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/*
* Copyright (C) 2020 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.
*/
#pragma once
#include <stdint.h>
#include <map>
#include <memory>
#include <string_view>
#include <utility>
#include <android-base/logging.h>
#include <log/log.h>
#include "zip_error.h"
/*
* Round up to the next highest power of 2.
*
* Found on http://graphics.stanford.edu/~seander/bithacks.html.
*
* TODO: could switch to use std::bit_ceil() once ready
*/
static constexpr uint32_t RoundUpPower2(uint32_t val) {
val--;
val |= val >> 1;
val |= val >> 2;
val |= val >> 4;
val |= val >> 8;
val |= val >> 16;
val++;
return val;
}
// This class is the interface of the central directory entries map. The map
// helps to locate a particular cd entry based on the filename.
class CdEntryMapInterface {
public:
virtual ~CdEntryMapInterface() = default;
// Adds an entry to the map. The |name| should internally points to the
// filename field of a cd entry. And |start| points to the beginning of the
// central directory. Returns 0 on success.
virtual ZipError AddToMap(std::string_view name, const uint8_t* start) = 0;
// For the zip entry |entryName|, finds the offset of its filename field in
// the central directory. Returns a pair of [status, offset]. The value of
// the status is 0 on success.
virtual std::pair<ZipError, uint64_t> GetCdEntryOffset(std::string_view name,
const uint8_t* cd_start) const = 0;
// Resets the iterator to the beginning of the map.
virtual void ResetIteration() = 0;
// Returns the [name, cd offset] of the current element. Also increments the
// iterator to points to the next element. Returns an empty pair we have read
// past boundary.
virtual std::pair<std::string_view, uint64_t> Next(const uint8_t* cd_start) = 0;
static std::unique_ptr<CdEntryMapInterface> Create(uint64_t num_entries,
size_t cd_length, uint16_t max_file_name_length);
};
/**
* More space efficient string representation of strings in an mmaped zipped
* file than std::string_view. Using std::string_view as an entry in the
* ZipArchive hash table wastes space. std::string_view stores a pointer to a
* string (on 64 bit, 8 bytes) and the length to read from that pointer,
* 2 bytes. Because of alignment, the structure consumes 16 bytes, wasting
* 6 bytes.
*/
/**
* ZipStringOffset20 stores 20-bit for offset from a fixed location in the memory
* mapped file instead of the entire address, with 12-bit for filename length (i.e.
* typical PATH_MAX), consuming 4 bytes in total
*/
struct ZipStringOffset20 {
static constexpr size_t offset_max = (1u << 20) - 1;
static constexpr size_t length_max = (1u << 12) - 1;
uint32_t name_offset : 20;
uint16_t name_length : 12;
};
static_assert(sizeof(struct ZipStringOffset20) == 4);
/**
* ZipStringOffset32 stores a 4 byte offset from a fixed location in the memory
* mapped file instead of the entire address, consuming 8 bytes with alignment.
*/
struct ZipStringOffset32 {
uint32_t name_offset;
uint16_t name_length;
};
// This implementation of CdEntryMap uses an array hash table. It uses less
// memory than std::map; and it's used as the default implementation for zip
// archives without zip64 extension.
template <typename ZipStringOffset>
class CdEntryMapZip32 : public CdEntryMapInterface {
public:
ZipError AddToMap(std::string_view name, const uint8_t* start) override;
std::pair<ZipError, uint64_t> GetCdEntryOffset(std::string_view name,
const uint8_t* cd_start) const override;
void ResetIteration() override;
std::pair<std::string_view, uint64_t> Next(const uint8_t* cd_start) override;
explicit CdEntryMapZip32(uint16_t num_entries) {
/*
* Create hash table. We have a minimum 75% load factor, possibly as
* low as 50% after we round off to a power of 2. There must be at
* least one unused entry to avoid an infinite loop during creation.
*/
hash_table_size_ = RoundUpPower2(1 + (num_entries * 4) / 3);
hash_table_.reset(static_cast<ZipStringOffset*>(
calloc(hash_table_size_, sizeof(ZipStringOffset))));
CHECK(hash_table_ != nullptr)
<< "Zip: unable to allocate the " << hash_table_size_
<< " entry hash_table, entry size: " << sizeof(ZipStringOffset);
}
// We know how many entries are in the Zip archive, so we can have a
// fixed-size hash table. We define a load factor of 0.75 and over
// allocate so the maximum number entries can never be higher than
// ((4 * UINT16_MAX) / 3 + 1) which can safely fit into a uint32_t.
struct FreeDeleter {
void operator()(void* ptr) const { ::free(ptr); }
};
std::unique_ptr<ZipStringOffset[], FreeDeleter> hash_table_;
uint32_t hash_table_size_{0};
private:
// The position of element for the current iteration.
uint32_t current_position_{0};
};
// This implementation of CdEntryMap uses a std::map
class CdEntryMapZip64 : public CdEntryMapInterface {
public:
ZipError AddToMap(std::string_view name, const uint8_t* start) override;
std::pair<ZipError, uint64_t> GetCdEntryOffset(std::string_view name,
const uint8_t* cd_start) const override;
void ResetIteration() override;
std::pair<std::string_view, uint64_t> Next(const uint8_t* cd_start) override;
CdEntryMapZip64() = default;
private:
std::map<std::string_view, uint64_t> entry_table_;
std::map<std::string_view, uint64_t>::iterator iterator_;
};
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