Rename ResourcePathShortener to Obfuscator
ResourcePathShortener is a part of Obfuscator. Obfuscator will not
only shorten the path but also handle obfuscating resource names.
Format C++ code by clang-format.
Bug: 228192695
Test: atest aapt2_test idmap2_test
Change-Id: I27b4b1af44061e3cd8a6717ffd46b8a187cdc41d
diff --git a/tools/aapt2/optimize/Obfuscator.cpp b/tools/aapt2/optimize/Obfuscator.cpp
new file mode 100644
index 0000000..f704f26
--- /dev/null
+++ b/tools/aapt2/optimize/Obfuscator.cpp
@@ -0,0 +1,118 @@
+/*
+ * 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/Obfuscator.h"
+
+#include <set>
+#include <string>
+#include <unordered_set>
+
+#include "ResourceTable.h"
+#include "ValueVisitor.h"
+#include "androidfw/StringPiece.h"
+#include "util/Util.h"
+
+static const char base64_chars[] =
+ "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+ "abcdefghijklmnopqrstuvwxyz"
+ "0123456789-_";
+
+namespace aapt {
+
+Obfuscator::Obfuscator(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 Obfuscator::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