include/androidfw/AssetManager2.h

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ANDROIDFW_ASSETMANAGER2_H_
#define ANDROIDFW_ASSETMANAGER2_H_

#include "android-base/macros.h"

#include <limits>
#include <unordered_map>

#include "androidfw/ApkAssets.h"
#include "androidfw/Asset.h"
#include "androidfw/AssetManager.h"
#include "androidfw/ResourceTypes.h"
#include "androidfw/Util.h"

namespace android {

class Theme;

using ApkAssetsCookie = int32_t;

enum : ApkAssetsCookie {
  kInvalidCookie = -1,
};

// Holds a bag that has been merged with its parent, if one exists.
struct ResolvedBag {
  // A single key-value entry in a bag.
  struct Entry {
    // The key, as described in ResTable_map::name.
    uint32_t key;

    Res_value value;

    // Which ApkAssets this entry came from.
    ApkAssetsCookie cookie;

    ResStringPool* key_pool;
    ResStringPool* type_pool;
  };

  // Denotes the configuration axis that this bag varies with.
  // If a configuration changes with respect to one of these axis,
  // the bag should be reloaded.
  uint32_t type_spec_flags;

  // The number of entries in this bag. Access them by indexing into `entries`.
  uint32_t entry_count;

  // The array of entries for this bag. An empty array is a neat trick to force alignment
  // of the Entry structs that follow this structure and avoids a bunch of casts.
  Entry entries[0];
};

// AssetManager2 is the main entry point for accessing assets and resources.
// AssetManager2 provides caching of resources retrieved via the underlying
// ApkAssets.
class AssetManager2 : public ::AAssetManager {
 public:
  struct ResourceName {
    const char* package = nullptr;
    size_t package_len = 0u;

    const char* type = nullptr;
    const char16_t* type16 = nullptr;
    size_t type_len = 0u;

    const char* entry = nullptr;
    const char16_t* entry16 = nullptr;
    size_t entry_len = 0u;
  };

  AssetManager2();

  // Sets/resets the underlying ApkAssets for this AssetManager. The ApkAssets
  // are not owned by the AssetManager, and must have a longer lifetime.
  //
  // Only pass invalidate_caches=false when it is known that the structure
  // change in ApkAssets is due to a safe addition of resources with completely
  // new resource IDs.
  bool SetApkAssets(const std::vector<const ApkAssets*>& apk_assets, bool invalidate_caches = true);

  const std::vector<const ApkAssets*> GetApkAssets() const;

  // Returns the string pool for the given asset cookie.
  // Use the string pool returned here with a valid Res_value object of
  // type Res_value::TYPE_STRING.
  const ResStringPool* GetStringPoolForCookie(ApkAssetsCookie cookie) const;

  // Sets/resets the configuration for this AssetManager. This will cause all
  // caches that are related to the configuration change to be invalidated.
  void SetConfiguration(const ResTable_config& configuration);

  const ResTable_config& GetConfiguration() const;

  // Searches the set of APKs loaded by this AssetManager and opens the first one found located
  // in the assets/ directory.
  // `mode` controls how the file is opened.
  //
  // NOTE: The loaded APKs are searched in reverse order.
  std::unique_ptr<Asset> Open(const std::string& filename, Asset::AccessMode mode);

  // Opens a file within the assets/ directory of the APK specified by `cookie`.
  // `mode` controls how the file is opened.
  std::unique_ptr<Asset> Open(const std::string& filename, ApkAssetsCookie cookie,
                              Asset::AccessMode mode);

  // Searches the set of APKs loaded by this AssetManager and opens the first one found.
  // `mode` controls how the file is opened.
  // `out_cookie` is populated with the cookie of the APK this file was found in.
  //
  // NOTE: The loaded APKs are searched in reverse order.
  std::unique_ptr<Asset> OpenNonAsset(const std::string& filename, Asset::AccessMode mode,
                                      ApkAssetsCookie* out_cookie = nullptr);

  // Opens a file in the APK specified by `cookie`. `mode` controls how the file is opened.
  // This is typically used to open a specific AndroidManifest.xml, or a binary XML file
  // referenced by a resource lookup with GetResource().
  std::unique_ptr<Asset> OpenNonAsset(const std::string& filename, ApkAssetsCookie cookie,
                                      Asset::AccessMode mode);

  // Populates the `out_name` parameter with resource name information.
  // Utf8 strings are preferred, and only if they are unavailable are
  // the Utf16 variants populated.
  // Returns false if the resource was not found or the name was missing/corrupt.
  bool GetResourceName(uint32_t resid, ResourceName* out_name);

  // Populates `out_flags` with the bitmask of configuration axis that this resource varies with.
  // See ResTable_config for the list of configuration axis.
  // Returns false if the resource was not found.
  bool GetResourceFlags(uint32_t resid, uint32_t* out_flags);

  // Retrieves the best matching resource with ID `resid`. The resource value is filled into
  // `out_value` and the configuration for the selected value is populated in `out_selected_config`.
  // `out_flags` holds the same flags as retrieved with GetResourceFlags().
  // If `density_override` is non-zero, the configuration to match against is overridden with that
  // density.
  //
  // Returns a valid cookie if the resource was found. If the resource was not found, or if the
  // resource was a map/bag type, then kInvalidCookie is returned. If `may_be_bag` is false,
  // this function logs if the resource was a map/bag type before returning kInvalidCookie.
  ApkAssetsCookie GetResource(uint32_t resid, bool may_be_bag, uint16_t density_override,
                              Res_value* out_value, ResTable_config* out_selected_config,
                              uint32_t* out_flags);

  // Retrieves the best matching bag/map resource with ID `resid`.
  // This method will resolve all parent references for this bag and merge keys with the child.
  // To iterate over the keys, use the following idiom:
  //
  //  const AssetManager2::ResolvedBag* bag = asset_manager->GetBag(id);
  //  if (bag != nullptr) {
  //    for (auto iter = begin(bag); iter != end(bag); ++iter) {
  //      ...
  //    }
  //  }
  const ResolvedBag* GetBag(uint32_t resid);

  // Creates a new Theme from this AssetManager.
  std::unique_ptr<Theme> NewTheme();

 private:
  DISALLOW_COPY_AND_ASSIGN(AssetManager2);

  // Finds the best entry for `resid` amongst all the ApkAssets. The entry can be a simple
  // Res_value, or a complex map/bag type.
  //
  // `density_override` overrides the density of the current configuration when doing a search.
  //
  // When `stop_at_first_match` is true, the first match found is selected and the search
  // terminates. This is useful for methods that just look up the name of a resource and don't
  // care about the value. In this case, the value of `out_flags` is incomplete and should not
  // be used.
  //
  // `out_flags` stores the resulting bitmask of configuration axis with which the resource
  // value varies.
  ApkAssetsCookie FindEntry(uint32_t resid, uint16_t density_override, bool stop_at_first_match,
                            LoadedArsc::Entry* out_entry, ResTable_config* out_selected_config,
                            uint32_t* out_flags);

  // Purge all resources that are cached and vary by the configuration axis denoted by the
  // bitmask `diff`.
  void InvalidateCaches(uint32_t diff);

  // The ordered list of ApkAssets to search. These are not owned by the AssetManager, and must
  // have a longer lifetime.
  std::vector<const ApkAssets*> apk_assets_;

  // The current configuration set for this AssetManager. When this changes, cached resources
  // may need to be purged.
  ResTable_config configuration_;

  // Cached set of bags. These are cached because they can inherit keys from parent bags,
  // which involves some calculation.
  std::unordered_map<uint32_t, util::unique_cptr<ResolvedBag>> cached_bags_;
};

class Theme {
  friend class AssetManager2;

 public:
  // Applies the style identified by `resid` to this theme. This can be called
  // multiple times with different styles. By default, any theme attributes that
  // are already defined before this call are not overridden. If `force` is set
  // to true, this behavior is changed and all theme attributes from the style at
  // `resid` are applied.
  // Returns false if the style failed to apply.
  bool ApplyStyle(uint32_t resid, bool force = false);

  // Sets this Theme to be a copy of `o` if `o` has the same AssetManager as this Theme.
  // Returns false if the AssetManagers of the Themes were not compatible.
  bool SetTo(const Theme& o);

  void Clear();

  inline const AssetManager2* GetAssetManager() const { return asset_manager_; }

  // Returns a bit mask of configuration changes that will impact this
  // theme (and thus require completely reloading it).
  inline uint32_t GetChangingConfigurations() const { return type_spec_flags_; }

  // Retrieve a value in the theme. If the theme defines this value,
  // returns an asset cookie indicating which ApkAssets it came from
  // and populates `out_value` with the value. If `out_flags` is non-null,
  // populates it with a bitmask of the configuration axis the resource
  // varies with.
  //
  // If the attribute is not found, returns kInvalidCookie.
  //
  // NOTE: This function does not do reference traversal. If you want
  // to follow references to other resources to get the "real" value to
  // use, you need to call ResolveReference() after this function.
  ApkAssetsCookie GetAttribute(uint32_t resid, Res_value* out_value,
                               uint32_t* out_flags = nullptr) const;

  // This is like AssetManager2::ResolveReference(), but also takes
  // care of resolving attribute references to the theme.
  ApkAssetsCookie ResolveAttributeReference(Res_value* in_out_value, ApkAssetsCookie src_cookie,
                                            uint32_t* out_last_ref = nullptr,
                                            uint32_t* in_out_type_spec_flags = nullptr,
                                            ResTable_config* out_selected_config = nullptr) const;

 private:
  DISALLOW_COPY_AND_ASSIGN(Theme);

  // Called by AssetManager2.
  explicit inline Theme(AssetManager2* asset_manager) : asset_manager_(asset_manager) {}

  struct Entry {
    ApkAssetsCookie cookie;
    uint32_t type_spec_flags;
    Res_value value;
  };

  struct Type {
    // Use uint32_t for fewer cycles when loading from memory.
    uint32_t entry_count;
    uint32_t entry_capacity;
    Entry entries[0];
  };

  static constexpr const size_t kPackageCount = std::numeric_limits<uint8_t>::max() + 1;
  static constexpr const size_t kTypeCount = std::numeric_limits<uint8_t>::max() + 1;

  struct Package {
    // Each element of Type will be a dynamically sized object
    // allocated to have the entries stored contiguously with the Type.
    util::unique_cptr<Type> types[kTypeCount];
  };

  AssetManager2* asset_manager_;
  uint32_t type_spec_flags_ = 0u;
  std::unique_ptr<Package> packages_[kPackageCount];
};

inline const ResolvedBag::Entry* begin(const ResolvedBag* bag) { return bag->entries; }

inline const ResolvedBag::Entry* end(const ResolvedBag* bag) {
  return bag->entries + bag->entry_count;
}

}  // namespace android

#endif /* ANDROIDFW_ASSETMANAGER2_H_ */