android: skip SAF directory picker if unsupported

updates tailscale/corp#30254

This adds an upfront isAndroidTV check before we set the
SAF directory picker activity.  We'll check both that we can
actually launch the activity and that this isn't and AndroidTV
device where the directory picker activity isn't supported or
has a tendency to throw ActivityNotFound exceptions.

Author: barnstar

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

@@ -53,7 +53,7 @@ import com.tailscale.ipn.mdm.ShowHide
 import com.tailscale.ipn.ui.model.Ipn
 import com.tailscale.ipn.ui.notifier.Notifier
 import com.tailscale.ipn.ui.theme.AppTheme
-import com.tailscale.ipn.ui.util.AndroidTVUtil
+import com.tailscale.ipn.ui.util.AndroidTVUtil.isAndroidTV
 import com.tailscale.ipn.ui.util.set
 import com.tailscale.ipn.ui.util.universalFit
 import com.tailscale.ipn.ui.view.AboutView
@@ -177,49 +177,53 @@ class MainActivity : ComponentActivity() {
         }
     viewModel.setVpnPermissionLauncher(vpnPermissionLauncher)
 
-    val directoryPickerLauncher =
-        registerForActivityResult(ActivityResultContracts.OpenDocumentTree()) { uri: Uri? ->
-          if (uri != null) {
-            try {
-              // Try to take persistable permissions for both read and write.
-              contentResolver.takePersistableUriPermission(
-                  uri,
-                  Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
-            } catch (e: SecurityException) {
-              TSLog.e("MainActivity", "Failed to persist permissions: $e")
-            }
+    var directoryPickerLauncher: ActivityResultLauncher<Uri?>? = null
+    if (canOpenDocumentTree()) {
+      directoryPickerLauncher =
+          registerForActivityResult(ActivityResultContracts.OpenDocumentTree()) { uri: Uri? ->
+            if (uri != null) {
+              try {
+                // Try to take persistable permissions for both read and write.
+                contentResolver.takePersistableUriPermission(
+                    uri,
+                    Intent.FLAG_GRANT_READ_URI_PERMISSION or Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+              } catch (e: SecurityException) {
+                TSLog.e("MainActivity", "Failed to persist permissions: $e")
+              }
 
-            // Check if write permission is actually granted.
-            val writePermission =
-                this.checkUriPermission(
-                    uri, Process.myPid(), Process.myUid(), Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
-            if (writePermission == PackageManager.PERMISSION_GRANTED) {
-              TSLog.d("MainActivity", "Write permission granted for $uri")
-
-              lifecycleScope.launch(Dispatchers.IO) {
-                try {
-                  Libtailscale.setDirectFileRoot(uri.toString())
-                  TaildropDirectoryStore.saveFileDirectory(uri)
-                  permissionsViewModel.refreshCurrentDir()
-                } catch (e: Exception) {
-                  TSLog.e("MainActivity", "Failed to set Taildrop root: $e")
+              // Check if write permission is actually granted.
+              val writePermission =
+                  this.checkUriPermission(
+                      uri, Process.myPid(), Process.myUid(), Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
+              if (writePermission == PackageManager.PERMISSION_GRANTED) {
+                TSLog.d("MainActivity", "Write permission granted for $uri")
+
+                lifecycleScope.launch(Dispatchers.IO) {
+                  try {
+                    Libtailscale.setDirectFileRoot(uri.toString())
+                    TaildropDirectoryStore.saveFileDirectory(uri)
+                    permissionsViewModel.refreshCurrentDir()
+                  } catch (e: Exception) {
+                    TSLog.e("MainActivity", "Failed to set Taildrop root: $e")
+                  }
                 }
+              } else {
+                TSLog.d(
+                    "MainActivity",
+                    "Write access not granted for $uri. Falling back to internal storage.")
+                // Don't save directory URI and fall back to internal storage.
               }
             } else {
               TSLog.d(
                   "MainActivity",
-                  "Write access not granted for $uri. Falling back to internal storage.")
-              // Don't save directory URI and fall back to internal storage.
-            }
-          } else {
-            TSLog.d(
-                "MainActivity", "Taildrop directory not saved. Will fall back to internal storage.")
+                  "Taildrop directory not saved. Will fall back to internal storage.")
 
-            // Fall back to internal storage.
+              // Fall back to internal storage.
+            }
           }
-        }
 
-    viewModel.setDirectoryPickerLauncher(directoryPickerLauncher)
+      viewModel.setDirectoryPickerLauncher(directoryPickerLauncher)
+    }
 
     setContent {
       navController = rememberNavController()
@@ -354,9 +358,11 @@ class MainActivity : ComponentActivity() {
                         { navController.navigate("taildropDir") },
                         { navController.navigate("notifications") })
                   }
-                  composable("taildropDir") {
-                    TaildropDirView(
-                        backTo("permissions"), directoryPickerLauncher, permissionsViewModel)
+                  directoryPickerLauncher?.let {
+                    val launcher = it
+                    composable("taildropDir") {
+                      TaildropDirView(backTo("permissions"), launcher, permissionsViewModel)
+                    }
                   }
                   composable("notifications") {
                     NotificationsView(backTo("permissions"), ::openApplicationSettings)
@@ -406,6 +412,16 @@ class MainActivity : ComponentActivity() {
     lifecycleScope.launch { Notifier.loginFinished.collect { _ -> loginQRCode.set(null) } }
   }
 
+  // Most AndroidTV's don't support this and the UX is completely broken regardless.   We have
+  // reports of some old devices throwing ActivityNotFound exceptions on TV as well, so we
+  // carefully guard against the attempt.
+  private fun Context.canOpenDocumentTree(): Boolean {
+    return !isAndroidTV() &&
+        Intent(Intent.ACTION_OPEN_DOCUMENT_TREE)
+            .addCategory(Intent.CATEGORY_DEFAULT)
+            .resolveActivity(packageManager) != null
+  }
+
   private fun showOtherVPNConflictDialog() {
     AlertDialog.Builder(this)
         .setTitle(R.string.vpn_permission_denied)
@@ -437,7 +453,7 @@ class MainActivity : ComponentActivity() {
   // Returns true if we should render a QR code instead of launching a browser
   // for login requests
   private fun useQRCodeLogin(): Boolean {
-    return AndroidTVUtil.isAndroidTV()
+    return isAndroidTV()
   }
 
   override fun onNewIntent(intent: Intent) {

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

@@ -221,8 +221,10 @@ class MainViewModel(private val vpnViewModel: VpnViewModel) : IpnViewModel() {
   }
 
   fun showDirectoryPickerLauncher() {
-    _showDirectoryPickerInterstitial.set(false)
-    directoryPickerLauncher?.launch(null)
+    directoryPickerLauncher?.let {
+      _showDirectoryPickerInterstitial.set(false)
+      it.launch(null)
+    }
   }
 
   fun checkIfTaildropDirectorySelected() {
@@ -233,17 +235,23 @@ class MainViewModel(private val vpnViewModel: VpnViewModel) : IpnViewModel() {
     val app = App.get()
     val storedUri = app.getStoredDirectoryUri()
     if (storedUri == null) {
-      // No stored URI, so launch the directory picker.
-      _showDirectoryPickerInterstitial.set(true)
+      if (directoryPickerLauncher != null) {
+        // No stored URI, so launch the directory picker.
+        _showDirectoryPickerInterstitial.set(true)
+      }
       return
     }
 
     val documentFile = DocumentFile.fromTreeUri(app, storedUri)
     if (documentFile == null || !documentFile.exists() || !documentFile.canWrite()) {
-      TSLog.d(
-          "MainViewModel",
-          "Stored directory URI is invalid or inaccessible; launching directory picker.")
-      _showDirectoryPickerInterstitial.set(true)
+      if (directoryPickerLauncher != null) {
+        TSLog.d(
+            "MainViewModel",
+            "Stored directory URI is invalid or inaccessible; launching directory picker.")
+        _showDirectoryPickerInterstitial.set(true)
+      } else {
+        TSLog.d("MainViewModel", "Directory picker activity not available")
+      }
     } else {
       TSLog.d("MainViewModel", "Using stored directory URI: $storedUri")
     }