From d0c22cc8e51c5297d11f708be706ba1ce0582426 Mon Sep 17 00:00:00 2001
From: Yurii Zubrytskyi <zyy@google.com>
Date: Thu, 10 Nov 2022 14:11:05 -0800
Subject: [PATCH] IsFabricatedOverlay() optimization

This function is used mostly to select what type should
be parsing the very same file, so instead of opening that file
again later make it able to accept an opened fd

Bug: 237583012
Test: build + boot
Change-Id: I9ca1f44d6fe16fec0dd4732bfc9f0d6272d3b1e7
---
 libs/androidfw/ApkAssets.cpp                  |  9 ++++----
 libs/androidfw/AssetsProvider.cpp             |  4 ++--
 libs/androidfw/ResourceTypes.cpp              | 23 +++++++++++++++----
 .../include/androidfw/AssetsProvider.h        |  2 +-
 .../include/androidfw/ResourceTypes.h         |  3 +++
 5 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/libs/androidfw/ApkAssets.cpp b/libs/androidfw/ApkAssets.cpp
index 9aa37872b8de6..c0fa63a08fac6 100755
--- a/libs/androidfw/ApkAssets.cpp
+++ b/libs/androidfw/ApkAssets.cpp
@@ -83,15 +83,16 @@ std::unique_ptr<ApkAssets> ApkAssets::LoadOverlay(const std::string& idmap_path,
     return {};
   }
 
+  std::string overlay_path(loaded_idmap->OverlayApkPath());
+  auto fd = unique_fd(::open(overlay_path.c_str(), O_RDONLY|O_CLOEXEC));
   std::unique_ptr<AssetsProvider> overlay_assets;
-  const std::string overlay_path(loaded_idmap->OverlayApkPath());
-  if (IsFabricatedOverlay(overlay_path)) {
+  if (IsFabricatedOverlay(fd)) {
     // Fabricated overlays do not contain resource definitions. All of the overlay resource values
     // are defined inline in the idmap.
-    overlay_assets = EmptyAssetsProvider::Create(overlay_path);
+    overlay_assets = EmptyAssetsProvider::Create(std::move(overlay_path));
   } else {
     // The overlay should be an APK.
-    overlay_assets = ZipAssetsProvider::Create(overlay_path, flags);
+    overlay_assets = ZipAssetsProvider::Create(std::move(fd), std::move(overlay_path), flags);
   }
   if (overlay_assets == nullptr) {
     return {};
diff --git a/libs/androidfw/AssetsProvider.cpp b/libs/androidfw/AssetsProvider.cpp
index 289d7e6604025..80e560747a3e3 100644
--- a/libs/androidfw/AssetsProvider.cpp
+++ b/libs/androidfw/AssetsProvider.cpp
@@ -393,8 +393,8 @@ std::unique_ptr<AssetsProvider> EmptyAssetsProvider::Create() {
   return std::unique_ptr<EmptyAssetsProvider>(new EmptyAssetsProvider({}));
 }
 
-std::unique_ptr<AssetsProvider> EmptyAssetsProvider::Create(const std::string& path) {
-  return std::unique_ptr<EmptyAssetsProvider>(new EmptyAssetsProvider(path));
+std::unique_ptr<AssetsProvider> EmptyAssetsProvider::Create(std::string path) {
+  return std::unique_ptr<EmptyAssetsProvider>(new EmptyAssetsProvider(std::move(path)));
 }
 
 std::unique_ptr<Asset> EmptyAssetsProvider::OpenInternal(const std::string& /* path */,
diff --git a/libs/androidfw/ResourceTypes.cpp b/libs/androidfw/ResourceTypes.cpp
index 035ed4f394554..4a41ab521faa4 100644
--- a/libs/androidfw/ResourceTypes.cpp
+++ b/libs/androidfw/ResourceTypes.cpp
@@ -33,7 +33,9 @@
 #include <type_traits>
 #include <vector>
 
+#include <android-base/file.h>
 #include <android-base/macros.h>
+#include <android-base/utf8.h>
 #include <androidfw/ByteBucketArray.h>
 #include <androidfw/ResourceTypes.h>
 #include <androidfw/TypeWrappers.h>
@@ -236,12 +238,23 @@ void Res_png_9patch::serialize(const Res_png_9patch& patch, const int32_t* xDivs
 }
 
 bool IsFabricatedOverlay(const std::string& path) {
-  std::ifstream fin(path);
-  uint32_t magic;
-  if (fin.read(reinterpret_cast<char*>(&magic), sizeof(uint32_t))) {
-    return magic == kFabricatedOverlayMagic;
+  return IsFabricatedOverlay(path.c_str());
+}
+
+bool IsFabricatedOverlay(const char* path) {
+  auto fd = base::unique_fd(base::utf8::open(path, O_RDONLY|O_CLOEXEC));
+  if (fd < 0) {
+    return false;
   }
-  return false;
+  return IsFabricatedOverlay(fd);
+}
+
+bool IsFabricatedOverlay(base::borrowed_fd fd) {
+  uint32_t magic;
+  if (!base::ReadFullyAtOffset(fd, &magic, sizeof(magic), 0)) {
+    return false;
+  }
+  return magic == kFabricatedOverlayMagic;
 }
 
 static bool assertIdmapHeader(const void* idmap, size_t size) {
diff --git a/libs/androidfw/include/androidfw/AssetsProvider.h b/libs/androidfw/include/androidfw/AssetsProvider.h
index 13cbe3bab84ca..af6e7f41e6bbc 100644
--- a/libs/androidfw/include/androidfw/AssetsProvider.h
+++ b/libs/androidfw/include/androidfw/AssetsProvider.h
@@ -181,7 +181,7 @@ struct MultiAssetsProvider : public AssetsProvider {
 // Does not provide any assets.
 struct EmptyAssetsProvider : public AssetsProvider {
   static std::unique_ptr<AssetsProvider> Create();
-  static std::unique_ptr<AssetsProvider> Create(const std::string& path);
+  static std::unique_ptr<AssetsProvider> Create(std::string path);
 
   bool ForEachFile(const std::string& path,
                    const std::function<void(StringPiece, FileType)>& f) const override;
diff --git a/libs/androidfw/include/androidfw/ResourceTypes.h b/libs/androidfw/include/androidfw/ResourceTypes.h
index d98e97ad32f08..6968977d7d12a 100644
--- a/libs/androidfw/include/androidfw/ResourceTypes.h
+++ b/libs/androidfw/include/androidfw/ResourceTypes.h
@@ -21,6 +21,7 @@
 #define _LIBS_UTILS_RESOURCE_TYPES_H
 
 #include <android-base/expected.h>
+#include <android-base/unique_fd.h>
 
 #include <androidfw/Asset.h>
 #include <androidfw/Errors.h>
@@ -58,6 +59,8 @@ constexpr const uint32_t kFabricatedOverlayCurrentVersion = 3;
 
 // Returns whether or not the path represents a fabricated overlay.
 bool IsFabricatedOverlay(const std::string& path);
+bool IsFabricatedOverlay(const char* path);
+bool IsFabricatedOverlay(android::base::borrowed_fd fd);
 
 /**
  * In C++11, char16_t is defined as *at least* 16 bits. We do a lot of