str_icase.hpp

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#pragma once
 
/// @file userver/utils/str_icase.hpp
/// @brief Case insensitive ASCII comparators and hashers
/// @ingroup userver_universal
 
#include <cstdint>
#include <string_view>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// The seed structure used by underlying hashing implementation
struct HashSeed final {
    std::uint64_t k0;
    std::uint64_t k1;
};
 
/// @brief Case sensitive ASCII hashing functor
class StrCaseHash {
public:
    using is_transparent [[maybe_unused]] = void;
 
    /// Generates a new random hash seed for each hasher instance
    StrCaseHash();
 
    /// Uses the provided seed. Use with caution: a constant seed makes the hasher
    /// vulnerable to HashDOS attacks when arbitrary keys are allowed.
    explicit StrCaseHash(HashSeed seed) noexcept;
 
    std::size_t operator()(std::string_view s) const& noexcept;
 
    template <class StringStrongTypedef>
    auto operator()(const StringStrongTypedef& s
    ) const& noexcept -> decltype(operator()(std::string_view{s.GetUnderlying()})) {
        static_assert(
            noexcept((*this)(std::string_view{s.GetUnderlying()})),
            "GetUnderlying() should not throw as this affects efficiency "
            "on some platforms"
        );
 
        return (*this)(std::string_view{s.GetUnderlying()});
    }
 
    HashSeed GetSeed() const noexcept { return seed_; }
 
private:
    HashSeed seed_;
};
 
/// @brief Case insensitive ASCII hashing functor
class StrIcaseHash {
public:
    using is_transparent [[maybe_unused]] = void;
 
    /// Generates a new random hash seed for each hasher instance
    StrIcaseHash();
 
    /// Uses the provided seed. Use with caution: a constant seed makes the hasher
    /// vulnerable to HashDOS attacks when arbitrary keys are allowed.
    explicit StrIcaseHash(HashSeed seed) noexcept;
 
    std::size_t operator()(std::string_view s) const& noexcept;
 
private:
    HashSeed seed_;
};
 
/// Case insensitive ASCII 3-way comparison functor
class StrIcaseCompareThreeWay {
public:
    // TODO: std::weak_ordering
 
    /// @returns integer <0 when `lhs < rhs`, >0 when `lhs > rhs` and 0 otherwise
    int operator()(std::string_view lhs, std::string_view rhs) const noexcept;
};
 
/// Case insensitive ASCII equality comparison functor
class StrIcaseEqual {
public:
    using is_transparent [[maybe_unused]] = void;
 
    bool operator()(std::string_view lhs, std::string_view rhs) const noexcept;
};
 
/// Case insensitive ASCII less comparison functor
class StrIcaseLess {
public:
    using is_transparent [[maybe_unused]] = void;
 
    bool operator()(std::string_view lhs, std::string_view rhs) const noexcept;
};
 
}  // namespace utils
 
USERVER_NAMESPACE_END