From 4316a6b2eda33e2f5140bbcf7d811cf225d2eed1 Mon Sep 17 00:00:00 2001
From: David Iglesias <ditman@gmail.com>
Date: Tue, 25 May 2021 18:09:01 -0700
Subject: [PATCH] [web] Ensure handleNavigationMessage can receive null
 arguments. (flutter/engine#26406)

---
 .../lib/web_ui/lib/src/engine/window.dart     |  9 ++++---
 .../flutter/lib/web_ui/test/window_test.dart  | 27 ++++++++++++++++++-
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/engine/src/flutter/lib/web_ui/lib/src/engine/window.dart b/engine/src/flutter/lib/web_ui/lib/src/engine/window.dart
index 3d2c1d213a3..5f355a68ca4 100644
--- a/engine/src/flutter/lib/web_ui/lib/src/engine/window.dart
+++ b/engine/src/flutter/lib/web_ui/lib/src/engine/window.dart
@@ -113,7 +113,7 @@ class EngineFlutterWindow extends ui.SingletonFlutterWindow {
 
   Future<bool> handleNavigationMessage(ByteData? data) async {
     final MethodCall decoded = JSONMethodCodec().decodeMethodCall(data);
-    final Map<String, dynamic> arguments = decoded.arguments;
+    final Map<String, dynamic>? arguments = decoded.arguments;
     switch (decoded.method) {
       case 'selectMultiEntryHistory':
         await _useMultiEntryBrowserHistory();
@@ -121,13 +121,16 @@ class EngineFlutterWindow extends ui.SingletonFlutterWindow {
       case 'selectSingleEntryHistory':
         await _useSingleEntryBrowserHistory();
         return true;
+      // the following cases assert that arguments are not null
       case 'routeUpdated': // deprecated
+        assert(arguments != null);
         await _useSingleEntryBrowserHistory();
-        browserHistory.setRouteName(arguments['routeName']);
+        browserHistory.setRouteName(arguments!['routeName']);
         return true;
       case 'routeInformationUpdated':
+        assert(arguments != null);
         browserHistory.setRouteName(
-          arguments['location'],
+          arguments!['location'],
           state: arguments['state'],
         );
         return true;
diff --git a/engine/src/flutter/lib/web_ui/test/window_test.dart b/engine/src/flutter/lib/web_ui/test/window_test.dart
index 9dea67f8f60..bb823cf7335 100644
--- a/engine/src/flutter/lib/web_ui/test/window_test.dart
+++ b/engine/src/flutter/lib/web_ui/test/window_test.dart
@@ -82,7 +82,7 @@ void testMain() {
     ), useSingle: false);
     expect(window.browserHistory, isA<MultiEntriesBrowserHistory>());
 
-    Future<void> check<T>(String method, Map<String, Object?> arguments) async {
+    Future<void> check<T>(String method, Object? arguments) async {
       callback = Completer<void>();
       window.sendPlatformMessage(
         'flutter/navigation',
@@ -93,6 +93,10 @@ void testMain() {
       expect(window.browserHistory, isA<T>());
     }
 
+    // These may be initialized as `null`
+    // See https://github.com/flutter/flutter/issues/83158#issuecomment-847483010
+    await check<SingleEntryBrowserHistory>('selectSingleEntryHistory', null); // -> single
+    await check<MultiEntriesBrowserHistory>('selectMultiEntryHistory', null); // -> multi
     await check<SingleEntryBrowserHistory>('selectSingleEntryHistory', <String, dynamic>{}); // -> single
     await check<MultiEntriesBrowserHistory>('selectMultiEntryHistory', <String, dynamic>{}); // -> multi
     await check<SingleEntryBrowserHistory>('routeUpdated', <String, dynamic>{'routeName': '/bar'}); // -> single
@@ -101,6 +105,27 @@ void testMain() {
     await check<MultiEntriesBrowserHistory>('routeInformationUpdated', <String, dynamic>{'location': '/bar'}); // does not change mode
   });
 
+  test('handleNavigationMessage throws for route update methods called with null arguments',
+      () async {
+    expect(() async {
+      await window.handleNavigationMessage(
+        JSONMethodCodec().encodeMethodCall(MethodCall(
+          'routeUpdated',
+          null, // boom
+        ))
+      );
+    }, throwsAssertionError);
+
+    expect(() async {
+      await window.handleNavigationMessage(
+        JSONMethodCodec().encodeMethodCall(MethodCall(
+          'routeInformationUpdated',
+          null, // boom
+        ))
+      );
+    }, throwsAssertionError);
+  });
+
   test('should not throw when using nav1 and nav2 together',
       () async {
     await window.debugInitializeHistory(TestUrlStrategy.fromEntry(