From e8df7055bcc870fb7dc810da6c4fd69e43bc6cd6 Mon Sep 17 00:00:00 2001
From: Ryan Macnak <rmacnak@google.com>
Date: Tue, 19 Jun 2018 14:24:19 -0700
Subject: [PATCH] Replace AssetResolver GetAsBuffer with GetAsMapping.
 (flutter/engine#5546)

Toward no-copy loading of kernel.
---
 engine/src/flutter/assets/asset_manager.cc    | 15 ++---
 engine/src/flutter/assets/asset_manager.h     |  4 +-
 engine/src/flutter/assets/asset_resolver.h    |  6 +-
 .../flutter/assets/directory_asset_bundle.cc  | 20 +++----
 .../flutter/assets/directory_asset_bundle.h   |  4 +-
 engine/src/flutter/assets/zip_asset_store.cc  | 24 ++++----
 engine/src/flutter/assets/zip_asset_store.h   |  4 +-
 .../ui/text/asset_manager_font_provider.cc    | 19 +++---
 .../flutter/lib/ui/text/font_collection.cc    | 19 +++---
 .../lib/ui/window/platform_message_response.h |  3 +-
 .../window/platform_message_response_dart.cc  |  8 ++-
 .../window/platform_message_response_dart.h   |  2 +-
 engine/src/flutter/lib/ui/window/window.cc    |  3 +-
 engine/src/flutter/shell/common/engine.cc     | 14 +++--
 .../shell/common/isolate_configuration.cc     | 60 +++++++++----------
 .../platform/android/apk_asset_provider.cc    | 37 +++++++-----
 .../platform/android/apk_asset_provider.h     |  4 +-
 .../platform_message_response_android.cc      | 14 +++--
 .../platform_message_response_android.h       |  2 +-
 .../platform/android/platform_view_android.cc |  6 +-
 .../android/platform_view_android_jni.cc      |  8 +--
 .../darwin/common/buffer_conversions.h        |  6 ++
 .../darwin/common/buffer_conversions.mm       |  8 +++
 .../Source/platform_message_response_darwin.h |  4 +-
 .../Source/platform_message_router.mm         |  2 +-
 .../shell/platform/embedder/embedder.cc       |  3 +-
 26 files changed, 165 insertions(+), 134 deletions(-)

diff --git a/engine/src/flutter/assets/asset_manager.cc b/engine/src/flutter/assets/asset_manager.cc
index d7da9aeb87..fce313d01c 100644
--- a/engine/src/flutter/assets/asset_manager.cc
+++ b/engine/src/flutter/assets/asset_manager.cc
@@ -34,19 +34,20 @@ void AssetManager::PushBack(std::unique_ptr<AssetResolver> resolver) {
 }
 
 // |blink::AssetResolver|
-bool AssetManager::GetAsBuffer(const std::string& asset_name,
-                               std::vector<uint8_t>* data) const {
+std::unique_ptr<fml::Mapping> AssetManager::GetAsMapping(
+    const std::string& asset_name) const {
   if (asset_name.size() == 0) {
-    return false;
+    return nullptr;
   }
-  TRACE_EVENT0("flutter", "AssetManager::GetAsBuffer");
+  TRACE_EVENT0("flutter", "AssetManager::GetAsMapping");
   for (const auto& resolver : resolvers_) {
-    if (resolver->GetAsBuffer(asset_name, data)) {
-      return true;
+    auto mapping = resolver->GetAsMapping(asset_name);
+    if (mapping != nullptr) {
+      return mapping;
     }
   }
   FML_DLOG(WARNING) << "Could not find asset: " << asset_name;
-  return false;
+  return nullptr;
 }
 
 // |blink::AssetResolver|
diff --git a/engine/src/flutter/assets/asset_manager.h b/engine/src/flutter/assets/asset_manager.h
index 2389ea8705..4ab58ed0f2 100644
--- a/engine/src/flutter/assets/asset_manager.h
+++ b/engine/src/flutter/assets/asset_manager.h
@@ -26,8 +26,8 @@ class AssetManager final : public AssetResolver,
   bool IsValid() const override;
 
   // |blink::AssetResolver|
-  bool GetAsBuffer(const std::string& asset_name,
-                   std::vector<uint8_t>* data) const override;
+  std::unique_ptr<fml::Mapping> GetAsMapping(
+      const std::string& asset_name) const override;
 
  private:
   std::deque<std::unique_ptr<AssetResolver>> resolvers_;
diff --git a/engine/src/flutter/assets/asset_resolver.h b/engine/src/flutter/assets/asset_resolver.h
index 1d70791c6c..d0a68f0bf2 100644
--- a/engine/src/flutter/assets/asset_resolver.h
+++ b/engine/src/flutter/assets/asset_resolver.h
@@ -9,6 +9,7 @@
 #include <vector>
 
 #include "flutter/fml/macros.h"
+#include "flutter/fml/mapping.h"
 
 namespace blink {
 
@@ -20,8 +21,9 @@ class AssetResolver {
 
   virtual bool IsValid() const = 0;
 
-  virtual bool GetAsBuffer(const std::string& asset_name,
-                           std::vector<uint8_t>* data) const = 0;
+  FML_WARN_UNUSED_RESULT
+  virtual std::unique_ptr<fml::Mapping> GetAsMapping(
+      const std::string& asset_name) const = 0;
 
  private:
   FML_DISALLOW_COPY_AND_ASSIGN(AssetResolver);
diff --git a/engine/src/flutter/assets/directory_asset_bundle.cc b/engine/src/flutter/assets/directory_asset_bundle.cc
index 732161589d..830e96d9f5 100644
--- a/engine/src/flutter/assets/directory_asset_bundle.cc
+++ b/engine/src/flutter/assets/directory_asset_bundle.cc
@@ -28,29 +28,23 @@ bool DirectoryAssetBundle::IsValid() const {
 }
 
 // |blink::AssetResolver|
-bool DirectoryAssetBundle::GetAsBuffer(const std::string& asset_name,
-                                       std::vector<uint8_t>* data) const {
-  if (data == nullptr) {
-    return false;
-  }
-
+std::unique_ptr<fml::Mapping> DirectoryAssetBundle::GetAsMapping(
+    const std::string& asset_name) const {
   if (!is_valid_) {
     FML_DLOG(WARNING) << "Asset bundle was not valid.";
-    return false;
+    return nullptr;
   }
 
-  fml::FileMapping mapping(
+  auto mapping = std::make_unique<fml::FileMapping>(
       fml::OpenFile(descriptor_, asset_name.c_str(), fml::OpenPermission::kRead,
                     false /* directory */),
       false /* executable */);
 
-  if (mapping.GetMapping() == nullptr) {
-    return false;
+  if (mapping->GetMapping() == nullptr) {
+    return nullptr;
   }
 
-  data->resize(mapping.GetSize());
-  memmove(data->data(), mapping.GetMapping(), mapping.GetSize());
-  return true;
+  return mapping;
 }
 
 }  // namespace blink
diff --git a/engine/src/flutter/assets/directory_asset_bundle.h b/engine/src/flutter/assets/directory_asset_bundle.h
index b436eaf4f9..f61ac147ff 100644
--- a/engine/src/flutter/assets/directory_asset_bundle.h
+++ b/engine/src/flutter/assets/directory_asset_bundle.h
@@ -26,8 +26,8 @@ class DirectoryAssetBundle : public AssetResolver {
   bool IsValid() const override;
 
   // |blink::AssetResolver|
-  bool GetAsBuffer(const std::string& asset_name,
-                   std::vector<uint8_t>* data) const override;
+  std::unique_ptr<fml::Mapping> GetAsMapping(
+      const std::string& asset_name) const override;
 
   FML_DISALLOW_COPY_AND_ASSIGN(DirectoryAssetBundle);
 };
diff --git a/engine/src/flutter/assets/zip_asset_store.cc b/engine/src/flutter/assets/zip_asset_store.cc
index 1b9216bd34..532461ff32 100644
--- a/engine/src/flutter/assets/zip_asset_store.cc
+++ b/engine/src/flutter/assets/zip_asset_store.cc
@@ -35,19 +35,19 @@ bool ZipAssetStore::IsValid() const {
 }
 
 // |blink::AssetResolver|
-bool ZipAssetStore::GetAsBuffer(const std::string& asset_name,
-                                std::vector<uint8_t>* data) const {
-  TRACE_EVENT0("flutter", "ZipAssetStore::GetAsBuffer");
+std::unique_ptr<fml::Mapping> ZipAssetStore::GetAsMapping(
+    const std::string& asset_name) const {
+  TRACE_EVENT0("flutter", "ZipAssetStore::GetAsMapping");
   auto found = stat_cache_.find(asset_name);
 
   if (found == stat_cache_.end()) {
-    return false;
+    return nullptr;
   }
 
   auto unzipper = CreateUnzipper();
 
   if (!unzipper.is_valid()) {
-    return false;
+    return nullptr;
   }
 
   int result = UNZ_OK;
@@ -55,27 +55,27 @@ bool ZipAssetStore::GetAsBuffer(const std::string& asset_name,
   result = unzGoToFilePos(unzipper.get(), &(found->second.file_pos));
   if (result != UNZ_OK) {
     FXL_LOG(WARNING) << "unzGetCurrentFileInfo failed, error=" << result;
-    return false;
+    return nullptr;
   }
 
   result = unzOpenCurrentFile(unzipper.get());
   if (result != UNZ_OK) {
     FXL_LOG(WARNING) << "unzOpenCurrentFile failed, error=" << result;
-    return false;
+    return nullptr;
   }
 
-  data->resize(found->second.uncompressed_size);
+  std::vector<uint8_t> data(found->second.uncompressed_size);
   int total_read = 0;
-  while (total_read < static_cast<int>(data->size())) {
+  while (total_read < static_cast<int>(data.size())) {
     int bytes_read = unzReadCurrentFile(
-        unzipper.get(), data->data() + total_read, data->size() - total_read);
+        unzipper.get(), data.data() + total_read, data.size() - total_read);
     if (bytes_read <= 0) {
-      return false;
+      return nullptr;
     }
     total_read += bytes_read;
   }
 
-  return true;
+  return std::make_unique<fml::DataMapping>(std::move(data));
 }
 
 void ZipAssetStore::BuildStatCache() {
diff --git a/engine/src/flutter/assets/zip_asset_store.h b/engine/src/flutter/assets/zip_asset_store.h
index 558678e25b..61b09474a6 100644
--- a/engine/src/flutter/assets/zip_asset_store.h
+++ b/engine/src/flutter/assets/zip_asset_store.h
@@ -36,8 +36,8 @@ class ZipAssetStore final : public AssetResolver {
   bool IsValid() const override;
 
   // |blink::AssetResolver|
-  bool GetAsBuffer(const std::string& asset_name,
-                   std::vector<uint8_t>* data) const override;
+  std::unique_ptr<fml::Mapping> GetAsMapping(
+      const std::string& asset_name) const override;
 
   void BuildStatCache();
 
diff --git a/engine/src/flutter/lib/ui/text/asset_manager_font_provider.cc b/engine/src/flutter/lib/ui/text/asset_manager_font_provider.cc
index 68cb4ac3a9..bbb9a19785 100644
--- a/engine/src/flutter/lib/ui/text/asset_manager_font_provider.cc
+++ b/engine/src/flutter/lib/ui/text/asset_manager_font_provider.cc
@@ -14,8 +14,8 @@ namespace blink {
 
 namespace {
 
-void VectorReleaseProc(const void* ptr, void* context) {
-  delete reinterpret_cast<std::vector<uint8_t>*>(context);
+void MappingReleaseProc(const void* ptr, void* context) {
+  delete reinterpret_cast<fml::Mapping*>(context);
 }
 
 }  // anonymous namespace
@@ -90,15 +90,16 @@ SkTypeface* AssetManagerFontStyleSet::createTypeface(int i) {
 
   TypefaceAsset& asset = assets_[index];
   if (!asset.typeface) {
-    std::unique_ptr<std::vector<uint8_t>> asset_buf =
-        std::make_unique<std::vector<uint8_t>>();
-    if (!asset_manager_->GetAsBuffer(asset.asset, asset_buf.get()))
+    std::unique_ptr<fml::Mapping> asset_mapping =
+        asset_manager_->GetAsMapping(asset.asset);
+    if (asset_mapping == nullptr) {
       return nullptr;
+    }
 
-    std::vector<uint8_t>* asset_buf_ptr = asset_buf.release();
-    sk_sp<SkData> asset_data =
-        SkData::MakeWithProc(asset_buf_ptr->data(), asset_buf_ptr->size(),
-                             VectorReleaseProc, asset_buf_ptr);
+    fml::Mapping* asset_mapping_ptr = asset_mapping.release();
+    sk_sp<SkData> asset_data = SkData::MakeWithProc(
+        asset_mapping_ptr->GetMapping(), asset_mapping_ptr->GetSize(),
+        MappingReleaseProc, asset_mapping_ptr);
     std::unique_ptr<SkMemoryStream> stream = SkMemoryStream::Make(asset_data);
 
     // Ownership of the stream is transferred.
diff --git a/engine/src/flutter/lib/ui/text/font_collection.cc b/engine/src/flutter/lib/ui/text/font_collection.cc
index f0c0f7d699..279fb1b480 100644
--- a/engine/src/flutter/lib/ui/text/font_collection.cc
+++ b/engine/src/flutter/lib/ui/text/font_collection.cc
@@ -31,19 +31,18 @@ std::shared_ptr<txt::FontCollection> FontCollection::GetFontCollection() const {
 }
 
 void FontCollection::RegisterFonts(fml::RefPtr<AssetManager> asset_manager) {
-  std::vector<uint8_t> manifest_data;
-  if (!asset_manager->GetAsBuffer("FontManifest.json", &manifest_data)) {
+  std::unique_ptr<fml::Mapping> manifest_mapping =
+      asset_manager->GetAsMapping("FontManifest.json");
+  if (manifest_mapping == nullptr) {
     FXL_DLOG(WARNING) << "Could not find the font manifest in the asset store.";
     return;
   }
 
   rapidjson::Document document;
-  static_assert(sizeof(decltype(manifest_data)::value_type) ==
-                    sizeof(decltype(document)::Ch),
-                "");
-  document.Parse(
-      reinterpret_cast<decltype(document)::Ch*>(manifest_data.data()),
-      manifest_data.size());
+  static_assert(sizeof(decltype(document)::Ch) == sizeof(uint8_t), "");
+  document.Parse(reinterpret_cast<const decltype(document)::Ch*>(
+                     manifest_mapping->GetMapping()),
+                 manifest_mapping->GetSize());
 
   if (document.HasParseError()) {
     FXL_DLOG(WARNING) << "Error parsing the font manifest in the asset store.";
@@ -82,8 +81,8 @@ void FontCollection::RegisterFonts(fml::RefPtr<AssetManager> asset_manager) {
       }
 
       // TODO: Handle weights and styles.
-      font_provider->RegisterAsset(
-          family_name->value.GetString(), font_asset->value.GetString());
+      font_provider->RegisterAsset(family_name->value.GetString(),
+                                   font_asset->value.GetString());
     }
   }
 
diff --git a/engine/src/flutter/lib/ui/window/platform_message_response.h b/engine/src/flutter/lib/ui/window/platform_message_response.h
index 10105e1823..7e25908829 100644
--- a/engine/src/flutter/lib/ui/window/platform_message_response.h
+++ b/engine/src/flutter/lib/ui/window/platform_message_response.h
@@ -7,6 +7,7 @@
 
 #include <vector>
 
+#include "flutter/fml/mapping.h"
 #include "lib/fxl/memory/ref_counted.h"
 #include "lib/fxl/memory/ref_ptr.h"
 
@@ -18,7 +19,7 @@ class PlatformMessageResponse
 
  public:
   // Callable on any thread.
-  virtual void Complete(std::vector<uint8_t> data) = 0;
+  virtual void Complete(std::unique_ptr<fml::Mapping> data) = 0;
   virtual void CompleteEmpty() = 0;
 
   bool is_complete() const { return is_complete_; }
diff --git a/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc b/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
index 5d6af0ab87..59660fe8d1 100644
--- a/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
+++ b/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
@@ -39,6 +39,12 @@ Dart_Handle WrapByteData(std::vector<uint8_t> data) {
   }
 }
 
+Dart_Handle WrapByteData(std::unique_ptr<fml::Mapping> mapping) {
+  std::vector<uint8_t> data(mapping->GetSize());
+  memcpy(data.data(), mapping->GetMapping(), mapping->GetSize());
+  return WrapByteData(std::move(data));
+}
+
 }  // anonymous namespace
 
 PlatformMessageResponseDart::PlatformMessageResponseDart(
@@ -56,7 +62,7 @@ PlatformMessageResponseDart::~PlatformMessageResponseDart() {
   }
 }
 
-void PlatformMessageResponseDart::Complete(std::vector<uint8_t> data) {
+void PlatformMessageResponseDart::Complete(std::unique_ptr<fml::Mapping> data) {
   if (callback_.is_empty())
     return;
   FXL_DCHECK(!is_complete_);
diff --git a/engine/src/flutter/lib/ui/window/platform_message_response_dart.h b/engine/src/flutter/lib/ui/window/platform_message_response_dart.h
index 67bfb3d359..1d65c82b65 100644
--- a/engine/src/flutter/lib/ui/window/platform_message_response_dart.h
+++ b/engine/src/flutter/lib/ui/window/platform_message_response_dart.h
@@ -16,7 +16,7 @@ class PlatformMessageResponseDart : public PlatformMessageResponse {
 
  public:
   // Callable on any thread.
-  void Complete(std::vector<uint8_t> data) override;
+  void Complete(std::unique_ptr<fml::Mapping> data) override;
   void CompleteEmpty() override;
 
  protected:
diff --git a/engine/src/flutter/lib/ui/window/window.cc b/engine/src/flutter/lib/ui/window/window.cc
index 0fe9a12efa..5878dd26e4 100644
--- a/engine/src/flutter/lib/ui/window/window.cc
+++ b/engine/src/flutter/lib/ui/window/window.cc
@@ -98,6 +98,7 @@ void RespondToPlatformMessage(Dart_Handle window,
     UIDartState::Current()->window()->CompletePlatformMessageEmptyResponse(
         response_id);
   } else {
+    // TODO(engine): Avoid this copy.
     const uint8_t* buffer = static_cast<const uint8_t*>(data.data());
     UIDartState::Current()->window()->CompletePlatformMessageResponse(
         response_id,
@@ -288,7 +289,7 @@ void Window::CompletePlatformMessageResponse(int response_id,
     return;
   auto response = std::move(it->second);
   pending_responses_.erase(it);
-  response->Complete(std::move(data));
+  response->Complete(std::make_unique<fml::DataMapping>(std::move(data)));
 }
 
 void Window::RegisterNatives(tonic::DartLibraryNatives* natives) {
diff --git a/engine/src/flutter/shell/common/engine.cc b/engine/src/flutter/shell/common/engine.cc
index de3fd23489..f06c155dbc 100644
--- a/engine/src/flutter/shell/common/engine.cc
+++ b/engine/src/flutter/shell/common/engine.cc
@@ -391,12 +391,16 @@ void Engine::HandleAssetPlatformMessage(
   std::string asset_name(reinterpret_cast<const char*>(data.data()),
                          data.size());
 
-  std::vector<uint8_t> asset_data;
-  if (asset_manager_ && asset_manager_->GetAsBuffer(asset_name, &asset_data)) {
-    response->Complete(std::move(asset_data));
-  } else {
-    response->CompleteEmpty();
+  if (asset_manager_) {
+    std::unique_ptr<fml::Mapping> asset_mapping =
+        asset_manager_->GetAsMapping(asset_name);
+    if (asset_mapping) {
+      response->Complete(std::move(asset_mapping));
+      return;
+    }
   }
+
+  response->CompleteEmpty();
 }
 
 }  // namespace shell
diff --git a/engine/src/flutter/shell/common/isolate_configuration.cc b/engine/src/flutter/shell/common/isolate_configuration.cc
index c971740568..60610e4770 100644
--- a/engine/src/flutter/shell/common/isolate_configuration.cc
+++ b/engine/src/flutter/shell/common/isolate_configuration.cc
@@ -135,60 +135,56 @@ std::unique_ptr<IsolateConfiguration> IsolateConfiguration::InferFromSettings(
   }
 
   // Running from kernel snapshot.
-  {
-    // TODO(engine): Add AssetManager::GetAsMapping or such to avoid the copy.
-    std::vector<uint8_t> kernel;
-    if (asset_manager && asset_manager->GetAsBuffer(
-                             settings.application_kernel_asset, &kernel)) {
-      return CreateForSnapshot(
-          std::make_unique<fml::DataMapping>(std::move(kernel)));
+  if (asset_manager) {
+    std::unique_ptr<fml::Mapping> kernel =
+        asset_manager->GetAsMapping(settings.application_kernel_asset);
+    if (kernel) {
+      return CreateForSnapshot(std::move(kernel));
     }
   }
 
   // Running from script snapshot.
-  {
-    // TODO(engine): Add AssetManager::GetAsMapping or such to avoid the copy.
-    std::vector<uint8_t> script_snapshot;
-    if (asset_manager && asset_manager->GetAsBuffer(
-                             settings.script_snapshot_path, &script_snapshot)) {
-      return CreateForSnapshot(
-          std::make_unique<fml::DataMapping>(std::move(script_snapshot)));
+  if (asset_manager) {
+    std::unique_ptr<fml::Mapping> script_snapshot =
+        asset_manager->GetAsMapping(settings.script_snapshot_path);
+    if (script_snapshot) {
+      return CreateForSnapshot(std::move(script_snapshot));
     }
   }
 
   // Running from kernel divided into several pieces (for sharing).
-  {
-    // TODO(fuchsia): Add AssetManager::GetAsMapping or such to avoid the copy.
-    // TODO(fuchsia): Use async blobfs API once it becomes available.
-    std::vector<uint8_t> kernel_list;
-    if (asset_manager &&
-        asset_manager->GetAsBuffer(settings.application_kernel_list_asset,
-                                   &kernel_list)) {
+  // TODO(fuchsia): Use async blobfs API once it becomes available.
+  if (asset_manager) {
+    std::unique_ptr<fml::Mapping> kernel_list =
+        asset_manager->GetAsMapping(settings.application_kernel_list_asset);
+    if (kernel_list) {
+      const char* kernel_list_str =
+          reinterpret_cast<const char*>(kernel_list->GetMapping());
+      size_t kernel_list_size = kernel_list->GetSize();
+
       std::vector<std::unique_ptr<fml::Mapping>> kernel_pieces;
 
       size_t piece_path_start = 0;
-      while (piece_path_start < kernel_list.size()) {
+      while (piece_path_start < kernel_list_size) {
         size_t piece_path_end = piece_path_start;
-        while ((piece_path_end < kernel_list.size()) &&
-               (kernel_list[piece_path_end] != '\n')) {
+        while ((piece_path_end < kernel_list_size) &&
+               (kernel_list_str[piece_path_end] != '\n')) {
           piece_path_end++;
         }
 
-        std::string piece_path(
-            reinterpret_cast<const char*>(&kernel_list[piece_path_start]),
-            piece_path_end - piece_path_start);
-        std::vector<uint8_t> piece;
-        if (!asset_manager->GetAsBuffer(piece_path, &piece)) {
+        std::string piece_path(&kernel_list_str[piece_path_start],
+                               piece_path_end - piece_path_start);
+        std::unique_ptr<fml::Mapping> piece =
+            asset_manager->GetAsMapping(piece_path);
+        if (piece == nullptr) {
           FXL_LOG(ERROR) << "Failed to load: " << piece_path;
           return nullptr;
         }
 
-        kernel_pieces.emplace_back(
-            std::make_unique<fml::DataMapping>(std::move(piece)));
+        kernel_pieces.emplace_back(std::move(piece));
 
         piece_path_start = piece_path_end + 1;
       }
-
       return CreateForKernelList(std::move(kernel_pieces));
     }
   }
diff --git a/engine/src/flutter/shell/platform/android/apk_asset_provider.cc b/engine/src/flutter/shell/platform/android/apk_asset_provider.cc
index 268897ef5c..27f524cc0b 100644
--- a/engine/src/flutter/shell/platform/android/apk_asset_provider.cc
+++ b/engine/src/flutter/shell/platform/android/apk_asset_provider.cc
@@ -21,28 +21,35 @@ bool APKAssetProvider::IsValid() const {
   return true;
 }
 
-bool APKAssetProvider::GetAsBuffer(const std::string& asset_name,
-                                   std::vector<uint8_t>* data) const {
+class APKAssetMapping : public fml::Mapping {
+ public:
+  APKAssetMapping(AAsset* asset) : asset_(asset) {}
+
+  ~APKAssetMapping() override { AAsset_close(asset_); }
+
+  size_t GetSize() const override { return AAsset_getLength(asset_); }
+
+  const uint8_t* GetMapping() const override {
+    return reinterpret_cast<const uint8_t*>(AAsset_getBuffer(asset_));
+  }
+
+ private:
+  AAsset* const asset_;
+
+  FML_DISALLOW_COPY_AND_ASSIGN(APKAssetMapping);
+};
+
+std::unique_ptr<fml::Mapping> APKAssetProvider::GetAsMapping(
+    const std::string& asset_name) const {
   std::stringstream ss;
   ss << directory_.c_str() << "/" << asset_name;
   AAsset* asset =
       AAssetManager_open(assetManager_, ss.str().c_str(), AASSET_MODE_BUFFER);
   if (!asset) {
-    return false;
+    return nullptr;
   }
 
-  uint8_t* buffer = (uint8_t*)AAsset_getBuffer(asset);
-  if (!buffer) {
-    FXL_LOG(ERROR) << "Got null trying to acquire buffer for asset:" << asset;
-    AAsset_close(asset);
-    return false;
-  }
-
-  data->resize(AAsset_getLength(asset));
-  std::copy(buffer, buffer + data->size(), data->begin());
-
-  AAsset_close(asset);
-  return true;
+  return std::make_unique<APKAssetMapping>(asset);
 }
 
 }  // namespace blink
diff --git a/engine/src/flutter/shell/platform/android/apk_asset_provider.h b/engine/src/flutter/shell/platform/android/apk_asset_provider.h
index 7c3f8e12a2..81164733a5 100644
--- a/engine/src/flutter/shell/platform/android/apk_asset_provider.h
+++ b/engine/src/flutter/shell/platform/android/apk_asset_provider.h
@@ -30,8 +30,8 @@ class APKAssetProvider final : public AssetResolver {
   bool IsValid() const override;
 
   // |blink::AssetResolver|
-  virtual bool GetAsBuffer(const std::string& asset_name,
-                           std::vector<uint8_t>* data) const override;
+  std::unique_ptr<fml::Mapping> GetAsMapping(
+      const std::string& asset_name) const override;
 
   FXL_DISALLOW_COPY_AND_ASSIGN(APKAssetProvider);
 };
diff --git a/engine/src/flutter/shell/platform/android/platform_message_response_android.cc b/engine/src/flutter/shell/platform/android/platform_message_response_android.cc
index b1bdc49147..a625cdcb6d 100644
--- a/engine/src/flutter/shell/platform/android/platform_message_response_android.cc
+++ b/engine/src/flutter/shell/platform/android/platform_message_response_android.cc
@@ -18,7 +18,8 @@ PlatformMessageResponseAndroid::PlatformMessageResponseAndroid(
       platform_task_runner_(std::move(platform_task_runner)) {}
 
 // |blink::PlatformMessageResponse|
-void PlatformMessageResponseAndroid::Complete(std::vector<uint8_t> data) {
+void PlatformMessageResponseAndroid::Complete(
+    std::unique_ptr<fml::Mapping> data) {
   platform_task_runner_->PostTask(
       fxl::MakeCopyable([response = response_id_,               //
                          weak_java_object = weak_java_object_,  //
@@ -37,9 +38,10 @@ void PlatformMessageResponseAndroid::Complete(std::vector<uint8_t> data) {
 
         // Convert the vector to a Java byte array.
         fml::jni::ScopedJavaLocalRef<jbyteArray> data_array(
-            env, env->NewByteArray(data.size()));
-        env->SetByteArrayRegion(data_array.obj(), 0, data.size(),
-                                reinterpret_cast<const jbyte*>(data.data()));
+            env, env->NewByteArray(data->GetSize()));
+        env->SetByteArrayRegion(
+            data_array.obj(), 0, data->GetSize(),
+            reinterpret_cast<const jbyte*>(data->GetMapping()));
 
         // Make the response call into Java.
         FlutterViewHandlePlatformMessageResponse(env, java_object.obj(),
@@ -50,8 +52,8 @@ void PlatformMessageResponseAndroid::Complete(std::vector<uint8_t> data) {
 // |blink::PlatformMessageResponse|
 void PlatformMessageResponseAndroid::CompleteEmpty() {
   platform_task_runner_->PostTask(
-      fxl::MakeCopyable([response = response_id_,               //
-                         weak_java_object = weak_java_object_   //
+      fxl::MakeCopyable([response = response_id_,              //
+                         weak_java_object = weak_java_object_  //
   ]() {
         // We are on the platform thread. Attempt to get the strong reference to
         // the Java object.
diff --git a/engine/src/flutter/shell/platform/android/platform_message_response_android.h b/engine/src/flutter/shell/platform/android/platform_message_response_android.h
index 2ee7f3336a..bca5c5e123 100644
--- a/engine/src/flutter/shell/platform/android/platform_message_response_android.h
+++ b/engine/src/flutter/shell/platform/android/platform_message_response_android.h
@@ -15,7 +15,7 @@ namespace shell {
 class PlatformMessageResponseAndroid : public blink::PlatformMessageResponse {
  public:
   // |blink::PlatformMessageResponse|
-  void Complete(std::vector<uint8_t> data) override;
+  void Complete(std::unique_ptr<fml::Mapping> data) override;
 
   // |blink::PlatformMessageResponse|
   void CompleteEmpty() override;
diff --git a/engine/src/flutter/shell/platform/android/platform_view_android.cc b/engine/src/flutter/shell/platform/android/platform_view_android.cc
index f5ab79542a..a13d9bed14 100644
--- a/engine/src/flutter/shell/platform/android/platform_view_android.cc
+++ b/engine/src/flutter/shell/platform/android/platform_view_android.cc
@@ -106,7 +106,8 @@ void PlatformViewAndroid::InvokePlatformMessageResponseCallback(
       response_data, response_data + java_response_position);
   auto message_response = std::move(it->second);
   pending_responses_.erase(it);
-  message_response->Complete(std::move(response));
+  message_response->Complete(
+      std::make_unique<fml::DataMapping>(std::move(response)));
 }
 
 void PlatformViewAndroid::InvokePlatformMessageEmptyResponseCallback(
@@ -190,7 +191,8 @@ void PlatformViewAndroid::UpdateSemantics(blink::SemanticsNodeUpdates update) {
     size_t num_bytes = 0;
     for (const auto& value : update) {
       num_bytes += kBytesPerNode;
-      num_bytes += value.second.childrenInTraversalOrder.size() * kBytesPerChild;
+      num_bytes +=
+          value.second.childrenInTraversalOrder.size() * kBytesPerChild;
       num_bytes += value.second.childrenInHitTestOrder.size() * kBytesPerChild;
     }
 
diff --git a/engine/src/flutter/shell/platform/android/platform_view_android_jni.cc b/engine/src/flutter/shell/platform/android/platform_view_android_jni.cc
index 3c4e03ff85..30648d5bd2 100644
--- a/engine/src/flutter/shell/platform/android/platform_view_android_jni.cc
+++ b/engine/src/flutter/shell/platform/android/platform_view_android_jni.cc
@@ -174,10 +174,10 @@ std::unique_ptr<IsolateConfiguration> CreateIsolateConfiguration(
   const auto configuration_from_blob =
       [&asset_manager](const std::string& snapshot_name)
       -> std::unique_ptr<IsolateConfiguration> {
-    std::vector<uint8_t> blob;
-    if (asset_manager.GetAsBuffer(snapshot_name, &blob)) {
-      return IsolateConfiguration::CreateForSnapshot(
-          std::make_unique<fml::DataMapping>(std::move(blob)));
+    std::unique_ptr<fml::Mapping> blob =
+        asset_manager.GetAsMapping(snapshot_name);
+    if (blob) {
+      return IsolateConfiguration::CreateForSnapshot(std::move(blob));
     }
     return nullptr;
   };
diff --git a/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.h b/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.h
index 68ebdc032a..7b48a0c8b9 100644
--- a/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.h
+++ b/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.h
@@ -9,12 +9,18 @@
 
 #include <vector>
 
+#include "flutter/fml/mapping.h"
+
 namespace shell {
 
 std::vector<uint8_t> GetVectorFromNSData(NSData* data);
 
 NSData* GetNSDataFromVector(const std::vector<uint8_t>& buffer);
 
+std::unique_ptr<fml::Mapping> GetMappingFromNSData(NSData* data);
+
+NSData* GetNSDataFromMapping(std::unique_ptr<fml::Mapping> mapping);
+
 }  // namespace shell
 
 #endif  // FLUTTER_SHELL_PLATFORM_DARWIN_COMMON_BUFFER_CONVERSIONS_H_
diff --git a/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.mm b/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.mm
index e892228f0f..f7238f104d 100644
--- a/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.mm
+++ b/engine/src/flutter/shell/platform/darwin/common/buffer_conversions.mm
@@ -15,4 +15,12 @@ NSData* GetNSDataFromVector(const std::vector<uint8_t>& buffer) {
   return [NSData dataWithBytes:buffer.data() length:buffer.size()];
 }
 
+std::unique_ptr<fml::Mapping> GetMappingFromNSData(NSData* data) {
+  return std::make_unique<fml::DataMapping>(GetVectorFromNSData(data));
+}
+
+NSData* GetNSDataFromMapping(std::unique_ptr<fml::Mapping> mapping) {
+  return [NSData dataWithBytes:mapping->GetMapping() length:mapping->GetSize()];
+}
+
 }  // namespace shell
diff --git a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h
index b861c5036e..2d925e2836 100644
--- a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h
+++ b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_response_darwin.h
@@ -20,10 +20,10 @@ namespace shell {
 
 class PlatformMessageResponseDarwin : public blink::PlatformMessageResponse {
  public:
-  void Complete(std::vector<uint8_t> data) override {
+  void Complete(std::unique_ptr<fml::Mapping> data) override {
     fxl::RefPtr<PlatformMessageResponseDarwin> self(this);
     platform_task_runner_->PostTask(fxl::MakeCopyable([self, data = std::move(data)]() mutable {
-      self->callback_.get()(shell::GetNSDataFromVector(data));
+      self->callback_.get()(shell::GetNSDataFromMapping(std::move(data)));
     }));
   }
 
diff --git a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.mm b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.mm
index 3ab75bff52..9beee4bb89 100644
--- a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.mm
+++ b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/platform_message_router.mm
@@ -27,7 +27,7 @@ void PlatformMessageRouter::HandlePlatformMessage(
     handler(data, ^(NSData* reply) {
       if (completer) {
         if (reply) {
-          completer->Complete(GetVectorFromNSData(reply));
+          completer->Complete(GetMappingFromNSData(reply));
         } else {
           completer->CompleteEmpty();
         }
diff --git a/engine/src/flutter/shell/platform/embedder/embedder.cc b/engine/src/flutter/shell/platform/embedder/embedder.cc
index db1e4cbc32..f14553471c 100644
--- a/engine/src/flutter/shell/platform/embedder/embedder.cc
+++ b/engine/src/flutter/shell/platform/embedder/embedder.cc
@@ -360,7 +360,8 @@ FlutterResult FlutterEngineSendPlatformMessageResponse(
   if (data_length == 0) {
     response->CompleteEmpty();
   } else {
-    response->Complete({data, data + data_length});
+    response->Complete(std::make_unique<fml::DataMapping>(
+        std::vector<uint8_t>({data, data + data_length})));
   }
 
   delete handle;