Revert "[windows] Expose the binary messenger from FlutterEngine (#20399)" (#20550)

This reverts commit 7fa21a45.

ci/licenses_golden/licenses_flutter

@@ -836,9 +836,7 @@ FILE: ../../../flutter/shell/platform/android/surface/android_surface_mock.h
 FILE: ../../../flutter/shell/platform/android/vsync_waiter_android.cc
 FILE: ../../../flutter/shell/platform/android/vsync_waiter_android.h
 FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/basic_message_channel_unittests.cc
-FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/binary_messenger_impl.h
 FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/byte_buffer_streams.h
-FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/core_implementations.cc
 FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/encodable_value_unittests.cc
 FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/engine_method_result.cc
 FILE: ../../../flutter/shell/platform/common/cpp/client_wrapper/event_channel_unittests.cc

shell/platform/common/cpp/client_wrapper/BUILD.gn

@@ -8,8 +8,7 @@ import("core_wrapper_files.gni")
 # Client library build for internal use by the shell implementation.
 source_set("client_wrapper") {
   sources = core_cpp_client_wrapper_sources
-  public = core_cpp_client_wrapper_includes +
-           core_cpp_client_wrapper_internal_headers
+  public = core_cpp_client_wrapper_includes
 
   deps = [ "//flutter/shell/platform/common/cpp:common_cpp_library_headers" ]
 

shell/platform/common/cpp/client_wrapper/binary_messenger_impl.h

-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef FLUTTER_SHELL_PLATFORM_COMMON_CPP_CLIENT_WRAPPER_BINARY_MESSENGER_IMPL_H_
-#define FLUTTER_SHELL_PLATFORM_COMMON_CPP_CLIENT_WRAPPER_BINARY_MESSENGER_IMPL_H_
-
-#include <flutter_messenger.h>
-
-#include <map>
-#include <string>
-
-#include "include/flutter/binary_messenger.h"
-
-namespace flutter {
-
-// Wrapper around a FlutterDesktopMessengerRef that implements the
-// BinaryMessenger API.
-class BinaryMessengerImpl : public BinaryMessenger {
- public:
-  explicit BinaryMessengerImpl(FlutterDesktopMessengerRef core_messenger);
-
-  virtual ~BinaryMessengerImpl();
-
-  // Prevent copying.
-  BinaryMessengerImpl(BinaryMessengerImpl const&) = delete;
-  BinaryMessengerImpl& operator=(BinaryMessengerImpl const&) = delete;
-
-  // |flutter::BinaryMessenger|
-  void Send(const std::string& channel,
-            const uint8_t* message,
-            size_t message_size,
-            BinaryReply reply) const override;
-
-  // |flutter::BinaryMessenger|
-  void SetMessageHandler(const std::string& channel,
-                         BinaryMessageHandler handler) override;
-
- private:
-  // Handle for interacting with the C API.
-  FlutterDesktopMessengerRef messenger_;
-
-  // A map from channel names to the BinaryMessageHandler that should be called
-  // for incoming messages on that channel.
-  std::map<std::string, BinaryMessageHandler> handlers_;
-};
-
-}  // namespace flutter
-
-#endif  // FLUTTER_SHELL_PLATFORM_COMMON_CPP_CLIENT_WRAPPER_BINARY_MESSENGER_IMPL_H_

shell/platform/common/cpp/client_wrapper/core_implementations.cc

-// Copyright 2013 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// This file contains the implementations of any class in the wrapper that
-// - is not fully inline, and
-// - is necessary for all clients of the wrapper (either app or plugin).
-// It exists instead of the usual structure of having some_class_name.cc files
-// so that changes to the set of things that need non-header implementations
-// are not breaking changes for the template.
-//
-// If https://github.com/flutter/flutter/issues/57146 is fixed, this can be
-// removed in favor of the normal structure since templates will no longer
-// manually include files.
-
-#include <assert.h>
-
-#include <iostream>
-
-#include "binary_messenger_impl.h"
-#include "include/flutter/engine_method_result.h"
-
-namespace flutter {
-
-// ========== binary_messenger_impl.h ==========
-
-namespace {
-// Passes |message| to |user_data|, which must be a BinaryMessageHandler, along
-// with a BinaryReply that will send a response on |message|'s response handle.
-//
-// This serves as an adaptor between the function-pointer-based message callback
-// interface provided by the C API and the std::function-based message handler
-// interface of BinaryMessenger.
-void ForwardToHandler(FlutterDesktopMessengerRef messenger,
-                      const FlutterDesktopMessage* message,
-                      void* user_data) {
-  auto* response_handle = message->response_handle;
-  BinaryReply reply_handler = [messenger, response_handle](
-                                  const uint8_t* reply,
-                                  size_t reply_size) mutable {
-    if (!response_handle) {
-      std::cerr << "Error: Response can be set only once. Ignoring "
-                   "duplicate response."
-                << std::endl;
-      return;
-    }
-    FlutterDesktopMessengerSendResponse(messenger, response_handle, reply,
-                                        reply_size);
-    // The engine frees the response handle once
-    // FlutterDesktopSendMessageResponse is called.
-    response_handle = nullptr;
-  };
-
-  const BinaryMessageHandler& message_handler =
-      *static_cast<BinaryMessageHandler*>(user_data);
-
-  message_handler(message->message, message->message_size,
-                  std::move(reply_handler));
-}
-}  // namespace
-
-BinaryMessengerImpl::BinaryMessengerImpl(
-    FlutterDesktopMessengerRef core_messenger)
-    : messenger_(core_messenger) {}
-
-BinaryMessengerImpl::~BinaryMessengerImpl() = default;
-
-void BinaryMessengerImpl::Send(const std::string& channel,
-                               const uint8_t* message,
-                               size_t message_size,
-                               BinaryReply reply) const {
-  if (reply == nullptr) {
-    FlutterDesktopMessengerSend(messenger_, channel.c_str(), message,
-                                message_size);
-    return;
-  }
-  struct Captures {
-    BinaryReply reply;
-  };
-  auto captures = new Captures();
-  captures->reply = reply;
-
-  auto message_reply = [](const uint8_t* data, size_t data_size,
-                          void* user_data) {
-    auto captures = reinterpret_cast<Captures*>(user_data);
-    captures->reply(data, data_size);
-    delete captures;
-  };
-  bool result = FlutterDesktopMessengerSendWithReply(
-      messenger_, channel.c_str(), message, message_size, message_reply,
-      captures);
-  if (!result) {
-    delete captures;
-  }
-}
-
-void BinaryMessengerImpl::SetMessageHandler(const std::string& channel,
-                                            BinaryMessageHandler handler) {
-  if (!handler) {
-    handlers_.erase(channel);
-    FlutterDesktopMessengerSetCallback(messenger_, channel.c_str(), nullptr,
-                                       nullptr);
-    return;
-  }
-  // Save the handler, to keep it alive.
-  handlers_[channel] = std::move(handler);
-  BinaryMessageHandler* message_handler = &handlers_[channel];
-  // Set an adaptor callback that will invoke the handler.
-  FlutterDesktopMessengerSetCallback(messenger_, channel.c_str(),
-                                     ForwardToHandler, message_handler);
-}
-
-// ========== engine_method_result.h ==========
-
-namespace internal {
-
-ReplyManager::ReplyManager(BinaryReply reply_handler)
-    : reply_handler_(std::move(reply_handler)) {
-  assert(reply_handler_);
-}
-
-ReplyManager::~ReplyManager() {
-  if (reply_handler_) {
-    // Warn, rather than send a not-implemented response, since the engine may
-    // no longer be valid at this point.
-    std::cerr
-        << "Warning: Failed to respond to a message. This is a memory leak."
-        << std::endl;
-  }
-}
-
-void ReplyManager::SendResponseData(const std::vector<uint8_t>* data) {
-  if (!reply_handler_) {
-    std::cerr
-        << "Error: Only one of Success, Error, or NotImplemented can be "
-           "called,"
-        << " and it can be called exactly once. Ignoring duplicate result."
-        << std::endl;
-    return;
-  }
-
-  const uint8_t* message = data && !data->empty() ? data->data() : nullptr;
-  size_t message_size = data ? data->size() : 0;
-  reply_handler_(message, message_size);
-  reply_handler_ = nullptr;
-}
-
-}  // namespace internal
-
-}  // namespace flutter

shell/platform/common/cpp/client_wrapper/core_wrapper_files.gni

@@ -27,26 +27,13 @@ core_cpp_client_wrapper_includes =
                   ],
                   "abspath")
 
-# Headers that aren't public for clients of the wrapper, but are considered
-# public for the purpose of BUILD dependencies (e.g., to allow
-# windows/client_wrapper implementation files to include them).
-core_cpp_client_wrapper_internal_headers =
-    get_path_info([
-                    "binary_messenger_impl.h",
-                    "byte_buffer_streams.h",
-                  ],
-                  "abspath")
-
 # TODO: Once the wrapper API is more stable, consolidate to as few files as is
 # reasonable (without forcing different kinds of clients to take unnecessary
 # code) to simplify use.
 core_cpp_client_wrapper_sources = get_path_info([
-                                                  "core_implementations.cc",
+                                                  "byte_buffer_streams.h",
+                                                  "engine_method_result.cc",
                                                   "plugin_registrar.cc",
                                                   "standard_codec.cc",
                                                 ],
                                                 "abspath")
-
-# Temporary shim, published for backwards compatibility.
-# See comment in the file for more detail.
-temporary_shim_files = get_path_info([ "engine_method_result.cc" ], "abspath")

shell/platform/common/cpp/client_wrapper/engine_method_result.cc

@@ -2,10 +2,44 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// This file is deprecated in favor of core_implementations.cc. This is a
-// temporary forwarding implementation so that the switch to
-// core_implementations.cc isn't an immediate breaking change, allowing for the
-// template to be updated to include it and update the template version before
-// removing this file.
+#include "include/flutter/engine_method_result.h"
 
-#include "core_implementations.cc"
+#include <assert.h>
+#include <iostream>
+
+namespace flutter {
+namespace internal {
+
+ReplyManager::ReplyManager(BinaryReply reply_handler)
+    : reply_handler_(std::move(reply_handler)) {
+  assert(reply_handler_);
+}
+
+ReplyManager::~ReplyManager() {
+  if (reply_handler_) {
+    // Warn, rather than send a not-implemented response, since the engine may
+    // no longer be valid at this point.
+    std::cerr
+        << "Warning: Failed to respond to a message. This is a memory leak."
+        << std::endl;
+  }
+}
+
+void ReplyManager::SendResponseData(const std::vector<uint8_t>* data) {
+  if (!reply_handler_) {
+    std::cerr
+        << "Error: Only one of Success, Error, or NotImplemented can be "
+           "called,"
+        << " and it can be called exactly once. Ignoring duplicate result."
+        << std::endl;
+    return;
+  }
+
+  const uint8_t* message = data && !data->empty() ? data->data() : nullptr;
+  size_t message_size = data ? data->size() : 0;
+  reply_handler_(message, message_size);
+  reply_handler_ = nullptr;
+}
+
+}  // namespace internal
+}  // namespace flutter

shell/platform/common/cpp/client_wrapper/plugin_registrar.cc

@@ -7,12 +7,125 @@
 #include <iostream>
 #include <map>
 
-#include "binary_messenger_impl.h"
 #include "include/flutter/engine_method_result.h"
 #include "include/flutter/method_channel.h"
 
 namespace flutter {
 
+namespace {
+
+// Passes |message| to |user_data|, which must be a BinaryMessageHandler, along
+// with a BinaryReply that will send a response on |message|'s response handle.
+//
+// This serves as an adaptor between the function-pointer-based message callback
+// interface provided by the C API and the std::function-based message handler
+// interface of BinaryMessenger.
+void ForwardToHandler(FlutterDesktopMessengerRef messenger,
+                      const FlutterDesktopMessage* message,
+                      void* user_data) {
+  auto* response_handle = message->response_handle;
+  BinaryReply reply_handler = [messenger, response_handle](
+                                  const uint8_t* reply,
+                                  size_t reply_size) mutable {
+    if (!response_handle) {
+      std::cerr << "Error: Response can be set only once. Ignoring "
+                   "duplicate response."
+                << std::endl;
+      return;
+    }
+    FlutterDesktopMessengerSendResponse(messenger, response_handle, reply,
+                                        reply_size);
+    // The engine frees the response handle once
+    // FlutterDesktopSendMessageResponse is called.
+    response_handle = nullptr;
+  };
+
+  const BinaryMessageHandler& message_handler =
+      *static_cast<BinaryMessageHandler*>(user_data);
+
+  message_handler(message->message, message->message_size,
+                  std::move(reply_handler));
+}
+
+}  // namespace
+
+// Wrapper around a FlutterDesktopMessengerRef that implements the
+// BinaryMessenger API.
+class BinaryMessengerImpl : public BinaryMessenger {
+ public:
+  explicit BinaryMessengerImpl(FlutterDesktopMessengerRef core_messenger)
+      : messenger_(core_messenger) {}
+
+  virtual ~BinaryMessengerImpl() = default;
+
+  // Prevent copying.
+  BinaryMessengerImpl(BinaryMessengerImpl const&) = delete;
+  BinaryMessengerImpl& operator=(BinaryMessengerImpl const&) = delete;
+
+  // |flutter::BinaryMessenger|
+  void Send(const std::string& channel,
+            const uint8_t* message,
+            size_t message_size,
+            BinaryReply reply) const override;
+
+  // |flutter::BinaryMessenger|
+  void SetMessageHandler(const std::string& channel,
+                         BinaryMessageHandler handler) override;
+
+ private:
+  // Handle for interacting with the C API.
+  FlutterDesktopMessengerRef messenger_;
+
+  // A map from channel names to the BinaryMessageHandler that should be called
+  // for incoming messages on that channel.
+  std::map<std::string, BinaryMessageHandler> handlers_;
+};
+
+void BinaryMessengerImpl::Send(const std::string& channel,
+                               const uint8_t* message,
+                               size_t message_size,
+                               BinaryReply reply) const {
+  if (reply == nullptr) {
+    FlutterDesktopMessengerSend(messenger_, channel.c_str(), message,
+                                message_size);
+    return;
+  }
+  struct Captures {
+    BinaryReply reply;
+  };
+  auto captures = new Captures();
+  captures->reply = reply;
+
+  auto message_reply = [](const uint8_t* data, size_t data_size,
+                          void* user_data) {
+    auto captures = reinterpret_cast<Captures*>(user_data);
+    captures->reply(data, data_size);
+    delete captures;
+  };
+  bool result = FlutterDesktopMessengerSendWithReply(
+      messenger_, channel.c_str(), message, message_size, message_reply,
+      captures);
+  if (!result) {
+    delete captures;
+  }
+}
+
+void BinaryMessengerImpl::SetMessageHandler(const std::string& channel,
+                                            BinaryMessageHandler handler) {
+  if (!handler) {
+    handlers_.erase(channel);
+    FlutterDesktopMessengerSetCallback(messenger_, channel.c_str(), nullptr,
+                                       nullptr);
+    return;
+  }
+  // Save the handler, to keep it alive.
+  handlers_[channel] = std::move(handler);
+  BinaryMessageHandler* message_handler = &handlers_[channel];
+  // Set an adaptor callback that will invoke the handler.
+  FlutterDesktopMessengerSetCallback(messenger_, channel.c_str(),
+                                     ForwardToHandler, message_handler);
+}
+
 // ===== PluginRegistrar =====
 
 PluginRegistrar::PluginRegistrar(FlutterDesktopPluginRegistrarRef registrar)

shell/platform/common/cpp/client_wrapper/publish.gni

@@ -71,9 +71,7 @@ template("publish_client_wrapper_core") {
                              "visibility",
                            ])
     public = core_cpp_client_wrapper_includes
-    sources = core_cpp_client_wrapper_sources +
-              core_cpp_client_wrapper_internal_headers + [ _wrapper_readme ] +
-              temporary_shim_files
+    sources = core_cpp_client_wrapper_sources + [ _wrapper_readme ]
   }
 }
 

shell/platform/common/cpp/client_wrapper/testing/stub_flutter_api.cc

@@ -52,6 +52,14 @@ void FlutterDesktopRegistrarSetDestructionHandler(
   }
 }
 
+void FlutterDesktopRegistrarEnableInputBlocking(
+    FlutterDesktopPluginRegistrarRef registrar,
+    const char* channel) {
+  if (s_stub_implementation) {
+    s_stub_implementation->RegistrarEnableInputBlocking(channel);
+  }
+}
+
 bool FlutterDesktopMessengerSend(FlutterDesktopMessengerRef messenger,
                                  const char* channel,
                                  const uint8_t* message,

shell/platform/common/cpp/client_wrapper/testing/stub_flutter_api.h

@@ -38,6 +38,9 @@ class StubFlutterApi {
   virtual void RegistrarSetDestructionHandler(
       FlutterDesktopOnRegistrarDestroyed callback) {}
 
+  // Called for FlutterDesktopRegistrarEnableInputBlocking.
+  virtual void RegistrarEnableInputBlocking(const char* channel) {}
+
   // Called for FlutterDesktopMessengerSend.
   virtual bool MessengerSend(const char* channel,
                              const uint8_t* message,

shell/platform/common/cpp/public/flutter_plugin_registrar.h

@@ -31,6 +31,19 @@ FLUTTER_EXPORT void FlutterDesktopRegistrarSetDestructionHandler(
     FlutterDesktopPluginRegistrarRef registrar,
     FlutterDesktopOnRegistrarDestroyed callback);
 
+// Enables input blocking on the given channel.
+//
+// If set, then the Flutter window will disable input callbacks
+// while waiting for the handler for messages on that channel to run. This is
+// useful if handling the message involves showing a modal window, for instance.
+//
+// This must be called after FlutterDesktopSetMessageHandler, as setting a
+// handler on a channel will reset the input blocking state back to the
+// default of disabled.
+FLUTTER_EXPORT void FlutterDesktopRegistrarEnableInputBlocking(
+    FlutterDesktopPluginRegistrarRef registrar,
+    const char* channel);
+
 #if defined(__cplusplus)
 }  // extern "C"
 #endif

shell/platform/glfw/client_wrapper/testing/stub_flutter_glfw_api.cc

@@ -182,11 +182,3 @@ FlutterDesktopPluginRegistrarRef FlutterDesktopGetPluginRegistrar(
   // The stub ignores this, so just return an arbitrary non-zero value.
   return reinterpret_cast<FlutterDesktopPluginRegistrarRef>(2);
 }
-
-void FlutterDesktopRegistrarEnableInputBlocking(
-    FlutterDesktopPluginRegistrarRef registrar,
-    const char* channel) {
-  if (s_stub_implementation) {
-    s_stub_implementation->RegistrarEnableInputBlocking(channel);
-  }
-}

shell/platform/glfw/client_wrapper/testing/stub_flutter_glfw_api.h

@@ -88,9 +88,6 @@ class StubFlutterGlfwApi {
 
   // Called for FlutterDesktopShutDownEngine.
   virtual bool ShutDownEngine() { return true; }
-
-  // Called for FlutterDesktopRegistrarEnableInputBlocking.
-  virtual void RegistrarEnableInputBlocking(const char* channel) {}
 };
 
 // A test helper that owns a stub implementation, making it the test stub for

shell/platform/glfw/public/flutter_glfw.h

@@ -219,26 +219,10 @@ FLUTTER_EXPORT bool FlutterDesktopShutDownEngine(
     FlutterDesktopEngineRef engine);
 
 // Returns the window associated with this registrar's engine instance.
-//
 // This is a GLFW shell-specific extension to flutter_plugin_registrar.h
 FLUTTER_EXPORT FlutterDesktopWindowRef
 FlutterDesktopRegistrarGetWindow(FlutterDesktopPluginRegistrarRef registrar);
 
-// Enables input blocking on the given channel.
-//
-// If set, then the Flutter window will disable input callbacks
-// while waiting for the handler for messages on that channel to run. This is
-// useful if handling the message involves showing a modal window, for instance.
-//
-// This must be called after FlutterDesktopSetMessageHandler, as setting a
-// handler on a channel will reset the input blocking state back to the
-// default of disabled.
-//
-// This is a GLFW shell-specific extension to flutter_plugin_registrar.h
-FLUTTER_EXPORT void FlutterDesktopRegistrarEnableInputBlocking(
-    FlutterDesktopPluginRegistrarRef registrar,
-    const char* channel);
-
 #if defined(__cplusplus)
 }  // extern "C"
 #endif

shell/platform/windows/client_wrapper/BUILD.gn

@@ -20,12 +20,10 @@ _wrapper_sources = [
 
 # This code will be merged into .../common/cpp/client_wrapper for client use,
 # so uses header paths that assume the merged state. Include the header
-# directories of the core wrapper files so these includes will work.
+# header directory of the core wrapper files so these includes will work.
 config("relative_core_wrapper_headers") {
-  include_dirs = [
-    "//flutter/shell/platform/common/cpp/client_wrapper",
-    "//flutter/shell/platform/common/cpp/client_wrapper/include/flutter",
-  ]
+  include_dirs =
+      [ "//flutter/shell/platform/common/cpp/client_wrapper/include/flutter" ]
 }
 
 # Windows client wrapper build for internal use by the shell implementation.

shell/platform/windows/client_wrapper/flutter_engine.cc

@@ -7,8 +7,6 @@
 #include <algorithm>
 #include <iostream>
 
-#include "binary_messenger_impl.h"
-
 namespace flutter {
 
 FlutterEngine::FlutterEngine(const DartProject& project) {
@@ -27,9 +25,6 @@ FlutterEngine::FlutterEngine(const DartProject& project) {
   }
 
   engine_ = FlutterDesktopEngineCreate(c_engine_properties);
-
-  auto core_messenger = FlutterDesktopEngineGetMessenger(engine_);
-  messenger_ = std::make_unique<BinaryMessengerImpl>(core_messenger);
 }
 
 FlutterEngine::~FlutterEngine() {

shell/platform/windows/client_wrapper/flutter_engine_unittests.cc

@@ -93,14 +93,4 @@ TEST(FlutterEngineTest, ProcessMessages) {
   EXPECT_EQ(next_event_time.count(), 99);
 }
 
-TEST(FlutterEngineTest, GetMessenger) {
-  DartProject project(L"data");
-  testing::ScopedStubFlutterWindowsApi scoped_api_stub(
-      std::make_unique<TestFlutterWindowsApi>());
-  auto test_api = static_cast<TestFlutterWindowsApi*>(scoped_api_stub.stub());
-
-  FlutterEngine engine(DartProject(L"fake/project/path"));
-  EXPECT_NE(engine.messenger(), nullptr);
-}
-
 }  // namespace flutter

shell/platform/windows/client_wrapper/include/flutter/flutter_engine.h

@@ -12,7 +12,6 @@
 #include <memory>
 #include <string>
 
-#include "binary_messenger.h"
 #include "dart_project.h"
 #include "plugin_registrar.h"
 #include "plugin_registry.h"
@@ -58,12 +57,6 @@ class FlutterEngine : public PluginRegistry {
   FlutterDesktopPluginRegistrarRef GetRegistrarForPlugin(
       const std::string& plugin_name) override;
 
-  // Returns the messenger to use for creating channels to communicate with the
-  // Flutter engine.
-  //
-  // This pointer will remain valid for the lifetime of this instance.
-  BinaryMessenger* messenger() { return messenger_.get(); }
-
  private:
   // For access to RelinquishEngine.
   friend class FlutterViewController;
@@ -77,9 +70,6 @@ class FlutterEngine : public PluginRegistry {
   // Handle for interacting with the C API's engine reference.
   FlutterDesktopEngineRef engine_ = nullptr;
 
-  // Messenger for communicating with the engine.
-  std::unique_ptr<BinaryMessenger> messenger_;
-
   // Whether or not this wrapper owns |engine_|.
   bool owns_engine_ = true;
 

shell/platform/windows/client_wrapper/testing/stub_flutter_windows_api.cc

@@ -101,12 +101,6 @@ FlutterDesktopPluginRegistrarRef FlutterDesktopEngineGetPluginRegistrar(
   return reinterpret_cast<FlutterDesktopPluginRegistrarRef>(1);
 }
 
-FlutterDesktopMessengerRef FlutterDesktopEngineGetMessenger(
-    FlutterDesktopEngineRef engine) {
-  // The stub ignores this, so just return an arbitrary non-zero value.
-  return reinterpret_cast<FlutterDesktopMessengerRef>(2);
-}
-
 HWND FlutterDesktopViewGetHWND(FlutterDesktopViewRef controller) {
   if (s_stub_implementation) {
     return s_stub_implementation->ViewGetHWND();

shell/platform/windows/flutter_windows.cc

@@ -119,11 +119,6 @@ FlutterDesktopPluginRegistrarRef FlutterDesktopEngineGetPluginRegistrar(
   return EngineFromHandle(engine)->GetRegistrar();
 }
 
-FlutterDesktopMessengerRef FlutterDesktopEngineGetMessenger(
-    FlutterDesktopEngineRef engine) {
-  return EngineFromHandle(engine)->messenger();
-}
-
 HWND FlutterDesktopViewGetHWND(FlutterDesktopViewRef view_ref) {
   return std::get<HWND>(*view_ref->view->GetRenderTarget());
 }
@@ -156,7 +151,7 @@ void FlutterDesktopResyncOutputStreams() {
 
 FlutterDesktopMessengerRef FlutterDesktopRegistrarGetMessenger(
     FlutterDesktopPluginRegistrarRef registrar) {
-  return registrar->messenger;
+  return registrar->messenger.get();
 }
 
 void FlutterDesktopRegistrarSetDestructionHandler(

shell/platform/windows/flutter_windows_engine.cc

@@ -85,15 +85,15 @@ FlutterWindowsEngine::FlutterWindowsEngine(const FlutterProjectBundle& project)
         }
       });
 
-  // Set up the structure of the state/handle objects; engine and view
-  // paramaters will be filled in later.
-  messenger_ = std::make_unique<FlutterDesktopMessenger>();
+  // Set up the structure of the state/handle objects; engine and view paramater
+  // will be filled in late.
+  auto messenger = std::make_unique<FlutterDesktopMessenger>();
   message_dispatcher_ =
-      std::make_unique<IncomingMessageDispatcher>(messenger_.get());
-  messenger_->dispatcher = message_dispatcher_.get();
+      std::make_unique<IncomingMessageDispatcher>(messenger.get());
+  messenger->dispatcher = message_dispatcher_.get();
 
   plugin_registrar_ = std::make_unique<FlutterDesktopPluginRegistrar>();
-  plugin_registrar_->messenger = messenger_.get();
+  plugin_registrar_->messenger = std::move(messenger);
   plugin_registrar_->view = std::make_unique<FlutterDesktopView>();
 }
 

shell/platform/windows/flutter_windows_engine.h

@@ -60,8 +60,6 @@ class FlutterWindowsEngine {
 
   FLUTTER_API_SYMBOL(FlutterEngine) engine() { return engine_; }
 
-  FlutterDesktopMessengerRef messenger() { return messenger_.get(); }
-
   Win32TaskRunner* task_runner() { return task_runner_.get(); }
 
   // Callback passed to Flutter engine for notifying window of platform
@@ -83,9 +81,6 @@ class FlutterWindowsEngine {
   // Task runner for tasks posted from the engine.
   std::unique_ptr<Win32TaskRunner> task_runner_;
 
-  // The plugin messenger handle given to API clients.
-  std::unique_ptr<FlutterDesktopMessenger> messenger_;
-
   // Message dispatch manager for messages from engine_.
   std::unique_ptr<IncomingMessageDispatcher> message_dispatcher_;
 

shell/platform/windows/public/flutter_windows.h

@@ -136,10 +136,6 @@ FLUTTER_EXPORT FlutterDesktopPluginRegistrarRef
 FlutterDesktopEngineGetPluginRegistrar(FlutterDesktopEngineRef engine,
                                        const char* plugin_name);
 
-// Returns the messenger associated with the engine.
-FLUTTER_EXPORT FlutterDesktopMessengerRef
-FlutterDesktopEngineGetMessenger(FlutterDesktopEngineRef engine);
-
 // ========== View ==========
 
 // Return backing HWND for manipulation in host application.

shell/platform/windows/window_state.h

@@ -35,7 +35,7 @@ struct FlutterDesktopView {
 // State associated with the plugin registrar.
 struct FlutterDesktopPluginRegistrar {
   // The plugin messenger handle given to API clients.
-  FlutterDesktopMessenger* messenger;
+  std::unique_ptr<FlutterDesktopMessenger> messenger;
 
   // The handle for the view associated with this registrar.
   std::unique_ptr<FlutterDesktopView> view;