file_backed_buffer.h

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#ifndef CVMFS_UTIL_FILE_BACKED_BUFFER_H_
#define CVMFS_UTIL_FILE_BACKED_BUFFER_H_

#include <stdint.h>

#include <string>

#include "gtest/gtest_prod.h"
#include "util/export.h"
#include "util/mmap_file.h"
#include "util/single_copy.h"

class CVMFS_EXPORT FileBackedBuffer : SingleCopy {
  FRIEND_TEST(T_FileBackedBuffer, SimpleWriteAndRead);
  FRIEND_TEST(T_FileBackedBuffer, EmptyBuffer);
  FRIEND_TEST(T_FileBackedBuffer, EmptyWrite);
  FRIEND_TEST(T_FileBackedBuffer, StraightToFile);
  FRIEND_TEST(T_FileBackedBuffer, OnlyInMemory);

 public:
  static FileBackedBuffer *Create(uint64_t in_memory_threshold,
                                  const std::string &tmp_dir = "/tmp/");

  ~FileBackedBuffer();
  void Append(const void *source, uint64_t len);
  void Commit();
  int64_t Data(void** ptr, int64_t len, uint64_t pos);
  int64_t Read(void* ptr, int64_t len);
  int64_t ReadP(void* ptr, int64_t len, uint64_t pos);
  void Rewind();

  uint64_t GetSize() const;

 private:
  FileBackedBuffer(uint64_t in_memory_threshold, const std::string &tmp_dir);
  void SaveToFile();

  const uint64_t in_memory_threshold_;
  const std::string tmp_dir_;

  enum {
    kWriteState = 0,
    kReadState
  } state_;

  enum {
    kMemoryMode = 0,
    kFileMode
  } mode_;

  uint64_t size_;
  // used for writing and reading in kMemoryMode
  unsigned char *buf_;
  // used for reading and writing in both modes
  uint64_t pos_;
  // used for writing in kFileMode
  FILE *fp_;
  // used for writing and reading (opened mmapped_) in kFileMode
  std::string file_path_;
  // used for reading in kFileMode
  MemoryMappedFile *mmapped_;
};

#endif  // CVMFS_UTIL_FILE_BACKED_BUFFER_H_