java/net/Inet6AddressImpl.java - platform/prebuilts/fullsdk/sources/android-28 - Git at Google

 /*
  * Copyright (C) 2014 The Android Open Source Project
  * Copyright (c) 2002, 2013, 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 android.system.ErrnoException;
 import android.system.GaiException;
 import android.system.StructAddrinfo;
 import android.system.StructIcmpHdr;

 import dalvik.system.BlockGuard;

 import libcore.io.IoBridge;
 import libcore.io.Libcore;

 import java.io.FileDescriptor;
 import java.io.IOException;

 import static android.system.OsConstants.AF_INET;
 import static android.system.OsConstants.AF_INET6;
 import static android.system.OsConstants.AF_UNSPEC;
 import static android.system.OsConstants.AI_ADDRCONFIG;
 import static android.system.OsConstants.EACCES;
 import static android.system.OsConstants.ECONNREFUSED;
 import static android.system.OsConstants.NI_NAMEREQD;
 import static android.system.OsConstants.ICMP6_ECHO_REPLY;
 import static android.system.OsConstants.ICMP_ECHOREPLY;
 import static android.system.OsConstants.IPPROTO_ICMP;
 import static android.system.OsConstants.IPPROTO_ICMPV6;
 import static android.system.OsConstants.SOCK_DGRAM;
 import static android.system.OsConstants.SOCK_STREAM;

 // Android-note: Android-specific behavior and Linux-based implementation
 // http://b/36933260 Implement root-less ICMP for isReachable()
 // http://b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
 // http://b/25861497 Add BlockGuard checks.
 // http://b/26700324 Fix odd dependency chains of the static InetAddress.
 // anyLocalAddress() Let anyLocalAddress() always return an IPv6 address.
 // Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.
 // Rewrote hostname lookup methods on top of Libcore.os. Merge implementation from InetAddress
 //   and remove native methods in this class
 /*
  * Package private implementation of InetAddressImpl for dual
  * IPv4/IPv6 stack. {@code #anyLocalAddress()} will always return an IPv6 address.
  *
  * @since 1.4
  */

 class Inet6AddressImpl implements InetAddressImpl {

     // @GuardedBy(Inet6AddressImpl.class)
     private static InetAddress anyLocalAddress;
     // @GuardedBy(Inet6AddressImpl.class)
     private static InetAddress[] loopbackAddresses;

     private static final AddressCache addressCache = new AddressCache();

     // BEGIN Android-changed: Rewrote hostname lookup methods on top of Libcore.os.
     /*
     public native String getLocalHostName() throws UnknownHostException;
     public native InetAddress[]
         lookupAllHostAddr(String hostname) throws UnknownHostException;
     public native String getHostByAddr(byte[] addr) throws UnknownHostException;
     private native boolean isReachable0(byte[] addr, int scope, int timeout, byte[] inf, int ttl, int if_scope) throws IOException;
     */
     @Override
     public InetAddress[] lookupAllHostAddr(String host, int netId) throws UnknownHostException {
         if (host == null || host.isEmpty()) {
             // Android-changed: Return both the Inet4 and Inet6 loopback addresses
             // when host == null or empty.
             return loopbackAddresses();
         }

         // Is it a numeric address?
         InetAddress result = InetAddress.parseNumericAddressNoThrow(host);
         if (result != null) {
             result = InetAddress.disallowDeprecatedFormats(host, result);
             if (result == null) {
                 throw new UnknownHostException("Deprecated IPv4 address format: " + host);
             }
             return new InetAddress[] { result };
         }

         return lookupHostByName(host, netId);
     }

     /**
      * Resolves a hostname to its IP addresses using a cache.
      *
      * @param host the hostname to resolve.
      * @param netId the network to perform resolution upon.
      * @return the IP addresses of the host.
      */
     private static InetAddress[] lookupHostByName(String host, int netId)
             throws UnknownHostException {
         BlockGuard.getThreadPolicy().onNetwork();
         // Do we have a result cached?
         Object cachedResult = addressCache.get(host, netId);
         if (cachedResult != null) {
             if (cachedResult instanceof InetAddress[]) {
                 // A cached positive result.
                 return (InetAddress[]) cachedResult;
             } else {
                 // A cached negative result.
                 throw new UnknownHostException((String) cachedResult);
             }
         }
         try {
             StructAddrinfo hints = new StructAddrinfo();
             hints.ai_flags = AI_ADDRCONFIG;
             hints.ai_family = AF_UNSPEC;
             // If we don't specify a socket type, every address will appear twice, once
             // for SOCK_STREAM and one for SOCK_DGRAM. Since we do not return the family
             // anyway, just pick one.
             hints.ai_socktype = SOCK_STREAM;
             InetAddress[] addresses = Libcore.os.android_getaddrinfo(host, hints, netId);
             // TODO: should getaddrinfo set the hostname of the InetAddresses it returns?
             for (InetAddress address : addresses) {
                 address.holder().hostName = host;
                 address.holder().originalHostName = host;
             }
             addressCache.put(host, netId, addresses);
             return addresses;
         } catch (GaiException gaiException) {
             // If the failure appears to have been a lack of INTERNET permission, throw a clear
             // SecurityException to aid in debugging this common mistake.
             // http://code.google.com/p/android/issues/detail?id=15722
             if (gaiException.getCause() instanceof ErrnoException) {
                 if (((ErrnoException) gaiException.getCause()).errno == EACCES) {
                     throw new SecurityException("Permission denied (missing INTERNET permission?)", gaiException);
                 }
             }
             // Otherwise, throw an UnknownHostException.
             String detailMessage = "Unable to resolve host \"" + host + "\": " + Libcore.os.gai_strerror(gaiException.error);
             addressCache.putUnknownHost(host, netId, detailMessage);
             throw gaiException.rethrowAsUnknownHostException(detailMessage);
         }
     }

     @Override
     public String getHostByAddr(byte[] addr) throws UnknownHostException {
         BlockGuard.getThreadPolicy().onNetwork();

         return getHostByAddr0(addr);
     }

     @Override
     public void clearAddressCache() {
         addressCache.clear();
     }
     // END Android-changed: Rewrote hostname lookup methods on top of Libcore.os.

     @Override
     public boolean isReachable(InetAddress addr, int timeout, NetworkInterface netif, int ttl) throws IOException {
         // Android-changed: rewritten on the top of IoBridge and Libcore.os.
         InetAddress sourceAddr = null;
         if (netif != null) {
             /*
              * Let's make sure we bind to an address of the proper family.
              * Which means same family as addr because at this point it could
              * be either an IPv6 address or an IPv4 address (case of a dual
              * stack system).
              */
             java.util.Enumeration<InetAddress> it = netif.getInetAddresses();
             InetAddress inetaddr = null;
             while (it.hasMoreElements()) {
                 inetaddr = it.nextElement();
                 if (inetaddr.getClass().isInstance(addr)) {
                     sourceAddr = inetaddr;
                     break;
                 }
             }

             if (sourceAddr == null) {
                 // Interface doesn't support the address family of
                 // the destination
                 return false;
             }
         }

         // Android-changed: http://b/36933260 Implement root-less ICMP for isReachable().
         /*
         if (addr instanceof Inet6Address)
             scope = ((Inet6Address) addr).getScopeId();
         return isReachable0(addr.getAddress(), scope, timeout, ifaddr, ttl, netif_scope);
         */
         // Try ICMP first
         if (icmpEcho(addr, timeout, sourceAddr, ttl)) {
             return true;
         }

         // No good, let's fall back to TCP
         return tcpEcho(addr, timeout, sourceAddr, ttl);
     }

     // BEGIN Android-added: http://b/36933260 Implement root-less ICMP for isReachable().
     private boolean tcpEcho(InetAddress addr, int timeout, InetAddress sourceAddr, int ttl)
             throws IOException {
         FileDescriptor fd = null;
         try {
             fd = IoBridge.socket(AF_INET6, SOCK_STREAM, 0);
             if (ttl > 0) {
                 IoBridge.setSocketOption(fd, IoBridge.JAVA_IP_TTL, ttl);
             }
             if (sourceAddr != null) {
                 IoBridge.bind(fd, sourceAddr, 0);
             }
             IoBridge.connect(fd, addr, 7 /* Echo-protocol port */, timeout);
             return true;
         } catch (IOException e) {
             // Connection refused by remote (ECONNREFUSED) implies reachable. Otherwise silently
             // ignore the exception and return false.
             Throwable cause = e.getCause();
             return cause instanceof ErrnoException
                     && ((ErrnoException) cause).errno == ECONNREFUSED;
         } finally {
             IoBridge.closeAndSignalBlockedThreads(fd);
         }
     }

     protected boolean icmpEcho(InetAddress addr, int timeout, InetAddress sourceAddr, int ttl)
             throws IOException {

         FileDescriptor fd = null;
         try {
             boolean isIPv4 = addr instanceof Inet4Address;
             int domain = isIPv4 ? AF_INET : AF_INET6;
             int icmpProto = isIPv4 ? IPPROTO_ICMP : IPPROTO_ICMPV6;
             fd = IoBridge.socket(domain, SOCK_DGRAM, icmpProto);

             if (ttl > 0) {
                 IoBridge.setSocketOption(fd, IoBridge.JAVA_IP_TTL, ttl);
             }
             if (sourceAddr != null) {
                 IoBridge.bind(fd, sourceAddr, 0);
             }

             byte[] packet;

             // ICMP is unreliable, try sending requests every second until timeout.
             for (int to = timeout, seq = 0; to > 0; ++seq) {
                 int sockTo = to >= 1000 ? 1000 : to;

                 IoBridge.setSocketOption(fd, SocketOptions.SO_TIMEOUT, sockTo);

                 packet = StructIcmpHdr.IcmpEchoHdr(isIPv4, seq).getBytes();
                 IoBridge.sendto(fd, packet, 0, packet.length, 0, addr, 0);
                 final int icmpId = IoBridge.getLocalInetSocketAddress(fd).getPort();

                 byte[] received = new byte[packet.length];
                 DatagramPacket receivedPacket = new DatagramPacket(received, packet.length);
                 int size = IoBridge
                         .recvfrom(true, fd, received, 0, received.length, 0, receivedPacket, false);
                 if (size == packet.length) {
                     byte expectedType = isIPv4 ? (byte) ICMP_ECHOREPLY
                             : (byte) ICMP6_ECHO_REPLY;
                     if (receivedPacket.getAddress().equals(addr)
                             && received[0] == expectedType
                             && received[4] == (byte) (icmpId >> 8)
                             && received[5] == (byte) icmpId
                             && received[6] == (byte) (seq >> 8)
                             && received[7] == (byte) seq) {
                         // This is the packet we're expecting.
                         return true;
                     }
                 }
                 to -= sockTo;
             }
         } catch (IOException e) {
             // Silently ignore and fall back.
         } finally {
             if (fd != null) {
                 try {
                     Libcore.os.close(fd);
                 } catch (ErrnoException e) { }
             }
         }

         return false;
     }
     // END Android-added: http://b/36933260 Implement root-less ICMP for isReachable().

     // BEGIN Android-changed: Let anyLocalAddress() always return an IPv6 address.
     @Override
     public InetAddress anyLocalAddress() {
         synchronized (Inet6AddressImpl.class) {
             // We avoid initializing anyLocalAddress during <clinit> to avoid issues
             // caused by the dependency chains of these classes. InetAddress depends on
             // InetAddressImpl, but Inet6Address & Inet4Address are its subclasses.
             // Also see {@code loopbackAddresses). http://b/26700324
             if (anyLocalAddress == null) {
                 Inet6Address anyAddress = new Inet6Address();
                 anyAddress.holder().hostName = "::";
                 anyLocalAddress = anyAddress;
             }

             return anyLocalAddress;
         }
     }
     // END Android-changed: Let anyLocalAddress() always return an IPv6 address.

     // BEGIN Android-changed: Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.
     @Override
     public InetAddress[] loopbackAddresses() {
         synchronized (Inet6AddressImpl.class) {
             // We avoid initializing anyLocalAddress during <clinit> to avoid issues
             // caused by the dependency chains of these classes. InetAddress depends on
             // InetAddressImpl, but Inet6Address & Inet4Address are its subclasses.
             // Also see {@code anyLocalAddress).
             if (loopbackAddresses == null) {
                 loopbackAddresses = new InetAddress[]{Inet6Address.LOOPBACK, Inet4Address.LOOPBACK};
             }

             return loopbackAddresses;
         }
     }
     // END Android-changed: Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.

     // BEGIN Android-changed: b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
     private String getHostByAddr0(byte[] addr) throws UnknownHostException {
         // Android-changed: Rewritten on the top of Libcore.os
         InetAddress hostaddr = InetAddress.getByAddress(addr);
         try {
             return Libcore.os.getnameinfo(hostaddr, NI_NAMEREQD);
         } catch (GaiException e) {
             UnknownHostException uhe = new UnknownHostException(hostaddr.toString());
             uhe.initCause(e);
             throw uhe;
         }
     }
     // END Android-changed: b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
 }
	/*
	* Copyright (C) 2014 The Android Open Source Project
	* Copyright (c) 2002, 2013, 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 android.system.ErrnoException;
	import android.system.GaiException;
	import android.system.StructAddrinfo;
	import android.system.StructIcmpHdr;

	import dalvik.system.BlockGuard;

	import libcore.io.IoBridge;
	import libcore.io.Libcore;

	import java.io.FileDescriptor;
	import java.io.IOException;

	import static android.system.OsConstants.AF_INET;
	import static android.system.OsConstants.AF_INET6;
	import static android.system.OsConstants.AF_UNSPEC;
	import static android.system.OsConstants.AI_ADDRCONFIG;
	import static android.system.OsConstants.EACCES;
	import static android.system.OsConstants.ECONNREFUSED;
	import static android.system.OsConstants.NI_NAMEREQD;
	import static android.system.OsConstants.ICMP6_ECHO_REPLY;
	import static android.system.OsConstants.ICMP_ECHOREPLY;
	import static android.system.OsConstants.IPPROTO_ICMP;
	import static android.system.OsConstants.IPPROTO_ICMPV6;
	import static android.system.OsConstants.SOCK_DGRAM;
	import static android.system.OsConstants.SOCK_STREAM;

	// Android-note: Android-specific behavior and Linux-based implementation
	// http://b/36933260 Implement root-less ICMP for isReachable()
	// http://b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
	// http://b/25861497 Add BlockGuard checks.
	// http://b/26700324 Fix odd dependency chains of the static InetAddress.
	// anyLocalAddress() Let anyLocalAddress() always return an IPv6 address.
	// Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.
	// Rewrote hostname lookup methods on top of Libcore.os. Merge implementation from InetAddress
	// and remove native methods in this class
	/*
	* Package private implementation of InetAddressImpl for dual
	* IPv4/IPv6 stack. {@code #anyLocalAddress()} will always return an IPv6 address.
	*
	* @since 1.4
	*/

	class Inet6AddressImpl implements InetAddressImpl {

	// @GuardedBy(Inet6AddressImpl.class)
	private static InetAddress anyLocalAddress;
	// @GuardedBy(Inet6AddressImpl.class)
	private static InetAddress[] loopbackAddresses;

	private static final AddressCache addressCache = new AddressCache();

	// BEGIN Android-changed: Rewrote hostname lookup methods on top of Libcore.os.
	/*
	public native String getLocalHostName() throws UnknownHostException;
	public native InetAddress[]
	lookupAllHostAddr(String hostname) throws UnknownHostException;
	public native String getHostByAddr(byte[] addr) throws UnknownHostException;
	private native boolean isReachable0(byte[] addr, int scope, int timeout, byte[] inf, int ttl, int if_scope) throws IOException;
	*/
	@Override
	public InetAddress[] lookupAllHostAddr(String host, int netId) throws UnknownHostException {
	if (host == null \|\| host.isEmpty()) {
	// Android-changed: Return both the Inet4 and Inet6 loopback addresses
	// when host == null or empty.
	return loopbackAddresses();
	}

	// Is it a numeric address?
	InetAddress result = InetAddress.parseNumericAddressNoThrow(host);
	if (result != null) {
	result = InetAddress.disallowDeprecatedFormats(host, result);
	if (result == null) {
	throw new UnknownHostException("Deprecated IPv4 address format: " + host);
	}
	return new InetAddress[] { result };
	}

	return lookupHostByName(host, netId);
	}

	/**
	* Resolves a hostname to its IP addresses using a cache.
	*
	* @param host the hostname to resolve.
	* @param netId the network to perform resolution upon.
	* @return the IP addresses of the host.
	*/
	private static InetAddress[] lookupHostByName(String host, int netId)
	throws UnknownHostException {
	BlockGuard.getThreadPolicy().onNetwork();
	// Do we have a result cached?
	Object cachedResult = addressCache.get(host, netId);
	if (cachedResult != null) {
	if (cachedResult instanceof InetAddress[]) {
	// A cached positive result.
	return (InetAddress[]) cachedResult;
	} else {
	// A cached negative result.
	throw new UnknownHostException((String) cachedResult);
	}
	}
	try {
	StructAddrinfo hints = new StructAddrinfo();
	hints.ai_flags = AI_ADDRCONFIG;
	hints.ai_family = AF_UNSPEC;
	// If we don't specify a socket type, every address will appear twice, once
	// for SOCK_STREAM and one for SOCK_DGRAM. Since we do not return the family
	// anyway, just pick one.
	hints.ai_socktype = SOCK_STREAM;
	InetAddress[] addresses = Libcore.os.android_getaddrinfo(host, hints, netId);
	// TODO: should getaddrinfo set the hostname of the InetAddresses it returns?
	for (InetAddress address : addresses) {
	address.holder().hostName = host;
	address.holder().originalHostName = host;
	}
	addressCache.put(host, netId, addresses);
	return addresses;
	} catch (GaiException gaiException) {
	// If the failure appears to have been a lack of INTERNET permission, throw a clear
	// SecurityException to aid in debugging this common mistake.
	// http://code.google.com/p/android/issues/detail?id=15722
	if (gaiException.getCause() instanceof ErrnoException) {
	if (((ErrnoException) gaiException.getCause()).errno == EACCES) {
	throw new SecurityException("Permission denied (missing INTERNET permission?)", gaiException);
	}
	}
	// Otherwise, throw an UnknownHostException.
	String detailMessage = "Unable to resolve host \"" + host + "\": " + Libcore.os.gai_strerror(gaiException.error);
	addressCache.putUnknownHost(host, netId, detailMessage);
	throw gaiException.rethrowAsUnknownHostException(detailMessage);
	}
	}

	@Override
	public String getHostByAddr(byte[] addr) throws UnknownHostException {
	BlockGuard.getThreadPolicy().onNetwork();

	return getHostByAddr0(addr);
	}

	@Override
	public void clearAddressCache() {
	addressCache.clear();
	}
	// END Android-changed: Rewrote hostname lookup methods on top of Libcore.os.

	@Override
	public boolean isReachable(InetAddress addr, int timeout, NetworkInterface netif, int ttl) throws IOException {
	// Android-changed: rewritten on the top of IoBridge and Libcore.os.
	InetAddress sourceAddr = null;
	if (netif != null) {
	/*
	* Let's make sure we bind to an address of the proper family.
	* Which means same family as addr because at this point it could
	* be either an IPv6 address or an IPv4 address (case of a dual
	* stack system).
	*/
	java.util.Enumeration<InetAddress> it = netif.getInetAddresses();
	InetAddress inetaddr = null;
	while (it.hasMoreElements()) {
	inetaddr = it.nextElement();
	if (inetaddr.getClass().isInstance(addr)) {
	sourceAddr = inetaddr;
	break;
	}
	}

	if (sourceAddr == null) {
	// Interface doesn't support the address family of
	// the destination
	return false;
	}
	}

	// Android-changed: http://b/36933260 Implement root-less ICMP for isReachable().
	/*
	if (addr instanceof Inet6Address)
	scope = ((Inet6Address) addr).getScopeId();
	return isReachable0(addr.getAddress(), scope, timeout, ifaddr, ttl, netif_scope);
	*/
	// Try ICMP first
	if (icmpEcho(addr, timeout, sourceAddr, ttl)) {
	return true;
	}

	// No good, let's fall back to TCP
	return tcpEcho(addr, timeout, sourceAddr, ttl);
	}

	// BEGIN Android-added: http://b/36933260 Implement root-less ICMP for isReachable().
	private boolean tcpEcho(InetAddress addr, int timeout, InetAddress sourceAddr, int ttl)
	throws IOException {
	FileDescriptor fd = null;
	try {
	fd = IoBridge.socket(AF_INET6, SOCK_STREAM, 0);
	if (ttl > 0) {
	IoBridge.setSocketOption(fd, IoBridge.JAVA_IP_TTL, ttl);
	}
	if (sourceAddr != null) {
	IoBridge.bind(fd, sourceAddr, 0);
	}
	IoBridge.connect(fd, addr, 7 /* Echo-protocol port */, timeout);
	return true;
	} catch (IOException e) {
	// Connection refused by remote (ECONNREFUSED) implies reachable. Otherwise silently
	// ignore the exception and return false.
	Throwable cause = e.getCause();
	return cause instanceof ErrnoException
	&& ((ErrnoException) cause).errno == ECONNREFUSED;
	} finally {
	IoBridge.closeAndSignalBlockedThreads(fd);
	}
	}

	protected boolean icmpEcho(InetAddress addr, int timeout, InetAddress sourceAddr, int ttl)
	throws IOException {

	FileDescriptor fd = null;
	try {
	boolean isIPv4 = addr instanceof Inet4Address;
	int domain = isIPv4 ? AF_INET : AF_INET6;
	int icmpProto = isIPv4 ? IPPROTO_ICMP : IPPROTO_ICMPV6;
	fd = IoBridge.socket(domain, SOCK_DGRAM, icmpProto);

	if (ttl > 0) {
	IoBridge.setSocketOption(fd, IoBridge.JAVA_IP_TTL, ttl);
	}
	if (sourceAddr != null) {
	IoBridge.bind(fd, sourceAddr, 0);
	}

	byte[] packet;

	// ICMP is unreliable, try sending requests every second until timeout.
	for (int to = timeout, seq = 0; to > 0; ++seq) {
	int sockTo = to >= 1000 ? 1000 : to;

	IoBridge.setSocketOption(fd, SocketOptions.SO_TIMEOUT, sockTo);

	packet = StructIcmpHdr.IcmpEchoHdr(isIPv4, seq).getBytes();
	IoBridge.sendto(fd, packet, 0, packet.length, 0, addr, 0);
	final int icmpId = IoBridge.getLocalInetSocketAddress(fd).getPort();

	byte[] received = new byte[packet.length];
	DatagramPacket receivedPacket = new DatagramPacket(received, packet.length);
	int size = IoBridge
	.recvfrom(true, fd, received, 0, received.length, 0, receivedPacket, false);
	if (size == packet.length) {
	byte expectedType = isIPv4 ? (byte) ICMP_ECHOREPLY
	: (byte) ICMP6_ECHO_REPLY;
	if (receivedPacket.getAddress().equals(addr)
	&& received[0] == expectedType
	&& received[4] == (byte) (icmpId >> 8)
	&& received[5] == (byte) icmpId
	&& received[6] == (byte) (seq >> 8)
	&& received[7] == (byte) seq) {
	// This is the packet we're expecting.
	return true;
	}
	}
	to -= sockTo;
	}
	} catch (IOException e) {
	// Silently ignore and fall back.
	} finally {
	if (fd != null) {
	try {
	Libcore.os.close(fd);
	} catch (ErrnoException e) { }
	}
	}

	return false;
	}
	// END Android-added: http://b/36933260 Implement root-less ICMP for isReachable().

	// BEGIN Android-changed: Let anyLocalAddress() always return an IPv6 address.
	@Override
	public InetAddress anyLocalAddress() {
	synchronized (Inet6AddressImpl.class) {
	// We avoid initializing anyLocalAddress during <clinit> to avoid issues
	// caused by the dependency chains of these classes. InetAddress depends on
	// InetAddressImpl, but Inet6Address & Inet4Address are its subclasses.
	// Also see {@code loopbackAddresses). http://b/26700324
	if (anyLocalAddress == null) {
	Inet6Address anyAddress = new Inet6Address();
	anyAddress.holder().hostName = "::";
	anyLocalAddress = anyAddress;
	}

	return anyLocalAddress;
	}
	}
	// END Android-changed: Let anyLocalAddress() always return an IPv6 address.

	// BEGIN Android-changed: Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.
	@Override
	public InetAddress[] loopbackAddresses() {
	synchronized (Inet6AddressImpl.class) {
	// We avoid initializing anyLocalAddress during <clinit> to avoid issues
	// caused by the dependency chains of these classes. InetAddress depends on
	// InetAddressImpl, but Inet6Address & Inet4Address are its subclasses.
	// Also see {@code anyLocalAddress).
	if (loopbackAddresses == null) {
	loopbackAddresses = new InetAddress[]{Inet6Address.LOOPBACK, Inet4Address.LOOPBACK};
	}

	return loopbackAddresses;
	}
	}
	// END Android-changed: Let loopbackAddresses() return both Inet4 and Inet6 loopbacks.

	// BEGIN Android-changed: b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
	private String getHostByAddr0(byte[] addr) throws UnknownHostException {
	// Android-changed: Rewritten on the top of Libcore.os
	InetAddress hostaddr = InetAddress.getByAddress(addr);
	try {
	return Libcore.os.getnameinfo(hostaddr, NI_NAMEREQD);
	} catch (GaiException e) {
	UnknownHostException uhe = new UnknownHostException(hostaddr.toString());
	uhe.initCause(e);
	throw uhe;
	}
	}
	// END Android-changed: b/28609551 Rewrite getHostByAddr0 using POSIX library Libcore.os.
	}