From 7b1240382ce3b722fc5f0534771b3e9ef2ad6aa9 Mon Sep 17 00:00:00 2001
From: Niklas Schulze <me@jns.io>
Date: Tue, 17 Jan 2023 12:46:29 +0100
Subject: [PATCH] [windows] Fix crash when calling
 FlutterDesktopMessengerSetCallback after engine shutdown

---
 shell/platform/windows/flutter_windows.cc     | 10 ++++++----
 .../windows/flutter_windows_unittests.cc      | 20 +++++++++++++++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/shell/platform/windows/flutter_windows.cc b/shell/platform/windows/flutter_windows.cc
index 76aa1e6854fdb..71224efdfd11f 100644
--- a/shell/platform/windows/flutter_windows.cc
+++ b/shell/platform/windows/flutter_windows.cc
@@ -292,10 +292,12 @@ void FlutterDesktopMessengerSetCallback(FlutterDesktopMessengerRef messenger,
                                         const char* channel,
                                         FlutterDesktopMessageCallback callback,
                                         void* user_data) {
-  flutter::FlutterDesktopMessenger::FromRef(messenger)
-      ->GetEngine()
-      ->message_dispatcher()
-      ->SetMessageCallback(channel, callback, user_data);
+  auto engine =
+      flutter::FlutterDesktopMessenger::FromRef(messenger)->GetEngine();
+  if (engine) {
+    engine->message_dispatcher()->SetMessageCallback(channel, callback,
+                                                     user_data);
+  }
 }
 
 FlutterDesktopMessengerRef FlutterDesktopMessengerAddRef(
diff --git a/shell/platform/windows/flutter_windows_unittests.cc b/shell/platform/windows/flutter_windows_unittests.cc
index 23f2abb89643f..91e9c9cb8ef4b 100644
--- a/shell/platform/windows/flutter_windows_unittests.cc
+++ b/shell/platform/windows/flutter_windows_unittests.cc
@@ -279,5 +279,25 @@ TEST_F(WindowsTest, GetGraphicsAdapter) {
   ASSERT_TRUE(SUCCEEDED(dxgi_adapter->GetDesc(&desc)));
 }
 
+// Verify that calling FlutterDesktopMessengerSetCallback
+// after shutting the engine down is safe.
+// Prevent regression: https://github.com/flutter/flutter/issues/118611
+TEST_F(WindowsTest, SetMessengerCallbackAfterEngineShutdown) {
+  auto& context = GetContext();
+  WindowsConfigBuilder builder(context);
+  EnginePtr engine{builder.InitializeEngine()};
+  ASSERT_NE(engine, nullptr);
+
+  auto messenger = FlutterDesktopEngineGetMessenger(engine.get());
+  FlutterDesktopMessengerAddRef(messenger);
+  ASSERT_TRUE(FlutterDesktopMessengerIsAvailable(messenger));
+
+  engine.reset();
+
+  ASSERT_FALSE(FlutterDesktopMessengerIsAvailable(messenger));
+  FlutterDesktopMessengerSetCallback(messenger, "my_channel", nullptr, nullptr);
+  FlutterDesktopMessengerRelease(messenger);
+}
+
 }  // namespace testing
 }  // namespace flutter