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// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.
#include <string>
#include <stdint.h>
#include "leveldb/slice.h"
#include "leveldb/status.h"
#include "leveldb/table_builder.h"
namespace leveldb {
class Block;
class RandomAccessFile;
struct ReadOptions;
// BlockHandle is a pointer to the extent of a file that stores a data
// block or a meta block.
class BlockHandle {
// The offset of the block in the file.
uint64_t offset() const { return offset_; }
void set_offset(uint64_t offset) { offset_ = offset; }
// The size of the stored block
uint64_t size() const { return size_; }
void set_size(uint64_t size) { size_ = size; }
void EncodeTo(std::string* dst) const;
Status DecodeFrom(Slice* input);
// Maximum encoding length of a BlockHandle
enum { kMaxEncodedLength = 10 + 10 };
uint64_t offset_;
uint64_t size_;
// Footer encapsulates the fixed information stored at the tail
// end of every table file.
class Footer {
Footer() { }
// The block handle for the metaindex block of the table
const BlockHandle& metaindex_handle() const { return metaindex_handle_; }
void set_metaindex_handle(const BlockHandle& h) { metaindex_handle_ = h; }
// The block handle for the index block of the table
const BlockHandle& index_handle() const {
return index_handle_;
void set_index_handle(const BlockHandle& h) {
index_handle_ = h;
void EncodeTo(std::string* dst) const;
Status DecodeFrom(Slice* input);
// Encoded length of a Footer. Note that the serialization of a
// Footer will always occupy exactly this many bytes. It consists
// of two block handles and a magic number.
enum {
kEncodedLength = 2*BlockHandle::kMaxEncodedLength + 8
BlockHandle metaindex_handle_;
BlockHandle index_handle_;
// kTableMagicNumber was picked by running
// echo | sha1sum
// and taking the leading 64 bits.
static const uint64_t kTableMagicNumber = 0xdb4775248b80fb57ull;
// 1-byte type + 32-bit crc
static const size_t kBlockTrailerSize = 5;
// Read the block identified by "handle" from "file". On success,
// store a pointer to the heap-allocated result in *block and return
// OK. On failure store NULL in *block and return non-OK.
extern Status ReadBlock(RandomAccessFile* file,
const ReadOptions& options,
const BlockHandle& handle,
Block** block);
// Implementation details follow. Clients should ignore,
inline BlockHandle::BlockHandle()
: offset_(~static_cast<uint64_t>(0)),
size_(~static_cast<uint64_t>(0)) {