mmap.h

 
#pragma once
 
#include <iterator>
#include <string>
#include <system_error>
#include <cstdint>
#include "span.h"
#include <filesystem>

/*
struct incremental_position_checkpoint
{
private:
    mmap_sink& mapping;
    struct checkpoint_struct
    {
        size_t position[4];
    };
    checkpoint_struct* mapped_checkpoint;
    bool last_version_2 = false;
public:
    incremental_position_checkpoint(mmap_sink& in_file, size_at loc)
        : mapping(in_file),
        , mapped_checkpoint(mapping.data() + loc)
    {
        assert(mapping.size() <= loc + sizeof(checkpoint_struct));
    }
 
    void reset(size_t to_position = 0)
    {
        mapped_checkpoint = {0,0,0,0};
        mapping.flush();
        last_version_2 = false;
    }
    
    void checkpoint(size_t position)
    {
        mapped_checkpoint.position[last_version_2 * 2] = position;
        mapping.flush();
        mapped_checkpoint.position[last_version_2 * 2 + 1] = position;
        mapping.flush();
        last_version_2 = !last_version_2;
    }
 
    size_t position() const
    {
        const auto copy = *mapped_checkpoint;
        const auto healthy[2] = { copy.position[0] == copy.position[1], copy.position[2] == copy.position[3] };
        if (healthy[0] && healthy[1])
            return std::max(copy.position[0], copy.position[2]);
        else if (healthy[0])
            return position[0];
        else if (healthy[1])
            return position[2];
        else
            throw "no valid position";
    }
};
*/
 
namespace ghassanpl
{
    static constexpr size_t map_entire_file = 0;
 
#ifdef _WIN32
    using file_handle_type = void*;
#else
    using file_handle_type = int;
#endif
 
    const inline file_handle_type invalid_handle = (file_handle_type)-1;
 
    namespace detail
    {
        bool create_file(std::filesystem::path const& path, size_t size, std::error_code& error) noexcept;
    }


    template <typename VALUE_TYPE>
    //requires std::is_integral_v<VALUE_TYPE>
    struct basic_mmap_base
    {
        static_assert(sizeof(VALUE_TYPE) == sizeof(std::byte));
 
        using value_type = VALUE_TYPE;
        using size_type = size_t;
        using reference = value_type&;
        using const_reference = const value_type&;
        using pointer = value_type*;
        using const_pointer = const value_type*;
        using difference_type = std::ptrdiff_t;
        using iterator = pointer;
        using const_iterator = const_pointer;
        using reverse_iterator = std::reverse_iterator<iterator>;
        using const_reverse_iterator = std::reverse_iterator<const_iterator>;
        using iterator_category = std::random_access_iterator_tag;
        using handle_type = file_handle_type;
 
        basic_mmap_base() noexcept = default;
        basic_mmap_base(basic_mmap_base&& other) noexcept
            : data_(std::exchange(other.data_, nullptr))
            , length_(std::exchange(other.length_, 0))
            , mapped_length_(std::exchange(other.mapped_length_, 0))
            , file_handle_(std::exchange(other.file_handle_, invalid_handle))
            , file_mapping_handle_(std::exchange(other.file_mapping_handle_, invalid_handle))
        {
        }
 
        [[nodiscard]] handle_type file_handle() const noexcept { return file_handle_; }
        [[nodiscard]] handle_type mapping_handle() const noexcept { return file_mapping_handle_ == invalid_handle ? file_handle_ : file_mapping_handle_; }
 
        [[nodiscard]] bool is_open() const noexcept { return file_handle_ != invalid_handle; }
 
        [[nodiscard]] bool empty() const noexcept { return length() == 0; }
 
        [[nodiscard]] bool is_mapped() const noexcept
        {
#ifdef _WIN32
            return file_mapping_handle_ != invalid_handle;
#else // POSIX
            return is_open();
#endif
        }
 
        template <typename T = VALUE_TYPE>
        [[nodiscard]] std::span<T const> to_span() const noexcept { return { reinterpret_cast<T const*>(data()), size() }; }
 
        [[nodiscard]] size_type size() const noexcept { return length(); }
        [[nodiscard]] size_type length() const noexcept { return length_; }
        [[nodiscard]] size_type mapped_length() const noexcept { return mapped_length_; }
 
        [[nodiscard]] size_type mapping_offset() const noexcept
        {
            return mapped_length_ - length_;
        }
 
        [[nodiscard]] const_pointer data() const noexcept { return data_; }
 
        [[nodiscard]] const_iterator begin() const noexcept { return data(); }
        [[nodiscard]] const_iterator cbegin() const noexcept { return data(); }
 
        [[nodiscard]] const_iterator end() const noexcept { return data() + length(); }
        [[nodiscard]] const_iterator cend() const noexcept { return data() + length(); }
 
        [[nodiscard]] const_reverse_iterator rbegin() const noexcept
        {
            return const_reverse_iterator(end());
        }
 
        [[nodiscard]] const_reverse_iterator crbegin() const noexcept
        {
            return const_reverse_iterator(end());
        }
 
        [[nodiscard]] const_reverse_iterator rend() const noexcept
        {
            return const_reverse_iterator(begin());
        }
        [[nodiscard]] const_reverse_iterator crend() const noexcept
        {
            return const_reverse_iterator(begin());
        }
 
        [[nodiscard]] const_reference operator[](const size_type i) const noexcept { return data_[i]; }
 
        void swap(basic_mmap_base& other) noexcept
        {
            if (this != &other)
            {
                using std::swap;
                swap(data_, other.data_);
                swap(file_handle_, other.file_handle_);
                swap(file_mapping_handle_, other.file_mapping_handle_);
                swap(length_, other.length_);
                swap(mapped_length_, other.mapped_length_);
            }
        }
 
        void unmap() noexcept;
 
    protected:
 
        struct mmap_context
        {
            VALUE_TYPE* data;
            int64_t length;
            int64_t mapped_length;
            file_handle_type file_mapping_handle;
        };
 
        pointer data_ = nullptr;
 
        size_type length_ = 0;
        size_type mapped_length_ = 0;
 
        handle_type file_handle_ = invalid_handle;
        handle_type file_mapping_handle_ = invalid_handle;
 
        const_pointer get_mapping_start() const noexcept
        {
            return !data() ? nullptr : data() - mapping_offset();
        }
 
    };
 
    template <typename CRTP, typename VALUE_TYPE = std::byte>
    struct basic_mmap : public basic_mmap_base<VALUE_TYPE>
    { 
        using typename basic_mmap_base<VALUE_TYPE>::size_type;
        using typename basic_mmap_base<VALUE_TYPE>::handle_type;
        using typename basic_mmap_base<VALUE_TYPE>::pointer;
 
        basic_mmap() noexcept = default;
        basic_mmap(const std::filesystem::path& path, const size_type offset = 0, const size_t length = map_entire_file)
        {
            std::error_code error;
            map(path, offset, length, error);
            if (error) { throw std::system_error{ error }; }
        }
        basic_mmap(const handle_type handle, const size_type offset = 0, const size_type length = map_entire_file)
        {
            std::error_code error;
            map(handle, offset, length, error);
            if (error) { throw std::system_error{ error }; }
        }
 
        basic_mmap(const basic_mmap&) = delete;
        basic_mmap(basic_mmap&&) noexcept = default;
        basic_mmap& operator=(const basic_mmap&) = delete;
        basic_mmap& operator=(basic_mmap&& other) noexcept
        {
            if (this != &other)
            {
                this->unmap();
 
                this->data_ = std::exchange(other.data_, nullptr);
                this->length_ = std::exchange(other.length_, 0);
                this->mapped_length_ = std::exchange(other.mapped_length_, 0);
                this->file_handle_ = std::exchange(other.file_handle_, invalid_handle);
                this->file_mapping_handle_ = std::exchange(other.file_mapping_handle_, invalid_handle);
            }
            return *this;
        }
 
        ~basic_mmap() noexcept
        {
            static_cast<CRTP*>(this)->conditional_sync();
            this->unmap();
        }
 
    protected:
 
        void map(const std::filesystem::path& path, const size_type offset, const size_type length, std::error_code& error) noexcept
        {
            error.clear();
            if (path.empty())
            {
                error = std::make_error_code(std::errc::invalid_argument);
                return;
            }
 
            error.clear();
            const auto file_size = std::filesystem::file_size(path, error);
            if (error)
                return;
 
            if (file_size == 0) 
            {
                error = std::make_error_code(std::errc::file_too_large);
                return;
            }
 
            error.clear();
            const auto handle = static_cast<CRTP*>(this)->open_file(path, error);
            if (error)
                return;
 
            error.clear();
            if (handle == invalid_handle)
            {
                error = std::make_error_code(std::errc::bad_file_descriptor);
                return;
            }
 
            if (offset + length > file_size)
            {
                error = std::make_error_code(std::errc::invalid_argument);
                return;
            }
 
            const auto ctx = static_cast<CRTP*>(this)->memory_map(handle, offset, length == map_entire_file ? (file_size - offset) : length, error);
            if (!error)
            {
                // We must unmap the previous mapping that may have existed prior to this call.
                // Note that this must only be invoked after a new mapping has been created in
                // order to provide the strong guarantee that, should the new mapping fail, the
                // `map` function leaves this instance in a state as though the function had
                // never been invoked.
                this->unmap();
 
                this->file_handle_ = handle;
                this->data_ = reinterpret_cast<pointer>(ctx.data);
                this->length_ = ctx.length;
                this->mapped_length_ = ctx.mapped_length;
                this->file_mapping_handle_ = ctx.file_mapping_handle;
            }
        }
 
        void map(const std::filesystem::path& path, std::error_code& error) noexcept
        {
            this->map(path, 0, map_entire_file, error);
        }
 
    };
        
    template <typename VALUE_TYPE = std::byte>
    struct mmap_source : public basic_mmap<mmap_source<VALUE_TYPE>, VALUE_TYPE>
    {
        using basic_mmap<mmap_source<VALUE_TYPE>, VALUE_TYPE>::basic_mmap;
        using typename basic_mmap<mmap_source<VALUE_TYPE>, VALUE_TYPE>::mmap_context;
 
        template <typename VALUE_TYPE_>
        friend mmap_source<VALUE_TYPE_> make_mmap_source(const std::filesystem::path& path, typename mmap_source<VALUE_TYPE_>::size_type offset, typename mmap_source<VALUE_TYPE_>::size_type length, std::error_code& error) noexcept;
 
        operator std::basic_string_view<VALUE_TYPE>() const noexcept
        {
            return std::basic_string_view<VALUE_TYPE>{ this->data(), this->size() };
        }
 
    protected:
 
        friend struct basic_mmap<mmap_source<VALUE_TYPE>, VALUE_TYPE>;
 
        static file_handle_type open_file(const std::filesystem::path& path, std::error_code& error) noexcept;
 
        static mmap_context memory_map(const file_handle_type file_handle, const int64_t offset, const int64_t length, std::error_code& error) noexcept;
 
        void conditional_sync() {}
    };
 
    
    using byte_mmap_source = mmap_source<std::byte>;
    using u8_mmap_source = mmap_source<std::uint8_t>;
    using char_mmap_source = mmap_source<char>;
    using char8_mmap_source = mmap_source<char8_t>;
    
    template <typename VALUE_TYPE = std::byte>
    struct mmap_sink : public basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>
    {
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::basic_mmap;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::reference;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::size_type;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::mmap_context;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::pointer;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::iterator;
        using typename basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::reverse_iterator;
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::operator[];
        [[nodiscard]] reference operator[](const size_type i) const noexcept { return this->data_[i]; }
 
        //void unmap();
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::data;
        [[nodiscard]] pointer data() noexcept { return this->data_; }
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::begin;
        [[nodiscard]] iterator begin() noexcept { return this->data(); }
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::end;
        [[nodiscard]] iterator end() noexcept { return this->data() + this->length(); }
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::rbegin;
        [[nodiscard]] reverse_iterator rbegin() noexcept { return reverse_iterator(this->end()); }
 
        using basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>::rend;
        [[nodiscard]] reverse_iterator rend() noexcept { return reverse_iterator(this->begin()); }
 
        void sync(std::error_code& error) noexcept;
 
    protected:
 
        friend struct basic_mmap<mmap_sink<VALUE_TYPE>, VALUE_TYPE>;
 
        static file_handle_type open_file(const std::filesystem::path& path, std::error_code& error) noexcept;
 
        static mmap_context memory_map(const file_handle_type file_handle, const int64_t offset, const int64_t length, std::error_code& error) noexcept;
 
        pointer get_mapping_start() noexcept
        {
            return !this->data() ? nullptr : this->data() - this->mapping_offset();
        }
 
        void conditional_sync()
        {
            std::error_code ec;
            sync(ec);
        }
    };
 
    template <typename VALUE_TYPE = char>
    [[nodiscard]] mmap_source<VALUE_TYPE> make_mmap_source(const std::filesystem::path& path, typename mmap_source<VALUE_TYPE>::size_type offset, typename mmap_source<VALUE_TYPE>::size_type length, std::error_code& error) noexcept
    {
        mmap_source<VALUE_TYPE> mmap;
        mmap.map(path, offset, length, error);
        return mmap;
    }
 
    template <typename VALUE_TYPE = char>
    [[nodiscard]] mmap_source<VALUE_TYPE> make_mmap_source(const std::filesystem::path& path, std::error_code& error) noexcept
    {
        return make_mmap_source<VALUE_TYPE>(path, 0, map_entire_file, error);
    }
 
    template <typename VALUE_TYPE = char>
    [[nodiscard]] mmap_source<VALUE_TYPE> make_mmap_source(const std::filesystem::path& path, typename mmap_source<VALUE_TYPE>::size_type offset, typename mmap_source<VALUE_TYPE>::size_type length)
    {
        return mmap_source<VALUE_TYPE>{ path, offset, length };
    }
 
    template <typename VALUE_TYPE = char>
    [[nodiscard]] mmap_source<VALUE_TYPE> make_mmap_source(const std::filesystem::path& path)
    {
        return make_mmap_source<VALUE_TYPE>(path, 0, map_entire_file);
    }
 
    template <typename VALUE_TYPE>
    [[nodiscard]] mmap_sink<VALUE_TYPE> make_mmap_sink(const std::filesystem::path& path, typename mmap_sink<VALUE_TYPE>::size_type offset, typename mmap_sink<VALUE_TYPE>::size_type length, std::error_code& error) noexcept
    {
        if (!detail::create_file(path, offset + length, error))
            return mmap_sink<VALUE_TYPE>{};
 
        mmap_sink<VALUE_TYPE> mmap;
        mmap.map(path, offset, length, error);
        return mmap;
    }
 
    template <typename VALUE_TYPE>
    [[nodiscard]] mmap_sink<VALUE_TYPE> make_mmap_sink(const std::filesystem::path& path, std::error_code& error) noexcept
    {
        return make_mmap_sink<VALUE_TYPE>(path, 0, map_entire_file, error);
    }
 
    template <typename VALUE_TYPE>
    [[nodiscard]] mmap_sink<VALUE_TYPE> make_mmap_sink(const std::filesystem::path& path, typename mmap_sink<VALUE_TYPE>::size_type offset, typename mmap_sink<VALUE_TYPE>::size_type length)
    {
        std::error_code error;
        if (!detail::create_file(path, offset + length, error))
            return mmap_sink<VALUE_TYPE>{};
 
        return mmap_sink<VALUE_TYPE>{ path, offset, length };
    }
 
    template <typename VALUE_TYPE>
    [[nodiscard]] mmap_sink<VALUE_TYPE> make_mmap_sink(const std::filesystem::path& path)
    {
        return make_mmap_sink<VALUE_TYPE>(path, 0, map_entire_file);
    }

}
 
#ifdef GHASSANPL_MMAP_IMPL
#include "mmap_impl.h"
#endif