tunnel: auto-detect IPv6/IPv4 preference

Detect IP address change.
Request non-VPN network.
Update endpoint when needed.
Unregister network on wgTurnOff and use IPv4 if network is not known.

5 files changed, 229 insertions, 20 deletions

diff --git a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
index 5d544f56..e8148c04 100644
--- a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -9,7 +9,11 @@ import android.content.Context;
 import android.content.Intent;
 import android.content.pm.PackageManager;
 import android.net.ConnectivityManager;
+import android.net.LinkProperties;
 import android.net.LocalSocketAddress;
+import android.net.Network;
+import android.net.NetworkCapabilities;
+import android.net.NetworkRequest;
 import android.net.ProxyInfo;
 import android.net.Uri;
 import android.os.Build;
@@ -25,6 +29,8 @@ import com.google.protobuf.Empty;
 import com.wireguard.android.backend.BackendException.Reason;
 import com.wireguard.android.backend.Tunnel.State;
 import com.wireguard.android.backend.gen.GetConnectionOwnerUidResponse;
+import com.wireguard.android.backend.gen.IpcSetRequest;
+import com.wireguard.android.backend.gen.IpcSetResponse;
 import com.wireguard.android.backend.gen.LibwgGrpc;
 import com.wireguard.android.backend.gen.ReverseRequest;
 import com.wireguard.android.backend.gen.ReverseResponse;
@@ -32,6 +38,7 @@ import com.wireguard.android.backend.gen.StartHttpProxyRequest;
 import com.wireguard.android.backend.gen.StartHttpProxyResponse;
 import com.wireguard.android.backend.gen.StopHttpProxyRequest;
 import com.wireguard.android.backend.gen.StopHttpProxyResponse;
+import com.wireguard.android.backend.gen.TunnelHandle;
 import com.wireguard.android.backend.gen.VersionRequest;
 import com.wireguard.android.backend.gen.VersionResponse;
 import com.wireguard.android.util.SharedLibraryLoader;
@@ -43,6 +50,7 @@ import com.wireguard.config.Peer;
 import com.wireguard.crypto.Key;
 import com.wireguard.crypto.KeyFormatException;
 import com.wireguard.util.NonNullForAll;
+import com.wireguard.util.Resolver;
 
 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
@@ -94,6 +102,8 @@ public final class GoBackend implements Backend {
     private int currentTunnelHandle = -1;
     private ManagedChannel channel;
     private ConnectivityManager connectivityManager;
+    private ConnectivityManager.NetworkCallback myNetworkCallback = new MyNetworkCallback();
+    @Nullable private Network activeNetwork;
 
     /**
      * Public constructor for GoBackend.
@@ -448,13 +458,19 @@ public final class GoBackend implements Backend {
             }
 
 
+            activeNetwork = connectivityManager.getActiveNetwork();
+            if (!connectivityManager.getNetworkCapabilities(activeNetwork).hasCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)) {
+                Log.w(TAG, "VPN network is active, null activeNetwork");
+                activeNetwork = null;
+            }
+            final Resolver resolver = new Resolver(activeNetwork, connectivityManager.getLinkProperties(activeNetwork));
             dnsRetry: for (int i = 0; i < DNS_RESOLUTION_RETRIES; ++i) {
                 // Pre-resolve IPs so they're cached when building the userspace string
                 for (final Peer peer : config.getPeers()) {
                     final InetEndpoint ep = peer.getEndpoint().orElse(null);
                     if (ep == null)
                         continue;
-                    if (ep.getResolved().orElse(null) == null) {
+                    if (ep.getResolved(resolver, true).orElse(null) == null) {
                         if (i < DNS_RESOLUTION_RETRIES - 1) {
                             Log.w(TAG, "DNS host \"" + ep.getHost() + "\" failed to resolve; trying again");
                             Thread.sleep(1000);
@@ -467,7 +483,7 @@ public final class GoBackend implements Backend {
             }
 
             // Build config
-            final String goConfig = config.toWgUserspaceString();
+            final String goConfig = config.toWgUserspaceString(resolver);
 
             // Create the vpn tunnel with android API
             final VpnService.Builder builder = service.getBuilder();
@@ -541,6 +557,9 @@ public final class GoBackend implements Backend {
 
             service.protect(wgGetSocketV4(currentTunnelHandle));
             service.protect(wgGetSocketV6(currentTunnelHandle));
+
+            NetworkRequest req = new NetworkRequest.Builder().addCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN).build();
+            connectivityManager.requestNetwork(req,  myNetworkCallback);
         } else {
             if (currentTunnelHandle == -1) {
                 Log.w(TAG, "Tunnel already down");
@@ -551,6 +570,8 @@ public final class GoBackend implements Backend {
             currentTunnelHandle = -1;
             currentConfig = null;
             stopHttpProxy();
+            connectivityManager.unregisterNetworkCallback(myNetworkCallback);
+            activeNetwork = null;
             wgTurnOff(handleToClose);
         }
 
@@ -616,8 +637,11 @@ public final class GoBackend implements Backend {
                 owner.stopHttpProxy();
                 final Tunnel tunnel = owner.currentTunnel;
                 if (tunnel != null) {
-                    if (owner.currentTunnelHandle != -1)
+                    if (owner.currentTunnelHandle != -1) {
+                        owner.connectivityManager.unregisterNetworkCallback(owner.myNetworkCallback);
+                        owner.activeNetwork = null;
                         wgTurnOff(owner.currentTunnelHandle);
+                    }
                     owner.currentTunnel = null;
                     owner.currentTunnelHandle = -1;
                     owner.currentConfig = null;
@@ -643,4 +667,27 @@ public final class GoBackend implements Backend {
             this.owner = owner;
         }
     }
+
+    private class MyNetworkCallback extends ConnectivityManager.NetworkCallback {
+        @Override
+        public void onAvailable(Network network) {
+            activeNetwork = network;
+            Log.w(TAG, "onAvailable: " + activeNetwork);
+        }
+
+        @Override
+        public void onLinkPropertiesChanged(Network network, LinkProperties linkProperties) {
+            Log.w(TAG, "onLinkPropertiesChanged: " + network + " is default:" + (network.equals(activeNetwork)));
+            if (network.equals(activeNetwork) && currentConfig != null && currentTunnelHandle > -1) {
+                final Resolver resolver = new Resolver(network, linkProperties);
+                final String goConfig = currentConfig.toWgUserspaceStringWithChangedEndpoints(resolver);
+                Log.w(TAG, "is default network, config:" + goConfig);
+
+                LibwgGrpc.LibwgBlockingStub stub = LibwgGrpc.newBlockingStub(channel);
+                TunnelHandle tunnel = TunnelHandle.newBuilder().setHandle(currentTunnelHandle).build();
+                IpcSetRequest request = IpcSetRequest.newBuilder().setTunnel(tunnel).setConfig(goConfig).build();
+                IpcSetResponse resp = stub.ipcSet(request);
+            }
+        }
+    }
 }
diff --git a/tunnel/src/main/java/com/wireguard/config/Config.java b/tunnel/src/main/java/com/wireguard/config/Config.java
index 807ebec8..ea05e9c8 100644
--- a/tunnel/src/main/java/com/wireguard/config/Config.java
+++ b/tunnel/src/main/java/com/wireguard/config/Config.java
@@ -9,6 +9,7 @@ import com.wireguard.config.BadConfigException.Location;
 import com.wireguard.config.BadConfigException.Reason;
 import com.wireguard.config.BadConfigException.Section;
 import com.wireguard.util.NonNullForAll;
+import com.wireguard.util.Resolver;
 
 import java.io.BufferedReader;
 import java.io.IOException;
@@ -173,12 +174,19 @@ public final class Config {
      *
      * @return the {@code Config} represented as a series of "key=value" lines
      */
-    public String toWgUserspaceString() {
+    public String toWgUserspaceString(Resolver resolver) {
         final StringBuilder sb = new StringBuilder();
         sb.append(interfaze.toWgUserspaceString());
         sb.append("replace_peers=true\n");
         for (final Peer peer : peers)
-            sb.append(peer.toWgUserspaceString());
+            sb.append(peer.toWgUserspaceString(resolver));
+        return sb.toString();
+    }
+
+    public String toWgUserspaceStringWithChangedEndpoints(Resolver resolver) {
+        final StringBuilder sb = new StringBuilder();
+        for (final Peer peer : peers)
+            sb.append(peer.toWgUserspaceStringWithChangedEndpoint(resolver));
         return sb.toString();
     }
 
diff --git a/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
index 66855f11..abd888c8 100644
--- a/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
+++ b/tunnel/src/main/java/com/wireguard/config/InetEndpoint.java
@@ -6,6 +6,7 @@
 package com.wireguard.config;
 
 import com.wireguard.util.NonNullForAll;
+import com.wireguard.util.Resolver;
 
 import java.net.Inet4Address;
 import java.net.InetAddress;
@@ -87,24 +88,34 @@ public final class InetEndpoint {
      *
      * @return the resolved endpoint, or {@link Optional#empty()}
      */
-    public Optional<InetEndpoint> getResolved() {
-        if (isResolved)
+    public Optional<InetEndpoint> getResolved(Resolver resolver) {
+        return getResolved(resolver, false, false);
+    }
+
+    public Optional<InetEndpoint> getResolved(Resolver resolver, Boolean force) {
+        return getResolved(resolver, force, false);
+    }
+
+    public Optional<InetEndpoint> getResolvedIfChanged(Resolver resolver) {
+        return getResolved(resolver, true, true);
+    }
+
+    public Optional<InetEndpoint> getResolved(Resolver resolver, Boolean force, Boolean ifChanged) {
+        if (!force && isResolved)
             return Optional.of(this);
         synchronized (lock) {
             //TODO(zx2c4): Implement a real timeout mechanism using DNS TTL
-            if (Duration.between(lastResolution, Instant.now()).toMinutes() > 1) {
+            if (force || Duration.between(lastResolution, Instant.now()).toMinutes() > 1) {
                 try {
-                    // Prefer v4 endpoints over v6 to work around DNS64 and IPv6 NAT issues.
-                    final InetAddress[] candidates = InetAddress.getAllByName(host);
-                    InetAddress address = candidates[0];
-                    for (final InetAddress candidate : candidates) {
-                        if (candidate instanceof Inet4Address) {
-                            address = candidate;
-                            break;
-                        }
-                    }
-                    resolved = new InetEndpoint(address.getHostAddress(), true, port);
+                    InetAddress address = resolver.resolve(host);
+                    InetEndpoint resolvedNow = new InetEndpoint(address.getHostAddress(), true, port);
                     lastResolution = Instant.now();
+
+                    if (ifChanged && resolvedNow.equals(resolved)) {
+                        return Optional.empty();
+                    }
+
+                    resolved = resolvedNow;
                 } catch (final UnknownHostException e) {
                     resolved = null;
                 }
diff --git a/tunnel/src/main/java/com/wireguard/config/Peer.java b/tunnel/src/main/java/com/wireguard/config/Peer.java
index 9b87b397..3cf5dc15 100644
--- a/tunnel/src/main/java/com/wireguard/config/Peer.java
+++ b/tunnel/src/main/java/com/wireguard/config/Peer.java
@@ -11,6 +11,7 @@ import com.wireguard.config.BadConfigException.Section;
 import com.wireguard.crypto.Key;
 import com.wireguard.crypto.KeyFormatException;
 import com.wireguard.util.NonNullForAll;
+import com.wireguard.util.Resolver;
 
 import java.util.Collection;
 import java.util.Collections;
@@ -190,18 +191,26 @@ public final class Peer {
      *
      * @return the {@code Peer} represented as a series of "key=value" lines
      */
-    public String toWgUserspaceString() {
+    public String toWgUserspaceString(Resolver resolver) {
         final StringBuilder sb = new StringBuilder();
         // The order here is important: public_key signifies the beginning of a new peer.
         sb.append("public_key=").append(publicKey.toHex()).append('\n');
         for (final InetNetwork allowedIp : allowedIps)
             sb.append("allowed_ip=").append(allowedIp).append('\n');
-        endpoint.flatMap(InetEndpoint::getResolved).ifPresent(ep -> sb.append("endpoint=").append(ep).append('\n'));
+        endpoint.flatMap(ep -> ep.getResolved(resolver)).ifPresent(ep -> sb.append("endpoint=").append(ep).append('\n'));
         persistentKeepalive.ifPresent(pk -> sb.append("persistent_keepalive_interval=").append(pk).append('\n'));
         preSharedKey.ifPresent(psk -> sb.append("preshared_key=").append(psk.toHex()).append('\n'));
         return sb.toString();
     }
 
+    public String toWgUserspaceStringWithChangedEndpoint(Resolver resolver) {
+        final StringBuilder sb = new StringBuilder();
+        // The order here is important: public_key signifies the beginning of a new peer.
+        sb.append("public_key=").append(publicKey.toHex()).append('\n');
+        endpoint.flatMap(ep -> ep.getResolved(resolver, true)).ifPresent(ep -> sb.append("endpoint=").append(ep).append('\n'));
+        return sb.toString();
+    }
+
     @SuppressWarnings("UnusedReturnValue")
     public static final class Builder {
         // See wg(8)
diff --git a/tunnel/src/main/java/com/wireguard/util/Resolver.java b/tunnel/src/main/java/com/wireguard/util/Resolver.java
new file mode 100644
index 00000000..f401b584
--- /dev/null
+++ b/tunnel/src/main/java/com/wireguard/util/Resolver.java
@@ -0,0 +1,134 @@
+/*
+ * 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.util.Log;
+
+import androidx.annotation.Nullable;
+
+@NonNullForAll
+public class Resolver {
+    private static final String TAG = "WireGuard/Resolver";
+    @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();
+        }
+    }
+
+    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 {
+        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();
+                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;
+    }
+}