GoBackend: Use the android VpnService to encapsulate the go backend

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/AndroidManifest.xml

@@ -50,6 +50,14 @@
             </intent-filter>
         </receiver>
 
+        <service
+            android:name=".backend.GoBackend$VpnService"
+            android:permission="android.permission.BIND_VPN_SERVICE" >
+            <intent-filter>
+                <action android:name="android.net.VpnService" />
+            </intent-filter>
+        </service>
+
         <service
             android:name=".QuickTileService"
             android:icon="@drawable/ic_tile"

app/src/main/java/com/wireguard/android/activity/BaseActivity.java

@@ -1,11 +1,13 @@
 package com.wireguard.android.activity;
 
 import android.app.Activity;
+import android.content.Intent;
 import android.databinding.CallbackRegistry;
 import android.databinding.CallbackRegistry.NotifierCallback;
 import android.os.Bundle;
 
 import com.wireguard.android.Application;
+import com.wireguard.android.backend.GoBackend;
 import com.wireguard.android.model.Tunnel;
 import com.wireguard.android.model.TunnelManager;
 
@@ -42,8 +44,16 @@ public abstract class BaseActivity extends Activity {
             final TunnelManager tunnelManager = Application.getComponent().getTunnelManager();
             selectedTunnel = tunnelManager.getTunnels().get(savedTunnelName);
         }
+
         // The selected tunnel must be set before the superclass method recreates fragments.
         super.onCreate(savedInstanceState);
+
+        if (Application.getComponent().getBackendType() == GoBackend.class) {
+            Intent intent = GoBackend.VpnService.prepare(this);
+            if (intent != null) {
+                startActivityForResult(intent, 0);
+            }
+        }
     }
 
     @Override

app/src/main/java/com/wireguard/android/backend/GoBackend.java

@@ -1,6 +1,8 @@
 package com.wireguard.android.backend;
 
 import android.content.Context;
+import android.content.Intent;
+import android.os.ParcelFileDescriptor;
 import android.support.v4.util.ArraySet;
 import android.util.Log;
 
@@ -23,13 +25,36 @@ public final class GoBackend implements Backend {
         System.loadLibrary("wg-go");
     }
 
-    private final Context context;
     private Tunnel currentTunnel;
+    private int currentTunnelHandle = -1;
 
-    public GoBackend(final Context context) {
+    private Context context;
+
+    public GoBackend(Context context) {
         this.context = context;
+        context.startService(new Intent(context, VpnService.class));
     }
 
+    public static class VpnService extends android.net.VpnService {
+        @Override
+        public void onCreate() {
+            super.onCreate();
+            vpnService = this;
+        }
+
+        @Override
+        public void onDestroy() {
+            super.onDestroy();
+            vpnService = null;
+        }
+
+        public Builder getBuilder() {
+            return new Builder();
+        }
+    }
+
+    private static VpnService vpnService = null;
+
     private static native int wgGetSocketV4(int handle);
 
     private static native int wgGetSocketV6(int handle);
@@ -90,10 +115,22 @@ public final class GoBackend implements Backend {
 
     private void setStateInternal(final Tunnel tunnel, final Config config, final State state)
             throws Exception {
-        if (state == State.UP) {
-            // Do something (context.startService()...).
-            currentTunnel = tunnel;
 
+        if (state == State.UP) {
+            Log.i(TAG, "Bringing tunnel up");
+
+            if (VpnService.prepare(context) != null)
+                throw new Exception("VPN service not authorized by user");
+
+            if (vpnService == null)
+                throw new Exception("Android VPN service is not running");
+
+            if (currentTunnelHandle != -1) {
+                Log.w(TAG, "Tunnel already up");
+                return;
+            }
+
+            // Build config
             Formatter fmt = new Formatter(new StringBuilder());
             final Interface iface = config.getInterface();
             fmt.format("replace_peers=true\n");
@@ -116,10 +153,47 @@ public final class GoBackend implements Backend {
                     }
                 }
             }
-            wgTurnOn(tunnel.getName(), -1, fmt.toString());
+
+            // Create the vpn tunnel with android API
+            VpnService.Builder builder = vpnService.getBuilder();
+            builder.setSession(tunnel.getName());
+            builder.addAddress(config.getInterface().getAddress(), 32);
+            if (config.getInterface().getDns() != null)
+                builder.addDnsServer(config.getInterface().getDns());
+
+            for (final Peer peer : config.getPeers()) {
+                if (peer.getAllowedIPs() != null) {
+                    for (final String allowedIp : peer.getAllowedIPs().split(" *, *")) {
+                        String[] part = allowedIp.split("/", 2);
+                        builder.addRoute(part[0], Integer.parseInt(part[1]));
+                    }
+                }
+            }
+
+            builder.setBlocking(true);
+            ParcelFileDescriptor tun = builder.establish();
+            if (tun == null)
+                throw new Exception("Unable to create tun device");
+
+            currentTunnelHandle = wgTurnOn(tunnel.getName(), tun.detachFd(), fmt.toString());
+            if (currentTunnelHandle < 0)
+                throw new Exception("Unable to turn tunnel on (wgTurnOn return " + currentTunnelHandle + ")");
+
+            currentTunnel = tunnel;
+
+            vpnService.protect(wgGetSocketV4(currentTunnelHandle));
+            vpnService.protect(wgGetSocketV6(currentTunnelHandle));
         } else {
-            // Do something else.
+            Log.i(TAG, "Bringing tunnel down");
+
+            if (currentTunnelHandle == -1) {
+                Log.w(TAG, "Tunnel already down");
+                return;
+            }
+
+            wgTurnOff(currentTunnelHandle);
             currentTunnel = null;
+            currentTunnelHandle = -1;
         }
     }
 }