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