put back web only workaround for now

lib/mobile_scanner.dart

@@ -11,7 +11,8 @@ export 'src/enums/phone_type.dart';
 export 'src/enums/torch_state.dart';
 export 'src/mobile_scanner.dart';
 export 'src/mobile_scanner_controller.dart';
-export 'src/mobile_scanner_exception.dart';
+export 'src/mobile_scanner_exception.dart'
+    hide PermissionRequestPendingException;
 export 'src/mobile_scanner_platform_interface.dart';
 export 'src/objects/address.dart';
 export 'src/objects/barcode.dart';

lib/src/mobile_scanner_controller.dart

@@ -242,6 +242,13 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
       );
     }
 
+    // Permission was denied, do nothing.
+    // When the controller is stopped,
+    // the error is reset so the permission can be requested again if possible.
+    if (value.error?.errorCode == MobileScannerErrorCode.permissionDenied) {
+      return;
+    }
+
     // Do nothing if the camera is already running.
     if (value.isRunning) {
       return;
@@ -280,9 +287,6 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
         );
       }
     } on MobileScannerException catch (error) {
-      // TODO: if the error code is `controllerAlreadyInitialized` ignore the error
-      // TODO: update the error reporting from the native side to report proper error codes.
-
       // The initialization finished with an error.
       // To avoid stale values, reset the output size,
       // torch state and zoom scale to the defaults.
@@ -297,6 +301,8 @@ class MobileScannerController extends ValueNotifier<MobileScannerState> {
           zoomScale: 1.0,
         );
       }
+    } on PermissionRequestPendingException catch (_) {
+      // If a permission request was already pending, do nothing.
     }
   }
 

lib/src/mobile_scanner_exception.dart

@@ -39,3 +39,10 @@ class MobileScannerErrorDetails {
   /// The error message from the [PlatformException].
   final String? message;
 }
+
+/// This class represents an exception that is thrown
+/// when the scanner was (re)started while a permission request was pending.
+///
+/// This exception type is only used internally,
+/// and is not part of the public API.
+class PermissionRequestPendingException implements Exception {}

lib/src/web/mobile_scanner_web.dart

@@ -38,6 +38,12 @@ class MobileScannerWeb extends MobileScannerPlatform {
   /// The container div element for the camera view.
   late HTMLDivElement _divElement;
 
+  /// The flag that keeps track of whether a permission request is in progress.
+  ///
+  /// On the web, a permission request triggers a dialog, that in turn triggers a lifecycle change.
+  /// While the permission request is in progress, any attempts at (re)starting the camera should be ignored.
+  bool _permissionRequestInProgress = false;
+
   /// The stream controller for the media track settings stream.
   ///
   /// Currently, only the facing mode setting can be supported,
@@ -180,12 +186,17 @@ class MobileScannerWeb extends MobileScannerPlatform {
     }
 
     try {
+      _permissionRequestInProgress = true;
+
       // Retrieving the media devices requests the camera permission.
       final MediaStream videoStream =
           await window.navigator.mediaDevices.getUserMedia(constraints).toDart;
 
+      _permissionRequestInProgress = false;
+
       return videoStream;
     } on DOMException catch (error, stackTrace) {
+      _permissionRequestInProgress = false;
       final String errorMessage = error.toString();
 
       MobileScannerErrorCode errorCode = MobileScannerErrorCode.genericError;
@@ -245,15 +256,11 @@ class MobileScannerWeb extends MobileScannerPlatform {
 
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
-    // TODO: ignore double starts in the controller.
-    if (_barcodeReader != null) {
-      throw const MobileScannerException(
-        errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
-        errorDetails: MobileScannerErrorDetails(
-          message:
-              'The scanner was already started. Call stop() before calling start() again.',
-        ),
-      );
+    // If the permission request has not yet completed,
+    // the camera view is not ready yet.
+    // Prevent the permission popup from triggering a restart of the scanner.
+    if (_permissionRequestInProgress) {
+      throw PermissionRequestPendingException();
     }
 
     _barcodeReader = ZXingBarcodeReader();
@@ -263,7 +270,6 @@ class MobileScannerWeb extends MobileScannerPlatform {
     );
 
     if (_barcodeReader?.isScanning ?? false) {
-      // TODO: ignore double starts in the controller.
       throw const MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
         errorDetails: MobileScannerErrorDetails(