mio.hpp

/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_MMAP_HEADER
#define MIO_MMAP_HEADER

// #include "mio/page.hpp"
/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_PAGE_HEADER
#define MIO_PAGE_HEADER

#ifdef _WIN32
# include <windows.h>
#else
# include <unistd.h>
#endif

namespace mio {

/**
 * This is used by `basic_mmap` to determine whether to create a read-only or
 * a read-write memory mapping.
 */
enum class access_mode
{
    read,
    write
};

/**
 * Determines the operating system's page allocation granularity.
 *
 * On the first call to this function, it invokes the operating system specific syscall
 * to determine the page size, caches the value, and returns it. Any subsequent call to
 * this function serves the cached value, so no further syscalls are made.
 */
inline size_t page_size()
{
    static const size_t page_size = []
    {
#ifdef _WIN32
        SYSTEM_INFO SystemInfo;
        GetSystemInfo(&SystemInfo);
        return SystemInfo.dwAllocationGranularity;
#else
        return sysconf(_SC_PAGE_SIZE);
#endif
    }();
    return page_size;
}

/**
 * Alligns `offset` to the operating's system page size such that it subtracts the
 * difference until the nearest page boundary before `offset`, or does nothing if
 * `offset` is already page aligned.
 */
inline size_t make_offset_page_aligned(size_t offset) noexcept
{
    const size_t page_size_ = page_size();
    // Use integer division to round down to the nearest page alignment.
    return offset / page_size_ * page_size_;
}

} // namespace mio

#endif // MIO_PAGE_HEADER


#include <iterator>
#include <string>
#include <system_error>
#include <cstdint>

#ifdef _WIN32
# ifndef WIN32_LEAN_AND_MEAN
#  define WIN32_LEAN_AND_MEAN
# endif // WIN32_LEAN_AND_MEAN
# include <windows.h>
#else // ifdef _WIN32
# define INVALID_HANDLE_VALUE -1
#endif // ifdef _WIN32

namespace mio {

// This value may be provided as the `length` parameter to the constructor or
// `map`, in which case a memory mapping of the entire file is created.
enum { map_entire_file = 0 };

#ifdef _WIN32
using file_handle_type = HANDLE;
#else
using file_handle_type = int;
#endif

// This value represents an invalid file handle type. This can be used to
// determine whether `basic_mmap::file_handle` is valid, for example.
const static file_handle_type invalid_handle = INVALID_HANDLE_VALUE;

template<access_mode AccessMode, typename ByteT>
struct basic_mmap
{
    using value_type = ByteT;
    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;

    static_assert(sizeof(ByteT) == sizeof(char), "ByteT must be the same size as char.");

private:
    // Points to the first requested byte, and not to the actual start of the mapping.
    pointer data_ = nullptr;

    // Length--in bytes--requested by user (which may not be the length of the
    // full mapping) and the length of the full mapping.
    size_type length_ = 0;
    size_type mapped_length_ = 0;

    // Letting user map a file using both an existing file handle and a path
    // introcudes some complexity (see `is_handle_internal_`).
    // On POSIX, we only need a file handle to create a mapping, while on
    // Windows systems the file handle is necessary to retrieve a file mapping
    // handle, but any subsequent operations on the mapped region must be done
    // through the latter.
    handle_type file_handle_ = INVALID_HANDLE_VALUE;
#ifdef _WIN32
    handle_type file_mapping_handle_ = INVALID_HANDLE_VALUE;
#endif

    // Letting user map a file using both an existing file handle and a path
    // introcudes some complexity in that we must not close the file handle if
    // user provided it, but we must close it if we obtained it using the
    // provided path. For this reason, this flag is used to determine when to
    // close `file_handle_`.
    bool is_handle_internal_;

public:
    /**
     * The default constructed mmap object is in a non-mapped state, that is,
     * any operation that attempts to access nonexistent underlying data will
     * result in undefined behaviour/segmentation faults.
     */
    basic_mmap() = default;

#ifdef __cpp_exceptions
    /**
     * The same as invoking the `map` function, except any error that may occur
     * while establishing the mapping is wrapped in a `std::system_error` and is
     * thrown.
     */
    template<typename String>
    basic_mmap(const String& path, const size_type offset = 0, const size_type length = map_entire_file)
    {
        std::error_code error;
        map(path, offset, length, error);
        if(error) { throw std::system_error(error); }
    }

    /**
     * The same as invoking the `map` function, except any error that may occur
     * while establishing the mapping is wrapped in a `std::system_error` and is
     * thrown.
     */
    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); }
    }
#endif // __cpp_exceptions

    /**
     * `basic_mmap` has single-ownership semantics, so transferring ownership
     * may only be accomplished by moving the object.
     */
    basic_mmap(const basic_mmap&) = delete;
    basic_mmap(basic_mmap&&);
    basic_mmap& operator=(const basic_mmap&) = delete;
    basic_mmap& operator=(basic_mmap&&);

    /**
     * If this is a read-write mapping, the destructor invokes sync. Regardless
     * of the access mode, unmap is invoked as a final step.
     */
    ~basic_mmap();

    /**
     * On UNIX systems 'file_handle' and 'mapping_handle' are the same. On Windows,
     * however, a mapped region of a file gets its own handle, which is returned by
     * 'mapping_handle'.
     */
    handle_type file_handle() const noexcept { return file_handle_; }
    handle_type mapping_handle() const noexcept;

    /** Returns whether a valid memory mapping has been created. */
    bool is_open() const noexcept { return file_handle_ != invalid_handle; }

    /**
     * Returns true if no mapping was established, that is, conceptually the
     * same as though the length that was mapped was 0. This function is
     * provided so that this class has Container semantics.
     */
    bool empty() const noexcept { return length() == 0; }

    /** Returns true if a mapping was established. */
    bool is_mapped() const noexcept;

    /**
     * `size` and `length` both return the logical length, i.e. the number of bytes
     * user requested to be mapped, while `mapped_length` returns the actual number of
     * bytes that were mapped which is a multiple of the underlying operating system's
     * page allocation granularity.
     */
    size_type size() const noexcept { return length(); }
    size_type length() const noexcept { return length_; }
    size_type mapped_length() const noexcept { return mapped_length_; }

    /** Returns the offset relative to the start of the mapping. */
    size_type mapping_offset() const noexcept
    {
        return mapped_length_ - length_;
    }

    /**
     * Returns a pointer to the first requested byte, or `nullptr` if no memory mapping
     * exists.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > pointer data() noexcept { return data_; }
    const_pointer data() const noexcept { return data_; }

    /**
     * Returns an iterator to the first requested byte, if a valid memory mapping
     * exists, otherwise this function call is undefined behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > iterator begin() noexcept { return data(); }
    const_iterator begin() const noexcept { return data(); }
    const_iterator cbegin() const noexcept { return data(); }

    /**
     * Returns an iterator one past the last requested byte, if a valid memory mapping
     * exists, otherwise this function call is undefined behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > iterator end() noexcept { return data() + length(); }
    const_iterator end() const noexcept { return data() + length(); }
    const_iterator cend() const noexcept { return data() + length(); }

    /**
     * Returns a reverse iterator to the last memory mapped byte, if a valid
     * memory mapping exists, otherwise this function call is undefined
     * behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
    const_reverse_iterator rbegin() const noexcept
    { return const_reverse_iterator(end()); }
    const_reverse_iterator crbegin() const noexcept
    { return const_reverse_iterator(end()); }

    /**
     * Returns a reverse iterator past the first mapped byte, if a valid memory
     * mapping exists, otherwise this function call is undefined behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
    const_reverse_iterator rend() const noexcept
    { return const_reverse_iterator(begin()); }
    const_reverse_iterator crend() const noexcept
    { return const_reverse_iterator(begin()); }

    /**
     * Returns a reference to the `i`th byte from the first requested byte (as returned
     * by `data`). If this is invoked when no valid memory mapping has been created
     * prior to this call, undefined behaviour ensues.
     */
    reference operator[](const size_type i) noexcept { return data_[i]; }
    const_reference operator[](const size_type i) const noexcept { return data_[i]; }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `path`, which must be a path to an existing file, is used to retrieve a file
     * handle (which is closed when the object destructs or `unmap` is called), which is
     * then used to memory map the requested region. Upon failure, `error` is set to
     * indicate the reason and the object remains in an unmapped state.
     *
     * `offset` is the number of bytes, relative to the start of the file, where the
     * mapping should begin. When specifying it, there is no need to worry about
     * providing a value that is aligned with the operating system's page allocation
     * granularity. This is adjusted by the implementation such that the first requested
     * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
     * `offset` from the start of the file.
     *
     * `length` is the number of bytes to map. It may be `map_entire_file`, in which
     * case a mapping of the entire file is created.
     */
    template<typename String>
    void map(const String& path, const size_type offset,
            const size_type length, std::error_code& error);

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `path`, which must be a path to an existing file, is used to retrieve a file
     * handle (which is closed when the object destructs or `unmap` is called), which is
     * then used to memory map the requested region. Upon failure, `error` is set to
     * indicate the reason and the object remains in an unmapped state.
     *
     * The entire file is mapped.
     */
    template<typename String>
    void map(const String& path, std::error_code& error)
    {
        map(path, 0, map_entire_file, error);
    }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is
     * unsuccesful, the reason is reported via `error` and the object remains in
     * a state as if this function hadn't been called.
     *
     * `handle`, which must be a valid file handle, which is used to memory map the
     * requested region. Upon failure, `error` is set to indicate the reason and the
     * object remains in an unmapped state.
     *
     * `offset` is the number of bytes, relative to the start of the file, where the
     * mapping should begin. When specifying it, there is no need to worry about
     * providing a value that is aligned with the operating system's page allocation
     * granularity. This is adjusted by the implementation such that the first requested
     * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
     * `offset` from the start of the file.
     *
     * `length` is the number of bytes to map. It may be `map_entire_file`, in which
     * case a mapping of the entire file is created.
     */
    void map(const handle_type handle, const size_type offset,
            const size_type length, std::error_code& error);

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is
     * unsuccesful, the reason is reported via `error` and the object remains in
     * a state as if this function hadn't been called.
     *
     * `handle`, which must be a valid file handle, which is used to memory map the
     * requested region. Upon failure, `error` is set to indicate the reason and the
     * object remains in an unmapped state.
     *
     * The entire file is mapped.
     */
    void map(const handle_type handle, std::error_code& error)
    {
        map(handle, 0, map_entire_file, error);
    }

    /**
     * If a valid memory mapping has been created prior to this call, this call
     * instructs the kernel to unmap the memory region and disassociate this object
     * from the file.
     *
     * The file handle associated with the file that is mapped is only closed if the
     * mapping was created using a file path. If, on the other hand, an existing
     * file handle was used to create the mapping, the file handle is not closed.
     */
    void unmap();

    void swap(basic_mmap& other);

    /** Flushes the memory mapped page to disk. Errors are reported via `error`. */
    template<access_mode A = AccessMode>
    typename std::enable_if<A == access_mode::write, void>::type
    sync(std::error_code& error);

    /**
     * All operators compare the address of the first byte and size of the two mapped
     * regions.
     */

private:
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > pointer get_mapping_start() noexcept
    {
        return !data() ? nullptr : data() - mapping_offset();
    }

    const_pointer get_mapping_start() const noexcept
    {
        return !data() ? nullptr : data() - mapping_offset();
    }

    /**
     * The destructor syncs changes to disk if `AccessMode` is `write`, but not
     * if it's `read`, but since the destructor cannot be templated, we need to
     * do SFINAE in a dedicated function, where one syncs and the other is a noop.
     */
    template<access_mode A = AccessMode>
    typename std::enable_if<A == access_mode::write, void>::type
    conditional_sync();
    template<access_mode A = AccessMode>
    typename std::enable_if<A == access_mode::read, void>::type conditional_sync();
};

template<access_mode AccessMode, typename ByteT>
bool operator==(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

template<access_mode AccessMode, typename ByteT>
bool operator!=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

template<access_mode AccessMode, typename ByteT>
bool operator<(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

template<access_mode AccessMode, typename ByteT>
bool operator<=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

template<access_mode AccessMode, typename ByteT>
bool operator>(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

template<access_mode AccessMode, typename ByteT>
bool operator>=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b);

/**
 * This is the basis for all read-only mmap objects and should be preferred over
 * directly using `basic_mmap`.
 */
template<typename ByteT>
using basic_mmap_source = basic_mmap<access_mode::read, ByteT>;

/**
 * This is the basis for all read-write mmap objects and should be preferred over
 * directly using `basic_mmap`.
 */
template<typename ByteT>
using basic_mmap_sink = basic_mmap<access_mode::write, ByteT>;

/**
 * These aliases cover the most common use cases, both representing a raw byte stream
 * (either with a char or an unsigned char/uint8_t).
 */
using mmap_source = basic_mmap_source<char>;
using ummap_source = basic_mmap_source<unsigned char>;

using mmap_sink = basic_mmap_sink<char>;
using ummap_sink = basic_mmap_sink<unsigned char>;

/**
 * Convenience factory method that constructs a mapping for any `basic_mmap` or
 * `basic_mmap` type.
 */
template<
    typename MMap,
    typename MappingToken
> MMap make_mmap(const MappingToken& token,
        int64_t offset, int64_t length, std::error_code& error)
{
    MMap mmap;
    mmap.map(token, offset, length, error);
    return mmap;
}

/**
 * Convenience factory method.
 *
 * MappingToken may be a String (`std::string`, `std::string_view`, `const char*`,
 * `std::filesystem::path`, `std::vector<char>`, or similar), or a
 * `mmap_source::handle_type`.
 */
template<typename MappingToken>
mmap_source make_mmap_source(const MappingToken& token, mmap_source::size_type offset,
        mmap_source::size_type length, std::error_code& error)
{
    return make_mmap<mmap_source>(token, offset, length, error);
}

template<typename MappingToken>
mmap_source make_mmap_source(const MappingToken& token, std::error_code& error)
{
    return make_mmap_source(token, 0, map_entire_file, error);
}

/**
 * Convenience factory method.
 *
 * MappingToken may be a String (`std::string`, `std::string_view`, `const char*`,
 * `std::filesystem::path`, `std::vector<char>`, or similar), or a
 * `mmap_sink::handle_type`.
 */
template<typename MappingToken>
mmap_sink make_mmap_sink(const MappingToken& token, mmap_sink::size_type offset,
        mmap_sink::size_type length, std::error_code& error)
{
    return make_mmap<mmap_sink>(token, offset, length, error);
}

template<typename MappingToken>
mmap_sink make_mmap_sink(const MappingToken& token, std::error_code& error)
{
    return make_mmap_sink(token, 0, map_entire_file, error);
}

} // namespace mio

// #include "detail/mmap.ipp"
/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_BASIC_MMAP_IMPL
#define MIO_BASIC_MMAP_IMPL

// #include "mio/mmap.hpp"

// #include "mio/page.hpp"

// #include "mio/detail/string_util.hpp"
/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_STRING_UTIL_HEADER
#define MIO_STRING_UTIL_HEADER

#include <type_traits>

namespace mio {
namespace detail {

template<
    typename S,
    typename C = typename std::decay<S>::type,
    typename = decltype(std::declval<C>().data()),
    typename = typename std::enable_if<
        std::is_same<typename C::value_type, char>::value
#ifdef _WIN32
        || std::is_same<typename C::value_type, wchar_t>::value
#endif
    >::type
> struct char_type_helper {
    using type = typename C::value_type;
};

template<class T>
struct char_type {
    using type = typename char_type_helper<T>::type;
};

// TODO: can we avoid this brute force approach?
template<>
struct char_type<char*> {
    using type = char;
};

template<>
struct char_type<const char*> {
    using type = char;
};

template<size_t N>
struct char_type<char[N]> {
    using type = char;
};

template<size_t N>
struct char_type<const char[N]> {
    using type = char;
};

#ifdef _WIN32
template<>
struct char_type<wchar_t*> {
    using type = wchar_t;
};

template<>
struct char_type<const wchar_t*> {
    using type = wchar_t;
};

template<size_t N>
struct char_type<wchar_t[N]> {
    using type = wchar_t;
};

template<size_t N>
struct char_type<const wchar_t[N]> {
    using type = wchar_t;
};
#endif // _WIN32

template<typename CharT, typename S>
struct is_c_str_helper
{
    static constexpr bool value = std::is_same<
        CharT*,
        // TODO: I'm so sorry for this... Can this be made cleaner?
        typename std::add_pointer<
            typename std::remove_cv<
                typename std::remove_pointer<
                    typename std::decay<
                        S
                    >::type
                >::type
            >::type
        >::type
    >::value;
};

template<typename S>
struct is_c_str
{
    static constexpr bool value = is_c_str_helper<char, S>::value;
};

#ifdef _WIN32
template<typename S>
struct is_c_wstr
{
    static constexpr bool value = is_c_str_helper<wchar_t, S>::value;
};
#endif // _WIN32

template<typename S>
struct is_c_str_or_c_wstr
{
    static constexpr bool value = is_c_str<S>::value
#ifdef _WIN32
        || is_c_wstr<S>::value
#endif
        ;
};

template<
    typename String,
    typename = decltype(std::declval<String>().data()),
    typename = typename std::enable_if<!is_c_str_or_c_wstr<String>::value>::type
> const typename char_type<String>::type* c_str(const String& path)
{
    return path.data();
}

template<
    typename String,
    typename = decltype(std::declval<String>().empty()),
    typename = typename std::enable_if<!is_c_str_or_c_wstr<String>::value>::type
> bool empty(const String& path)
{
    return path.empty();
}

template<
    typename String,
    typename = typename std::enable_if<is_c_str_or_c_wstr<String>::value>::type
> const typename char_type<String>::type* c_str(String path)
{
    return path;
}

template<
    typename String,
    typename = typename std::enable_if<is_c_str_or_c_wstr<String>::value>::type
> bool empty(String path)
{
    return !path || (*path == 0);
}

} // namespace detail
} // namespace mio

#endif // MIO_STRING_UTIL_HEADER


#include <algorithm>

#ifndef _WIN32
# include <unistd.h>
# include <fcntl.h>
# include <sys/mman.h>
# include <sys/stat.h>
#endif

namespace mio {
namespace detail {

#ifdef _WIN32
namespace win {

/** Returns the 4 upper bytes of an 8-byte integer. */
inline DWORD int64_high(int64_t n) noexcept
{
    return n >> 32;
}

/** Returns the 4 lower bytes of an 8-byte integer. */
inline DWORD int64_low(int64_t n) noexcept
{
    return n & 0xffffffff;
}

template<
    typename String,
    typename = typename std::enable_if<
        std::is_same<typename char_type<String>::type, char>::value
    >::type
> file_handle_type open_file_helper(const String& path, const access_mode mode)
{
    return ::CreateFileA(c_str(path),
            mode == access_mode::read ? GENERIC_READ : GENERIC_READ | GENERIC_WRITE,
            FILE_SHARE_READ | FILE_SHARE_WRITE,
            0,
            OPEN_EXISTING,
            FILE_ATTRIBUTE_NORMAL,
            0);
}

template<typename String>
typename std::enable_if<
    std::is_same<typename char_type<String>::type, wchar_t>::value,
    file_handle_type
>::type open_file_helper(const String& path, const access_mode mode)
{
    return ::CreateFileW(c_str(path),
            mode == access_mode::read ? GENERIC_READ : GENERIC_READ | GENERIC_WRITE,
            FILE_SHARE_READ | FILE_SHARE_WRITE,
            0,
            OPEN_EXISTING,
            FILE_ATTRIBUTE_NORMAL,
            0);
}

} // win
#endif // _WIN32

/**
 * Returns the last platform specific system error (errno on POSIX and
 * GetLastError on Win) as a `std::error_code`.
 */
inline std::error_code last_error() noexcept
{
    std::error_code error;
#ifdef _WIN32
    error.assign(GetLastError(), std::system_category());
#else
    error.assign(errno, std::system_category());
#endif
    return error;
}

template<typename String>
file_handle_type open_file(const String& path, const access_mode mode,
        std::error_code& error)
{
    error.clear();
    if(detail::empty(path))
    {
        error = std::make_error_code(std::errc::invalid_argument);
        return invalid_handle;
    }
#ifdef _WIN32
    const auto handle = win::open_file_helper(path, mode);
#else // POSIX
    const auto handle = ::open(c_str(path),
            mode == access_mode::read ? O_RDONLY : O_RDWR);
#endif
    if(handle == invalid_handle)
    {
        error = detail::last_error();
    }
    return handle;
}

inline size_t query_file_size(file_handle_type handle, std::error_code& error)
{
    error.clear();
#ifdef _WIN32
    LARGE_INTEGER file_size;
    if(::GetFileSizeEx(handle, &file_size) == 0)
    {
        error = detail::last_error();
        return 0;
    }
    return static_cast<int64_t>(file_size.QuadPart);
#else // POSIX
    struct stat sbuf;
    if(::fstat(handle, &sbuf) == -1)
    {
        error = detail::last_error();
        return 0;
    }
    return sbuf.st_size;
#endif
}

struct mmap_context
{
    char* data;
    int64_t length;
    int64_t mapped_length;
#ifdef _WIN32
    file_handle_type file_mapping_handle;
#endif
};

inline mmap_context memory_map(const file_handle_type file_handle, const int64_t offset,
    const int64_t length, const access_mode mode, std::error_code& error)
{
    const int64_t aligned_offset = make_offset_page_aligned(offset);
    const int64_t length_to_map = offset - aligned_offset + length;
#ifdef _WIN32
    const int64_t max_file_size = offset + length;
    const auto file_mapping_handle = ::CreateFileMapping(
            file_handle,
            0,
            mode == access_mode::read ? PAGE_READONLY : PAGE_READWRITE,
            win::int64_high(max_file_size),
            win::int64_low(max_file_size),
            0);
    if(file_mapping_handle == invalid_handle)
    {
        error = detail::last_error();
        return {};
    }
    char* mapping_start = static_cast<char*>(::MapViewOfFile(
            file_mapping_handle,
            mode == access_mode::read ? FILE_MAP_READ : FILE_MAP_WRITE,
            win::int64_high(aligned_offset),
            win::int64_low(aligned_offset),
            length_to_map));
    if(mapping_start == nullptr)
    {
        // Close file handle if mapping it failed.
        ::CloseHandle(file_mapping_handle);
        error = detail::last_error();
        return {};
    }
#else // POSIX
    char* mapping_start = static_cast<char*>(::mmap(
            0, // Don't give hint as to where to map.
            length_to_map,
            mode == access_mode::read ? PROT_READ : PROT_WRITE,
            MAP_SHARED,
            file_handle,
            aligned_offset));
    if(mapping_start == MAP_FAILED)
    {
        error = detail::last_error();
        return {};
    }
#endif
    mmap_context ctx;
    ctx.data = mapping_start + offset - aligned_offset;
    ctx.length = length;
    ctx.mapped_length = length_to_map;
#ifdef _WIN32
    ctx.file_mapping_handle = file_mapping_handle;
#endif
    return ctx;
}

} // namespace detail

// -- basic_mmap --

template<access_mode AccessMode, typename ByteT>
basic_mmap<AccessMode, ByteT>::~basic_mmap()
{
    conditional_sync();
    unmap();
}

template<access_mode AccessMode, typename ByteT>
basic_mmap<AccessMode, ByteT>::basic_mmap(basic_mmap&& other)
    : data_(std::move(other.data_))
    , length_(std::move(other.length_))
    , mapped_length_(std::move(other.mapped_length_))
    , file_handle_(std::move(other.file_handle_))
#ifdef _WIN32
    , file_mapping_handle_(std::move(other.file_mapping_handle_))
#endif
    , is_handle_internal_(std::move(other.is_handle_internal_))
{
    other.data_ = nullptr;
    other.length_ = other.mapped_length_ = 0;
    other.file_handle_ = invalid_handle;
#ifdef _WIN32
    other.file_mapping_handle_ = invalid_handle;
#endif
}

template<access_mode AccessMode, typename ByteT>
basic_mmap<AccessMode, ByteT>&
basic_mmap<AccessMode, ByteT>::operator=(basic_mmap&& other)
{
    if(this != &other)
    {
        // First the existing mapping needs to be removed.
        unmap();
        data_ = std::move(other.data_);
        length_ = std::move(other.length_);
        mapped_length_ = std::move(other.mapped_length_);
        file_handle_ = std::move(other.file_handle_);
#ifdef _WIN32
        file_mapping_handle_ = std::move(other.file_mapping_handle_);
#endif
        is_handle_internal_ = std::move(other.is_handle_internal_);

        // The moved from basic_mmap's fields need to be reset, because
        // otherwise other's destructor will unmap the same mapping that was
        // just moved into this.
        other.data_ = nullptr;
        other.length_ = other.mapped_length_ = 0;
        other.file_handle_ = invalid_handle;
#ifdef _WIN32
        other.file_mapping_handle_ = invalid_handle;
#endif
        other.is_handle_internal_ = false;
    }
    return *this;
}

template<access_mode AccessMode, typename ByteT>
typename basic_mmap<AccessMode, ByteT>::handle_type
basic_mmap<AccessMode, ByteT>::mapping_handle() const noexcept
{
#ifdef _WIN32
    return file_mapping_handle_;
#else
    return file_handle_;
#endif
}

template<access_mode AccessMode, typename ByteT>
template<typename String>
void basic_mmap<AccessMode, ByteT>::map(const String& path, const size_type offset,
        const size_type length, std::error_code& error)
{
    error.clear();
    if(detail::empty(path))
    {
        error = std::make_error_code(std::errc::invalid_argument);
        return;
    }
    const auto handle = detail::open_file(path, AccessMode, error);
    if(error)
    {
        return;
    }

    map(handle, offset, length, error);
    // This MUST be after the call to map, as that sets this to true.
    if(!error)
    {
        is_handle_internal_ = true;
    }
}

template<access_mode AccessMode, typename ByteT>
void basic_mmap<AccessMode, ByteT>::map(const handle_type handle,
        const size_type offset, const size_type length, std::error_code& error)
{
    error.clear();
    if(handle == invalid_handle)
    {
        error = std::make_error_code(std::errc::bad_file_descriptor);
        return;
    }

    const auto file_size = detail::query_file_size(handle, error);
    if(error)
    {
        return;
    }

    if(offset + length > file_size)
    {
        error = std::make_error_code(std::errc::invalid_argument);
        return;
    }

    const auto ctx = detail::memory_map(handle, offset,
            length == map_entire_file ? (file_size - offset) : length,
            AccessMode, 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.
        unmap();
        file_handle_ = handle;
        is_handle_internal_ = false;
        data_ = reinterpret_cast<pointer>(ctx.data);
        length_ = ctx.length;
        mapped_length_ = ctx.mapped_length;
#ifdef _WIN32
        file_mapping_handle_ = ctx.file_mapping_handle;
#endif
    }
}

template<access_mode AccessMode, typename ByteT>
template<access_mode A>
typename std::enable_if<A == access_mode::write, void>::type
basic_mmap<AccessMode, ByteT>::sync(std::error_code& error)
{
    error.clear();
    if(!is_open())
    {
        error = std::make_error_code(std::errc::bad_file_descriptor);
        return;
    }

    if(data())
    {
#ifdef _WIN32
        if(::FlushViewOfFile(get_mapping_start(), mapped_length_) == 0
           || ::FlushFileBuffers(file_handle_) == 0)
#else // POSIX
        if(::msync(get_mapping_start(), mapped_length_, MS_SYNC) != 0)
#endif
        {
            error = detail::last_error();
            return;
        }
    }
#ifdef _WIN32
    if(::FlushFileBuffers(file_handle_) == 0)
    {
        error = detail::last_error();
    }
#endif
}

template<access_mode AccessMode, typename ByteT>
void basic_mmap<AccessMode, ByteT>::unmap()
{
    if(!is_open()) { return; }
    // TODO do we care about errors here?
#ifdef _WIN32
    if(is_mapped())
    {
        ::UnmapViewOfFile(get_mapping_start());
        ::CloseHandle(file_mapping_handle_);
    }
#else // POSIX
    if(data_) { ::munmap(const_cast<pointer>(get_mapping_start()), mapped_length_); }
#endif

    // If `file_handle_` was obtained by our opening it (when map is called with
    // a path, rather than an existing file handle), we need to close it,
    // otherwise it must not be closed as it may still be used outside this
    // instance.
    if(is_handle_internal_)
    {
#ifdef _WIN32
        ::CloseHandle(file_handle_);
#else // POSIX
        ::close(file_handle_);
#endif
    }

    // Reset fields to their default values.
    data_ = nullptr;
    length_ = mapped_length_ = 0;
    file_handle_ = invalid_handle;
#ifdef _WIN32
    file_mapping_handle_ = invalid_handle;
#endif
}

template<access_mode AccessMode, typename ByteT>
bool basic_mmap<AccessMode, ByteT>::is_mapped() const noexcept
{
#ifdef _WIN32
    return file_mapping_handle_ != invalid_handle;
#else // POSIX
    return is_open();
#endif
}

template<access_mode AccessMode, typename ByteT>
void basic_mmap<AccessMode, ByteT>::swap(basic_mmap& other)
{
    if(this != &other)
    {
        using std::swap;
        swap(data_, other.data_);
        swap(file_handle_, other.file_handle_);
#ifdef _WIN32
        swap(file_mapping_handle_, other.file_mapping_handle_);
#endif
        swap(length_, other.length_);
        swap(mapped_length_, other.mapped_length_);
        swap(is_handle_internal_, other.is_handle_internal_);
    }
}

template<access_mode AccessMode, typename ByteT>
template<access_mode A>
typename std::enable_if<A == access_mode::write, void>::type
basic_mmap<AccessMode, ByteT>::conditional_sync()
{
    // This is invoked from the destructor, so not much we can do about
    // failures here.
    std::error_code ec;
    sync(ec);
}

template<access_mode AccessMode, typename ByteT>
template<access_mode A>
typename std::enable_if<A == access_mode::read, void>::type
basic_mmap<AccessMode, ByteT>::conditional_sync()
{
    // noop
}

template<access_mode AccessMode, typename ByteT>
bool operator==(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    return a.data() == b.data()
        && a.size() == b.size();
}

template<access_mode AccessMode, typename ByteT>
bool operator!=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    return !(a == b);
}

template<access_mode AccessMode, typename ByteT>
bool operator<(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    if(a.data() == b.data()) { return a.size() < b.size(); }
    return a.data() < b.data();
}

template<access_mode AccessMode, typename ByteT>
bool operator<=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    return !(a > b);
}

template<access_mode AccessMode, typename ByteT>
bool operator>(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    if(a.data() == b.data()) { return a.size() > b.size(); }
    return a.data() > b.data();
}

template<access_mode AccessMode, typename ByteT>
bool operator>=(const basic_mmap<AccessMode, ByteT>& a,
        const basic_mmap<AccessMode, ByteT>& b)
{
    return !(a < b);
}

} // namespace mio

#endif // MIO_BASIC_MMAP_IMPL


#endif // MIO_MMAP_HEADER
/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_PAGE_HEADER
#define MIO_PAGE_HEADER

#ifdef _WIN32
# include <windows.h>
#else
# include <unistd.h>
#endif

namespace mio {

/**
 * This is used by `basic_mmap` to determine whether to create a read-only or
 * a read-write memory mapping.
 */
enum class access_mode
{
    read,
    write
};

/**
 * Determines the operating system's page allocation granularity.
 *
 * On the first call to this function, it invokes the operating system specific syscall
 * to determine the page size, caches the value, and returns it. Any subsequent call to
 * this function serves the cached value, so no further syscalls are made.
 */
inline size_t page_size()
{
    static const size_t page_size = []
    {
#ifdef _WIN32
        SYSTEM_INFO SystemInfo;
        GetSystemInfo(&SystemInfo);
        return SystemInfo.dwAllocationGranularity;
#else
        return sysconf(_SC_PAGE_SIZE);
#endif
    }();
    return page_size;
}

/**
 * Alligns `offset` to the operating's system page size such that it subtracts the
 * difference until the nearest page boundary before `offset`, or does nothing if
 * `offset` is already page aligned.
 */
inline size_t make_offset_page_aligned(size_t offset) noexcept
{
    const size_t page_size_ = page_size();
    // Use integer division to round down to the nearest page alignment.
    return offset / page_size_ * page_size_;
}

} // namespace mio

#endif // MIO_PAGE_HEADER
/* Copyright 2017 https://github.com/mandreyel
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this
 * software and associated documentation files (the "Software"), to deal in the Software
 * without restriction, including without limitation the rights to use, copy, modify,
 * merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies
 * or substantial portions of the Software.
 *
 * 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF
 * CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
 * OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */

#ifndef MIO_SHARED_MMAP_HEADER
#define MIO_SHARED_MMAP_HEADER

// #include "mio/mmap.hpp"


#include <system_error> // std::error_code
#include <memory> // std::shared_ptr

namespace mio {

/**
 * Exposes (nearly) the same interface as `basic_mmap`, but endowes it with
 * `std::shared_ptr` semantics.
 *
 * This is not the default behaviour of `basic_mmap` to avoid allocating on the heap if
 * shared semantics are not required.
 */
template<
    access_mode AccessMode,
    typename ByteT
> class basic_shared_mmap
{
    using impl_type = basic_mmap<AccessMode, ByteT>;
    std::shared_ptr<impl_type> pimpl_;

public:
    using value_type = typename impl_type::value_type;
    using size_type = typename impl_type::size_type;
    using reference = typename impl_type::reference;
    using const_reference = typename impl_type::const_reference;
    using pointer = typename impl_type::pointer;
    using const_pointer = typename impl_type::const_pointer;
    using difference_type = typename impl_type::difference_type;
    using iterator = typename impl_type::iterator;
    using const_iterator = typename impl_type::const_iterator;
    using reverse_iterator = typename impl_type::reverse_iterator;
    using const_reverse_iterator = typename impl_type::const_reverse_iterator;
    using iterator_category = typename impl_type::iterator_category;
    using handle_type = typename impl_type::handle_type;
    using mmap_type = impl_type;

    basic_shared_mmap() = default;
    basic_shared_mmap(const basic_shared_mmap&) = default;
    basic_shared_mmap& operator=(const basic_shared_mmap&) = default;
    basic_shared_mmap(basic_shared_mmap&&) = default;
    basic_shared_mmap& operator=(basic_shared_mmap&&) = default;

    /** Takes ownership of an existing mmap object. */
    basic_shared_mmap(mmap_type&& mmap)
        : pimpl_(std::make_shared<mmap_type>(std::move(mmap)))
    {}

    /** Takes ownership of an existing mmap object. */
    basic_shared_mmap& operator=(mmap_type&& mmap)
    {
        pimpl_ = std::make_shared<mmap_type>(std::move(mmap));
        return *this;
    }

    /** Initializes this object with an already established shared mmap. */
    basic_shared_mmap(std::shared_ptr<mmap_type> mmap) : pimpl_(std::move(mmap)) {}

    /** Initializes this object with an already established shared mmap. */
    basic_shared_mmap& operator=(std::shared_ptr<mmap_type> mmap)
    {
        pimpl_ = std::move(mmap);
        return *this;
    }

#ifdef __cpp_exceptions
    /**
     * The same as invoking the `map` function, except any error that may occur
     * while establishing the mapping is wrapped in a `std::system_error` and is
     * thrown.
     */
    template<typename String>
    basic_shared_mmap(const String& path, const size_type offset = 0, const size_type length = map_entire_file)
    {
        std::error_code error;
        map(path, offset, length, error);
        if(error) { throw std::system_error(error); }
    }

    /**
     * The same as invoking the `map` function, except any error that may occur
     * while establishing the mapping is wrapped in a `std::system_error` and is
     * thrown.
     */
    basic_shared_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); }
    }
#endif // __cpp_exceptions

    /**
     * If this is a read-write mapping and the last reference to the mapping,
     * the destructor invokes sync. Regardless of the access mode, unmap is
     * invoked as a final step.
     */
    ~basic_shared_mmap() = default;

    /** Returns the underlying `std::shared_ptr` instance that holds the mmap. */
    std::shared_ptr<mmap_type> get_shared_ptr() { return pimpl_; }

    /**
     * On UNIX systems 'file_handle' and 'mapping_handle' are the same. On Windows,
     * however, a mapped region of a file gets its own handle, which is returned by
     * 'mapping_handle'.
     */
    handle_type file_handle() const noexcept
    {
        return pimpl_ ? pimpl_->file_handle() : invalid_handle;
    }

    handle_type mapping_handle() const noexcept
    {
        return pimpl_ ? pimpl_->mapping_handle() : invalid_handle;
    }

    /** Returns whether a valid memory mapping has been created. */
    bool is_open() const noexcept { return pimpl_ && pimpl_->is_open(); }

    /**
     * Returns true if no mapping was established, that is, conceptually the
     * same as though the length that was mapped was 0. This function is
     * provided so that this class has Container semantics.
     */
    bool empty() const noexcept { return !pimpl_ || pimpl_->empty(); }

    /**
     * `size` and `length` both return the logical length, i.e. the number of bytes
     * user requested to be mapped, while `mapped_length` returns the actual number of
     * bytes that were mapped which is a multiple of the underlying operating system's
     * page allocation granularity.
     */
    size_type size() const noexcept { return pimpl_ ? pimpl_->length() : 0; }
    size_type length() const noexcept { return pimpl_ ? pimpl_->length() : 0; }
    size_type mapped_length() const noexcept
    {
        return pimpl_ ? pimpl_->mapped_length() : 0;
    }

    /**
     * Returns a pointer to the first requested byte, or `nullptr` if no memory mapping
     * exists.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > pointer data() noexcept { return pimpl_->data(); }
    const_pointer data() const noexcept { return pimpl_ ? pimpl_->data() : nullptr; }

    /**
     * Returns an iterator to the first requested byte, if a valid memory mapping
     * exists, otherwise this function call is undefined behaviour.
     */
    iterator begin() noexcept { return pimpl_->begin(); }
    const_iterator begin() const noexcept { return pimpl_->begin(); }
    const_iterator cbegin() const noexcept { return pimpl_->cbegin(); }

    /**
     * Returns an iterator one past the last requested byte, if a valid memory mapping
     * exists, otherwise this function call is undefined behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > iterator end() noexcept { return pimpl_->end(); }
    const_iterator end() const noexcept { return pimpl_->end(); }
    const_iterator cend() const noexcept { return pimpl_->cend(); }

    /**
     * Returns a reverse iterator to the last memory mapped byte, if a valid
     * memory mapping exists, otherwise this function call is undefined
     * behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > reverse_iterator rbegin() noexcept { return pimpl_->rbegin(); }
    const_reverse_iterator rbegin() const noexcept { return pimpl_->rbegin(); }
    const_reverse_iterator crbegin() const noexcept { return pimpl_->crbegin(); }

    /**
     * Returns a reverse iterator past the first mapped byte, if a valid memory
     * mapping exists, otherwise this function call is undefined behaviour.
     */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > reverse_iterator rend() noexcept { return pimpl_->rend(); }
    const_reverse_iterator rend() const noexcept { return pimpl_->rend(); }
    const_reverse_iterator crend() const noexcept { return pimpl_->crend(); }

    /**
     * Returns a reference to the `i`th byte from the first requested byte (as returned
     * by `data`). If this is invoked when no valid memory mapping has been created
     * prior to this call, undefined behaviour ensues.
     */
    reference operator[](const size_type i) noexcept { return (*pimpl_)[i]; }
    const_reference operator[](const size_type i) const noexcept { return (*pimpl_)[i]; }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `path`, which must be a path to an existing file, is used to retrieve a file
     * handle (which is closed when the object destructs or `unmap` is called), which is
     * then used to memory map the requested region. Upon failure, `error` is set to
     * indicate the reason and the object remains in an unmapped state.
     *
     * `offset` is the number of bytes, relative to the start of the file, where the
     * mapping should begin. When specifying it, there is no need to worry about
     * providing a value that is aligned with the operating system's page allocation
     * granularity. This is adjusted by the implementation such that the first requested
     * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
     * `offset` from the start of the file.
     *
     * `length` is the number of bytes to map. It may be `map_entire_file`, in which
     * case a mapping of the entire file is created.
     */
    template<typename String>
    void map(const String& path, const size_type offset,
        const size_type length, std::error_code& error)
    {
        map_impl(path, offset, length, error);
    }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `path`, which must be a path to an existing file, is used to retrieve a file
     * handle (which is closed when the object destructs or `unmap` is called), which is
     * then used to memory map the requested region. Upon failure, `error` is set to
     * indicate the reason and the object remains in an unmapped state.
     *
     * The entire file is mapped.
     */
    template<typename String>
    void map(const String& path, std::error_code& error)
    {
        map_impl(path, 0, map_entire_file, error);
    }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `handle`, which must be a valid file handle, which is used to memory map the
     * requested region. Upon failure, `error` is set to indicate the reason and the
     * object remains in an unmapped state.
     *
     * `offset` is the number of bytes, relative to the start of the file, where the
     * mapping should begin. When specifying it, there is no need to worry about
     * providing a value that is aligned with the operating system's page allocation
     * granularity. This is adjusted by the implementation such that the first requested
     * byte (as returned by `data` or `begin`), so long as `offset` is valid, will be at
     * `offset` from the start of the file.
     *
     * `length` is the number of bytes to map. It may be `map_entire_file`, in which
     * case a mapping of the entire file is created.
     */
    void map(const handle_type handle, const size_type offset,
        const size_type length, std::error_code& error)
    {
        map_impl(handle, offset, length, error);
    }

    /**
     * Establishes a memory mapping with AccessMode. If the mapping is unsuccesful, the
     * reason is reported via `error` and the object remains in a state as if this
     * function hadn't been called.
     *
     * `handle`, which must be a valid file handle, which is used to memory map the
     * requested region. Upon failure, `error` is set to indicate the reason and the
     * object remains in an unmapped state.
     *
     * The entire file is mapped.
     */
    void map(const handle_type handle, std::error_code& error)
    {
        map_impl(handle, 0, map_entire_file, error);
    }

    /**
     * If a valid memory mapping has been created prior to this call, this call
     * instructs the kernel to unmap the memory region and disassociate this object
     * from the file.
     *
     * The file handle associated with the file that is mapped is only closed if the
     * mapping was created using a file path. If, on the other hand, an existing
     * file handle was used to create the mapping, the file handle is not closed.
     */
    void unmap() { if(pimpl_) pimpl_->unmap(); }

    void swap(basic_shared_mmap& other) { pimpl_.swap(other.pimpl_); }

    /** Flushes the memory mapped page to disk. Errors are reported via `error`. */
    template<
        access_mode A = AccessMode,
        typename = typename std::enable_if<A == access_mode::write>::type
    > void sync(std::error_code& error) { if(pimpl_) pimpl_->sync(error); }

    /** All operators compare the underlying `basic_mmap`'s addresses. */

    friend bool operator==(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return a.pimpl_ == b.pimpl_;
    }

    friend bool operator!=(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return !(a == b);
    }

    friend bool operator<(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return a.pimpl_ < b.pimpl_;
    }

    friend bool operator<=(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return a.pimpl_ <= b.pimpl_;
    }

    friend bool operator>(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return a.pimpl_ > b.pimpl_;
    }

    friend bool operator>=(const basic_shared_mmap& a, const basic_shared_mmap& b)
    {
        return a.pimpl_ >= b.pimpl_;
    }

private:
    template<typename MappingToken>
    void map_impl(const MappingToken& token, const size_type offset,
        const size_type length, std::error_code& error)
    {
        if(!pimpl_)
        {
            mmap_type mmap = make_mmap<mmap_type>(token, offset, length, error);
            if(error) { return; }
            pimpl_ = std::make_shared<mmap_type>(std::move(mmap));
        }
        else
        {
            pimpl_->map(token, offset, length, error);
        }
    }
};

/**
 * This is the basis for all read-only mmap objects and should be preferred over
 * directly using basic_shared_mmap.
 */
template<typename ByteT>
using basic_shared_mmap_source = basic_shared_mmap<access_mode::read, ByteT>;

/**
 * This is the basis for all read-write mmap objects and should be preferred over
 * directly using basic_shared_mmap.
 */
template<typename ByteT>
using basic_shared_mmap_sink = basic_shared_mmap<access_mode::write, ByteT>;

/**
 * These aliases cover the most common use cases, both representing a raw byte stream
 * (either with a char or an unsigned char/uint8_t).
 */
using shared_mmap_source = basic_shared_mmap_source<char>;
using shared_ummap_source = basic_shared_mmap_source<unsigned char>;

using shared_mmap_sink = basic_shared_mmap_sink<char>;
using shared_ummap_sink = basic_shared_mmap_sink<unsigned char>;

} // namespace mio

#endif // MIO_SHARED_MMAP_HEADER