file_handle.h

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/*
  Copyright (c) 2020, 2025, Oracle and/or its affiliates.
 
  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License, version 2.0,
  as published by the Free Software Foundation.
 
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  as designated in a particular file or component or in included license
  documentation.  The authors of MySQL hereby grant you an additional
  permission to link the program and your derivative works with the
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  the program or referenced in the documentation.
 
  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
#ifndef MYSQL_HARNESS_STDX_FILE_HANDLE_INCLUDED
#define MYSQL_HARNESS_STDX_FILE_HANDLE_INCLUDED
 
#include <cstdint>
#include <string>
#include <system_error>
#include <utility>  // exchange
 
#ifndef _WIN32
#include <sys/types.h>  // ino_t
#endif
 
#include "mysql/harness/stdx/expected.h"
#include "mysql/harness/stdx/filesystem.h"
#include "mysql/harness/stdx_export.h"
 
// (Partial) Implementation of P1883r1
//
// see: http://wg21.link/p1883
//
// barely enough implementation to replace all uses of
//
// - open()
// - close()
 
namespace stdx {
namespace io {
 
enum class creation {
  open_existing = 0,
  only_if_not_exist,
  if_needed,
  truncate_existing,
  // always_new
};
 
enum class mode {
  unchanged = 0,
  read = 6,
  write = 7,
  append = 9,
};
 
enum class caching {
  unchanged = 0,
  none = 1,
  all = 6,
  temporary = 8,
};
 
class flag {
 public:
  using value_type = uint64_t;
 
  static constexpr value_type none{0};
  static constexpr value_type unlink_on_first_close{1 << 0};
 
  constexpr flag(value_type v) : value_{v} {}
 
  constexpr value_type value() const noexcept { return value_; }
 
  constexpr value_type operator&(const value_type &other) {
    return value() & other;
  }
 
 private:
  value_type value_;
};
 
class path_handle {
 public:
  path_handle() = default;
};
 
class HARNESS_STDX_EXPORT file_handle {
 public:
  using path_type = filesystem::path;
  using path_view_type = filesystem::path;
 
  using native_handle_type = int;
#ifdef _WIN32
  using dev_t = ::_dev_t;
  using ino_t = ::_ino_t;
#else
  using dev_t = ::dev_t;
  using ino_t = ::ino_t;
#endif
 
  static constexpr const native_handle_type invalid_handle{-1};
 
  file_handle(native_handle_type h, dev_t devid, ino_t inode,
              caching caching = caching::none, flag flags = flag::none) noexcept
      : handle_{h},
        devid_{devid},
        inode_{inode},
        caching_{caching},
        flags_{flags} {}
 
  file_handle(const file_handle &) = delete;
  file_handle &operator=(const file_handle &) = delete;
 
  file_handle(file_handle &&rhs)
      : handle_{std::exchange(rhs.handle_, invalid_handle)},
        devid_{std::move(rhs.devid_)},
        inode_{std::move(rhs.inode_)},
        caching_{std::move(rhs.caching_)},
        flags_{std::move(rhs.flags_)} {}
 
  ~file_handle() {
    if (handle_ != invalid_handle) {
      close();
    }
  }
 
  static stdx::expected<file_handle, std::error_code> file(
      const path_handle &base, file_handle::path_view_type path,
      mode _mode = mode::read, creation _creation = creation::open_existing,
      caching _caching = caching::all, flag flags = flag::none) noexcept;
 
  static stdx::expected<file_handle, std::error_code> uniquely_named_file(
      const path_handle &base, mode _mode = mode::write,
      caching _caching = caching::temporary, flag flags = flag::none) noexcept;
 
  stdx::expected<void, std::error_code> unlink();
 
  stdx::expected<void, std::error_code> close() noexcept;
 
  stdx::expected<size_t, std::error_code> write(const char *data,
                                                const size_t len);
 
  native_handle_type release() noexcept {
    return std::exchange(handle_, invalid_handle);
  }
 
  caching kernel_caching() const noexcept { return caching_; }
  flag flags() const noexcept { return flags_; }
 
  native_handle_type native_handle() const noexcept { return handle_; }
 
  dev_t st_dev() const noexcept { return devid_; }
  ino_t st_ino() const noexcept { return inode_; }
 
  // get path of the current file_handle
  stdx::expected<path_type, std::error_code> current_path() const noexcept;
 
 private:
  native_handle_type handle_{invalid_handle};
 
  dev_t devid_;
  ino_t inode_;
  caching caching_;
  flag flags_;
};
 
}  // namespace io
}  // namespace stdx
 
#endif