[dart:ui] add an explicit API for loading assets

lib/ui/BUILD.gn

@@ -8,6 +8,8 @@ import("//flutter/testing/testing.gni")
 
 source_set("ui") {
   sources = [
+    "assets.cc",
+    "assets.h",
     "compositing/scene.cc",
     "compositing/scene.h",
     "compositing/scene_builder.cc",

lib/ui/assets.cc

@@ -0,0 +1,74 @@
+// 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.
+
+#include "flutter/lib/ui/assets.h"
+
+#include "flutter/assets/asset_manager.h"
+#include "flutter/lib/ui/ui_dart_state.h"
+#include "flutter/lib/ui/window/platform_configuration.h"
+#include "third_party/tonic/dart_binding_macros.h"
+#include "third_party/tonic/dart_library_natives.h"
+#include "third_party/tonic/logging/dart_invoke.h"
+#include "third_party/tonic/typed_data/dart_byte_data.h"
+#include "third_party/tonic/typed_data/typed_list.h"
+
+using tonic::DartInvoke;
+using tonic::DartPersistentValue;
+using tonic::ToDart;
+
+namespace flutter {
+
+  void FinalizeSkData(void* isolate_callback_data,
+                    Dart_WeakPersistentHandle handle,
+                    void* peer) {
+
+}
+
+void Assets::loadAssetBytes(Dart_NativeArguments args) {
+  UIDartState::ThrowIfUIOperationsProhibited();
+  Dart_Handle callback = Dart_GetNativeArgument(args, 1);
+  if (!Dart_IsClosure(callback)) {
+    Dart_SetReturnValue(args, tonic::ToDart("Callback must be a function"));
+    return;
+  }
+  Dart_Handle asset_name_handle = Dart_GetNativeArgument(args, 0);
+  uint8_t* chars = nullptr;
+  intptr_t asset_length = 0;
+  Dart_Handle result =
+      Dart_StringToUTF8(asset_name_handle, &chars, &asset_length);
+  if (Dart_IsError(result)) {
+    Dart_PropagateError(result);
+    return;
+  }
+  std::string asset_name = std::string{reinterpret_cast<const char*>(chars),
+                                       static_cast<size_t>(asset_length)};
+
+  std::shared_ptr<AssetManager> asset_manager = UIDartState::Current()
+                                                    ->platform_configuration()
+                                                    ->client()
+                                                    ->GetAssetManager();
+  std::unique_ptr<fml::Mapping> data = asset_manager->GetAsMapping(asset_name);
+
+  if (data == nullptr) {
+    return;
+  }
+  const void* bytes_ = static_cast<const void*>(data->GetMapping());
+  void* bytes = const_cast<void*>(bytes_);
+  const intptr_t length = data->GetSize();
+  void* peer = reinterpret_cast<void*>(data.release());
+  Dart_Handle byte_buffer = Dart_NewExternalTypedDataWithFinalizer(
+      Dart_TypedData_kUint8, bytes, length, peer, length, FinalizeSkData);
+
+  // Dart_Handle byte_buffer =
+  //     tonic::DartByteData::Create(data->GetMapping(), data->GetSize());
+  tonic::DartInvoke(callback, {ToDart(byte_buffer)});
+}
+
+void Assets::RegisterNatives(tonic::DartLibraryNatives* natives) {
+  natives->Register({
+      {"loadAssetBytes", loadAssetBytes, 2, true},
+  });
+}
+
+}  // namespace flutter

lib/ui/assets.dart

@@ -0,0 +1,23 @@
+// 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.
+
+// @dart = 2.10
+
+part of dart.ui;
+
+/// Load the asset bytes specified by [assetKey].
+///
+/// The [assetKey] is generally the filepath of the asset which is bundled
+/// into the flutter application. This API is not supported on the Web.
+///
+/// If the [assetKey] does not correspond to a real asset, returns `null`.
+ByteData? loadAsset(String assetKey) {
+  ByteData? result;
+  _loadAsset(assetKey, (Uint8List bytes) {
+    result = bytes.buffer.asByteData();
+  });
+  return result;
+}
+
+void _loadAsset(String asseyKey, void Function(Uint8List) onData) native 'loadAssetBytes';

lib/ui/assets.h

@@ -0,0 +1,26 @@
+// 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_LIB_UI_ASSETS_H_
+#define FLUTTER_LIB_UI_ASSETS_H_
+
+#include "flutter/assets/asset_manager.h"
+#include "flutter/lib/ui/ui_dart_state.h"
+#include "flutter/lib/ui/window/platform_configuration.h"
+#include "third_party/tonic/dart_binding_macros.h"
+#include "third_party/tonic/dart_library_natives.h"
+#include "third_party/tonic/logging/dart_invoke.h"
+#include "third_party/tonic/typed_data/dart_byte_data.h"
+#include "third_party/tonic/typed_data/typed_list.h"
+
+namespace flutter {
+
+class Assets {
+ public:
+  static void loadAssetBytes(Dart_NativeArguments args);
+
+  static void RegisterNatives(tonic::DartLibraryNatives* natives);
+};
+}  // namespace flutter
+#endif  // FLUTTER_LIB_UI_ASSETS_H_

lib/ui/dart_ui.cc

@@ -5,6 +5,7 @@
 #include "flutter/lib/ui/dart_ui.h"
 
 #include "flutter/fml/build_config.h"
+#include "flutter/lib/ui/assets.h"
 #include "flutter/lib/ui/compositing/scene.h"
 #include "flutter/lib/ui/compositing/scene_builder.h"
 #include "flutter/lib/ui/dart_runtime_hooks.h"
@@ -86,6 +87,7 @@ void DartUI::InitForGlobal() {
     SemanticsUpdateBuilder::RegisterNatives(g_natives);
     Vertices::RegisterNatives(g_natives);
     PlatformConfiguration::RegisterNatives(g_natives);
+    Assets::RegisterNatives(g_natives);
 #if defined(LEGACY_FUCHSIA_EMBEDDER)
     SceneHost::RegisterNatives(g_natives);
 #endif

lib/ui/ui.dart

@@ -24,6 +24,7 @@ import 'dart:nativewrappers';
 import 'dart:typed_data';
 
 part 'annotations.dart';
+part 'assets.dart';
 part 'channel_buffers.dart';
 part 'compositing.dart';
 part 'geometry.dart';

lib/ui/window/platform_configuration.h

@@ -11,6 +11,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/fml/time/time_point.h"
 #include "flutter/lib/ui/semantics/semantics_update.h"
 #include "flutter/lib/ui/window/platform_message.h"
@@ -111,6 +112,8 @@ class PlatformConfigurationClient {
   ///             creation.
   virtual FontCollection& GetFontCollection() = 0;
 
+  virtual std::shared_ptr<AssetManager> GetAssetManager() = 0;
+
   //--------------------------------------------------------------------------
   /// @brief      Notifies this client of the name of the root isolate and its
   ///             port when that isolate is launched, restarted (in the

lib/web_ui/lib/src/ui/assets.dart

@@ -0,0 +1,17 @@
+// 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.
+
+// @dart = 2.10
+part of ui;
+
+/// Load the asset bytes specified by [assetKey].
+///
+/// The [assetKey] is generally the filepath of the asset which is bundled
+/// into the flutter application. This API is not supported on the
+/// Web.
+///
+/// If the [assetKey] does not correspond to a real asset, returns `null`.
+ByteData? loadAsset(String assetKey) {
+  return null;
+}

lib/web_ui/lib/ui.dart

@@ -35,6 +35,7 @@ part 'src/ui/test_embedding.dart';
 part 'src/ui/text.dart';
 part 'src/ui/tile_mode.dart';
 part 'src/ui/window.dart';
+part 'src/ui/assets.dart';
 
 /// Provides a compile time constant to customize flutter framework and other
 /// users of ui engine for web runtime.

runtime/runtime_controller.cc

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "flutter/runtime/runtime_controller.h"
+#include "flutter/assets/asset_manager.h"
 
 #include "flutter/fml/message_loop.h"
 #include "flutter/fml/trace_event.h"
@@ -328,6 +329,11 @@ FontCollection& RuntimeController::GetFontCollection() {
   return client_.GetFontCollection();
 }
 
+// |PlatfromConfigurationClient|
+std::shared_ptr<AssetManager> RuntimeController::GetAssetManager() {
+  return client_.GetAssetManager();
+}
+
 // |PlatformConfigurationClient|
 void RuntimeController::UpdateIsolateDescription(const std::string isolate_name,
                                                  int64_t isolate_port) {

runtime/runtime_controller.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/common/task_runners.h"
 #include "flutter/flow/layers/layer_tree.h"
 #include "flutter/fml/macros.h"
@@ -499,6 +500,9 @@ class RuntimeController : public PlatformConfigurationClient {
   // |PlatformConfigurationClient|
   FontCollection& GetFontCollection() override;
 
+  // |PlatformConfigurationClient|
+  std::shared_ptr<AssetManager> GetAssetManager() override;
+
   // |PlatformConfigurationClient|
   void UpdateIsolateDescription(const std::string isolate_name,
                                 int64_t isolate_port) override;

runtime/runtime_delegate.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <vector>
 
+#include "flutter/assets/asset_manager.h"
 #include "flutter/flow/layers/layer_tree.h"
 #include "flutter/lib/ui/semantics/custom_accessibility_action.h"
 #include "flutter/lib/ui/semantics/semantics_node.h"
@@ -32,6 +33,8 @@ class RuntimeDelegate {
 
   virtual FontCollection& GetFontCollection() = 0;
 
+  virtual std::shared_ptr<AssetManager> GetAssetManager() = 0;
+
   virtual void UpdateIsolateDescription(const std::string isolate_name,
                                         int64_t isolate_port) = 0;
 

shell/common/engine.cc

@@ -513,6 +513,10 @@ FontCollection& Engine::GetFontCollection() {
   return font_collection_;
 }
 
+std::shared_ptr<AssetManager> Engine::GetAssetManager() {
+  return asset_manager_;
+}
+
 void Engine::DoDispatchPacket(std::unique_ptr<PointerDataPacket> packet,
                               uint64_t trace_flow_id) {
   animator_->EnqueueTraceFlowId(trace_flow_id);

shell/common/engine.h

@@ -751,6 +751,9 @@ class Engine final : public RuntimeDelegate, PointerDataDispatcher::Delegate {
   // |RuntimeDelegate|
   FontCollection& GetFontCollection() override;
 
+  // |RuntimeDelegate|
+  std::shared_ptr<AssetManager> GetAssetManager() override;
+
   // |PointerDataDispatcher::Delegate|
   void DoDispatchPacket(std::unique_ptr<PointerDataPacket> packet,
                         uint64_t trace_flow_id) override;

shell/common/engine_unittests.cc

@@ -46,6 +46,7 @@ class MockRuntimeDelegate : public RuntimeDelegate {
                void(SemanticsNodeUpdates, CustomAccessibilityActionUpdates));
   MOCK_METHOD1(HandlePlatformMessage, void(fml::RefPtr<PlatformMessage>));
   MOCK_METHOD0(GetFontCollection, FontCollection&());
+  MOCK_METHOD0(GetAssetManager, std::shared_ptr<AssetManager>());
   MOCK_METHOD2(UpdateIsolateDescription, void(const std::string, int64_t));
   MOCK_METHOD1(SetNeedsReportTimings, void(bool));
   MOCK_METHOD1(ComputePlatformResolvedLocale,

testing/dart/assets_test.dart

@@ -0,0 +1,18 @@
+// 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.
+
+// @dart = 2.6
+import 'dart:ui' as ui;
+
+import 'package:test/test.dart';
+
+void main() {
+  test('Loading an asset that does not exist returns null', () {
+    expect(ui.loadAsset('ThisDoesNotExist'), null);
+  });
+
+  test('returns the bytes of a bundled asset', () {
+    expect(ui.loadAsset('FontManifest.json'), isNotNull);
+  });
+}