flatfile.h raw

   1  // Copyright (c) 2009-2010 Satoshi Nakamoto
   2  // Copyright (c) 2009-present The Bitcoin Core developers
   3  // Distributed under the MIT software license, see the accompanying
   4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   5  
   6  #ifndef BITCOIN_FLATFILE_H
   7  #define BITCOIN_FLATFILE_H
   8  
   9  #include <string>
  10  
  11  #include <serialize.h>
  12  #include <util/fs.h>
  13  
  14  struct FlatFilePos
  15  {
  16      int32_t nFile{-1};
  17      uint32_t nPos{0};
  18  
  19      SERIALIZE_METHODS(FlatFilePos, obj) { READWRITE(VARINT_MODE(obj.nFile, VarIntMode::NONNEGATIVE_SIGNED), VARINT(obj.nPos)); }
  20  
  21      FlatFilePos() = default;
  22  
  23      FlatFilePos(int32_t nFileIn, uint32_t nPosIn)
  24          : nFile{nFileIn},
  25            nPos{nPosIn}
  26      {}
  27  
  28      friend bool operator==(const FlatFilePos &a, const FlatFilePos &b) {
  29          return (a.nFile == b.nFile && a.nPos == b.nPos);
  30      }
  31  
  32      bool IsNull() const { return (nFile == -1); }
  33  
  34      std::string ToString() const;
  35  };
  36  
  37  /**
  38   * FlatFileSeq represents a sequence of numbered files storing raw data. This class facilitates
  39   * access to and efficient management of these files.
  40   */
  41  class FlatFileSeq
  42  {
  43  private:
  44      const fs::path m_dir;
  45      const char* const m_prefix;
  46      const size_t m_chunk_size;
  47  
  48  public:
  49      /**
  50       * Constructor
  51       *
  52       * @param dir The base directory that all files live in.
  53       * @param prefix A short prefix given to all file names.
  54       * @param chunk_size Disk space is pre-allocated in multiples of this amount.
  55       */
  56      FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size);
  57  
  58      /** Get the name of the file at the given position. */
  59      fs::path FileName(const FlatFilePos& pos) const;
  60  
  61      /** Open a handle to the file at the given position. */
  62      FILE* Open(const FlatFilePos& pos, bool read_only = false) const;
  63  
  64      /**
  65       * Allocate additional space in a file after the given starting position. The amount allocated
  66       * will be the minimum multiple of the sequence chunk size greater than add_size.
  67       *
  68       * @param[in] pos The starting position that bytes will be allocated after.
  69       * @param[in] add_size The minimum number of bytes to be allocated.
  70       * @param[out] out_of_space Whether the allocation failed due to insufficient disk space.
  71       * @return The number of bytes successfully allocated.
  72       */
  73      size_t Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space) const;
  74  
  75      /**
  76       * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
  77       *
  78       * @param[in] pos The first unwritten position in the file to be flushed.
  79       * @param[in] finalize True if no more data will be written to this file.
  80       * @return true on success, false on failure.
  81       */
  82      bool Flush(const FlatFilePos& pos, bool finalize = false) const;
  83  };
  84  
  85  #endif // BITCOIN_FLATFILE_H
  86