Reapply: Android background platform channels (flutter#29346)

* Revert "Revert "Android Background Platform Channels (flutter#29147)""

This reverts commit 7ed91e14ccc1f5ffc4cb13d1d37e27d370c8f7cd.

* Made this PR less of a breaking change by keeping setMessageHandler's signature the same

ci/licenses_golden/licenses_flutter

@@ -708,6 +708,7 @@ FILE: ../../../flutter/shell/common/persistent_cache_unittests.cc
 FILE: ../../../flutter/shell/common/pipeline.cc
 FILE: ../../../flutter/shell/common/pipeline.h
 FILE: ../../../flutter/shell/common/pipeline_unittests.cc
+FILE: ../../../flutter/shell/common/platform_message_handler.h
 FILE: ../../../flutter/shell/common/platform_view.cc
 FILE: ../../../flutter/shell/common/platform_view.h
 FILE: ../../../flutter/shell/common/pointer_data_dispatcher.cc
@@ -842,6 +843,7 @@ FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/Flutte
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/dart/DartExecutor.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/dart/DartMessenger.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/dart/PlatformMessageHandler.java
+FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/dart/PlatformTaskQueue.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/DeferredComponentManager.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java
 FILE: ../../../flutter/shell/platform/android/io/flutter/embedding/engine/loader/ApplicationInfoLoader.java
@@ -939,6 +941,8 @@ FILE: ../../../flutter/shell/platform/android/jni/jni_mock_unittest.cc
 FILE: ../../../flutter/shell/platform/android/jni/platform_view_android_jni.cc
 FILE: ../../../flutter/shell/platform/android/jni/platform_view_android_jni.h
 FILE: ../../../flutter/shell/platform/android/library_loader.cc
+FILE: ../../../flutter/shell/platform/android/platform_message_handler_android.cc
+FILE: ../../../flutter/shell/platform/android/platform_message_handler_android.h
 FILE: ../../../flutter/shell/platform/android/platform_message_response_android.cc
 FILE: ../../../flutter/shell/platform/android/platform_message_response_android.h
 FILE: ../../../flutter/shell/platform/android/platform_view_android.cc

shell/common/BUILD.gn

@@ -73,6 +73,7 @@ source_set("common") {
     "engine.h",
     "pipeline.cc",
     "pipeline.h",
+    "platform_message_handler.h",
     "platform_view.cc",
     "platform_view.h",
     "pointer_data_dispatcher.cc",

shell/common/platform_message_handler.h

@@ -0,0 +1,39 @@
+// 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 SHELL_COMMON_PLATFORM_MESSAGE_HANDLER_H_
+#define SHELL_COMMON_PLATFORM_MESSAGE_HANDLER_H_
+
+#include <memory>
+
+#include "flutter/lib/ui/window/platform_message.h"
+
+namespace flutter {
+
+/// An interface over the ability to handle PlatformMessages that are being sent
+/// from Flutter to the host platform.
+class PlatformMessageHandler {
+ public:
+  virtual ~PlatformMessageHandler() = default;
+
+  /// Ultimately sends the PlatformMessage to the host platform.
+  /// This method is invoked on the ui thread.
+  virtual void HandlePlatformMessage(
+      std::unique_ptr<PlatformMessage> message) = 0;
+
+  /// Performs the return procedure for an associated call to
+  /// HandlePlatformMessage.
+  /// This method should be thread-safe and able to be invoked on any thread.
+  virtual void InvokePlatformMessageResponseCallback(
+      int response_id,
+      std::unique_ptr<fml::Mapping> mapping) = 0;
+
+  /// Performs the return procedure for an associated call to
+  /// HandlePlatformMessage where there is no return value.
+  /// This method should be thread-safe and able to be invoked on any thread.
+  virtual void InvokePlatformMessageEmptyResponseCallback(int response_id) = 0;
+};
+}  // namespace flutter
+
+#endif  // SHELL_COMMON_PLATFORM_MESSAGE_HANDLER_H_

shell/common/platform_view.cc

@@ -184,4 +184,9 @@ PlatformView::CreateSnapshotSurfaceProducer() {
   return nullptr;
 }
 
+std::shared_ptr<PlatformMessageHandler>
+PlatformView::GetPlatformMessageHandler() const {
+  return nullptr;
+}
+
 }  // namespace flutter

shell/common/platform_view.h

@@ -22,6 +22,7 @@
 #include "flutter/lib/ui/window/pointer_data_packet.h"
 #include "flutter/lib/ui/window/pointer_data_packet_converter.h"
 #include "flutter/lib/ui/window/viewport_metrics.h"
+#include "flutter/shell/common/platform_message_handler.h"
 #include "flutter/shell/common/pointer_data_dispatcher.h"
 #include "flutter/shell/common/vsync_waiter.h"
 #include "third_party/skia/include/core/SkSize.h"
@@ -810,6 +811,17 @@ class PlatformView {
   virtual std::unique_ptr<SnapshotSurfaceProducer>
   CreateSnapshotSurfaceProducer();
 
+  //--------------------------------------------------------------------------
+  /// @brief Specifies a delegate that will receive PlatformMessages from
+  /// Flutter to the host platform.
+  ///
+  /// @details If this returns `null` that means PlatformMessages should be sent
+  /// to the PlatformView.  That is to protect legacy behavior, any embedder
+  /// that wants to support executing Platform Channel handlers on background
+  /// threads should be returing a thread-safe PlatformMessageHandler instead.
+  virtual std::shared_ptr<PlatformMessageHandler> GetPlatformMessageHandler()
+      const;
+
  protected:
   PlatformView::Delegate& delegate_;
   const TaskRunners task_runners_;

shell/common/shell.cc

@@ -625,6 +625,7 @@ bool Shell::Setup(std::unique_ptr<PlatformView> platform_view,
   }
 
   platform_view_ = std::move(platform_view);
+  platform_message_handler_ = platform_view_->GetPlatformMessageHandler();
   engine_ = std::move(engine);
   rasterizer_ = std::move(rasterizer);
   io_manager_ = std::move(io_manager);
@@ -1192,13 +1193,17 @@ void Shell::OnEngineHandlePlatformMessage(
     return;
   }
 
-  task_runners_.GetPlatformTaskRunner()->PostTask(
-      fml::MakeCopyable([view = platform_view_->GetWeakPtr(),
-                         message = std::move(message)]() mutable {
-        if (view) {
-          view->HandlePlatformMessage(std::move(message));
-        }
-      }));
+  if (platform_message_handler_) {
+    platform_message_handler_->HandlePlatformMessage(std::move(message));
+  } else {
+    task_runners_.GetPlatformTaskRunner()->PostTask(
+        fml::MakeCopyable([view = platform_view_->GetWeakPtr(),
+                           message = std::move(message)]() mutable {
+          if (view) {
+            view->HandlePlatformMessage(std::move(message));
+          }
+        }));
+  }
 }
 
 void Shell::HandleEngineSkiaMessage(std::unique_ptr<PlatformMessage> message) {
@@ -1867,4 +1872,9 @@ fml::TimePoint Shell::GetCurrentTimePoint() {
   return fml::TimePoint::Now();
 }
 
+const std::shared_ptr<PlatformMessageHandler>&
+Shell::GetPlatformMessageHandler() const {
+  return platform_message_handler_;
+}
+
 }  // namespace flutter

shell/common/shell.h

@@ -395,6 +395,12 @@ class Shell final : public PlatformView::Delegate,
   /// @see        `CreateCompatibleGenerator`
   void RegisterImageDecoder(ImageGeneratorFactory factory, int32_t priority);
 
+  //----------------------------------------------------------------------------
+  /// @brief Returns the delegate object that handles PlatformMessage's from
+  ///        Flutter to the host platform (and its responses).
+  const std::shared_ptr<PlatformMessageHandler>& GetPlatformMessageHandler()
+      const;
+
  private:
   using ServiceProtocolHandler =
       std::function<bool(const ServiceProtocol::Handler::ServiceProtocolMap&,
@@ -412,6 +418,7 @@ class Shell final : public PlatformView::Delegate,
   std::unique_ptr<ShellIOManager> io_manager_;   // on IO task runner
   std::shared_ptr<fml::SyncSwitch> is_gpu_disabled_sync_switch_;
   std::shared_ptr<VolatilePathTracker> volatile_path_tracker_;
+  std::shared_ptr<PlatformMessageHandler> platform_message_handler_;
 
   fml::WeakPtr<Engine> weak_engine_;  // to be shared across threads
   fml::TaskRunnerAffineWeakPtr<Rasterizer>

shell/common/shell_test.cc

@@ -325,7 +325,8 @@ std::unique_ptr<Shell> ShellTest::CreateShell(
     std::shared_ptr<ShellTestExternalViewEmbedder>
         shell_test_external_view_embedder,
     bool is_gpu_disabled,
-    ShellTestPlatformView::BackendType rendering_backend) {
+    ShellTestPlatformView::BackendType rendering_backend,
+    Shell::CreateCallback<PlatformView> platform_view_create_callback) {
   const auto vsync_clock = std::make_shared<ShellTestVsyncClock>();
 
   CreateVsyncWaiter create_vsync_waiter = [&]() {
@@ -338,29 +339,29 @@ std::unique_ptr<Shell> ShellTest::CreateShell(
     }
   };
 
-  Shell::CreateCallback<PlatformView> platfrom_view_create_callback =
-      [vsync_clock,                        //
-       &create_vsync_waiter,               //
-       shell_test_external_view_embedder,  //
-       rendering_backend                   //
-  ](Shell& shell) {
-        return ShellTestPlatformView::Create(
-            shell,                             //
-            shell.GetTaskRunners(),            //
-            vsync_clock,                       //
-            std::move(create_vsync_waiter),    //
-            rendering_backend,                 //
-            shell_test_external_view_embedder  //
-        );
-      };
+  if (!platform_view_create_callback) {
+    platform_view_create_callback = [vsync_clock,                        //
+                                     &create_vsync_waiter,               //
+                                     shell_test_external_view_embedder,  //
+                                     rendering_backend                   //
+    ](Shell& shell) {
+      return ShellTestPlatformView::Create(shell,                             //
+                                           shell.GetTaskRunners(),            //
+                                           vsync_clock,                       //
+                                           std::move(create_vsync_waiter),    //
+                                           rendering_backend,                 //
+                                           shell_test_external_view_embedder  //
+      );
+    };
+  }
 
   Shell::CreateCallback<Rasterizer> rasterizer_create_callback =
       [](Shell& shell) { return std::make_unique<Rasterizer>(shell); };
 
   return Shell::Create(flutter::PlatformData(),        //
                        task_runners,                   //
                        settings,                       //
-                       platfrom_view_create_callback,  //
+                       platform_view_create_callback,  //
                        rasterizer_create_callback,     //
                        is_gpu_disabled                 //
   );

shell/common/shell_test.h

@@ -43,7 +43,9 @@ class ShellTest : public FixtureTest {
           shell_test_external_view_embedder = nullptr,
       bool is_gpu_disabled = false,
       ShellTestPlatformView::BackendType rendering_backend =
-          ShellTestPlatformView::BackendType::kDefaultBackend);
+          ShellTestPlatformView::BackendType::kDefaultBackend,
+      Shell::CreateCallback<PlatformView> platform_view_create_callback =
+          nullptr);
   void DestroyShell(std::unique_ptr<Shell> shell);
   void DestroyShell(std::unique_ptr<Shell> shell, TaskRunners task_runners);
   TaskRunners GetTaskRunnersForFixture();

shell/common/shell_unittests.cc

@@ -45,6 +45,10 @@
 
 namespace flutter {
 namespace testing {
+
+using ::testing::_;
+using ::testing::Return;
+
 namespace {
 class MockPlatformViewDelegate : public PlatformView::Delegate {
   MOCK_METHOD1(OnPlatformViewCreated, void(std::unique_ptr<Surface> surface));
@@ -119,6 +123,27 @@ class MockPlatformView : public PlatformView {
   MockPlatformView(MockPlatformViewDelegate& delegate, TaskRunners task_runners)
       : PlatformView(delegate, task_runners) {}
   MOCK_METHOD0(CreateRenderingSurface, std::unique_ptr<Surface>());
+  MOCK_CONST_METHOD0(GetPlatformMessageHandler,
+                     std::shared_ptr<PlatformMessageHandler>());
+};
+
+class MockPlatformMessageHandler : public PlatformMessageHandler {
+ public:
+  MOCK_METHOD1(HandlePlatformMessage,
+               void(std::unique_ptr<PlatformMessage> message));
+  MOCK_METHOD2(InvokePlatformMessageResponseCallback,
+               void(int response_id, std::unique_ptr<fml::Mapping> mapping));
+  MOCK_METHOD1(InvokePlatformMessageEmptyResponseCallback,
+               void(int response_id));
+};
+
+class MockPlatformMessageResponse : public PlatformMessageResponse {
+ public:
+  static fml::RefPtr<MockPlatformMessageResponse> Create() {
+    return fml::AdoptRef(new MockPlatformMessageResponse());
+  }
+  MOCK_METHOD1(Complete, void(std::unique_ptr<fml::Mapping> data));
+  MOCK_METHOD0(CompleteEmpty, void());
 };
 }  // namespace
 
@@ -3162,7 +3187,52 @@ TEST_F(ShellTest, UIWorkAfterOnPlatformViewDestroyed) {
       shell->GetTaskRunners().GetUITaskRunner(),
       [&ui_flush_latch]() { ui_flush_latch.Signal(); });
   ui_flush_latch.Wait();
+  DestroyShell(std::move(shell));
+}
 
+TEST_F(ShellTest, UsesPlatformMessageHandler) {
+  TaskRunners task_runners = GetTaskRunnersForFixture();
+  auto settings = CreateSettingsForFixture();
+  MockPlatformViewDelegate platform_view_delegate;
+  auto platform_message_handler =
+      std::make_shared<MockPlatformMessageHandler>();
+  int message_id = 1;
+  EXPECT_CALL(*platform_message_handler, HandlePlatformMessage(_));
+  EXPECT_CALL(*platform_message_handler,
+              InvokePlatformMessageEmptyResponseCallback(message_id));
+  Shell::CreateCallback<PlatformView> platform_view_create_callback =
+      [&platform_view_delegate, task_runners,
+       platform_message_handler](flutter::Shell& shell) {
+        auto result = std::make_unique<MockPlatformView>(platform_view_delegate,
+                                                         task_runners);
+        EXPECT_CALL(*result, GetPlatformMessageHandler())
+            .WillOnce(Return(platform_message_handler));
+        return result;
+      };
+  auto shell = CreateShell(
+      /*settings=*/std::move(settings),
+      /*task_runners=*/task_runners,
+      /*simulate_vsync=*/false,
+      /*shell_test_external_view_embedder=*/nullptr,
+      /*is_gpu_disabled=*/false,
+      /*rendering_backend=*/
+      ShellTestPlatformView::BackendType::kDefaultBackend,
+      /*platform_view_create_callback=*/platform_view_create_callback);
+
+  EXPECT_EQ(platform_message_handler, shell->GetPlatformMessageHandler());
+  PostSync(task_runners.GetUITaskRunner(), [&shell]() {
+    size_t data_size = 4;
+    fml::MallocMapping bytes =
+        fml::MallocMapping(static_cast<uint8_t*>(malloc(data_size)), data_size);
+    fml::RefPtr<MockPlatformMessageResponse> response =
+        MockPlatformMessageResponse::Create();
+    auto message = std::make_unique<PlatformMessage>(
+        /*channel=*/"foo", /*data=*/std::move(bytes), /*response=*/response);
+    (static_cast<Engine::Delegate*>(shell.get()))
+        ->OnEngineHandlePlatformMessage(std::move(message));
+  });
+  shell->GetPlatformMessageHandler()
+      ->InvokePlatformMessageEmptyResponseCallback(message_id);
   DestroyShell(std::move(shell));
 }
 

shell/platform/android/BUILD.gn

@@ -79,6 +79,8 @@ source_set("flutter_shell_native_src") {
     "flutter_main.cc",
     "flutter_main.h",
     "library_loader.cc",
+    "platform_message_handler_android.cc",
+    "platform_message_handler_android.h",
     "platform_message_response_android.cc",
     "platform_message_response_android.h",
     "platform_view_android.cc",
@@ -187,6 +189,7 @@ android_java_sources = [
   "io/flutter/embedding/engine/dart/DartExecutor.java",
   "io/flutter/embedding/engine/dart/DartMessenger.java",
   "io/flutter/embedding/engine/dart/PlatformMessageHandler.java",
+  "io/flutter/embedding/engine/dart/PlatformTaskQueue.java",
   "io/flutter/embedding/engine/deferredcomponents/DeferredComponentManager.java",
   "io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java",
   "io/flutter/embedding/engine/loader/ApplicationInfoLoader.java",

shell/platform/android/android_shell_holder.h

@@ -16,6 +16,7 @@
 #include "flutter/shell/common/shell.h"
 #include "flutter/shell/common/thread_host.h"
 #include "flutter/shell/platform/android/jni/platform_view_android_jni.h"
+#include "flutter/shell/platform/android/platform_message_handler_android.h"
 #include "flutter/shell/platform/android/platform_view_android.h"
 
 namespace flutter {
@@ -96,6 +97,11 @@ class AndroidShellHolder {
 
   void NotifyLowMemoryWarning();
 
+  const std::shared_ptr<PlatformMessageHandler>& GetPlatformMessageHandler()
+      const {
+    return shell_->GetPlatformMessageHandler();
+  }
+
  private:
   const flutter::Settings settings_;
   const std::shared_ptr<PlatformViewAndroidJNI> jni_facade_;