
1107             addrArray = IPAddressUtil.textToNumericFormatV4(addrStr);
1108             if (addrArray == null) {
1109                 addrArray = IPAddressUtil.textToNumericFormatV6(addrStr);
1110             }
1111             return addrArray;
1112         }
1113 
1114         /** host to ip address mapping */
1115         private String extractHostAddr(String hostEntry, String host) {
1116             String[] mapping = hostEntry.split("\\s+");
1117             String hostAddr = null;
1118 
1119             if (mapping.length >= 2) {
1120                 // look at the host aliases
1121                 for (int i = 1; i < mapping.length; i++) {
1122                     if (mapping[i].equalsIgnoreCase(host)) {
1123                         hostAddr = mapping[0];
1124                     }
1125                 }
1126             }
1127             return hostAddr;
1128         }
1129     }
1130 
1131     static final InetAddressImpl  impl;
1132 
1133     static {
1134         // create the impl
1135         impl = InetAddressImplFactory.create();
1136 
1137         // create name service
1138         nameService = createNameService();
1139     }
1140 
1141     /**
1142      * Create an instance of the NameService interface based on
1143      * the setting of the {@code jdk.net.hosts.file} system property.
1144      *
1145      * <p>The default NameService is the PlatformNameService, which typically
1146      * delegates name and address resolution calls to the underlying
1147      * OS network libraries.
1148      *
1149      * <p> A HostsFileNameService is created if the {@code jdk.net.hosts.file}
1150      * system property is set. If the specified file doesn't exist, the name or
1151      * address lookup will result in an UnknownHostException. Thus, non existent
1152      * hosts file is handled as if the file is empty.
1153      *
1154      * @return a NameService
1155      */
1156     private static NameService createNameService() {
1157 
1158         String hostsFileName =
1159                 GetPropertyAction.privilegedGetProperty("jdk.net.hosts.file");
1160         NameService theNameService;
1161         if (hostsFileName != null) {
1162             theNameService = new HostsFileNameService(hostsFileName);
1163         } else {
1164             theNameService = new PlatformNameService();
1165         }
1166         return theNameService;
1167     }
1168 
1169     /**
1170      * Creates an InetAddress based on the provided host name and IP address.
1171      * No name service is checked for the validity of the address.
1172      *
1173      * <p> The host name can either be a machine name, such as
1174      * "{@code www.example.com}", or a textual representation of its IP
1175      * address.
1176      * <p> No validity checking is done on the host name either.
1177      *
1178      * <p> If addr specifies an IPv4 address an instance of Inet4Address
1179      * will be returned; otherwise, an instance of Inet6Address
1180      * will be returned.
1181      *
1182      * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array
1183      * must be 16 bytes long
1184      *
1185      * @param host the specified host
1186      * @param addr the raw IP address in network byte order
1187      * @return  an InetAddress object created from the raw IP address.
1188      * @throws     UnknownHostException  if IP address is of illegal length
1189      * @since 1.4
1190      */
1191     public static InetAddress getByAddress(String host, byte[] addr)
1192         throws UnknownHostException {
1193         if (host != null && !host.isEmpty() && host.charAt(0) == '[') {
1194             if (host.charAt(host.length()-1) == ']') {
1195                 host = host.substring(1, host.length() -1);
1196             }
1197         }
1198         if (addr != null) {
1199             if (addr.length == Inet4Address.INADDRSZ) {
1200                 return new Inet4Address(host, addr);
1201             } else if (addr.length == Inet6Address.INADDRSZ) {
1202                 byte[] newAddr
1203                     = IPAddressUtil.convertFromIPv4MappedAddress(addr);
1204                 if (newAddr != null) {
1205                     return new Inet4Address(host, newAddr);
1206                 } else {
1207                     return new Inet6Address(host, addr);
1208                 }
1209             }
1210         }
1211         throw new UnknownHostException("addr is of illegal length");
1212     }
1213 
1214 
1215     /**
1216      * Determines the IP address of a host, given the host's name.
1217      *
1218      * <p> The host name can either be a machine name, such as
1219      * "{@code www.example.com}", or a textual representation of its
1220      * IP address. If a literal IP address is supplied, only the
1221      * validity of the address format is checked.
1222      *
1223      * <p> For {@code host} specified in literal IPv6 address,
1224      * either the form defined in RFC 2732 or the literal IPv6 address
1225      * format defined in RFC 2373 is accepted. IPv6 scoped addresses are also
1226      * supported. See <a href="Inet6Address.html#scoped">here</a> for a description of IPv6
1227      * scoped addresses.
1228      *
1229      * <p> If the host is {@code null} or {@code host.length()} is equal
1230      * to zero, then an {@code InetAddress} representing an address of the
1231      * loopback interface is returned.
1232      * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
1233      * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
1234      * section&nbsp;2.5.3.
1235      *
1236      * <p> If there is a security manager, and {@code host} is not {@code null}
1237      * or {@code host.length() } is not equal to zero, the security manager's
1238      * {@code checkConnect} method is called with the hostname and {@code -1}
1239      * as its arguments to determine if the operation is allowed.
1240      *
1241      * @param      host   the specified host, or {@code null}.
1242      * @return     an IP address for the given host name.
1243      * @throws     UnknownHostException  if no IP address for the
1244      *               {@code host} could be found, or if a scope_id was specified
1245      *               for a global IPv6 address.
1246      * @throws     SecurityException if a security manager exists
1247      *             and its checkConnect method doesn't allow the operation
1248      */
1249     public static InetAddress getByName(String host)
1250         throws UnknownHostException {
1251         return InetAddress.getAllByName(host)[0];
1252     }
1253 
1254     // called from deployment cache manager
1255     private static InetAddress getByName(String host, InetAddress reqAddr)
1256         throws UnknownHostException {
1257         return InetAddress.getAllByName(host, reqAddr)[0];
1258     }
1259 
1260     /**
1261      * Given the name of a host, returns an array of its IP addresses,
1262      * based on the configured name service on the system.
1263      *
1264      * <p> The host name can either be a machine name, such as
1265      * "{@code www.example.com}", or a textual representation of its IP
1266      * address. If a literal IP address is supplied, only the
1267      * validity of the address format is checked.
1268      *
1269      * <p> For {@code host} specified in <i>literal IPv6 address</i>,
1270      * either the form defined in RFC 2732 or the literal IPv6 address
1271      * format defined in RFC 2373 is accepted. A literal IPv6 address may
1272      * also be qualified by appending a scoped zone identifier or scope_id.
1273      * The syntax and usage of scope_ids is described
1274      * <a href="Inet6Address.html#scoped">here</a>.
1275      *
1276      * <p> If the host is {@code null} or {@code host.length()} is equal
1277      * to zero, then an {@code InetAddress} representing an address of the
1278      * loopback interface is returned.
1279      * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>
1280      * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>
1281      * section&nbsp;2.5.3. </p>
1282      *
1283      * <p> If there is a security manager, and {@code host} is not {@code null}
1284      * or {@code host.length() } is not equal to zero, the security manager's
1285      * {@code checkConnect} method is called with the hostname and {@code -1}
1286      * as its arguments to determine if the operation is allowed.
1287      *
1288      * @param      host   the name of the host, or {@code null}.
1289      * @return     an array of all the IP addresses for a given host name.
1290      *
1291      * @throws     UnknownHostException  if no IP address for the
1292      *               {@code host} could be found, or if a scope_id was specified
1293      *               for a global IPv6 address.
1294      * @throws     SecurityException  if a security manager exists and its
1295      *               {@code checkConnect} method doesn't allow the operation.
1296      *
1297      * @see SecurityManager#checkConnect
1298      */
1299     public static InetAddress[] getAllByName(String host)
1300         throws UnknownHostException {
1301         return getAllByName(host, null);
1302     }
1303 
1304     private static InetAddress[] getAllByName(String host, InetAddress reqAddr)
1305         throws UnknownHostException {
1306 
1307         if (host == null || host.isEmpty()) {
1308             InetAddress[] ret = new InetAddress[1];
1309             ret[0] = impl.loopbackAddress();
1310             return ret;
1311         }
1312 
1313         boolean ipv6Expected = false;
1314         if (host.charAt(0) == '[') {
1315             // This is supposed to be an IPv6 literal
1316             if (host.length() > 2 && host.charAt(host.length()-1) == ']') {
1317                 host = host.substring(1, host.length() -1);
1318                 ipv6Expected = true;
1319             } else {
1320                 // This was supposed to be a IPv6 address, but it's not!
1321                 throw new UnknownHostException(host + ": invalid IPv6 address");
1322             }
1323         }
1324 
1325         // if host is an IP address, we won't do further lookup
1326         if (Character.digit(host.charAt(0), 16) != -1
1327             || (host.charAt(0) == ':')) {
1328             byte[] addr = null;
1329             int numericZone = -1;
1330             String ifname = null;
1331             // see if it is IPv4 address
1332             addr = IPAddressUtil.textToNumericFormatV4(host);
1333             if (addr == null) {
1334                 // This is supposed to be an IPv6 literal
1335                 // Check if a numeric or string zone id is present
1336                 int pos;
1337                 if ((pos=host.indexOf ('%')) != -1) {
1338                     numericZone = checkNumericZone (host);
1339                     if (numericZone == -1) { /* remainder of string must be an ifname */
1340                         ifname = host.substring (pos+1);
1341                     }
1342                 }
1343                 if ((addr = IPAddressUtil.textToNumericFormatV6(host)) == null && host.contains(":")) {
1344                     throw new UnknownHostException(host + ": invalid IPv6 address");
1345                 }
1346             } else if (ipv6Expected) {
1347                 // Means an IPv4 literal between brackets!
1348                 throw new UnknownHostException("["+host+"]");
1349             }
1350             InetAddress[] ret = new InetAddress[1];
1351             if(addr != null) {
1352                 if (addr.length == Inet4Address.INADDRSZ) {
1353                     ret[0] = new Inet4Address(null, addr);
1354                 } else {
1355                     if (ifname != null) {
1356                         ret[0] = new Inet6Address(null, addr, ifname);
1357                     } else {
1358                         ret[0] = new Inet6Address(null, addr, numericZone);
1359                     }
1360                 }
1361                 return ret;
1362             }
1363         } else if (ipv6Expected) {
1364             // We were expecting an IPv6 Literal, but got something else
1365             throw new UnknownHostException("["+host+"]");
1366         }
1367         return getAllByName0(host, reqAddr, true, true);
1368     }
1369 
1370     /**
1371      * Returns the loopback address.
1372      * <p>
1373      * The InetAddress returned will represent the IPv4
1374      * loopback address, 127.0.0.1, or the IPv6 loopback
1375      * address, ::1. The IPv4 loopback address returned
1376      * is only one of many in the form 127.*.*.*
1377      *
1378      * @return  the InetAddress loopback instance.
1379      * @since 1.7
1380      */
1381     public static InetAddress getLoopbackAddress() {
1382         return impl.loopbackAddress();
1383     }
1384 
1385 
1386     /**
1387      * check if the literal address string has %nn appended
1388      * returns -1 if not, or the numeric value otherwise.
1389      *
1390      * %nn may also be a string that represents the displayName of
1391      * a currently available NetworkInterface.
1392      */
1393     private static int checkNumericZone (String s) throws UnknownHostException {
1394         int percent = s.indexOf ('%');
1395         int slen = s.length();
1396         int digit, zone=0;
1397         if (percent == -1) {
1398             return -1;
1399         }
1400         for (int i=percent+1; i<slen; i++) {
1401             char c = s.charAt(i);
1402             if (c == ']') {
1403                 if (i == percent+1) {
1404                     /* empty per-cent field */
1405                     return -1;
1406                 }
1407                 break;
1408             }
1409             if ((digit = Character.digit (c, 10)) < 0) {
1410                 return -1;
1411             }
1412             zone = (zone * 10) + digit;
1413         }
1414         return zone;
1415     }
1416 
1417     private static InetAddress[] getAllByName0 (String host)
1418         throws UnknownHostException
1419     {
1420         return getAllByName0(host, true);
1421     }
1422 
1423     /**
1424      * package private so SocketPermission can call it
1425      */
1426     static InetAddress[] getAllByName0 (String host, boolean check)
1427         throws UnknownHostException  {
1428         return getAllByName0 (host, null, check, true);
1429     }
1430 
1431     /**
1432      * Designated lookup method.
1433      *
1434      * @param host host name to look up
1435      * @param reqAddr requested address to be the 1st in returned array
1436      * @param check perform security check
1437      * @param useCache use cached value if not expired else always
1438      *                 perform name service lookup (and cache the result)
1439      * @return array of InetAddress(es)
1440      * @throws UnknownHostException if host name is not found
1441      */
1442     private static InetAddress[] getAllByName0(String host,
1443                                                InetAddress reqAddr,
1444                                                boolean check,
1445                                                boolean useCache)
1446         throws UnknownHostException  {
1447 
1448         /* If it gets here it is presumed to be a hostname */
1449 
1450         /* make sure the connection to the host is allowed, before we
1451          * give out a hostname
1452          */
1453         if (check) {
1454             @SuppressWarnings("removal")
1455             SecurityManager security = System.getSecurityManager();
1456             if (security != null) {
1457                 security.checkConnect(host, -1);
1458             }
1459         }
1460 
1461         // remove expired addresses from cache - expirySet keeps them ordered
1462         // by expiry time so we only need to iterate the prefix of the NavigableSet...
1463         long now = System.nanoTime();
1464         for (CachedAddresses caddrs : expirySet) {
1465             // compare difference of time instants rather than
1466             // time instants directly, to avoid possible overflow.
1467             // (see System.nanoTime() recommendations...)
1468             if ((caddrs.expiryTime - now) < 0L) {
1469                 // ConcurrentSkipListSet uses weakly consistent iterator,
1470                 // so removing while iterating is OK...
1471                 if (expirySet.remove(caddrs)) {
1472                     // ... remove from cache
1473                     cache.remove(caddrs.host, caddrs);
1474                 }
1475             } else {
1476                 // we encountered 1st element that expires in future
1477                 break;
1478             }
1479         }
1480 
1481         // look-up or remove from cache
1482         Addresses addrs;
1483         if (useCache) {
1484             addrs = cache.get(host);
1485         } else {
1486             addrs = cache.remove(host);
1487             if (addrs != null) {
1488                 if (addrs instanceof CachedAddresses) {
1489                     // try removing from expirySet too if CachedAddresses
1490                     expirySet.remove(addrs);
1491                 }
1492                 addrs = null;
1493             }
1494         }
1495 
1496         if (addrs == null) {
1497             // create a NameServiceAddresses instance which will look up
1498             // the name service and install it within cache...
1499             Addresses oldAddrs = cache.putIfAbsent(
1500                 host,
1501                 addrs = new NameServiceAddresses(host, reqAddr)
1502             );
1503             if (oldAddrs != null) { // lost putIfAbsent race
1504                 addrs = oldAddrs;
1505             }
1506         }
1507 
1508         // ask Addresses to get an array of InetAddress(es) and clone it
1509         return addrs.get().clone();
1510     }
1511 
1512     static InetAddress[] getAddressesFromNameService(String host, InetAddress reqAddr)
1513             throws UnknownHostException {
1514         InetAddress[] addresses = null;
1515         UnknownHostException ex = null;
1516 
1517         try {
1518             addresses = nameService.lookupAllHostAddr(host);
1519         } catch (UnknownHostException uhe) {
1520             if (host.equalsIgnoreCase("localhost")) {
1521                 addresses = new InetAddress[]{impl.loopbackAddress()};
1522             } else {
1523                 ex = uhe;
1524             }
1525         }
1526 
1527         if (addresses == null) {
1528             throw ex == null ? new UnknownHostException(host) : ex;
1529         }
1530 
1531         // More to do?
1532         if (reqAddr != null && addresses.length > 1 && !addresses[0].equals(reqAddr)) {
1533             // Find it?
1534             int i = 1;
1535             for (; i < addresses.length; i++) {
1536                 if (addresses[i].equals(reqAddr)) {
1537                     break;
1538                 }
1539             }
1540             // Rotate
1541             if (i < addresses.length) {
1542                 InetAddress tmp, tmp2 = reqAddr;
1543                 for (int j = 0; j < i; j++) {
1544                     tmp = addresses[j];
1545                     addresses[j] = tmp2;
1546                     tmp2 = tmp;
1547                 }
1548                 addresses[i] = tmp2;
1549             }
1550         }
1551 
1552         return addresses;
1553     }
1554 
1555     /**
1556      * Returns an {@code InetAddress} object given the raw IP address .
1557      * The argument is in network byte order: the highest order
1558      * byte of the address is in {@code getAddress()[0]}.
1559      *
1560      * <p> This method doesn't block, i.e. no reverse name service lookup
1561      * is performed.
1562      *
1563      * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array
1564      * must be 16 bytes long
1565      *
1566      * @param addr the raw IP address in network byte order
1567      * @return  an InetAddress object created from the raw IP address.
1568      * @throws     UnknownHostException  if IP address is of illegal length
1569      * @since 1.4
1570      */
1571     public static InetAddress getByAddress(byte[] addr)
1572         throws UnknownHostException {
1573         return getByAddress(null, addr);
1574     }
1575 
1576     private static final class CachedLocalHost {
1577         final String host;
1578         final InetAddress addr;
1579         final long expiryTime = System.nanoTime() + 5000_000_000L; // now + 5s;
1580 
1581         CachedLocalHost(String host, InetAddress addr) {
1582             this.host = host;
1583             this.addr = addr;
1584         }
1585     }
1586 
1587     private static volatile CachedLocalHost cachedLocalHost;
1588 
1589     /**
1590      * Returns the address of the local host. This is achieved by retrieving
1591      * the name of the host from the system, then resolving that name into
1592      * an {@code InetAddress}.
1593      *
1594      * <P>Note: The resolved address may be cached for a short period of time.
1595      * </P>
1596      *
1597      * <p>If there is a security manager, its
1598      * {@code checkConnect} method is called
1599      * with the local host name and {@code -1}
1600      * as its arguments to see if the operation is allowed.
1601      * If the operation is not allowed, an InetAddress representing
1602      * the loopback address is returned.
1603      *
1604      * @return     the address of the local host.
1605      *
1606      * @throws     UnknownHostException  if the local host name could not
1607      *             be resolved into an address.
1608      *
1609      * @see SecurityManager#checkConnect
1610      * @see java.net.InetAddress#getByName(java.lang.String)
1611      */
1612     public static InetAddress getLocalHost() throws UnknownHostException {
1613 
1614         @SuppressWarnings("removal")
1615         SecurityManager security = System.getSecurityManager();
1616         try {
1617             // is cached data still valid?
1618             CachedLocalHost clh = cachedLocalHost;
1619             if (clh != null && (clh.expiryTime - System.nanoTime()) >= 0L) {
1620                 if (security != null) {
1621                     security.checkConnect(clh.host, -1);
1622                 }
1623                 return clh.addr;
1624             }
1625 
1626             String local = impl.getLocalHostName();
1627 
1628             if (security != null) {
1629                 security.checkConnect(local, -1);
1630             }
1631 
1632             InetAddress localAddr;
1633             if (local.equals("localhost")) {
1634                 // shortcut for "localhost" host name
1635                 localAddr = impl.loopbackAddress();
1636             } else {
1637                 // call getAllByName0 without security checks and
1638                 // without using cached data
1639                 try {
1640                     localAddr = getAllByName0(local, null, false, false)[0];
1641                 } catch (UnknownHostException uhe) {
1642                     // Rethrow with a more informative error message.
1643                     UnknownHostException uhe2 =
1644                         new UnknownHostException(local + ": " +
1645                                                  uhe.getMessage());
1646                     uhe2.initCause(uhe);
1647                     throw uhe2;
1648                 }
1649             }
1650             cachedLocalHost = new CachedLocalHost(local, localAddr);
1651             return localAddr;
1652         } catch (java.lang.SecurityException e) {
1653             return impl.loopbackAddress();
1654         }
1655     }
1656 
1657     /**
1658      * Perform class load-time initializations.
1659      */
1660     private static native void init();
1661 
1662 
1663     /*
1664      * Returns the InetAddress representing anyLocalAddress
1665      * (typically 0.0.0.0 or ::0)
1666      */
1667     static InetAddress anyLocalAddress() {
1668         return impl.anyLocalAddress();
1669     }
1670 
1671     /**
1672      * Initializes an empty InetAddress.
1673      */
1674     @java.io.Serial
1675     private void readObjectNoData () {
1676         if (getClass().getClassLoader() != null) {
1677             throw new SecurityException ("invalid address type");
1678         }
1679     }
1680 
1681     private static final jdk.internal.misc.Unsafe UNSAFE
1682             = jdk.internal.misc.Unsafe.getUnsafe();
1683     private static final long FIELDS_OFFSET
1684             = UNSAFE.objectFieldOffset(InetAddress.class, "holder");
1685 
1686     /**
1687      * Restores the state of this object from the stream.
1688      *
1689      * @param  s the {@code ObjectInputStream} from which data is read
1690      * @throws IOException if an I/O error occurs
1691      * @throws ClassNotFoundException if a serialized class cannot be loaded
1692      */
1693     @java.io.Serial
1694     private void readObject (ObjectInputStream s) throws
1695                          IOException, ClassNotFoundException {
1696         if (getClass().getClassLoader() != null) {
1697             throw new SecurityException ("invalid address type");
1698         }
1699         GetField gf = s.readFields();
1700         String host = (String)gf.get("hostName", null);
1701         int address = gf.get("address", 0);
1702         int family = gf.get("family", 0);
1703         if (family != IPv4 && family != IPv6) {
1704             throw new InvalidObjectException("invalid address family type: " + family);
1705         }
1706         InetAddressHolder h = new InetAddressHolder(host, address, family);
1707         UNSAFE.putReference(this, FIELDS_OFFSET, h);
1708     }
1709 
1710     /* needed because the serializable fields no longer exist */
1711 
1712     /**
1713      * @serialField hostName String the hostname for this address
1714      * @serialField address int holds a 32-bit IPv4 address.
1715      * @serialField family int specifies the address family type, for instance,
1716      * {@code '1'} for IPv4 addresses, and {@code '2'} for IPv6 addresses.
1717      */
1718     @java.io.Serial
1719     private static final ObjectStreamField[] serialPersistentFields = {
1720         new ObjectStreamField("hostName", String.class),
1721         new ObjectStreamField("address", int.class),
1722         new ObjectStreamField("family", int.class),
1723     };
1724 
1725     /**
1726      * Writes the state of this object to the stream.
1727      *
1728      * @param  s the {@code ObjectOutputStream} to which data is written
1729      * @throws IOException if an I/O error occurs
1730      */
1731     @java.io.Serial
1732     private void writeObject (ObjectOutputStream s) throws
1733                         IOException {
1734         if (getClass().getClassLoader() != null) {
1735             throw new SecurityException ("invalid address type");
1736         }
1737         PutField pf = s.putFields();
1738         pf.put("hostName", holder().getHostName());
1739         pf.put("address", holder().getAddress());
1740         pf.put("family", holder().getFamily());
1741         s.writeFields();
1742     }
1743 }
1744 
1745 /*
1746  * Simple factory to create the impl
1747  */
1748 class InetAddressImplFactory {
1749 
1750     static InetAddressImpl create() {
1751         return isIPv6Supported() ?
1752                 new Inet6AddressImpl() : new Inet4AddressImpl();
1753     }
1754 
1755     static native boolean isIPv6Supported();
1756 }