bug: fix pause and resume not working on web

Author: juliansteenbakker

lib/src/web/barcode_reader.dart

@@ -13,6 +13,17 @@ import 'package:web/web.dart';
 abstract class BarcodeReader {
   const BarcodeReader();
 
+  /// Whether the video feed is paused
+  bool? get paused =>
+      throw UnimplementedError('paused has not been implemented.');
+
+  /// Pause the barcode reader.
+  void pause() => throw UnimplementedError('pause() has not been implemented.');
+
+  /// Pause the barcode reader.
+  Future<void> resume() =>
+      throw UnimplementedError('resume() has not been implemented.');
+
   /// Whether the scanner is currently scanning for barcodes.
   bool get isScanning {
     throw UnimplementedError('isScanning has not been implemented.');
@@ -128,11 +139,6 @@ abstract class BarcodeReader {
     throw UnimplementedError('start() has not been implemented.');
   }
 
-  /// Pause the barcode reader.
-  Future<void> pause() {
-    throw UnimplementedError('pause() has not been implemented.');
-  }
-
   /// Stop the barcode reader and dispose of the video stream.
   Future<void> stop() {
     throw UnimplementedError('stop() has not been implemented.');

lib/src/web/mobile_scanner_web.dart

@@ -263,6 +263,16 @@ class MobileScannerWeb extends MobileScannerPlatform {
   @override
   Future<MobileScannerViewAttributes> start(StartOptions startOptions) async {
     if (_barcodeReader != null) {
+      if (_barcodeReader!.paused ?? false) {
+        await _barcodeReader?.resume();
+        return MobileScannerViewAttributes(
+          // The torch of a media stream is not available for video tracks.
+          // See https://developer.mozilla.org/en-US/docs/Web/API/MediaTrackConstraints#instance_properties_of_video_tracks
+          currentTorchMode: TorchState.unavailable,
+          size: _barcodeReader?.videoSize ?? Size.zero,
+        );
+      }
+
       throw const MobileScannerException(
         errorCode: MobileScannerErrorCode.controllerAlreadyInitialized,
         errorDetails: MobileScannerErrorDetails(
@@ -365,7 +375,7 @@ class MobileScannerWeb extends MobileScannerPlatform {
   @override
   Future<void> pause() async {
     _barcodesSubscription?.pause();
-    await _barcodeReader?.pause();
+    _barcodeReader?.pause();
   }
 
   @override

lib/src/web/zxing/zxing_barcode_reader.dart

@@ -169,8 +169,15 @@ final class ZXingBarcodeReader extends BarcodeReader {
   }
 
   @override
-  Future<void> pause() async {
-    _reader?.videoElement?.pause();
+  bool? get paused => _reader?.videoElement?.paused;
+
+  @override
+  void pause() => _reader?.videoElement?.pause();
+
+  @override
+  Future<void> resume() async {
+    final result = _reader?.videoElement?.play();
+    await result?.toDart;
   }
 
   @override