android: fix vpn

-Move most of prepare and establish VPN logic out of Go into Android
-Fix prepareVPN argument to use request codes to differentiate sign in and prepare VPN
-Fix missing adapter implementation (setMtu)

Updates tailscale/corp#18202

Signed-off-by: kari-ts <kari@tailscale.com>

android/src/main/java/com/tailscale/ipn/App.kt

@@ -280,7 +280,7 @@ class App : Application(), libtailscale.AppContext {
         Runnable {
           val intent: Intent? = VpnService.prepare(act)
           if (intent == null) {
-            Libtailscale.onVPNPrepared()
+            startVPN()
           } else {
             startActivityForResult(act, intent, reqCode)
           }

android/src/main/java/com/tailscale/ipn/IPNService.kt

@@ -10,8 +10,8 @@ import android.os.Build
 import android.system.OsConstants
 import androidx.core.app.NotificationCompat
 import androidx.core.app.NotificationManagerCompat
-import java.util.UUID
 import libtailscale.Libtailscale
+import java.util.UUID
 
 open class IPNService : VpnService(), libtailscale.IPNService {
   private val randomID: String = UUID.randomUUID().toString()

android/src/main/java/com/tailscale/ipn/MainActivity.kt

@@ -22,6 +22,7 @@ import androidx.navigation.compose.composable
 import androidx.navigation.compose.rememberNavController
 import androidx.navigation.navArgument
 import androidx.navigation.navigation
+import com.tailscale.ipn.Peer.RequestCodes
 import com.tailscale.ipn.mdm.MDMSettings
 import com.tailscale.ipn.ui.notifier.Notifier
 import com.tailscale.ipn.ui.theme.AppTheme
@@ -43,12 +44,19 @@ import com.tailscale.ipn.ui.viewModel.SettingsNav
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
-import com.tailscale.ipn.App
 
 class MainActivity : ComponentActivity() {
   private var notifierScope: CoroutineScope? = null
   private lateinit var requestVpnPermission: ActivityResultLauncher<Unit>
 
+  companion object {
+    // Request codes for Android callbacks.
+    // requestSignin is for Google Sign-In.
+    @JvmStatic val requestSignin: Int = 1000
+    // requestPrepareVPN is for when Android's VpnService.prepare completes.
+    @JvmStatic val requestPrepareVPN: Int = 1001
+  }
+
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
 
@@ -107,7 +115,8 @@ class MainActivity : ComponentActivity() {
     }
     lifecycleScope.launch {
       Notifier.readyToPrepareVPN.collect { isReady ->
-        if (isReady) App.getApplication().prepareVPN(this@MainActivity, -1)
+        if (isReady)
+            App.getApplication().prepareVPN(this@MainActivity, RequestCodes.requestPrepareVPN)
       }
     }
   }

android/src/main/java/com/tailscale/ipn/Peer.java

@@ -6,11 +6,32 @@ package com.tailscale.ipn;
 import android.app.Fragment;
 import android.content.Intent;
 
-import libtailscale.Libtailscale;
-
 public class Peer extends Fragment {
+
+    private static int resultOK = -1;
+
+    public class RequestCodes {
+        public static final int requestSignin = 1000;
+        public static final int requestPrepareVPN = 1001;
+    }
+
     @Override
     public void onActivityResult(int requestCode, int resultCode, Intent data) {
-        Libtailscale.onActivityResult(requestCode, resultCode, MaybeGoogle.getIdTokenForActivity(getActivity()));
+        switch (requestCode) {
+            case RequestCodes.requestSignin:
+                if (resultCode != resultOK) {
+                    // TODO: send null Google token
+                    break;
+                }
+                // TODO: send Google token
+            case RequestCodes.requestPrepareVPN:
+                if (resultCode == resultOK) {
+                    App.getApplication().startVPN();
+                } else {
+                    App.getApplication().setWantRunning(false);
+                    // notify VPN revoked
+                }
+
+        }
     }
 }

android/src/main/java/com/tailscale/ipn/VPNServiceBuilder.kt

@@ -27,8 +27,8 @@ class VPNServiceBuilder(private val builder: VpnService.Builder) : libtailscale.
     return builder.establish()?.let { ParcelFileDescriptor(it) }
   }
 
-  override fun setMTU(p0: Long) {
-    TODO("Not yet implemented")
+  override fun setMTU(p0: Int) {
+    builder.setMtu(p0)
   }
 }
 

android/src/main/java/com/tailscale/ipn/ui/notifier/Notifier.kt

@@ -69,14 +69,9 @@ object Notifier {
             notify.LoginFinished?.let { loginFinished.set(it.property) }
             notify.Version?.let(version::set)
           }
-      var previousState: Ipn.State? = null
       state.collect { currstate ->
-        readyToPrepareVPN.set(
-            previousState != null &&
-                previousState!! <= Ipn.State.Stopped &&
-                currstate > Ipn.State.Stopped)
+        readyToPrepareVPN.set(currstate > Ipn.State.Stopped)
         tileReady.set(currstate >= Ipn.State.Stopped)
-        previousState = currstate
       }
       Log.d(TAG, "Stopped")
     }

libtailscale/callbacks.go

@@ -33,18 +33,6 @@ var (
 	onDNSConfigChanged = make(chan struct{}, 1)
 )
 
-const (
-	// Request codes for Android callbacks.
-	// requestSignin is for Google Sign-In.
-	requestSignin = 1000 + iota
-	// requestPrepareVPN is for when Android's VpnService.prepare
-	// completes.
-	requestPrepareVPN
-)
-
-// resultOK is Android's Activity.RESULT_OK.
-const resultOK = -1
-
 func OnShareIntent(nfiles int32, types []int32, mimes []string, items []string, names []string, sizes []int) {
 	// TODO(oxtoacart): actually implement this
 	// const (

libtailscale/interfaces.go

@@ -65,7 +65,7 @@ type IPNService interface {
 
 // VPNServiceBuilder corresponds to Android's VpnService.Builder.
 type VPNServiceBuilder interface {
-	SetMTU(int) error
+	SetMTU(int32) error
 	AddDNSServer(string) error
 	AddSearchDomain(string) error
 	AddRoute(string, int32) error
@@ -120,10 +120,6 @@ type InputStream interface {
 // The below are global callbacks that allow the Java application to notify Go
 // of various state changes.
 
-func OnVPNPrepared() {
-	notifyVPNPrepared()
-}
-
 func RequestVPN(service IPNService) {
 	onVPNRequested <- service
 }
@@ -131,21 +127,3 @@ func RequestVPN(service IPNService) {
 func ServiceDisconnect(service IPNService) {
 	onDisconnect <- service
 }
-
-func OnActivityResult(reqCode, resCode int, idToken string) {
-	switch reqCode {
-	case requestSignin:
-		if resCode != resultOK {
-			onGoogleToken <- ""
-			break
-		}
-		onGoogleToken <- idToken
-	case requestPrepareVPN:
-		if resCode == resultOK {
-			notifyVPNPrepared()
-		} else {
-			notifyVPNClosed()
-			notifyVPNRevoked()
-		}
-	}
-}