[webview_flutter_wkwebview] Fixes crash when sending undefined message via javascript channel

packages/webview_flutter/webview_flutter_wkwebview/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.18.5
+
+* Fixes crash when sending undefined message via JavaScript channel.
+
 ## 3.18.4
 
 * Fixes crash when native `WKFrameInfo.request` is nil.

packages/webview_flutter/webview_flutter_wkwebview/example/integration_test/webview_flutter_test.dart

@@ -278,6 +278,50 @@ Future<void> main() async {
     await expectLater(channelCompleter.future, completion('hello'));
   });
 
+  testWidgets('JavaScriptChannel can receive undefined and null',
+      (WidgetTester tester) async {
+    final Completer<void> pageFinished = Completer<void>();
+    final PlatformWebViewController controller = PlatformWebViewController(
+      const PlatformWebViewControllerCreationParams(),
+    );
+    unawaited(controller.setJavaScriptMode(JavaScriptMode.unrestricted));
+    final PlatformNavigationDelegate delegate = PlatformNavigationDelegate(
+      const PlatformNavigationDelegateCreationParams(),
+    );
+    unawaited(delegate.setOnPageFinished((_) => pageFinished.complete()));
+    unawaited(controller.setPlatformNavigationDelegate(delegate));
+
+    final List<String> messages = <String>[];
+    await controller.addJavaScriptChannel(
+      JavaScriptChannelParams(
+        name: 'Channel',
+        onMessageReceived: (JavaScriptMessage message) {
+          messages.add(message.message);
+        },
+      ),
+    );
+
+    await controller.loadHtmlString(
+      'data:text/html;charset=utf-8;base64,PCFET0NUWVBFIGh0bWw+',
+    );
+
+    await tester.pumpWidget(Builder(
+      builder: (BuildContext context) {
+        return PlatformWebViewWidget(
+          PlatformWebViewWidgetCreationParams(controller: controller),
+        ).build(context);
+      },
+    ));
+
+    await pageFinished.future;
+
+    await controller.runJavaScript('Channel.postMessage(undefined);');
+    await controller.runJavaScript('Channel.postMessage(null);');
+
+    await tester.pumpAndSettle();
+    expect(messages, <String>['undefined', 'null']);
+  });
+
   testWidgets('resize webview', (WidgetTester tester) async {
     final Completer<void> buttonTapResizeCompleter = Completer<void>();
     final Completer<void> onPageFinished = Completer<void>();

packages/webview_flutter/webview_flutter_wkwebview/lib/src/common/weak_reference_utils.dart

@@ -18,7 +18,7 @@
 ///       ) {
 ///         weakReference.target?.onJavascriptChannelMessage(
 ///           message.name,
-///           message.body!.toString(),
+///           message.body?.toString() ?? '',
 ///         );
 ///       };
 ///     },

packages/webview_flutter/webview_flutter_wkwebview/lib/src/webkit_webview_controller.dart

@@ -443,6 +443,7 @@ class WebKitWebViewController extends PlatformWebViewController {
         webKitParams.name,
       ),
     ]);
+    await _injectPostMessageOverride(webKitParams.name);
   }
 
   @override
@@ -768,6 +769,47 @@ window.addEventListener("error", function(e) {
     await controller.addUserScript(overrideScript);
   }
 
+  Future<void> _injectPostMessageOverride(String channelName) async {
+    final WKUserScript overrideScript =
+        _webKitParams.webKitProxy.newWKUserScript(
+      source: '''
+var _flutter_webview_plugin_overrides = _flutter_webview_plugin_overrides || {};
+
+_flutter_webview_plugin_overrides.originalPostMessageFunctions = _flutter_webview_plugin_overrides.originalPostMessageFunctions || {};
+
+(function() {
+  if (window.webkit && window.webkit.messageHandlers) {
+    const handlerName = "$channelName";
+    const handler = window.webkit.messageHandlers[handlerName];
+
+    if (handler && 
+        typeof handler.postMessage === 'function' &&
+        !_flutter_webview_plugin_overrides.originalPostMessageFunctions[handlerName]) {
+
+      _flutter_webview_plugin_overrides.originalPostMessageFunctions[handlerName] = handler.postMessage;
+
+      handler.postMessage = function(data) {
+        if (data === undefined) {
+          return _flutter_webview_plugin_overrides.originalPostMessageFunctions[handlerName].call(this, "undefined");
+        }
+        if (data === null) {
+          return _flutter_webview_plugin_overrides.originalPostMessageFunctions[handlerName].call(this, "null");
+        }
+        return _flutter_webview_plugin_overrides.originalPostMessageFunctions[handlerName].call(this, data);
+      };
+    }
+  }
+})();
+      ''',
+      injectionTime: UserScriptInjectionTime.atDocumentStart,
+      isForMainFrameOnly: false,
+    );
+
+    final WKUserContentController controller =
+        await _webView.configuration.getUserContentController();
+    await controller.addUserScript(overrideScript);
+  }
+
   // WKWebView does not support removing a single user script, so all user
   // scripts and all message handlers are removed instead. And the JavaScript
   // channels that shouldn't be removed are re-registered. Note that this
@@ -906,7 +948,7 @@ class WebKitJavaScriptChannelParams extends JavaScriptChannelParams {
               return (_, __, WKScriptMessage message) {
                 if (weakReference.target != null) {
                   weakReference.target!(
-                    JavaScriptMessage(message: message.body!.toString()),
+                    JavaScriptMessage(message: message.body?.toString() ?? ''),
                   );
                 }
               };

packages/webview_flutter/webview_flutter_wkwebview/pubspec.yaml

@@ -2,7 +2,7 @@ name: webview_flutter_wkwebview
 description: A Flutter plugin that provides a WebView widget based on Apple's WKWebView control.
 repository: https://github.com/flutter/packages/tree/main/packages/webview_flutter/webview_flutter_wkwebview
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+webview%22
-version: 3.18.4
+version: 3.18.5
 
 environment:
   sdk: ^3.5.0

packages/webview_flutter/webview_flutter_wkwebview/test/webkit_webview_controller_test.dart

@@ -863,7 +863,7 @@ void main() {
       final WKUserScript userScript =
           verify(mockUserContentController.addUserScript(captureAny))
               .captured
-              .single as WKUserScript;
+              .first as WKUserScript;
       expect(userScript.source, 'window.name = webkit.messageHandlers.name;');
       expect(
         userScript.injectionTime,
@@ -1008,7 +1008,7 @@ void main() {
       final WKUserScript userScript =
           verify(mockUserContentController.addUserScript(captureAny))
               .captured
-              .single as WKUserScript;
+              .first as WKUserScript;
       expect(userScript.source, 'window.name2 = webkit.messageHandlers.name2;');
       expect(
         userScript.injectionTime,