Web: show WASM/SharedArrayBuffer status on debug console

.vscode/settings.json

@@ -26,6 +26,7 @@
     "COLORSPACE",
     "COLORTYPE",
     "COMBOBOX",
+    "credentialless",
     "Cupertino",
     "dartify",
     "Dests",

lib/src/web/pdf.js.dart

@@ -4,8 +4,10 @@
 library;
 
 import 'dart:js_interop';
+import 'dart:js_interop_unsafe';
 import 'dart:typed_data';
 
+import 'package:flutter/material.dart';
 import 'package:synchronized/extension.dart';
 import 'package:web/web.dart' as web;
 
@@ -286,6 +288,21 @@ final _dummyJsSyncContext = {};
 
 bool _pdfjsInitialized = false;
 
+/// Whether SharedArrayBuffer is supported.
+///
+/// It actually means whether Flutter Web can take advantage of multiple threads or not.
+///
+/// See [Support for WebAssembly (Wasm) - Serve the built output with an HTTP server](https://docs.flutter.dev/platform-integration/web/wasm#serve-the-built-output-with-an-http-server)
+bool _determineWhetherSharedArrayBufferSupportedOrNot() {
+  try {
+    return web.window.hasProperty('SharedArrayBuffer'.toJS).toDart;
+  } catch (e) {
+    return false;
+  }
+}
+
+final bool _isSharedArrayBufferSupported = _determineWhetherSharedArrayBufferSupportedOrNot();
+
 Future<void> ensurePdfjsInitialized() async {
   if (_pdfjsInitialized) return;
   await _dummyJsSyncContext.synchronized(() async {
@@ -295,6 +312,20 @@ Future<void> ensurePdfjsInitialized() async {
       return;
     }
 
+    const isRunningWithWasm = bool.fromEnvironment('dart.tool.dart2wasm');
+    debugPrint(
+      'pdfrx Web status:\n'
+      '- Running WASM:      $isRunningWithWasm\n'
+      '- SharedArrayBuffer: $_isSharedArrayBufferSupported',
+    );
+    if (isRunningWithWasm && !_isSharedArrayBufferSupported) {
+      debugPrint(
+        'WARNING: SharedArrayBuffer is not enabled and WASM is running in single thread mode. Enable SharedArrayBuffer by setting the following HTTP header on your server:\n'
+        '  Cross-Origin-Embedder-Policy: require-corp|credentialless\n'
+        '  Cross-Origin-Opener-Policy: same-origin\n',
+      );
+    }
+
     final pdfJsSrc = PdfJsConfiguration.configuration?.pdfJsSrc ?? _pdfjsUrl;
     try {
       final script =