fix(share_plus): fallback for shareXFiles() to use download on web

packages/share_plus/share_plus/README.md

@@ -101,6 +101,12 @@ package.
 Share.shareXFiles([XFile('assets/hello.txt')], text: 'Great picture');
 ```
 
+File downloading fallback mechanism for web can be disabled by setting:
+
+```dart
+Share.downloadFallbackEnabled = false;
+```
+
 #### Share Data
 
 You can also share files that you dynamically generate from its data using [`XFile.fromData`](https://pub.dev/documentation/share_plus/latest/share_plus/XFile/XFile.fromData.html).

packages/share_plus/share_plus/example/lib/main.dart

@@ -19,6 +19,10 @@ import 'package:share_plus/share_plus.dart';
 import 'image_previews.dart';
 
 void main() {
+  // Set `downloadFallbackEnabled` to `false`
+  // to disable downloading files if `shareXFiles` fails on web.
+  Share.downloadFallbackEnabled = true;
+
   runApp(const DemoApp());
 }
 
@@ -241,39 +245,50 @@ class DemoAppState extends State<DemoApp> {
   void _onShareXFileFromAssets(BuildContext context) async {
     final box = context.findRenderObject() as RenderBox?;
     final scaffoldMessenger = ScaffoldMessenger.of(context);
-    final data = await rootBundle.load('assets/flutter_logo.png');
-    final buffer = data.buffer;
-    final shareResult = await Share.shareXFiles(
-      [
-        XFile.fromData(
-          buffer.asUint8List(data.offsetInBytes, data.lengthInBytes),
-          name: 'flutter_logo.png',
-          mimeType: 'image/png',
-        ),
-      ],
-      sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
-    );
-
-    scaffoldMessenger.showSnackBar(getResultSnackBar(shareResult));
+    try {
+      final data = await rootBundle.load('assets/flutter_logo.png');
+      final buffer = data.buffer;
+      final shareResult = await Share.shareXFiles(
+        [
+          XFile.fromData(
+            buffer.asUint8List(data.offsetInBytes, data.lengthInBytes),
+            name: 'flutter_logo.png',
+            mimeType: 'image/png',
+          ),
+        ],
+        sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+      );
+      scaffoldMessenger.showSnackBar(getResultSnackBar(shareResult));
+    } catch (e) {
+      scaffoldMessenger.showSnackBar(
+        SnackBar(content: Text('Error: $e')),
+      );
+    }
   }
 
   void _onShareTextAsXFile(BuildContext context) async {
     final box = context.findRenderObject() as RenderBox?;
     final scaffoldMessenger = ScaffoldMessenger.of(context);
-    final data = utf8.encode(text);
-    final shareResult = await Share.shareXFiles(
-      [
-        XFile.fromData(
-          data,
-          // name: fileName, // Notice, how setting the name here does not work.
-          mimeType: 'text/plain',
-        ),
-      ],
-      sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
-      fileNameOverrides: [fileName],
-    );
 
-    scaffoldMessenger.showSnackBar(getResultSnackBar(shareResult));
+    try {
+      final shareResult = await Share.shareXFiles(
+        [
+          XFile.fromData(
+            utf8.encode(text),
+            // name: fileName, // Notice, how setting the name here does not work.
+            mimeType: 'text/plain',
+          ),
+        ],
+        sharePositionOrigin: box!.localToGlobal(Offset.zero) & box.size,
+        fileNameOverrides: [fileName],
+      );
+
+      scaffoldMessenger.showSnackBar(getResultSnackBar(shareResult));
+    } catch (e) {
+      scaffoldMessenger.showSnackBar(
+        SnackBar(content: Text('Error: $e')),
+      );
+    }
   }
 
   SnackBar getResultSnackBar(ShareResult result) {

packages/share_plus/share_plus/lib/share_plus.dart

@@ -18,6 +18,9 @@ export 'src/share_plus_windows.dart'
 class Share {
   static SharePlatform get _platform => SharePlatform.instance;
 
+  /// Whether to fall back to downloading files if [shareXFiles] fails on web.
+  static bool downloadFallbackEnabled = true;
+
   /// Summons the platform's share sheet to share uri.
   ///
   /// Wraps the platform's native share dialog. Can share a URL.

packages/share_plus/share_plus/lib/src/share_plus_web.dart

@@ -6,6 +6,7 @@ import 'dart:ui';
 import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 import 'package:meta/meta.dart';
 import 'package:mime/mime.dart' show lookupMimeType;
+import 'package:share_plus/share_plus.dart';
 import 'package:share_plus_platform_interface/share_plus_platform_interface.dart';
 import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';
 import 'package:url_launcher_web/url_launcher_web.dart';
@@ -204,11 +205,19 @@ class SharePlusWebPlugin extends SharePlatform {
         error: e,
       );
 
-      throw Exception('Navigator.canShare() is unavailable');
+      return _downloadIfFallbackEnabled(
+        files,
+        fileNameOverrides,
+        'Navigator.canShare() is unavailable',
+      );
     }
 
     if (!canShare) {
-      throw Exception('Navigator.canShare() is false');
+      return _downloadIfFallbackEnabled(
+        files,
+        fileNameOverrides,
+        'Navigator.canShare() is false',
+      );
     }
 
     try {
@@ -217,16 +226,56 @@ class SharePlusWebPlugin extends SharePlatform {
       // actions is success, but can't get the action name
       return ShareResult.unavailable;
     } on DOMException catch (e) {
-      if (e.name case 'AbortError') {
+      final name = e.name;
+      final message = e.message;
+
+      if (name case 'AbortError') {
         return _resultDismissed;
       }
 
-      developer.log(
-        'Failed to share files',
-        error: '${e.name}: ${e.message}',
+      return _downloadIfFallbackEnabled(
+        files,
+        fileNameOverrides,
+        'Navigator.share() failed: $message',
       );
+    }
+  }
 
-      throw Exception('Navigator.share() failed: ${e.message}');
+  Future<ShareResult> _downloadIfFallbackEnabled(
+    List<XFile> files,
+    List<String>? fileNameOverrides,
+    String message,
+  ) {
+    developer.log(message);
+    if (Share.downloadFallbackEnabled) {
+      return _download(files, fileNameOverrides);
+    } else {
+      throw Exception(message);
+    }
+  }
+
+  Future<ShareResult> _download(
+    List<XFile> files,
+    List<String>? fileNameOverrides,
+  ) async {
+    developer.log('Download files as fallback');
+    try {
+      for (final (index, file) in files.indexed) {
+        final bytes = await file.readAsBytes();
+
+        final anchor = document.createElement('a') as HTMLAnchorElement
+          ..href = Uri.dataFromBytes(bytes).toString()
+          ..style.display = 'none'
+          ..download = fileNameOverrides?.elementAt(index) ?? file.name;
+        document.body!.children.add(anchor);
+        anchor.click();
+        anchor.remove();
+      }
+
+      return ShareResult.unavailable;
+    } catch (error) {
+      developer.log('Failed to download files', error: error);
+      throw Exception('Failed to to download files: $error');
     }
   }