xref: /libcore/ojluni/src/main/java/java/net/InetAddress.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 * Copyright (c) 1995, 2015, 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.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 sun.net.util.IPAddressUtil;
import sun.net.spi.nameservice.*;
import android.system.GaiException;
import android.system.StructAddrinfo;
import libcore.io.Libcore;
import static android.system.OsConstants.*;

/**
 * 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>
 *
 * <blockquote><table cellspacing=2 summary="Description of unicast and multicast address types">
 *   <tr><th valign=top><i>unicast</i></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 valign=top><i>multicast</i></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>
 * </table></blockquote>
 *
 * <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:
 *
 * <blockquote>
 * <dl>
 * <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 as 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 as 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>
 * </blockquote>
 *
 * @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 JDK1.0
 */
public
class InetAddress implements java.io.Serializable {

    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
         * sun.misc.JavaNetAccess, for SSL/TLS endpoint identification.
         *
         * Note: May define a new public method in the future if necessary.
         */
        private 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, AF_INET for IPv4
         * addresses, and AF_INET6 for IPv6 addresses.
         */
        int family;

        int getFamily() {
            return family;
        }
    }

    transient InetAddressHolder holder;

    InetAddressHolder holder() {
        return holder;
    }

    /* The implementation is always dual stack IPv6/IPv4 on android */
    static final InetAddressImpl impl = new Inet6AddressImpl();

    /* Used to store the name service provider */
    private static final NameService nameService = new NameService() {
        public InetAddress[] lookupAllHostAddr(String host, int netId)
                throws UnknownHostException {
            return impl.lookupAllHostAddr(host, netId);
        }
        public String getHostByAddr(byte[] addr)
                throws UnknownHostException {
            return impl.getHostByAddr(addr);
        }
    };

    /* Used to store the best available hostname */
    private transient String canonicalHostName = null;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 3286316764910316507L;

    /**
     * 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   JDK1.1
     */
    public boolean isMulticastAddress() {
        return false;
    }

    /**
     * Utility routine to check if the InetAddress in 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.
     * <p>
     * Android implementation attempts ICMP ECHO REQUESTs first, on failure it
     * will fall back to TCP ECHO REQUESTs. Success on either protocol will
     * return true.
     * <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);
    }

    /**
     * @hide For testing only
     */
    public boolean isReachableByICMP(int timeout) throws IOException {
        return ((Inet6AddressImpl) impl).icmpEcho(this, timeout, null, 0);
    }

    /**
     * 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() {
        if (holder().getHostName() == null) {
            holder().hostName = InetAddress.getHostFromNameService(this);
        }
        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() {
        if (canonicalHostName == null) {
            canonicalHostName = InetAddress.getHostFromNameService(this);
        }
        return canonicalHostName;
    }

    /**
     * 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.
     *
     * @see SecurityManager#checkConnect
     */
    private static String getHostFromNameService(InetAddress addr) {
        String host = null;
        try {
            // first lookup the hostname
            host = nameService.getHostByAddr(addr.getAddress());

                /* 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 = nameService.lookupAllHostAddr(host, NETID_UNSET);
            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 (UnknownHostException e) {
            host = addr.getHostAddress();
        }

        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   JDK1.0.2
     */
    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 ((hostName != null) ? hostName : "")
            + "/" + getHostAddress();
    }

    /**
     * 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 {
        return getByAddress(host, addr, -1 /* scopeId */);
    }

    // Do not delete. Called from native code.
    private static InetAddress getByAddress(String host, byte[] addr, int scopeId)
        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, scopeId);
                }
            }
        }
        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} 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&nbsp;2.5.3. </p>
     *
     * @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 impl.lookupAllHostAddr(host, NETID_UNSET)[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>.
     * <p> If the host is {@code null} 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&nbsp;2.5.3. </p>
     *
     * <p> If there is a security manager and {@code host} is not
     * null and {@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 see if the operation is allowed.
     *
     * @param      host   the name of the host, or {@code null}.
     * @return     an array of all the IP addresses for a 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
     *               {@code checkConnect} method doesn't allow the operation.
     *
     * @see SecurityManager#checkConnect
     */
    public static InetAddress[] getAllByName(String host)
        throws UnknownHostException {
        return impl.lookupAllHostAddr(host, NETID_UNSET).clone();
    }

    /**
     * Returns the loopback address.
     * <p>
     * The InetAddress returned will represent the IPv4
     * loopback address, 127.0.0.1, or the IPv6 loopback
     * address, ::1. The IPv4 loopback address returned
     * is only one of many in the form 127.*.*.*
     *
     * @return  the InetAddress loopback instance.
     * @since 1.7
     */
    public static InetAddress getLoopbackAddress() {
        return impl.loopbackAddresses()[0];
    }

    /**
     * Returns an {@code InetAddress} object given the raw IP address .
     * The argument is in network byte order: the highest order
     * byte of the address is in {@code getAddress()[0]}.
     *
     * <p> This method doesn't block, i.e. no reverse name service lookup
     * is performed.
     *
     * <p> IPv4 address byte array must be 4 bytes long and IPv6 byte array
     * must be 16 bytes long
     *
     * @param addr the raw IP address in 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(byte[] addr)
        throws UnknownHostException {
        return getByAddress(null, addr);
    }

    /**
     * Returns the address of the local host. This is achieved by retrieving
     * the name of the host from the system, then resolving that name into
     * an {@code InetAddress}.
     *
     * <P>Note: The resolved address may be cached for a short period of time.
     * </P>
     *
     * <p>If there is a security manager, its
     * {@code checkConnect} method is called
     * with the local host name and {@code -1}
     * as its arguments to see if the operation is allowed.
     * If the operation is not allowed, an InetAddress representing
     * the loopback address is returned.
     *
     * @return     the address of the local host.
     *
     * @exception  UnknownHostException  if the local host name could not
     *             be resolved into an address.
     *
     * @see SecurityManager#checkConnect
     * @see java.net.InetAddress#getByName(java.lang.String)
     */
    public static InetAddress getLocalHost() throws UnknownHostException {
        String local = Libcore.os.uname().nodename;
        return impl.lookupAllHostAddr(local, NETID_UNSET)[0];
    }

    /*
     * Returns the InetAddress representing anyLocalAddress
     * (typically 0.0.0.0 or ::0)
     */
    static InetAddress anyLocalAddress() {
        return impl.anyLocalAddress();
    }

    private void readObjectNoData (ObjectInputStream s) throws
                         IOException, ClassNotFoundException {
        // Android-changed: Don't use null to mean the boot classloader.
        if (getClass().getClassLoader() != BOOT_CLASSLOADER) {
            throw new SecurityException ("invalid address type");
        }
    }

    // Android-changed: Don't use null to mean the boot classloader.
    private static final ClassLoader BOOT_CLASSLOADER = Object.class.getClassLoader();

    private void readObject (ObjectInputStream s) throws
                         IOException, ClassNotFoundException {
        // Android-changed: Don't use null to mean the boot classloader.
        if (getClass().getClassLoader() != BOOT_CLASSLOADER) {
            throw new SecurityException ("invalid address type");
        }
        GetField gf = s.readFields();
        String host = (String)gf.get("hostName", null);
        int address= gf.get("address", 0);
        int family= gf.get("family", 0);
        holder = new InetAddressHolder(host, address, family);
    }

    /* needed because the serializable fields no longer exist */

    /**
     * @serialField hostName String
     * @serialField address int
     * @serialField family int
     */
    private static final ObjectStreamField[] serialPersistentFields = {
        new ObjectStreamField("hostName", String.class),
        new ObjectStreamField("address", int.class),
        new ObjectStreamField("family", int.class),
    };

    private void writeObject (ObjectOutputStream s) throws
                        IOException {
        // Android-changed: Don't use null to mean the boot classloader.
        if (getClass().getClassLoader() != BOOT_CLASSLOADER) {
            throw new SecurityException ("invalid address type");
        }
        PutField pf = s.putFields();
        pf.put("hostName", holder().hostName);
        pf.put("address", holder().address);
        pf.put("family", holder().family);
        s.writeFields();
        s.flush();
    }

    static final int NETID_UNSET = 0;

    /**
     * Returns true if the string is a valid numeric IPv4 or IPv6 address (such as "192.168.0.1").
     * This copes with all forms of address that Java supports, detailed in the {@link InetAddress}
     * class documentation.
     *
     * @hide used by frameworks/base to ensure that a getAllByName won't cause a DNS lookup.
     */
    public static boolean isNumeric(String address) {
        InetAddress inetAddress = parseNumericAddressNoThrow(address);
        return inetAddress != null && disallowDeprecatedFormats(address, inetAddress) != null;
    }

    static InetAddress parseNumericAddressNoThrow(String address) {
        // Accept IPv6 addresses (only) in square brackets for compatibility.
        if (address.startsWith("[") && address.endsWith("]") && address.indexOf(':') != -1) {
            address = address.substring(1, address.length() - 1);
        }
        StructAddrinfo hints = new StructAddrinfo();
        hints.ai_flags = AI_NUMERICHOST;
        InetAddress[] addresses = null;
        try {
            addresses = Libcore.os.android_getaddrinfo(address, hints, NETID_UNSET);
        } catch (GaiException ignored) {
        }
        return (addresses != null) ? addresses[0] : null;
    }

    static InetAddress disallowDeprecatedFormats(String address, InetAddress inetAddress) {
        // Only IPv4 addresses are problematic.
        if (!(inetAddress instanceof Inet4Address) || address.indexOf(':') != -1) {
            return inetAddress;
        }
        // If inet_pton(3) can't parse it, it must have been a deprecated format.
        // We need to return inet_pton(3)'s result to ensure that numbers assumed to be octal
        // by getaddrinfo(3) are reinterpreted by inet_pton(3) as decimal.
        return Libcore.os.inet_pton(AF_INET, address);
    }

    /**
     * Returns an InetAddress corresponding to the given numeric address (such
     * as {@code "192.168.0.1"} or {@code "2001:4860:800d::68"}).
     * This method will never do a DNS lookup. Non-numeric addresses are errors.
     *
     * @hide used by frameworks/base's NetworkUtils.numericToInetAddress
     * @throws IllegalArgumentException if {@code numericAddress} is not a numeric address
     */
    public static InetAddress parseNumericAddress(String numericAddress) {
        if (numericAddress == null || numericAddress.isEmpty()) {
            return Inet6Address.LOOPBACK;
        }
        InetAddress result = parseNumericAddressNoThrow(numericAddress);
        result = disallowDeprecatedFormats(numericAddress, result);
        if (result == null) {
            throw new IllegalArgumentException("Not a numeric address: " + numericAddress);
        }
        return result;
    }

    /**
     * Removes all entries from the VM's DNS cache. This does not affect the C library's DNS
     * cache, nor any caching DNS servers between you and the canonical server.
     * @hide
     */
    public static void clearDnsCache() {
        impl.clearAddressCache();
    }

    /**
     * Operates identically to {@code getByName} except host resolution is
     * performed on the network designated by {@code netId}.
     *
     * @param host
     *            the hostName to be resolved to an address or {@code null}.
     * @param netId the network to use for host resolution.
     * @return the {@code InetAddress} instance representing the host.
     * @throws UnknownHostException if the address lookup fails.
     * @hide internal use only
     */
    public static InetAddress getByNameOnNet(String host, int netId) throws UnknownHostException {
        return impl.lookupAllHostAddr(host, netId)[0];
    }

    /**
     * Operates identically to {@code getAllByName} except host resolution is
     * performed on the network designated by {@code netId}.
     *
     * @param host the hostname or literal IP string to be resolved.
     * @param netId the network to use for host resolution.
     * @return the array of addresses associated with the specified host.
     * @throws UnknownHostException if the address lookup fails.
     * @hide internal use only
     */
    public static InetAddress[] getAllByNameOnNet(String host, int netId) throws UnknownHostException {
        return impl.lookupAllHostAddr(host, netId).clone();
    }

    // Only called by java.net.SocketPermission.
    static InetAddress[] getAllByName0(String authHost, boolean check) throws UnknownHostException {
        throw new UnsupportedOperationException();
    }

    // Only called by java.net.SocketPermission.
    String getHostName(boolean check) {
        throw new UnsupportedOperationException();
    }
}