/*

 * Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.net;

import java.util.NavigableSet;

import java.util.ArrayList;

import java.util.Objects;

import java.util.Scanner;

import java.security.AccessController;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.ObjectStreamException;

import java.io.ObjectStreamField;

import java.io.IOException;

import java.io.ObjectInputStream;

import java.io.ObjectInputStream.GetField;

import java.io.ObjectOutputStream;

import java.io.ObjectOutputStream.PutField;

import java.lang.annotation.Native;

import java.util.concurrent.ConcurrentHashMap;

import java.util.concurrent.ConcurrentMap;

import java.util.concurrent.ConcurrentSkipListSet;

import java.util.concurrent.atomic.AtomicLong;

import jdk.internal.misc.JavaNetInetAddressAccess;

import jdk.internal.misc.SharedSecrets;

import sun.security.action.*;

import sun.net.InetAddressCachePolicy;

import sun.net.util.IPAddressUtil;

/**

 * This class represents an Internet Protocol (IP) address.

 *

 * <p> An IP address is either a 32-bit or 128-bit unsigned number

 * used by IP, a lower-level protocol on which protocols like UDP and

 * TCP are built. The IP address architecture is defined by <a

 * href="http://www.ietf.org/rfc/rfc790.txt"><i>RFC&nbsp;790:

 * Assigned Numbers</i></a>, <a

 * href="http://www.ietf.org/rfc/rfc1918.txt"> <i>RFC&nbsp;1918:

 * Address Allocation for Private Internets</i></a>, <a

 * href="http://www.ietf.org/rfc/rfc2365.txt"><i>RFC&nbsp;2365:

 * Administratively Scoped IP Multicast</i></a>, and <a

 * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IP

 * Version 6 Addressing Architecture</i></a>. An instance of an

 * InetAddress consists of an IP address and possibly its

 * corresponding host name (depending on whether it is constructed

 * with a host name or whether it has already done reverse host name

 * resolution).

 *

 * <h3> Address types </h3>

 *

 * <table class="striped" style="margin-left:2em">

 *   <caption style="display:none">Description of unicast and multicast address types</caption>

 *   <thead>

 *   <tr><th scope="col">Address Type</th><th scope="col">Description</th></tr>

 *   </thead>

 *   <tbody>

 *   <tr><th scope="row" style="vertical-align:top">unicast</th>

 *       <td>An identifier for a single interface. A packet sent to

 *         a unicast address is delivered to the interface identified by

 *         that address.

 *

 *         <p> The Unspecified Address -- Also called anylocal or wildcard

 *         address. It must never be assigned to any node. It indicates the

 *         absence of an address. One example of its use is as the target of

 *         bind, which allows a server to accept a client connection on any

 *         interface, in case the server host has multiple interfaces.

 *

 *         <p> The <i>unspecified</i> address must not be used as

 *         the destination address of an IP packet.

 *

 *         <p> The <i>Loopback</i> Addresses -- This is the address

 *         assigned to the loopback interface. Anything sent to this

 *         IP address loops around and becomes IP input on the local

 *         host. This address is often used when testing a

 *         client.</td></tr>

 *   <tr><th scope="row" style="vertical-align:top">multicast</th>

 *       <td>An identifier for a set of interfaces (typically belonging

 *         to different nodes). A packet sent to a multicast address is

 *         delivered to all interfaces identified by that address.</td></tr>

 * </tbody>

 * </table>

 *

 * <h4> IP address scope </h4>

 *

 * <p> <i>Link-local</i> addresses are designed to be used for addressing

 * on a single link for purposes such as auto-address configuration,

 * neighbor discovery, or when no routers are present.

 *

 * <p> <i>Site-local</i> addresses are designed to be used for addressing

 * inside of a site without the need for a global prefix.

 *

 * <p> <i>Global</i> addresses are unique across the internet.

 *

 * <h4> Textual representation of IP addresses </h4>

 *

 * The textual representation of an IP address is address family specific.

 *

 * <p>

 *

 * For IPv4 address format, please refer to <A

 * HREF="Inet4Address.html#format">Inet4Address#format</A>; For IPv6

 * address format, please refer to <A

 * HREF="Inet6Address.html#format">Inet6Address#format</A>.

 *

 * <P>There is a <a href="doc-files/net-properties.html#Ipv4IPv6">couple of

 * System Properties</a> affecting how IPv4 and IPv6 addresses are used.</P>

 *

 * <h4> Host Name Resolution </h4>

 *

 * Host name-to-IP address <i>resolution</i> is accomplished through

 * the use of a combination of local machine configuration information

 * and network naming services such as the Domain Name System (DNS)

 * and Network Information Service(NIS). The particular naming

 * services(s) being used is by default the local machine configured

 * one. For any host name, its corresponding IP address is returned.

 *

 * <p> <i>Reverse name resolution</i> means that for any IP address,

 * the host associated with the IP address is returned.

 *

 * <p> The InetAddress class provides methods to resolve host names to

 * their IP addresses and vice versa.

 *

 * <h4> InetAddress Caching </h4>

 *

 * The InetAddress class has a cache to store successful as well as

 * unsuccessful host name resolutions.

 *

 * <p> By default, when a security manager is installed, in order to

 * protect against DNS spoofing attacks,

 * the result of positive host name resolutions are

 * cached forever. When a security manager is not installed, the default

 * behavior is to cache entries for a finite (implementation dependent)

 * period of time. The result of unsuccessful host

 * name resolution is cached for a very short period of time (10

 * seconds) to improve performance.

 *

 * <p> If the default behavior is not desired, then a Java security property

 * can be set to a different Time-to-live (TTL) value for positive

 * caching. Likewise, a system admin can configure a different

 * negative caching TTL value when needed.

 *

 * <p> Two Java security properties control the TTL values used for

 *  positive and negative host name resolution caching:

 *

 * <dl style="margin-left:2em">

 * <dt><b>networkaddress.cache.ttl</b></dt>

 * <dd>Indicates the caching policy for successful name lookups from

 * the name service. The value is specified as an integer to indicate

 * the number of seconds to cache the successful lookup. The default

 * setting is to cache for an implementation specific period of time.

 * <p>

 * A value of -1 indicates "cache forever".

 * </dd>

 * <dt><b>networkaddress.cache.negative.ttl</b> (default: 10)</dt>

 * <dd>Indicates the caching policy for un-successful name lookups

 * from the name service. The value is specified as an integer to

 * indicate the number of seconds to cache the failure for

 * un-successful lookups.

 * <p>

 * A value of 0 indicates "never cache".

 * A value of -1 indicates "cache forever".

 * </dd>

 * </dl>

 *

 * @author  Chris Warth

 * @see     java.net.InetAddress#getByAddress(byte[])

 * @see     java.net.InetAddress#getByAddress(java.lang.String, byte[])

 * @see     java.net.InetAddress#getAllByName(java.lang.String)

 * @see     java.net.InetAddress#getByName(java.lang.String)

 * @see     java.net.InetAddress#getLocalHost()

 * @since 1.0

 */

public

class InetAddress implements java.io.Serializable {

    @Native static final int PREFER_IPV4_VALUE = 0;

    @Native static final int PREFER_IPV6_VALUE = 1;

    @Native static final int PREFER_SYSTEM_VALUE = 2;

    /**

     * Specify the address family: Internet Protocol, Version 4

     * @since 1.4

     */

    @Native static final int IPv4 = 1;

    /**

     * Specify the address family: Internet Protocol, Version 6

     * @since 1.4

     */

    @Native static final int IPv6 = 2;

    /* Specify address family preference */

    static transient final int preferIPv6Address;

    static class InetAddressHolder {

        /**

         * Reserve the original application specified hostname.

         *

         * The original hostname is useful for domain-based endpoint

         * identification (see RFC 2818 and RFC 6125).  If an address

         * was created with a raw IP address, a reverse name lookup

         * may introduce endpoint identification security issue via

         * DNS forging.

         *

         * Oracle JSSE provider is using this original hostname, via

         * jdk.internal.misc.JavaNetAccess, for SSL/TLS endpoint identification.

         *

         * Note: May define a new public method in the future if necessary.

         */

        String originalHostName;

        InetAddressHolder() {}

        InetAddressHolder(String hostName, int address, int family) {

            this.originalHostName = hostName;

            this.hostName = hostName;

            this.address = address;

            this.family = family;

        }

        void init(String hostName, int family) {

            this.originalHostName = hostName;

            this.hostName = hostName;

            if (family != -1) {

                this.family = family;

            }

        }

        String hostName;

        String getHostName() {

            return hostName;

        }

        String getOriginalHostName() {

            return originalHostName;

        }

        /**

         * Holds a 32-bit IPv4 address.

         */

        int address;

        int getAddress() {

            return address;

        }

        /**

         * Specifies the address family type, for instance, '1' for IPv4

         * addresses, and '2' for IPv6 addresses.

         */

        int family;

        int getFamily() {

            return family;

        }

    }

    /* Used to store the serializable fields of InetAddress */

    final transient InetAddressHolder holder;

    InetAddressHolder holder() {

        return holder;

    }

    /* Used to store the name service provider */

    private static transient NameService nameService = null;

    /**

     * Used to store the best available hostname.

     * Lazily initialized via a data race; safe because Strings are immutable.

     */

    private transient String canonicalHostName = null;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */

    private static final long serialVersionUID = 3286316764910316507L;

    /*

     * Load net library into runtime, and perform initializations.

     */

    static {

        String str = java.security.AccessController.doPrivileged(

                new GetPropertyAction("java.net.preferIPv6Addresses"));

        if (str == null) {

            preferIPv6Address = PREFER_IPV4_VALUE;

        } else if (str.equalsIgnoreCase("true")) {

            preferIPv6Address = PREFER_IPV6_VALUE;

        } else if (str.equalsIgnoreCase("false")) {

            preferIPv6Address = PREFER_IPV4_VALUE;

        } else if (str.equalsIgnoreCase("system")) {

            preferIPv6Address = PREFER_SYSTEM_VALUE;

        } else {

            preferIPv6Address = PREFER_IPV4_VALUE;

        }

        AccessController.doPrivileged(

            new java.security.PrivilegedAction<>() {

                public Void run() {

                    System.loadLibrary("net");

                    return null;

                }

            });

        SharedSecrets.setJavaNetInetAddressAccess(

                new JavaNetInetAddressAccess() {

                    public String getOriginalHostName(InetAddress ia) {

                        return ia.holder.getOriginalHostName();

                    }

                    public InetAddress getByName(String hostName,

                                                 InetAddress hostAddress)

                            throws UnknownHostException

                    {

                        return InetAddress.getByName(hostName, hostAddress);

                    }

                }

        );

        init();

    }

    /**

     * Constructor for the Socket.accept() method.

     * This creates an empty InetAddress, which is filled in by

     * the accept() method.  This InetAddress, however, is not

     * put in the address cache, since it is not created by name.

     */

    InetAddress() {

        holder = new InetAddressHolder();

    }

    /**

     * Replaces the de-serialized object with an Inet4Address object.

     *

     * @return the alternate object to the de-serialized object.

     *

     * @throws ObjectStreamException if a new object replacing this

     * object could not be created

     */

    private Object readResolve() throws ObjectStreamException {

        // will replace the deserialized 'this' object

        return new Inet4Address(holder().getHostName(), holder().getAddress());

    }

    /**

     * Utility routine to check if the InetAddress is an

     * IP multicast address.

     * @return a {@code boolean} indicating if the InetAddress is

     * an IP multicast address

     * @since   1.1

     */

    public boolean isMulticastAddress() {

        return false;

    }

    /**

     * Utility routine to check if the InetAddress is a wildcard address.

     * @return a {@code boolean} indicating if the Inetaddress is

     *         a wildcard address.

     * @since 1.4

     */

    public boolean isAnyLocalAddress() {

        return false;

    }

    /**

     * Utility routine to check if the InetAddress is a loopback address.

     *

     * @return a {@code boolean} indicating if the InetAddress is

     * a loopback address; or false otherwise.

     * @since 1.4

     */

    public boolean isLoopbackAddress() {

        return false;

    }

    /**

     * Utility routine to check if the InetAddress is an link local address.

     *

     * @return a {@code boolean} indicating if the InetAddress is

     * a link local address; or false if address is not a link local unicast address.

     * @since 1.4

     */

    public boolean isLinkLocalAddress() {

        return false;

    }

    /**

     * Utility routine to check if the InetAddress is a site local address.

     *

     * @return a {@code boolean} indicating if the InetAddress is

     * a site local address; or false if address is not a site local unicast address.

     * @since 1.4

     */

    public boolean isSiteLocalAddress() {

        return false;

    }

    /**

     * Utility routine to check if the multicast address has global scope.

     *

     * @return a {@code boolean} indicating if the address has

     *         is a multicast address of global scope, false if it is not

     *         of global scope or it is not a multicast address

     * @since 1.4

     */

    public boolean isMCGlobal() {

        return false;

    }

    /**

     * Utility routine to check if the multicast address has node scope.

     *

     * @return a {@code boolean} indicating if the address has

     *         is a multicast address of node-local scope, false if it is not

     *         of node-local scope or it is not a multicast address

     * @since 1.4

     */

    public boolean isMCNodeLocal() {

        return false;

    }

    /**

     * Utility routine to check if the multicast address has link scope.

     *

     * @return a {@code boolean} indicating if the address has

     *         is a multicast address of link-local scope, false if it is not

     *         of link-local scope or it is not a multicast address

     * @since 1.4

     */

    public boolean isMCLinkLocal() {

        return false;

    }

    /**

     * Utility routine to check if the multicast address has site scope.

     *

     * @return a {@code boolean} indicating if the address has

     *         is a multicast address of site-local scope, false if it is not

     *         of site-local scope or it is not a multicast address

     * @since 1.4

     */

    public boolean isMCSiteLocal() {

        return false;

    }

    /**

     * Utility routine to check if the multicast address has organization scope.

     *

     * @return a {@code boolean} indicating if the address has

     *         is a multicast address of organization-local scope,

     *         false if it is not of organization-local scope

     *         or it is not a multicast address

     * @since 1.4

     */

    public boolean isMCOrgLocal() {

        return false;

    }

    /**

     * Test whether that address is reachable. Best effort is made by the

     * implementation to try to reach the host, but firewalls and server

     * configuration may block requests resulting in a unreachable status

     * while some specific ports may be accessible.

     * A typical implementation will use ICMP ECHO REQUESTs if the

     * privilege can be obtained, otherwise it will try to establish

     * a TCP connection on port 7 (Echo) of the destination host.

     * <p>

     * The timeout value, in milliseconds, indicates the maximum amount of time

     * the try should take. If the operation times out before getting an

     * answer, the host is deemed unreachable. A negative value will result

     * in an IllegalArgumentException being thrown.

     *

     * @param   timeout the time, in milliseconds, before the call aborts

     * @return a {@code boolean} indicating if the address is reachable.

     * @throws IOException if a network error occurs

     * @throws  IllegalArgumentException if {@code timeout} is negative.

     * @since 1.5

     */

    public boolean isReachable(int timeout) throws IOException {

        return isReachable(null, 0 , timeout);

    }

    /**

     * Test whether that address is reachable. Best effort is made by the

     * implementation to try to reach the host, but firewalls and server

     * configuration may block requests resulting in a unreachable status

     * while some specific ports may be accessible.

     * A typical implementation will use ICMP ECHO REQUESTs if the

     * privilege can be obtained, otherwise it will try to establish

     * a TCP connection on port 7 (Echo) of the destination host.

     * <p>

     * The {@code network interface} and {@code ttl} parameters

     * let the caller specify which network interface the test will go through

     * and the maximum number of hops the packets should go through.

     * A negative value for the {@code ttl} will result in an

     * IllegalArgumentException being thrown.

     * <p>

     * The timeout value, in milliseconds, indicates the maximum amount of time

     * the try should take. If the operation times out before getting an

     * answer, the host is deemed unreachable. A negative value will result

     * in an IllegalArgumentException being thrown.

     *

     * @param   netif   the NetworkInterface through which the

     *                    test will be done, or null for any interface

     * @param   ttl     the maximum numbers of hops to try or 0 for the

     *                  default

     * @param   timeout the time, in milliseconds, before the call aborts

     * @throws  IllegalArgumentException if either {@code timeout}

     *                          or {@code ttl} are negative.

     * @return a {@code boolean}indicating if the address is reachable.

     * @throws IOException if a network error occurs

     * @since 1.5

     */

    public boolean isReachable(NetworkInterface netif, int ttl,

                               int timeout) throws IOException {

        if (ttl < 0)

            throw new IllegalArgumentException("ttl can't be negative");

        if (timeout < 0)

            throw new IllegalArgumentException("timeout can't be negative");

        return impl.isReachable(this, timeout, netif, ttl);

    }

    /**

     * Gets the host name for this IP address.

     *

     * <p>If this InetAddress was created with a host name,

     * this host name will be remembered and returned;

     * otherwise, a reverse name lookup will be performed

     * and the result will be returned based on the system

     * configured name lookup service. If a lookup of the name service

     * is required, call

     * {@link #getCanonicalHostName() getCanonicalHostName}.

     *

     * <p>If there is a security manager, its

     * {@code checkConnect} method is first called

     * with the hostname and {@code -1}

     * as its arguments to see if the operation is allowed.

     * If the operation is not allowed, it will return

     * the textual representation of the IP address.

     *

     * @return  the host name for this IP address, or if the operation

     *    is not allowed by the security check, the textual

     *    representation of the IP address.

     *

     * @see InetAddress#getCanonicalHostName

     * @see SecurityManager#checkConnect

     */

    public String getHostName() {

        return getHostName(true);

    }

    /**

     * Returns the hostname for this address.

     * If the host is equal to null, then this address refers to any

     * of the local machine's available network addresses.

     * this is package private so SocketPermission can make calls into

     * here without a security check.

     *

     * <p>If there is a security manager, this method first

     * calls its {@code checkConnect} method

     * with the hostname and {@code -1}

     * as its arguments to see if the calling code is allowed to know

     * the hostname for this IP address, i.e., to connect to the host.

     * If the operation is not allowed, it will return

     * the textual representation of the IP address.

     *

     * @return  the host name for this IP address, or if the operation

     *    is not allowed by the security check, the textual

     *    representation of the IP address.

     *

     * @param check make security check if true

     *

     * @see SecurityManager#checkConnect

     */

    String getHostName(boolean check) {

        if (holder().getHostName() == null) {

            holder().hostName = InetAddress.getHostFromNameService(this, check);

        }

        return holder().getHostName();

    }

    /**

     * Gets the fully qualified domain name for this IP address.

     * Best effort method, meaning we may not be able to return

     * the FQDN depending on the underlying system configuration.

     *

     * <p>If there is a security manager, this method first

     * calls its {@code checkConnect} method

     * with the hostname and {@code -1}

     * as its arguments to see if the calling code is allowed to know

     * the hostname for this IP address, i.e., to connect to the host.

     * If the operation is not allowed, it will return

     * the textual representation of the IP address.

     *

     * @return  the fully qualified domain name for this IP address,

     *    or if the operation is not allowed by the security check,

     *    the textual representation of the IP address.

     *

     * @see SecurityManager#checkConnect

     *

     * @since 1.4

     */

    public String getCanonicalHostName() {

        String value = canonicalHostName;

        if (value == null)

            canonicalHostName = value =

                InetAddress.getHostFromNameService(this, true);

        return value;

    }

    /**

     * Returns the hostname for this address.

     *

     * <p>If there is a security manager, this method first

     * calls its {@code checkConnect} method

     * with the hostname and {@code -1}

     * as its arguments to see if the calling code is allowed to know

     * the hostname for this IP address, i.e., to connect to the host.

     * If the operation is not allowed, it will return

     * the textual representation of the IP address.

     *

     * @return  the host name for this IP address, or if the operation

     *    is not allowed by the security check, the textual

     *    representation of the IP address.

     *

     * @param check make security check if true

     *

     * @see SecurityManager#checkConnect

     */

    private static String getHostFromNameService(InetAddress addr, boolean check) {

        String host = null;

            try {

                // first lookup the hostname

                host = nameService.getHostByAddr(addr.getAddress());

                /* check to see if calling code is allowed to know

                 * the hostname for this IP address, ie, connect to the host

                 */

                if (check) {

                    SecurityManager sec = System.getSecurityManager();

                    if (sec != null) {

                        sec.checkConnect(host, -1);

                    }

                }

                /* now get all the IP addresses for this hostname,

                 * and make sure one of them matches the original IP

                 * address. We do this to try and prevent spoofing.

                 */

                InetAddress[] arr = InetAddress.getAllByName0(host, check);

                boolean ok = false;

                if(arr != null) {

                    for(int i = 0; !ok && i < arr.length; i++) {

                        ok = addr.equals(arr[i]);

                    }

                }

                //XXX: if it looks a spoof just return the address?

                if (!ok) {

                    host = addr.getHostAddress();

                    return host;

                }

            } catch (SecurityException e) {

                host = addr.getHostAddress();

            } catch (UnknownHostException e) {

                host = addr.getHostAddress();

                // let next provider resolve the hostname

            }

        return host;

    }

    /**

     * Returns the raw IP address of this {@code InetAddress}

     * object. The result is in network byte order: the highest order

     * byte of the address is in {@code getAddress()[0]}.

     *

     * @return  the raw IP address of this object.

     */

    public byte[] getAddress() {

        return null;

    }

    /**

     * Returns the IP address string in textual presentation.

     *

     * @return  the raw IP address in a string format.

     * @since   1.0.2

     */

    public String getHostAddress() {

        return null;

     }

    /**

     * Returns a hashcode for this IP address.

     *

     * @return  a hash code value for this IP address.

     */

    public int hashCode() {

        return -1;

    }

    /**

     * Compares this object against the specified object.

     * The result is {@code true} if and only if the argument is

     * not {@code null} and it represents the same IP address as

     * this object.

     * <p>

     * Two instances of {@code InetAddress} represent the same IP

     * address if the length of the byte arrays returned by

     * {@code getAddress} is the same for both, and each of the

     * array components is the same for the byte arrays.

     *

     * @param   obj   the object to compare against.

     * @return  {@code true} if the objects are the same;

     *          {@code false} otherwise.

     * @see     java.net.InetAddress#getAddress()

     */

    public boolean equals(Object obj) {

        return false;

    }

    /**

     * Converts this IP address to a {@code String}. The

     * string returned is of the form: hostname / literal IP

     * address.

     *

     * If the host name is unresolved, no reverse name service lookup

     * is performed. The hostname part will be represented by an empty string.

     *

     * @return  a string representation of this IP address.

     */

    public String toString() {

        String hostName = holder().getHostName();

        return Objects.toString(hostName, "")

            + "/" + getHostAddress();

    }

    // mapping from host name to Addresses - either NameServiceAddresses (while

    // still being looked-up by NameService(s)) or CachedAddresses when cached

    private static final ConcurrentMap<String, Addresses> cache =

        new ConcurrentHashMap<>();

    // CachedAddresses that have to expire are kept ordered in this NavigableSet

    // which is scanned on each access

    private static final NavigableSet<CachedAddresses> expirySet =

        new ConcurrentSkipListSet<>();

    // common interface

    private interface Addresses {

        InetAddress[] get() throws UnknownHostException;

    }

    // a holder for cached addresses with required metadata

    private static final class CachedAddresses  implements Addresses, Comparable<CachedAddresses> {

        private static final AtomicLong seq = new AtomicLong();

        final String host;

        final InetAddress[] inetAddresses;

        final long expiryTime; // time of expiry (in terms of System.nanoTime())

        final long id = seq.incrementAndGet(); // each instance is unique

        CachedAddresses(String host, InetAddress[] inetAddresses, long expiryTime) {

            this.host = host;

            this.inetAddresses = inetAddresses;

            this.expiryTime = expiryTime;

        }

        @Override

        public InetAddress[] get() throws UnknownHostException {

            if (inetAddresses == null) {

                throw new UnknownHostException(host);

            }

            return inetAddresses;

        }

        @Override

        public int compareTo(CachedAddresses other) {

            // natural order is expiry time -

            // compare difference of expiry times rather than

            // expiry times directly, to avoid possible overflow.

            // (see System.nanoTime() recommendations...)

            long diff = this.expiryTime - other.expiryTime;

            if (diff < 0L) return -1;

            if (diff > 0L) return 1;

            // ties are broken using unique id

            return Long.compare(this.id, other.id);

        }

    }

    // a name service lookup based Addresses implementation which replaces itself

    // in cache when the result is obtained

    private static final class NameServiceAddresses implements Addresses {

        private final String host;

        private final InetAddress reqAddr;

        NameServiceAddresses(String host, InetAddress reqAddr) {

            this.host = host;

            this.reqAddr = reqAddr;

        }

        @Override

        public InetAddress[] get() throws UnknownHostException {

            Addresses addresses;

            // only one thread is doing lookup to name service

            // for particular host at any time.

            synchronized (this) {

                // re-check that we are still us + re-install us if slot empty

                addresses = cache.putIfAbsent(host, this);

                if (addresses == null) {

                    // this can happen when we were replaced by CachedAddresses in

                    // some other thread, then CachedAddresses expired and were

                    // removed from cache while we were waiting for lock...

                    addresses = this;

                }

                // still us ?

                if (addresses == this) {

                    // lookup name services

                    InetAddress[] inetAddresses;

                    UnknownHostException ex;

                    int cachePolicy;

                    try {

                        inetAddresses = getAddressesFromNameService(host, reqAddr);

                        ex = null;

                        cachePolicy = InetAddressCachePolicy.get();

                    } catch (UnknownHostException uhe) {

                        inetAddresses = null;

                        ex = uhe;

                        cachePolicy = InetAddressCachePolicy.getNegative();

                    }

                    // remove or replace us with cached addresses according to cachePolicy

                    if (cachePolicy == InetAddressCachePolicy.NEVER) {

                        cache.remove(host, this);

                    } else {

                        CachedAddresses cachedAddresses = new CachedAddresses(

                            host,

                            inetAddresses,

                            cachePolicy == InetAddressCachePolicy.FOREVER

                            ? 0L

                            // cachePolicy is in [s] - we need [ns]

                            : System.nanoTime() + 1000_000_000L * cachePolicy

                        );

                        if (cache.replace(host, this, cachedAddresses) &&

                            cachePolicy != InetAddressCachePolicy.FOREVER) {

                            // schedule expiry

                            expirySet.add(cachedAddresses);

                        }

                    }

                    if (inetAddresses == null) {

                        throw ex == null ? new UnknownHostException(host) : ex;

                    }

                    return inetAddresses;

                }

                // else addresses != this

            }

            // delegate to different addresses when we are already replaced

            // but outside of synchronized block to avoid any chance of dead-locking

            return addresses.get();

        }

    }

    /**

     * NameService provides host and address lookup service

     *

     * @since 9

     */

    private interface NameService {

        /**

         * Lookup a host mapping by name. Retrieve the IP addresses

         * associated with a host

         *

         * @param host the specified hostname

         * @return array of IP addresses for the requested host

         * @throws UnknownHostException

         *             if no IP address for the {@code host} could be found

         */

        InetAddress[] lookupAllHostAddr(String host)

                throws UnknownHostException;

        /**

         * Lookup the host corresponding to the IP address provided

         *

         * @param addr byte array representing an IP address

         * @return {@code String} representing the host name mapping

         * @throws UnknownHostException

         *             if no host found for the specified IP address

         */

        String getHostByAddr(byte[] addr) throws UnknownHostException;

    }

    /**

     * The default NameService implementation, which delegates to the underlying

     * OS network libraries to resolve host address mappings.

     *

     * @since 9

     */

    private static final class PlatformNameService implements NameService {

        public InetAddress[] lookupAllHostAddr(String host)

            throws UnknownHostException

        {

            return impl.lookupAllHostAddr(host);

        }

        public String getHostByAddr(byte[] addr)

            throws UnknownHostException

        {

            return impl.getHostByAddr(addr);

        }

    }

    /**

     * The HostsFileNameService provides host address mapping

     * by reading the entries in a hosts file, which is specified by

     * {@code jdk.net.hosts.file} system property

     *

     * <p>The file format is that which corresponds with the /etc/hosts file

     * IP Address host alias list.

     *

     * <p>When the file lookup is enabled it replaces the default NameService

     * implementation

     *

     * @since 9

     */

    private static final class HostsFileNameService implements NameService {

        private final String hostsFile;

        public HostsFileNameService (String hostsFileName) {

            this.hostsFile = hostsFileName;

        }

        private  String addrToString(byte addr[]) {

          String stringifiedAddress = null;

            if (addr.length == Inet4Address.INADDRSZ) {

                stringifiedAddress = Inet4Address.numericToTextFormat(addr);

            } else { // treat as an IPV6 jobby

                byte[] newAddr

                    = IPAddressUtil.convertFromIPv4MappedAddress(addr);

                if (newAddr != null) {

                   stringifiedAddress = Inet4Address.numericToTextFormat(addr);

                } else {

                    stringifiedAddress = Inet6Address.numericToTextFormat(addr);

                }

            }

            return stringifiedAddress;

        }

        /**

         * Lookup the host name  corresponding to the IP address provided.

         * Search the configured host file a host name corresponding to

         * the specified IP address.

         *

         * @param addr byte array representing an IP address

         * @return {@code String} representing the host name mapping

         * @throws UnknownHostException

         *             if no host found for the specified IP address

         */

        @Override

        public String getHostByAddr(byte[] addr) throws UnknownHostException {

            String hostEntry;

            String host = null;

            String addrString = addrToString(addr);

            try (Scanner hostsFileScanner = new Scanner(new File(hostsFile), "UTF-8")) {

                while (hostsFileScanner.hasNextLine()) {

                    hostEntry = hostsFileScanner.nextLine();

                    if (!hostEntry.startsWith("#")) {

                        hostEntry = removeComments(hostEntry);

                        if (hostEntry.contains(addrString)) {

                            host = extractHost(hostEntry, addrString);

                            if (host != null) {

                                break;

                            }

                        }

                    }

                }

            } catch (FileNotFoundException e) {

                throw new UnknownHostException("Unable to resolve address "

                        + addrString + " as hosts file " + hostsFile

                        + " not found ");

            }

            if ((host == null) || (host.equals("")) || (host.equals(" "))) {

                throw new UnknownHostException("Requested address "

                        + addrString

                        + " resolves to an invalid entry in hosts file "

                        + hostsFile);

            }

            return host;

        }

        /**

         * <p>Lookup a host mapping by name. Retrieve the IP addresses

         * associated with a host.

         *

         * <p>Search the configured hosts file for the addresses assocaited with

         * with the specified host name.

         *

         * @param host the specified hostname

         * @return array of IP addresses for the requested host

         * @throws UnknownHostException

         *             if no IP address for the {@code host} could be found

         */

        public InetAddress[] lookupAllHostAddr(String host)

                throws UnknownHostException {

            String hostEntry;

            String addrStr = null;

            InetAddress[] res = null;

            byte addr[] = new byte[4];

            ArrayList<InetAddress> inetAddresses = null;

            // lookup the file and create a list InetAddress for the specfied host

            try (Scanner hostsFileScanner = new Scanner(new File(hostsFile), "UTF-8")) {

                while (hostsFileScanner.hasNextLine()) {

                    hostEntry = hostsFileScanner.nextLine();

                    if (!hostEntry.startsWith("#")) {

                        hostEntry = removeComments(hostEntry);

                        if (hostEntry.contains(host)) {

                            addrStr = extractHostAddr(hostEntry, host);

                            if ((addrStr != null) && (!addrStr.equals(""))) {

                                addr = createAddressByteArray(addrStr);

                                if (inetAddresses == null) {

                                    inetAddresses = new ArrayList<>(1);

                                }

                                if (addr != null) {

                                    inetAddresses.add(InetAddress.getByAddress(host, addr));

                                }

                            }

                        }

                    }

                }

            } catch (FileNotFoundException e) {

                throw new UnknownHostException("Unable to resolve host " + host

                        + " as hosts file " + hostsFile + " not found ");

            }

            if (inetAddresses != null) {

                res = inetAddresses.toArray(new InetAddress[inetAddresses.size()]);

            } else {

                throw new UnknownHostException("Unable to resolve host " + host

                        + " in hosts file " + hostsFile);

            }

            return res;

        }

        private String removeComments(String hostsEntry) {

            String filteredEntry = hostsEntry;

            int hashIndex;

            if ((hashIndex = hostsEntry.indexOf("#")) != -1) {

                filteredEntry = hostsEntry.substring(0, hashIndex);

            }

            return filteredEntry;

        }

        private byte [] createAddressByteArray(String addrStr) {

            byte[] addrArray;

            // check if IPV4 address - most likely

            addrArray = IPAddressUtil.textToNumericFormatV4(addrStr);

            if (addrArray == null) {

                addrArray = IPAddressUtil.textToNumericFormatV6(addrStr);

            }

            return addrArray;

        }

        /** host to ip address mapping */

        private String extractHostAddr(String hostEntry, String host) {

            String[] mapping = hostEntry.split("\\s+");

            String hostAddr = null;

            if (mapping.length >= 2) {

                // look at the host aliases

                for (int i = 1; i < mapping.length; i++) {

                    if (mapping[i].equalsIgnoreCase(host)) {

                        hostAddr = mapping[0];

                    }

                }

            }

            return hostAddr;

        }

        /**

         * IP Address to host mapping

         * use first host alias in list

         */

        private String extractHost(String hostEntry, String addrString) {

            String[] mapping = hostEntry.split("\\s+");

            String host = null;

            if (mapping.length >= 2) {

                if (mapping[0].equalsIgnoreCase(addrString)) {

                    host = mapping[1];

                }

            }

            return host;

        }

    }

    static final InetAddressImpl  impl;

    static {

        // create the impl

        impl = InetAddressImplFactory.create();

        // create name service

        nameService = createNameService();

        }

    /**

     * Create an instance of the NameService interface based on

     * the setting of the {@code jdk.net.hosts.file} system property.

     *

     * <p>The default NameService is the PlatformNameService, which typically

     * delegates name and address resolution calls to the underlying

     * OS network libraries.

     *

     * <p> A HostsFileNameService is created if the {@code jdk.net.hosts.file}

     * system property is set. If the specified file doesn't exist, the name or

     * address lookup will result in an UnknownHostException. Thus, non existent

     * hosts file is handled as if the file is empty.

     *

     * @return a NameService

     */

    private static NameService createNameService() {

        String hostsFileName =

                GetPropertyAction.privilegedGetProperty("jdk.net.hosts.file");

        NameService theNameService;

        if (hostsFileName != null) {

            theNameService = new HostsFileNameService(hostsFileName);

        } else {

            theNameService = new PlatformNameService();

        }

        return theNameService;

    }

    /**

     * Creates an InetAddress based on the provided host name and IP address.

     * No name service is checked for the validity of the address.

     *

     * <p> The host name can either be a machine name, such as

     * "{@code java.sun.com}", or a textual representation of its IP

     * address.

     * <p> No validity checking is done on the host name either.

     *

     * <p> If addr specifies an IPv4 address an instance of Inet4Address

     * will be returned; otherwise, an instance of Inet6Address

     * will be returned.

     *

     * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array

     * must be 16 bytes long

     *

     * @param host the specified host

     * @param addr the raw IP address in network byte order

     * @return  an InetAddress object created from the raw IP address.

     * @exception  UnknownHostException  if IP address is of illegal length

     * @since 1.4

     */

    public static InetAddress getByAddress(String host, byte[] addr)

        throws UnknownHostException {

        if (host != null && host.length() > 0 && host.charAt(0) == '[') {

            if (host.charAt(host.length()-1) == ']') {

                host = host.substring(1, host.length() -1);

            }

        }

        if (addr != null) {

            if (addr.length == Inet4Address.INADDRSZ) {

                return new Inet4Address(host, addr);

            } else if (addr.length == Inet6Address.INADDRSZ) {

                byte[] newAddr

                    = IPAddressUtil.convertFromIPv4MappedAddress(addr);

                if (newAddr != null) {

                    return new Inet4Address(host, newAddr);

                } else {

                    return new Inet6Address(host, addr);

                }

            }

        }

        throw new UnknownHostException("addr is of illegal length");

    }

    /**

     * Determines the IP address of a host, given the host's name.

     *

     * <p> The host name can either be a machine name, such as

     * "{@code java.sun.com}", or a textual representation of its

     * IP address. If a literal IP address is supplied, only the

     * validity of the address format is checked.

     *

     * <p> For {@code host} specified in literal IPv6 address,

     * either the form defined in RFC 2732 or the literal IPv6 address

     * format defined in RFC 2373 is accepted. IPv6 scoped addresses are also

     * supported. See <a href="Inet6Address.html#scoped">here</a> for a description of IPv6

     * scoped addresses.

     *

     * <p> If the host is {@code null} or {@code host.length()} is equal

     * to zero, then an {@code InetAddress} representing an address of the

     * loopback interface is returned.

     * See <a href="http://www.ietf.org/rfc/rfc3330.txt">RFC&nbsp;3330</a>

     * section&nbsp;2 and <a href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>

     * section 2.5.3.

     *

     * <p> If there is a security manager, and {@code host} is not {@code null}

     * or {@code host.length() } is not equal to zero, the security manager's

     * {@code checkConnect} method is called with the hostname and {@code -1}

     * as its arguments to determine if the operation is allowed.

     *

     * @param      host   the specified host, or {@code null}.

     * @return     an IP address for the given host name.

     * @exception  UnknownHostException  if no IP address for the

     *               {@code host} could be found, or if a scope_id was specified

     *               for a global IPv6 address.

     * @exception  SecurityException if a security manager exists

     *             and its checkConnect method doesn't allow the operation

     */

    public static InetAddress getByName(String host)

        throws UnknownHostException {

        return InetAddress.getAllByName(host)[0];

    }

    // called from deployment cache manager

    private static InetAddress getByName(String host, InetAddress reqAddr)

        throws UnknownHostException {

        return InetAddress.getAllByName(host, reqAddr)[0];

    }

    /**

     * Given the name of a host, returns an array of its IP addresses,

     * based on the configured name service on the system.

     *

     * <p> The host name can either be a machine name, such as

     * "{@code java.sun.com}", or a textual representation of its IP

     * address. If a literal IP address is supplied, only the

     * validity of the address format is checked.

     *

     * <p> For {@code host} specified in <i>literal IPv6 address</i>,

     * either the form defined in RFC 2732 or the literal IPv6 address

     * format defined in RFC 2373 is accepted. A literal IPv6 address may

     * also be qualified by appending a scoped zone identifier or scope_id.

     * The syntax and usage of scope_ids is described

     * <a href="Inet6Address.html#scoped">here</a>.