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/*
* Copyright (C) 2018 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.
*/
#include "optimize/ResourcePathShortener.h"
#include <set>
#include <unordered_set>
#include "androidfw/StringPiece.h"
#include "ResourceTable.h"
#include "ValueVisitor.h"
#include "util/Util.h"
static const std::string base64_chars =
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz"
"0123456789-_";
namespace aapt {
ResourcePathShortener::ResourcePathShortener(
std::map<std::string, std::string>& path_map_out)
: path_map_(path_map_out) {
}
std::string ShortenFileName(const android::StringPiece& file_path, int output_length) {
std::size_t hash_num = std::hash<android::StringPiece>{}(file_path);
std::string result = "";
// Convert to (modified) base64 so that it is a proper file path.
for (int i = 0; i < output_length; i++) {
uint8_t sextet = hash_num & 0x3f;
hash_num >>= 6;
result += base64_chars[sextet];
}
return result;
}
// Return the optimal hash length such that at most 10% of resources collide in
// their shortened path.
// Reference: http://matt.might.net/articles/counting-hash-collisions/
int OptimalShortenedLength(int num_resources) {
if (num_resources > 4000) {
return 3;
} else {
return 2;
}
}
std::string GetShortenedPath(const android::StringPiece& shortened_filename,
const android::StringPiece& extension, int collision_count) {
std::string shortened_path = "res/" + shortened_filename.to_string();
if (collision_count > 0) {
shortened_path += std::to_string(collision_count);
}
shortened_path += extension;
return shortened_path;
}
// implement custom comparator of FileReference pointers so as to use the
// underlying filepath as key rather than the integer address. This is to ensure
// determinism of output for colliding files.
struct PathComparator {
bool operator() (const FileReference* lhs, const FileReference* rhs) const {
return lhs->path->compare(*rhs->path);
}
};
bool ResourcePathShortener::Consume(IAaptContext* context, ResourceTable* table) {
// used to detect collisions
std::unordered_set<std::string> shortened_paths;
std::set<FileReference*, PathComparator> file_refs;
for (auto& package : table->packages) {
for (auto& type : package->types) {
for (auto& entry : type->entries) {
for (auto& config_value : entry->values) {
FileReference* file_ref = ValueCast<FileReference>(config_value->value.get());
if (file_ref) {
file_refs.insert(file_ref);
}
}
}
}
}
int num_chars = OptimalShortenedLength(file_refs.size());
for (auto& file_ref : file_refs) {
android::StringPiece res_subdir, actual_filename, extension;
util::ExtractResFilePathParts(*file_ref->path, &res_subdir, &actual_filename, &extension);
// Android detects ColorStateLists via pathname, skip res/color*
if (util::StartsWith(res_subdir, "res/color"))
continue;
std::string shortened_filename = ShortenFileName(*file_ref->path, num_chars);
int collision_count = 0;
std::string shortened_path = GetShortenedPath(shortened_filename, extension, collision_count);
while (shortened_paths.find(shortened_path) != shortened_paths.end()) {
collision_count++;
shortened_path = GetShortenedPath(shortened_filename, extension, collision_count);
}
shortened_paths.insert(shortened_path);
path_map_.insert({*file_ref->path, shortened_path});
file_ref->path = table->string_pool.MakeRef(shortened_path, file_ref->path.GetContext());
}
return true;
}
} // namespace aapt
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