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flatfile.h
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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2019 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#ifndef BITCOIN_FLATFILE_H
#define BITCOIN_FLATFILE_H
#include <fs.h>
#include <serialize.h>
#include <string>
struct FlatFilePos {
int nFile;
unsigned int nPos;
SERIALIZE_METHODS(FlatFilePos, obj) {
READWRITE(VARINT_MODE(obj.nFile, VarIntMode::NONNEGATIVE_SIGNED),
VARINT(obj.nPos));
}
FlatFilePos() : nFile(-1), nPos(0) {}
FlatFilePos(int nFileIn, unsigned int nPosIn)
: nFile(nFileIn), nPos(nPosIn) {}
friend bool operator==(const FlatFilePos &a, const FlatFilePos &b) {
return (a.nFile == b.nFile && a.nPos == b.nPos);
}
friend bool operator!=(const FlatFilePos &a, const FlatFilePos &b) {
return !(a == b);
}
void SetNull() {
nFile = -1;
nPos = 0;
}
bool IsNull() const { return (nFile == -1); }
std::string ToString() const;
};
/**
* FlatFileSeq represents a sequence of numbered files storing raw data. This
* class facilitates access to and efficient management of these files.
*/
class FlatFileSeq {
private:
const fs::path m_dir;
const char *const m_prefix;
const size_t m_chunk_size;
public:
/**
* Constructor
*
* @param dir The base directory that all files live in.
* @param prefix A short prefix given to all file names.
* @param chunk_size Disk space is pre-allocated in multiples of this
* amount.
*/
FlatFileSeq(fs::path dir, const char *prefix, size_t chunk_size);
/** Get the name of the file at the given position. */
fs::path FileName(const FlatFilePos &pos) const;
/** Open a handle to the file at the given position. */
FILE *Open(const FlatFilePos &pos, bool read_only = false);
/**
* Allocate additional space in a file after the given starting position.
* The amount allocated will be the minimum multiple of the sequence chunk
* size greater than add_size.
*
* @param[in] pos The starting position that bytes will be allocated after.
* @param[in] add_size The minimum number of bytes to be allocated.
* @param[out] out_of_space Whether the allocation failed due to
* insufficient disk space.
* @return The number of bytes successfully allocated.
*/
size_t Allocate(const FlatFilePos &pos, size_t add_size,
bool &out_of_space);
/**
* Commit a file to disk, and optionally truncate off extra pre-allocated
* bytes if final.
*
* @param[in] pos The first unwritten position in the file to be flushed.
* @param[in] finalize True if no more data will be written to this file.
* @return true on success, false on failure.
*/
bool Flush(const FlatFilePos &pos, bool finalize = false);
};
#endif // BITCOIN_FLATFILE_H

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