chromium/net/disk_cache/simple/simple_entry_format.h

// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_FORMAT_H_
#define NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_FORMAT_H_

#include <stdint.h>

#include "net/base/net_export.h"

namespace disk_cache {

const uint64_t kSimpleInitialMagicNumber = …0xfcfb6d1ba7725c30);
const uint64_t kSimpleFinalMagicNumber = …0xf4fa6f45970d41d8);
const uint64_t kSimpleSparseRangeMagicNumber = …0xeb97bf016553676b);

// A file containing stream 0 and stream 1 in the Simple cache consists of:
//   - a SimpleFileHeader.
//   - the key.
//   - the data from stream 1.
//   - a SimpleFileEOF record for stream 1.
//   - the data from stream 0.
//   - (optionally) the SHA256 of the key.
//   - a SimpleFileEOF record for stream 0.
//
// Because stream 0 data (typically HTTP headers) is on the critical path of
// requests, on open, the cache reads the end of the record and does not
// read the SimpleFileHeader. If the key can be validated with a SHA256, then
// the stream 0 data can be returned to the caller without reading the
// SimpleFileHeader. If the key SHA256 is not present, then the cache must
// read the SimpleFileHeader to confirm key equality.

// A file containing stream 2 in the Simple cache consists of:
//   - a SimpleFileHeader.
//   - the key.
//   - the data.
//   - at the end, a SimpleFileEOF record.

// This is the number of files we can use for representing normal/dense streams.
static const int kSimpleEntryNormalFileCount = …;
static const int kSimpleEntryStreamCount = …;

// Total # of files name we can potentially use; this includes both normal
// API and sparse streams.
static const int kSimpleEntryTotalFileCount = …;

// Note that stream 0/stream 1 files rely on the footer to verify the entry,
// so if the format changes, it's insufficient to change the version here;
// likely the EOF magic should be updated as well.
struct NET_EXPORT_PRIVATE SimpleFileHeader { … };

struct NET_EXPORT_PRIVATE SimpleFileEOF { … };

struct SimpleFileSparseRangeHeader { … };

}  // namespace disk_cache

#endif  // NET_DISK_CACHE_SIMPLE_SIMPLE_ENTRY_FORMAT_H_