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/* Example of Outcome used with constructors
(C) 2017-2020 Niall Douglas <http://www.nedproductions.biz/> (5 commits)
Boost Software License - Version 1.0 - August 17th, 2003
Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:
The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/
#ifdef _WIN32
#define _CRT_SECURE_NO_WARNINGS
#define _CRT_NONSTDC_NO_WARNINGS
#include <fcntl.h>
#include <io.h>
#else
#define file_handle linux_file_handle
#include <fcntl.h>
#include <unistd.h>
#undef file_handle
#endif
#include <cstring> // for strerror
#include <sys/stat.h>
#include <sys/types.h>
#include "../../../include/boost/outcome.hpp"
#if __has_include(<filesystem>) && (__cplusplus >= 201700 || _HAS_CXX17)
#include <filesystem>
namespace filesystem = std::filesystem;
#else
#include <experimental/filesystem>
namespace filesystem = std::experimental::filesystem;
#endif
namespace outcome = BOOST_OUTCOME_V2_NAMESPACE;
//! [file_handle]
class file_handle
{
int _fd{-1}; // file descriptor
struct stat _stat
{
0
}; // stat of the fd at open
// Phase 1 private constexpr constructor
constexpr file_handle() {}
public:
using path_type = filesystem::path;
//! The behaviour of the handle: does it read, read and write, or atomic append?
enum class mode : unsigned char // bit 0 set means writable
{
unchanged = 0,
none = 2, //!< No ability to read or write anything, but can synchronise (SYNCHRONIZE or 0)
attr_read = 4, //!< Ability to read attributes (FILE_READ_ATTRIBUTES|SYNCHRONIZE or O_RDONLY)
attr_write = 5, //!< Ability to read and write attributes (FILE_READ_ATTRIBUTES|FILE_WRITE_ATTRIBUTES|SYNCHRONIZE or O_RDONLY)
read = 6, //!< Ability to read (READ_CONTROL|FILE_READ_DATA|FILE_READ_ATTRIBUTES|FILE_READ_EA|SYNCHRONISE or O_RDONLY)
write = 7, //!< Ability to read and write (READ_CONTROL|FILE_READ_DATA|FILE_READ_ATTRIBUTES|FILE_READ_EA|FILE_WRITE_DATA|FILE_WRITE_ATTRIBUTES|FILE_WRITE_EA|FILE_APPEND_DATA|SYNCHRONISE or O_RDWR)
append = 9 //!< All mainstream OSs and CIFS guarantee this is atomic with respect to all other appenders (FILE_APPEND_DATA|SYNCHRONISE or O_APPEND)
};
// Moves but not copies permitted
file_handle(const file_handle &) = delete;
file_handle(file_handle &&o) noexcept : _fd(o._fd) { o._fd = -1; }
file_handle &operator=(const file_handle &) = delete;
file_handle &operator=(file_handle &&o) noexcept
{
this->~file_handle();
new(this) file_handle(std::move(o));
return *this;
}
// Destruction closes the handle
~file_handle()
{
if(_fd != -1)
{
if(-1 == ::close(_fd))
{
int e = errno;
std::cerr << "FATAL: Closing the fd during destruction failed due to " << strerror(e) << std::endl;
std::terminate();
}
_fd = -1;
}
}
// Phase 2 static member constructor function, which cannot throw
static inline outcome::result<file_handle> file(path_type path, mode mode = mode::read) noexcept;
};
//! [file_handle]
//! [file]
// Phase 2 static member constructor function, which cannot throw
inline outcome::result<file_handle> file_handle::file(file_handle::path_type path, file_handle::mode mode) noexcept
{
// Perform phase 1 of object construction
file_handle ret;
// Perform phase 2 of object construction
int flags = 0;
switch(mode)
{
case mode::attr_read:
case mode::read:
flags = O_RDONLY;
break;
case mode::attr_write:
case mode::write:
flags = O_RDWR;
break;
case mode::append:
flags = O_APPEND;
break;
default:
return std::errc::invalid_argument;
}
ret._fd = ::open(path.u8string().c_str(), flags);
if(-1 == ret._fd)
{
// Note that if we bail out here, ~file_handle() will correctly not call ::close()
return {errno, std::system_category()};
}
if(-1 == ::fstat(ret._fd, &ret._stat))
{
// Note that if we bail out here, ~file_handle() will correctly call ::close()
return {errno, std::system_category()};
}
// Returning ret directly is an area full of compiler specific behaviour quirks,
// so be explicit by wrapping into an initialiser list with embedded move.
return {std::move(ret)};
}
//! [file]
//! [construct-declaration]
template <class T> struct make
{
outcome::result<T> operator()() const noexcept
{ //
static_assert(!std::is_same<T, T>::value, //
"make<T>() was not specialised for the type T supplied");
}
};
//! [construct-declaration]
//! [construct-specialisation]
template <> struct make<file_handle>
{
file_handle::path_type _path;
file_handle::mode _mode{file_handle::mode::read};
// Any other args, default initialised if necessary, follow here ...
outcome::result<file_handle> operator()() const noexcept //
{
return file_handle::file(std::move(_path));
}
};
//! [construct-specialisation]
int main()
{
//! [static-use]
outcome::result<file_handle> fh1 = file_handle::file("hello" /*, file_handle::mode::read */);
if(!fh1)
{
std::cerr << "Opening file 'hello' failed with " << fh1.error().message() << std::endl;
}
//! [static-use]
//! [construct-use]
outcome::result<file_handle> fh2 = make<file_handle>{"hello" /*, file_handle::mode::read */}();
if(!fh2)
{
std::cerr << "Opening file 'hello' failed with " << fh2.error().message() << std::endl;
}
//! [construct-use]
return 0;
}
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