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/*
* Copyright © 2023 WireGuard LLC. All Rights Reserved.
* SPDX-License-Identifier: Apache-2.0
*/
package com.wireguard.util;
import java.io.IOException;
import java.net.DatagramSocket;
import java.net.Inet4Address;
import java.net.Inet6Address;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import android.net.IpPrefix;
import android.net.LinkProperties;
import android.net.Network;
import android.net.TrafficStats;
import android.util.Log;
import androidx.annotation.Nullable;
@NonNullForAll
public class Resolver {
private static final String TAG = "WireGuard/Resolver";
private static final int STATS_TAG = 3; // FIXME
@Nullable private final Network network;
@Nullable private final LinkProperties linkProps;
@Nullable private IpPrefix nat64Prefix;
public Resolver(Network network, LinkProperties linkProps) {
this.network = network;
this.linkProps = linkProps;
if (linkProps != null) {
this.nat64Prefix = linkProps.getNat64Prefix();
}
}
public static boolean isULA(Inet6Address addr) {
byte[] raw = addr.getAddress();
return ((raw[0] & 0xfe) == 0xfc);
}
boolean isWithinNAT64Prefix(Inet6Address address) {
if (nat64Prefix == null)
return false;
int prefixLength = nat64Prefix.getPrefixLength();
byte[] rawAddr = address.getAddress();
byte[] rawPrefix = nat64Prefix.getRawAddress();
for (int i=0; i < prefixLength/8; i++) {
if (rawAddr[i] != rawPrefix[i])
return false;
}
return true;
}
boolean isPreferredIPv6(Inet6Address local, Inet6Address remote) {
if (linkProps == null) {
// Prefer IPv4 if there are not link properties that can
// be tested.
return false;
}
// * Prefer IPv4 if local or remote address is ULA
// * Prefer IPv4 if remote IPv6 is within NAT64 prefix.
// * Otherwise prefer IPv6
boolean isLocalULA = isULA(local);
boolean isRemoteULA = isULA(remote);
if (isLocalULA || isRemoteULA) {
return false;
}
if (isWithinNAT64Prefix(remote)) {
return false;
}
return true;
}
public InetAddress resolve(String host) throws UnknownHostException {
TrafficStats.setThreadStatsTag(STATS_TAG);
final InetAddress[] candidates = network != null ? network.getAllByName(host) : InetAddress.getAllByName(host);
InetAddress address = candidates[0];
for (final InetAddress candidate : candidates) {
DatagramSocket sock;
try {
sock = new DatagramSocket();
TrafficStats.tagDatagramSocket(sock);
if (network != null) {
network.bindSocket(sock);
}
} catch (SocketException e) {
// Return first candidate as fallback
Log.w(TAG, "DatagramSocket failed, fallback to: \"" + address);
return address;
} catch (IOException e) {
// Return first candidate as fallback
Log.w(TAG, "BindSocket failed, fallback to: \"" + address);
return address;
}
sock.connect(candidate, 51820);
if (sock.getLocalAddress().isAnyLocalAddress()) {
// Connect didn't find a local address.
Log.w(TAG, "No local address");
continue;
}
Log.w(TAG, "Local address: " + sock.getLocalAddress());
if (candidate instanceof Inet4Address) {
// Accept IPv4 as preferred address.
address = candidate;
break;
}
Inet6Address local = (Inet6Address)sock.getLocalAddress();
InetSocketAddress remoteSockAddr = (InetSocketAddress)sock.getRemoteSocketAddress();
Inet6Address remote = (Inet6Address)remoteSockAddr.getAddress();
sock.close();
if (isPreferredIPv6(local, remote)) {
address = candidate;
break;
}
}
Log.w(TAG, "Resolved \"" + host + "\" to: " + address);
return address;
}
}
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