blob: 460d6b18bddb01939286d86a1b3a21550248fb2b [file] [log] [blame]
// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "net/disk_cache/simple/simple_version_upgrade.h"
#include <cstring>
#include "base/files/file.h"
#include "base/files/file_path.h"
#include "base/files/file_util.h"
#include "base/files/memory_mapped_file.h"
#include "base/logging.h"
#include "base/pickle.h"
#include "net/disk_cache/simple/simple_backend_version.h"
#include "net/disk_cache/simple/simple_entry_format_history.h"
#include "third_party/zlib/zlib.h"
namespace {
// It is not possible to upgrade cache structures on disk that are of version
// below this, the entire cache should be dropped for them.
const uint32_t kMinVersionAbleToUpgrade = 5;
const char kFakeIndexFileName[] = "index";
const char kIndexFileName[] = "the-real-index";
void LogMessageFailedUpgradeFromVersion(int version) {
LOG(ERROR) << "Failed to upgrade Simple Cache from version: " << version;
bool WriteFakeIndexFile(const base::FilePath& file_name) {
base::File file(file_name, base::File::FLAG_CREATE | base::File::FLAG_WRITE);
if (!file.IsValid())
return false;
disk_cache::FakeIndexData file_contents;
file_contents.initial_magic_number =
file_contents.version = disk_cache::kSimpleVersion;
int bytes_written = file.Write(0, reinterpret_cast<char*>(&file_contents),
if (bytes_written != sizeof(file_contents)) {
LOG(ERROR) << "Failed to write fake index file: "
<< file_name.LossyDisplayName();
return false;
return true;
} // namespace
namespace disk_cache {
FakeIndexData::FakeIndexData() {
// Make hashing repeatable: leave no padding bytes untouched.
std::memset(this, 0, sizeof(*this));
// Migrates the cache directory from version 4 to version 5.
// Returns true iff it succeeds.
// The V5 and V6 caches differ in the name of the index file (it moved to a
// subdirectory) and in the file format (directory last-modified time observed
// by the index writer has gotten appended to the pickled format).
// To keep complexity small this specific upgrade code *deletes* the old index
// file. The directory for the new index file has to be created lazily anyway,
// so it is not done in the upgrader.
// Below is the detailed description of index file format differences. It is for
// reference purposes. This documentation would be useful to move closer to the
// next index upgrader when the latter gets introduced.
// Path:
// V5: $cachedir/the-real-index
// V6: $cachedir/index-dir/the-real-index
// Pickled file format:
// Both formats extend Pickle::Header by 32bit value of the CRC-32 of the
// pickled data.
// <v5-index> ::= <v5-index-metadata> <entry-info>*
// <v5-index-metadata> ::= UInt64(kSimpleIndexMagicNumber)
// UInt32(4)
// UInt64(<number-of-entries>)
// UInt64(<cache-size-in-bytes>)
// <entry-info> ::= UInt64(<hash-of-the-key>)
// Int64(<entry-last-used-time>)
// UInt64(<entry-size-in-bytes>)
// <v6-index> ::= <v6-index-metadata>
// <entry-info>*
// Int64(<cache-dir-mtime>)
// <v6-index-metadata> ::= UInt64(kSimpleIndexMagicNumber)
// UInt32(5)
// UInt64(<number-of-entries>)
// UInt64(<cache-size-in-bytes>)
// Where:
// <entry-size-in-bytes> is equal the sum of all file sizes of the entry.
// <cache-dir-mtime> is the last modification time with nanosecond precision
// of the directory, where all files for entries are stored.
// <hash-of-the-key> represent the first 64 bits of a SHA-1 of the key.
bool UpgradeIndexV5V6(const base::FilePath& cache_directory) {
const base::FilePath old_index_file =
if (!base::DeleteFile(old_index_file, /* recursive = */ false))
return false;
return true;
// Some points about the Upgrade process are still not clear:
// 1. if the upgrade path requires dropping cache it would be faster to just
// return an initialization error here and proceed with asynchronous cache
// cleanup in CacheCreator. Should this hack be considered valid? Some smart
// tests may fail.
// 2. Because Android process management allows for killing a process at any
// time, the upgrade process may need to deal with a partially completed
// previous upgrade. For example, while upgrading A -> A + 2 we are the
// process gets killed and some parts are remaining at version A + 1. There
// are currently no generic mechanisms to resolve this situation, co the
// upgrade codes need to ensure they can continue after being stopped in the
// middle. It also means that the "fake index" must be flushed in between the
// upgrade steps. Atomicity of this is an interesting research topic. The
// intermediate fake index flushing must be added as soon as we add more
// upgrade steps.
bool UpgradeSimpleCacheOnDisk(const base::FilePath& path) {
// There is a convention among disk cache backends: looking at the magic in
// the file "index" it should be sufficient to determine if the cache belongs
// to the currently running backend. The Simple Backend stores its index in
// the file "the-real-index" (see and the file "index"
// only signifies presence of the implementation's magic and version. There
// are two reasons for that:
// 1. Absence of the index is itself not a fatal error in the Simple Backend
// 2. The Simple Backend has pickled file format for the index making it hacky
// to have the magic in the right place.
const base::FilePath fake_index = path.AppendASCII(kFakeIndexFileName);
base::File fake_index_file(fake_index,
base::File::FLAG_OPEN | base::File::FLAG_READ);
if (!fake_index_file.IsValid()) {
if (fake_index_file.error_details() == base::File::FILE_ERROR_NOT_FOUND) {
return WriteFakeIndexFile(fake_index);
return false;
FakeIndexData file_header;
int bytes_read = fake_index_file.Read(0,
if (bytes_read != sizeof(file_header) ||
file_header.initial_magic_number !=
disk_cache::simplecache_v5::kSimpleInitialMagicNumber) {
LOG(ERROR) << "File structure does not match the disk cache backend.";
return false;
uint32_t version_from = file_header.version;
if (version_from < kMinVersionAbleToUpgrade ||
version_from > kSimpleVersion) {
LOG(ERROR) << "Inconsistent cache version.";
return false;
bool new_fake_index_needed = (version_from != kSimpleVersion);
// There should be one upgrade routine here for each incremental upgrade
// starting at kMinVersionAbleToUpgrade.
static_assert(kMinVersionAbleToUpgrade == 5, "upgrade routines don't match");
DCHECK_LE(5U, version_from);
if (version_from == 5) {
// Upgrade only the index for V5 -> V6 move.
if (!UpgradeIndexV5V6(path)) {
return false;
DCHECK_LE(6U, version_from);
if (version_from == 6) {
// No upgrade from V6 -> V7, because the entry format has not changed and
// the V7 index reader is backwards compatible.
DCHECK_EQ(kSimpleVersion, version_from);
if (!new_fake_index_needed)
return true;
const base::FilePath temp_fake_index = path.AppendASCII("upgrade-index");
if (!WriteFakeIndexFile(temp_fake_index)) {
base::DeleteFile(temp_fake_index, /* recursive = */ false);
LOG(ERROR) << "Failed to write a new fake index.";
return false;
if (!base::ReplaceFile(temp_fake_index, fake_index, NULL)) {
LOG(ERROR) << "Failed to replace the fake index.";
return false;
return true;
} // namespace disk_cache