concepts.h

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/**
 * Useful concepts that are available throughout the library
 * (C) 2023 Jack Lloyd
 *     2023 René Meusel - Rohde & Schwarz Cybersecurity
 *
 * Botan is released under the Simplified BSD License (see license.txt)
 */
 
#ifndef BOTAN_CONCEPTS_H_
#define BOTAN_CONCEPTS_H_
 
#include <botan/exceptn.h>
 
#include <concepts>
#include <iosfwd>
#include <ranges>
#include <span>
#include <type_traits>
 
namespace Botan {
 
template <typename T, typename Tag, typename... Capabilities>
class Strong;
 
template <typename... Ts>
struct is_strong_type : std::false_type {};
 
template <typename... Ts>
struct is_strong_type<Strong<Ts...>> : std::true_type {};
 
template <typename... Ts>
constexpr bool is_strong_type_v = is_strong_type<std::remove_const_t<Ts>...>::value;
 
template <typename T0 = void, typename... Ts>
struct all_same {
      static constexpr bool value = (std::is_same_v<T0, Ts> && ... && true);
};
 
template <typename... Ts>
static constexpr bool all_same_v = all_same<Ts...>::value;
 
namespace detail {
 
/**
 * Helper type to indicate that a certain type should be automatically
 * detected based on the context.
 */
struct AutoDetect {
      constexpr AutoDetect() = delete;
};
 
}  // namespace detail
 
namespace ranges {
 
/**
 * Models a std::ranges::contiguous_range that (optionally) restricts its
 * value_type to ValueT. In other words: a stretch of contiguous memory of
 * a certain type (optional ValueT).
 */
template <typename T, typename ValueT = std::ranges::range_value_t<T>>
concept contiguous_range = std::ranges::contiguous_range<T> && std::same_as<ValueT, std::ranges::range_value_t<T>>;
 
/**
 * Models a std::ranges::contiguous_range that satisfies
 * std::ranges::output_range with an arbitrary value_type. In other words: a
 * stretch of contiguous memory of a certain type (optional ValueT) that can be
 * written to.
 */
template <typename T, typename ValueT = std::ranges::range_value_t<T>>
concept contiguous_output_range = contiguous_range<T, ValueT> && std::ranges::output_range<T, ValueT>;
 
/**
 * Models a range that can be turned into a std::span<>. Typically, this is some
 * form of ranges::contiguous_range.
 */
template <typename T>
concept spanable_range = std::constructible_from<std::span<const std::ranges::range_value_t<T>>, T>;
 
/**
 * Models a range that can be turned into a std::span<> with a static extent.
 * Typically, this is a std::array or a std::span derived from an array.
 */
// clang-format off
template <typename T>
concept statically_spanable_range = spanable_range<T> &&
                                    decltype(std::span{std::declval<T&>()})::extent != std::dynamic_extent;
 
// clang-format on
 
/**
 * Find the length in bytes of a given contiguous range @p r.
 */
inline constexpr size_t size_bytes(const spanable_range auto& r) {
   return std::span{r}.size_bytes();
}
 
/**
 * Check that a given range @p r has a certain statically-known byte length. If
 * the range's extent is known at compile time, this is a static check,
 * otherwise a runtime argument check will be added.
 *
 * @throws Invalid_Argument  if range @p r has a dynamic extent and does not
 *                           feature the expected byte length.
 */
template <size_t expected, spanable_range R>
inline constexpr void assert_exact_byte_length(const R& r) {
   const std::span s{r};
   if constexpr(statically_spanable_range<R>) {
      static_assert(s.size_bytes() == expected, "memory region does not have expected byte lengths");
   } else {
      if(s.size_bytes() != expected) {
         throw Invalid_Argument("Memory regions did not have expected byte lengths");
      }
   }
}
 
/**
 * Check that a list of ranges (in @p r0 and @p rs) all have the same byte
 * lengths. If the first range's extent is known at compile time, this will be a
 * static check for all other ranges whose extents are known at compile time,
 * otherwise a runtime argument check will be added.
 *
 * @throws Invalid_Argument  if any range has a dynamic extent and not all
 *                           ranges feature the same byte length.
 */
template <spanable_range R0, spanable_range... Rs>
inline constexpr void assert_equal_byte_lengths(const R0& r0, const Rs&... rs)
   requires(sizeof...(Rs) > 0)
{
   const std::span s0{r0};
 
   if constexpr(statically_spanable_range<R0>) {
      constexpr size_t expected_size = s0.size_bytes();
      (assert_exact_byte_length<expected_size>(rs), ...);
   } else {
      const size_t expected_size = s0.size_bytes();
      const bool correct_size =
         ((std::span<const std::ranges::range_value_t<Rs>>{rs}.size_bytes() == expected_size) && ...);
 
      if(!correct_size) {
         throw Invalid_Argument("Memory regions did not have equal lengths");
      }
   }
}
 
}  // namespace ranges
 
namespace concepts {
 
// TODO: C++20 provides concepts like std::ranges::range or ::sized_range
//       but at the time of this writing clang had not caught up on all
//       platforms. E.g. clang 14 on Xcode does not support ranges properly.
 
template <typename IterT, typename ContainerT>
concept container_iterator =
   std::same_as<IterT, typename ContainerT::iterator> || std::same_as<IterT, typename ContainerT::const_iterator>;
 
template <typename PtrT, typename ContainerT>
concept container_pointer =
   std::same_as<PtrT, typename ContainerT::pointer> || std::same_as<PtrT, typename ContainerT::const_pointer>;
 
template <typename T>
concept container = requires(T a) {
   { a.begin() } -> container_iterator<T>;
   { a.end() } -> container_iterator<T>;
   { a.cbegin() } -> container_iterator<T>;
   { a.cend() } -> container_iterator<T>;
   { a.size() } -> std::same_as<typename T::size_type>;
   typename T::value_type;
};
 
template <typename T>
concept contiguous_container = container<T> && requires(T a) {
   { a.data() } -> container_pointer<T>;
};
 
template <typename T>
concept has_empty = requires(T a) {
   { a.empty() } -> std::same_as<bool>;
};
 
// clang-format off
template <typename T>
concept has_bounds_checked_accessors = container<T> && (
                                          requires(T a, const T ac, typename T::size_type s) {
                                             { a.at(s) } -> std::same_as<typename T::value_type&>;
                                             { ac.at(s) } -> std::same_as<const typename T::value_type&>;
                                          } ||
                                          requires(T a, const T ac, typename T::key_type k) {
                                             { a.at(k) } -> std::same_as<typename T::mapped_type&>;
                                             { ac.at(k) } -> std::same_as<const typename T::mapped_type&>;
                                          });
// clang-format on
 
template <typename T>
concept resizable_container = container<T> && requires(T& c, typename T::size_type s) {
   T(s);
   c.resize(s);
};
 
template <typename T>
concept reservable_container = container<T> && requires(T& c, typename T::size_type s) { c.reserve(s); };
 
template <typename T>
concept resizable_byte_buffer =
   contiguous_container<T> && resizable_container<T> && std::same_as<typename T::value_type, uint8_t>;
 
template <typename T>
concept streamable = requires(std::ostream& os, T a) { os << a; };
 
template <class T>
concept strong_type = is_strong_type_v<T>;
 
template <class T>
concept contiguous_strong_type = strong_type<T> && contiguous_container<T>;
 
template <class T>
concept integral_strong_type = strong_type<T> && std::integral<typename T::wrapped_type>;
 
template <class T>
concept unsigned_integral_strong_type = strong_type<T> && std::unsigned_integral<typename T::wrapped_type>;
 
template <typename T, typename Capability>
concept strong_type_with_capability = T::template has_capability<Capability>();
 
}  // namespace concepts
 
}  // namespace Botan
 
#endif