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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.
#ifndef STORAGE_LEVELDB_TABLE_FORMAT_H_
#define STORAGE_LEVELDB_TABLE_FORMAT_H_
#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 {
public:
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 };
private:
uint64_t offset_;
uint64_t size_;
};
// Footer encapsulates the fixed information stored at the tail
// end of every table file.
class Footer {
public:
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
};
private:
BlockHandle metaindex_handle_;
BlockHandle index_handle_;
};
// kTableMagicNumber was picked by running
// echo http://code.google.com/p/leveldb/ | 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;
struct BlockContents {
Slice data; // Actual contents of data
bool cachable; // True iff data can be cached
bool heap_allocated; // True iff caller should delete[] data.data()
};
// Read the block identified by "handle" from "file". On failure
// return non-OK. On success fill *result and return OK.
extern Status ReadBlock(RandomAccessFile* file,
const ReadOptions& options,
const BlockHandle& handle,
BlockContents* result);
// Implementation details follow. Clients should ignore,
inline BlockHandle::BlockHandle()
: offset_(~static_cast<uint64_t>(0)),
size_(~static_cast<uint64_t>(0)) {
}
} // namespace leveldb
#endif // STORAGE_LEVELDB_TABLE_FORMAT_H_
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