fix: download is not work under web/ wasm/ chromium env

lib/data/repositories/document_repository.dart

@@ -182,6 +182,7 @@ class DocumentStateNotifier extends StateNotifier<Document> {
       );
       if (result != null) return result;
     } catch (_) {
+      debugPrint('Warning: export in isolate failed');
       // Fall back to main-isolate export if isolate fails (e.g., engine limitations).
     }
 

lib/data/services/export_service.dart

@@ -6,6 +6,7 @@ import 'package:image/image.dart' as img;
 import 'package:pdf/widgets.dart' as pw;
 import 'package:pdf/pdf.dart' as pdf;
 import 'package:pdfrx_engine/pdfrx_engine.dart' as engine;
+import 'package:pdfrx/pdfrx.dart' show pdfrxFlutterInitialize;
 import '../../domain/models/model.dart';
 import '../../utils/rotation_utils.dart' as rot;
 import '../../utils/background_removal.dart' as br;
@@ -104,15 +105,14 @@ class ExportService {
     }
 
     // Initialize engine (safe to call multiple times)
-    try {
+    pdfrxFlutterInitialize();
-      await engine.pdfrxInitialize();
-    } catch (_) {}
 
     // Open source document from memory; if not supported, write temp file
     engine.PdfDocument? doc;
     try {
       doc = await engine.PdfDocument.openData(srcBytes);
     } catch (_) {
+      debugPrint('Warning: pdfrx openData failed');
       final tmp = File(
         '${Directory.systemTemp.path}/pdfrx_src_${DateTime.now().millisecondsSinceEpoch}.pdf',
       );
@@ -120,7 +120,9 @@ class ExportService {
       doc = await engine.PdfDocument.openFile(tmp.path);
       try {
         tmp.deleteSync();
-      } catch (_) {}
+      } catch (_) {
+        debugPrint('Warning: temp file delete failed');
+      }
     }
     // doc is guaranteed to be assigned by either openData or openFile above
 
@@ -221,6 +223,7 @@ class ExportService {
 
     final bytes = await out.save();
     doc.dispose();
+    debugPrint('exportSignedPdfFromBytes succeeded');
     return bytes;
   }
 
@@ -233,6 +236,7 @@ class ExportService {
       await file.writeAsBytes(bytes, flush: true);
       return true;
     } catch (_) {
+      debugPrint('Error: saveBytesToFile failed');
       return false;
     }
   }

lib/ui/features/pdf/widgets/pdf_screen.dart

@@ -221,6 +221,8 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
           if (out != null) {
             ok = await downloadBytes(out, filename: suggested);
             savedPath = suggested;
+          } else {
+            debugPrint('_saveSignedPdf: export to bytes failed');
           }
         }
         if (!kIsWeb) {
@@ -235,7 +237,6 @@ class _PdfSignatureHomePageState extends ConsumerState<PdfSignatureHomePage> {
               ),
             ),
           );
-          // ignore: avoid_print
           debugPrint('_saveSignedPdf: SnackBar shown ok=' + ok.toString());
         } else {
           messenger.showSnackBar(

lib/utils/download.dart

@@ -1,11 +1,17 @@
-import 'dart:typed_data';
+import 'package:flutter/foundation.dart';
 
-import 'download_stub.dart' if (dart.library.html) 'download_web.dart' as impl;
+// On modern Flutter Web (Wasm GC, e.g., Chromium), dart:html is not available.
+// Use js_interop capability to select the web implementation that relies on
+// package:web instead of dart:html.
+import 'download_stub.dart'
+    if (dart.library.js_interop) 'download_web.dart'
+    as impl;
 
 /// Initiates a platform-appropriate download/save operation.
 ///
 /// On Web: triggers a browser download with the provided filename.
 /// On non-Web: returns false (no-op). Use your existing IO save flow instead.
 Future<bool> downloadBytes(Uint8List bytes, {required String filename}) {
+  debugPrint('downloadBytes: initiating download');
   return impl.downloadBytes(bytes, filename: filename);
 }

lib/utils/download_stub.dart

@@ -1,6 +1,9 @@
 import 'dart:typed_data';
 
+import 'package:flutter/widgets.dart';
+
 Future<bool> downloadBytes(Uint8List bytes, {required String filename}) async {
   // Not supported on non-web. Return false so caller can fallback to file save.
+  debugPrint('downloadBytes: not supported on this platform');
   return false;
 }

lib/utils/download_web.dart

@@ -1,23 +1,28 @@
-// ignore_for_file: deprecated_member_use
+// Implementation for Web using package:web to support Wasm GC (Chromium)
-// ignore: avoid_web_libraries_in_flutter
+// without importing dart:html directly.
-import 'dart:html' as html;
+import 'dart:convert';
-import 'dart:typed_data';
+import 'package:flutter/foundation.dart';
+import 'package:web/web.dart' as web;
 
 Future<bool> downloadBytes(Uint8List bytes, {required String filename}) async {
   try {
-    final blob = html.Blob([bytes], 'application/pdf');
+    // Use a data URL to avoid Blob/typed array interop issues under Wasm GC.
-    final url = html.Url.createObjectUrlFromBlob(blob);
+    final url = 'data:application/pdf;base64,${base64Encode(bytes)}';
+
+    // Create an anchor element and trigger a click to download
     final anchor =
-        html.document.createElement('a') as html.AnchorElement
+        web.HTMLAnchorElement()
           ..href = url
           ..download = filename
           ..style.display = 'none';
-    html.document.body?.children.add(anchor);
+
+    web.document.body?.append(anchor);
     anchor.click();
     anchor.remove();
-    html.Url.revokeObjectUrl(url);
+
     return true;
-  } catch (_) {
+  } catch (e, st) {
+    debugPrint('Error: downloadBytes failed: $e\n$st');
     return false;
   }
 }

pubspec.yaml

@@ -62,6 +62,7 @@ dependencies:
   responsive_framework: ^1.5.1
   # disable_web_context_menu: ^1.1.0
   # ml_linalg: ^13.12.6
+  web: ^1.1.1
 
 dev_dependencies:
   flutter_test: