android: check if other VPN is active (#475)

Detect when another VPN is active and launch dialog giving user the option to navigate to settings to disable.
Update state string and toggle to require successful VPN preparation

To do in a follow-up: monitor VPN connection, and if Tailscale VPN disconnects due to another VPN connecting, update toggle and text
Updates tailscale/tailscale#12850

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

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

@@ -5,12 +5,15 @@ package com.tailscale.ipn
 
 import android.annotation.SuppressLint
 import android.app.Activity
+import android.app.AlertDialog
 import android.content.Context
 import android.content.Intent
 import android.content.RestrictionsManager
 import android.content.pm.ActivityInfo
 import android.content.res.Configuration.SCREENLAYOUT_SIZE_LARGE
 import android.content.res.Configuration.SCREENLAYOUT_SIZE_MASK
+import android.net.ConnectivityManager
+import android.net.NetworkCapabilities
 import android.os.Bundle
 import android.provider.Settings
 import android.util.Log
@@ -129,8 +132,13 @@ class MainActivity : ComponentActivity() {
             vpnViewModel.setVpnPrepared(true)
             App.get().startVPN()
           } else {
-            Log.d("VpnPermission", "VPN permission denied")
+            if (isAnotherVpnActive(this)) {
-            vpnViewModel.setVpnPrepared(false)
+              Log.d("VpnPermission", "Another VPN is likely active")
+              showOtherVPNConflictDialog()
+            } else {
+              Log.d("VpnPermission", "Permission was denied by the user")
+              viewModel.setVpnPrepared(false)
+            }
           }
         }
     viewModel.setVpnPermissionLauncher(vpnPermissionLauncher)
@@ -285,6 +293,34 @@ class MainActivity : ComponentActivity() {
     lifecycleScope.launch { Notifier.loginFinished.collect { _ -> loginQRCode.set(null) } }
   }
 
+  private fun showOtherVPNConflictDialog() {
+    AlertDialog.Builder(this)
+        .setTitle(R.string.vpn_permission_denied)
+        .setMessage(R.string.multiple_vpn_explainer)
+        .setPositiveButton(R.string.go_to_settings) { _, _ ->
+          // Intent to open the VPN settings
+          val intent = Intent(Settings.ACTION_VPN_SETTINGS)
+          startActivity(intent)
+        }
+        .setNegativeButton(R.string.cancel, null)
+        .show()
+  }
+
+  fun isAnotherVpnActive(context: Context): Boolean {
+    val connectivityManager =
+        context.getSystemService(Context.CONNECTIVITY_SERVICE) as ConnectivityManager
+
+    val activeNetwork = connectivityManager.activeNetwork
+    if (activeNetwork != null) {
+      val networkCapabilities = connectivityManager.getNetworkCapabilities(activeNetwork)
+      if (networkCapabilities != null &&
+          networkCapabilities.hasTransport(NetworkCapabilities.TRANSPORT_VPN)) {
+        return true
+      }
+    }
+    return false
+  }
+
   // Returns true if we should render a QR code instead of launching a browser
   // for login requests
   private fun useQRCodeLogin(): Boolean {

android/src/main/java/com/tailscale/ipn/ui/viewModel/MainViewModel.kt

@@ -100,8 +100,10 @@ class MainViewModel(private val vpnViewModel: VpnViewModel) : IpnViewModel() {
 
             val isOn =
                 when {
-                  currentState == State.Running || currentState == State.Starting -> true
+                  prepared && currentState == State.Running || currentState == State.Starting ->
-                  previousState == State.NoState && currentState == State.Starting -> true
+                      true
+                  previousState == State.NoState && currentState == State.Starting ->
+                      true
                   else -> false
                 }
 
@@ -182,7 +184,7 @@ private fun userStringRes(currentState: State?, previousState: State?, vpnPrepar
     currentState == State.NeedsMachineAuth -> R.string.needs_machine_auth
     currentState == State.Stopped -> R.string.stopped
     currentState == State.Starting -> R.string.starting
-    currentState == State.Running -> R.string.connected
+    currentState == State.Running -> if (vpnPrepared) R.string.connected else R.string.placeholder
     else -> R.string.placeholder
   }
 }

android/src/main/res/values/strings.xml

@@ -292,4 +292,11 @@
     <string name="health_warnings">Health warnings</string>
     <string name="no_issues_found">No issues found</string>
     <string name="tailscale_is_operating_normally">Tailscale is operating normally.</string>
+
+    <!-- Strings for the multiple VPNs dialog -->
+    <string name="vpn_permission_denied">VPN permission denied</string>
+    <string name="multiple_vpn_explainer">Only one VPN can be active, and it appears another is already running. Before starting Tailscale, disable the other VPN.</string>
+    <string name="go_to_settings">Go to Settings</string>
+    <string name="cancel">Cancel</string>
+
 </resources>