experimental/status-code/std_error_code.hpp

/* Proposed SG14 status_code
(C) 2018-2020 Niall Douglas <http://www.nedproductions.biz/> (5 commits)
File Created: Aug 2018


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
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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
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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*/

#ifndef BOOST_OUTCOME_SYSTEM_ERROR2_STD_ERROR_CODE_HPP
#define BOOST_OUTCOME_SYSTEM_ERROR2_STD_ERROR_CODE_HPP

#ifndef BOOST_OUTCOME_SYSTEM_ERROR2_NOT_POSIX
#include "posix_code.hpp"
#endif

#if defined(_WIN32) || defined(BOOST_OUTCOME_STANDARDESE_IS_IN_THE_HOUSE)
#include "win32_code.hpp"
#endif

#include <system_error>

BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE_BEGIN

class _std_error_code_domain;
//! A `status_code` representing exactly a `std::error_code`
using std_error_code = status_code<_std_error_code_domain>;

namespace mixins
{
  template <class Base> struct mixin<Base, _std_error_code_domain> : public Base
  {
    using Base::Base;

    //! Implicit constructor from a `std::error_code`
    inline mixin(std::error_code ec);

    //! Returns the error code category
    inline const std::error_category &category() const noexcept;
  };
}  // namespace mixins


/*! The implementation of the domain for `std::error_code` error codes.
 */
class _std_error_code_domain final : public status_code_domain
{
  template <class DomainType> friend class status_code;
  template <class StatusCode> friend class detail::indirecting_domain;
  using _base = status_code_domain;
  using _error_code_type = std::error_code;
  using _error_category_type = std::error_category;

  std::string _name;

  static _base::string_ref _make_string_ref(_error_code_type c) noexcept
  {
    try
    {
      std::string msg = c.message();
      auto *p = static_cast<char *>(malloc(msg.size() + 1));  // NOLINT
      if(p == nullptr)
      {
        return _base::string_ref("failed to allocate message");
      }
      memcpy(p, msg.c_str(), msg.size() + 1);
      return _base::atomic_refcounted_string_ref(p, msg.size());
    }
    catch(...)
    {
      return _base::string_ref("failed to allocate message");
    }
  }

public:
  //! The value type of the `std::error_code` code, which stores the `int` from the `std::error_code`
  using value_type = int;
  using _base::string_ref;

  //! Returns the error category singleton pointer this status code domain represents
  const _error_category_type &error_category() const noexcept
  {
    auto ptr = 0x223a160d20de97b4 ^ this->id();
    return *reinterpret_cast<const _error_category_type *>(ptr);
  }

  //! Default constructor
  explicit _std_error_code_domain(const _error_category_type &category) noexcept
      : _base(0x223a160d20de97b4 ^ reinterpret_cast<_base::unique_id_type>(&category))
      , _name("std_error_code_domain(")
  {
    _name.append(category.name());
    _name.push_back(')');
  }
  _std_error_code_domain(const _std_error_code_domain &) = default;
  _std_error_code_domain(_std_error_code_domain &&) = default;
  _std_error_code_domain &operator=(const _std_error_code_domain &) = default;
  _std_error_code_domain &operator=(_std_error_code_domain &&) = default;
  ~_std_error_code_domain() = default;

  static inline const _std_error_code_domain *get(_error_code_type ec);

  virtual string_ref name() const noexcept override { return string_ref(_name.c_str(), _name.size()); }  // NOLINT
protected:
  virtual bool _do_failure(const status_code<void> &code) const noexcept override;
  virtual bool _do_equivalent(const status_code<void> &code1, const status_code<void> &code2) const noexcept override;
  virtual generic_code _generic_code(const status_code<void> &code) const noexcept override;
  virtual string_ref _do_message(const status_code<void> &code) const noexcept override;
#if defined(_CPPUNWIND) || defined(__EXCEPTIONS) || defined(BOOST_OUTCOME_STANDARDESE_IS_IN_THE_HOUSE)
  BOOST_OUTCOME_SYSTEM_ERROR2_NORETURN virtual void _do_throw_exception(const status_code<void> &code) const override;
#endif
};

namespace detail
{
  extern inline _std_error_code_domain *std_error_code_domain_from_category(const std::error_category &category)
  {
    static constexpr size_t max_items = 64;
    static struct storage_t
    {
      std::atomic<unsigned> _lock;
      union item_t {
        int _init;
        _std_error_code_domain domain;
        constexpr item_t()
            : _init(0)
        {
        }
        ~item_t() {}
      } items[max_items];
      size_t count{0};

      void lock()
      {
        while(_lock.exchange(1, std::memory_order_acquire) != 0)
          ;
      }
      void unlock() { _lock.store(0, std::memory_order_release); }

      storage_t() {}
      ~storage_t()
      {
        lock();
        for(size_t n = 0; n < count; n++)
        {
          items[n].domain.~_std_error_code_domain();
        }
        unlock();
      }
      _std_error_code_domain *add(const std::error_category &category)
      {
        _std_error_code_domain *ret = nullptr;
        lock();
        for(size_t n = 0; n < count; n++)
        {
          if(items[n].domain.error_category() == category)
          {
            ret = &items[n].domain;
            break;
          }
        }
        if(ret == nullptr && count < max_items)
        {
          ret = new(&items[count++].domain) _std_error_code_domain(category);
        }
        unlock();
        return ret;
      }
    } storage;
    return storage.add(category);
  }
}  // namespace detail

namespace mixins
{
  template <class Base>
  inline mixin<Base, _std_error_code_domain>::mixin(std::error_code ec)
      : Base(typename Base::_value_type_constructor{}, _std_error_code_domain::get(ec), ec.value())
  {
  }

  template <class Base> inline const std::error_category &mixin<Base, _std_error_code_domain>::category() const noexcept
  {
    const auto &domain = static_cast<const _std_error_code_domain &>(this->domain());
    return domain.error_category();
  };
}  // namespace mixins

inline const _std_error_code_domain *_std_error_code_domain::get(std::error_code ec)
{
  auto *p = detail::std_error_code_domain_from_category(ec.category());
  assert(p != nullptr);
  if(p == nullptr)
  {
    abort();
  }
  return p;
}


inline bool _std_error_code_domain::_do_failure(const status_code<void> &code) const noexcept
{
  assert(code.domain() == *this);
  return static_cast<const std_error_code &>(code).value() != 0;  // NOLINT
}

inline bool _std_error_code_domain::_do_equivalent(const status_code<void> &code1, const status_code<void> &code2) const noexcept
{
  assert(code1.domain() == *this);
  const auto &c1 = static_cast<const std_error_code &>(code1);  // NOLINT
  const auto &cat1 = c1.category();
  // Are we comparing to another wrapped error_code?
  if(code2.domain() == *this)
  {
    const auto &c2 = static_cast<const std_error_code &>(code2);  // NOLINT
    const auto &cat2 = c2.category();
    // If the error code categories are identical, do literal comparison
    if(cat1 == cat2)
    {
      return c1.value() == c2.value();
    }
    // Otherwise fall back onto the _generic_code comparison, which uses default_error_condition()
    return false;
  }
  // Am I an error code with generic category?
  if(cat1 == std::generic_category())
  {
    // Convert to generic code, and compare that
    generic_code _c1(static_cast<errc>(c1.value()));
    return _c1 == code2;
  }
  // Am I an error code with system category?
  if(cat1 == std::system_category())
  {
// Convert to POSIX or Win32 code, and compare that
#ifdef _WIN32
    win32_code _c1((win32::DWORD) c1.value());
    return _c1 == code2;
#elif !defined(BOOST_OUTCOME_SYSTEM_ERROR2_NOT_POSIX)
    posix_code _c1(c1.value());
    return _c1 == code2;
#endif
  }
  return false;
}

inline generic_code _std_error_code_domain::_generic_code(const status_code<void> &code) const noexcept
{
  assert(code.domain() == *this);
  const auto &c = static_cast<const std_error_code &>(code);  // NOLINT
  // Ask my embedded error code for its mapping to std::errc, which is a subset of our generic_code errc.
  return generic_code(static_cast<errc>(c.category().default_error_condition(c.value()).value()));
}

inline _std_error_code_domain::string_ref _std_error_code_domain::_do_message(const status_code<void> &code) const noexcept
{
  assert(code.domain() == *this);
  const auto &c = static_cast<const std_error_code &>(code);  // NOLINT
  return _make_string_ref(_error_code_type(c.value(), c.category()));
}

#if defined(_CPPUNWIND) || defined(__EXCEPTIONS) || defined(BOOST_OUTCOME_STANDARDESE_IS_IN_THE_HOUSE)
BOOST_OUTCOME_SYSTEM_ERROR2_NORETURN inline void _std_error_code_domain::_do_throw_exception(const status_code<void> &code) const
{
  assert(code.domain() == *this);
  const auto &c = static_cast<const std_error_code &>(code);  // NOLINT
  throw std::system_error(std::error_code(c.value(), c.category()));
}
#endif

static_assert(sizeof(std_error_code) <= sizeof(void *) * 2, "std_error_code does not fit into a system_code!");

BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE_END

// Enable implicit construction of `std_error_code` from `std::error_code`.
namespace std
{
  inline BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE::std_error_code make_status_code(error_code c) noexcept { return BOOST_OUTCOME_SYSTEM_ERROR2_NAMESPACE::std_error_code(c); }
}  // namespace std

#endif