flatfile.h raw

   1  // Copyright (c) 2009-2010 Satoshi Nakamoto
   2  // Copyright (c) 2009-2020 The Limenka 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 LIMENKA_FLATFILE_H
   7  #define LIMENKA_FLATFILE_H
   8  
   9  #include <string>
  10  
  11  #include <serialize.h>
  12  #include <util/fs.h>
  13  
  14  struct FlatFilePos
  15  {
  16      int nFile{-1};
  17      unsigned int 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(int nFileIn, unsigned int 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      friend bool operator!=(const FlatFilePos &a, const FlatFilePos &b) {
  33          return !(a == b);
  34      }
  35  
  36      bool IsNull() const { return (nFile == -1) && (nPos == 0); }
  37  
  38      std::string ToString() const;
  39  };
  40  
  41  /**
  42   * FlatFileSeq represents a sequence of numbered files storing raw data. This class facilitates
  43   * access to and efficient management of these files.
  44   */
  45  class FlatFileSeq
  46  {
  47  private:
  48      const fs::path m_dir;
  49      const char* const m_prefix;
  50      const size_t m_chunk_size;
  51  
  52  public:
  53      /**
  54       * Constructor
  55       *
  56       * @param dir The base directory that all files live in.
  57       * @param prefix A short prefix given to all file names.
  58       * @param chunk_size Disk space is pre-allocated in multiples of this amount.
  59       */
  60      FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size);
  61  
  62      /** Get the name of the file at the given position. */
  63      fs::path FileName(const FlatFilePos& pos) const;
  64  
  65      /** Open a handle to the file at the given position. */
  66      FILE* Open(const FlatFilePos& pos, bool read_only = false) const;
  67  
  68      /**
  69       * Allocate additional space in a file after the given starting position. The amount allocated
  70       * will be the minimum multiple of the sequence chunk size greater than add_size.
  71       *
  72       * @param[in] pos The starting position that bytes will be allocated after.
  73       * @param[in] add_size The minimum number of bytes to be allocated.
  74       * @param[out] out_of_space Whether the allocation failed due to insufficient disk space.
  75       * @return The number of bytes successfully allocated.
  76       */
  77      size_t Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space) const;
  78  
  79      /**
  80       * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
  81       *
  82       * @param[in] pos The first unwritten position in the file to be flushed.
  83       * @param[in] finalize True if no more data will be written to this file.
  84       * @return true on success, false on failure.
  85       */
  86      bool Flush(const FlatFilePos& pos, bool finalize = false) const;
  87  };
  88  
  89  #endif // LIMENKA_FLATFILE_H
  90