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boost/beast/core/buffer_traits.hpp

//
// Copyright (c) 2016-2019 Vinnie Falco (vinnie dot falco at gmail dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// Official repository: https://github.com/boostorg/beast
//

#ifndef BOOST_BEAST_BUFFER_TRAITS_HPP
#define BOOST_BEAST_BUFFER_TRAITS_HPP

#include <boost/beast/core/detail/config.hpp>
#include <boost/beast/core/detail/buffer_traits.hpp>
#include <boost/beast/core/detail/static_const.hpp>
#include <boost/asio/buffer.hpp>
#include <boost/config/workaround.hpp>
#include <boost/mp11/function.hpp>
#include <type_traits>

namespace boost {
namespace beast {

/** Determine if a list of types satisfy the <em>ConstBufferSequence</em> requirements.

    This metafunction is used to determine if all of the specified types
    meet the requirements for constant buffer sequences. This type alias
    will be `std::true_type` if each specified type meets the requirements,
    otherwise, this type alias will be `std::false_type`.

    @tparam BufferSequence A list of zero or more types to check. If this
    list is empty, the resulting type alias will be `std::true_type`.
*/
template<class... BufferSequence>
#if BOOST_BEAST_DOXYGEN
using is_const_buffer_sequence = __see_below__;
#else
using is_const_buffer_sequence = mp11::mp_all<
    net::is_const_buffer_sequence<
        typename std::decay<BufferSequence>::type>...>;
#endif

/** Determine if a list of types satisfy the <em>MutableBufferSequence</em> requirements.

    This metafunction is used to determine if all of the specified types
    meet the requirements for mutable buffer sequences. This type alias
    will be `std::true_type` if each specified type meets the requirements,
    otherwise, this type alias will be `std::false_type`.

    @tparam BufferSequence A list of zero or more types to check. If this
    list is empty, the resulting type alias will be `std::true_type`.
*/
template<class... BufferSequence>
#if BOOST_BEAST_DOXYGEN
using is_mutable_buffer_sequence = __see_below__;
#else
using is_mutable_buffer_sequence = mp11::mp_all<
    net::is_mutable_buffer_sequence<
        typename std::decay<BufferSequence>::type>...>;
#endif

/** Type alias for the underlying buffer type of a list of buffer sequence types.

    This metafunction is used to determine the underlying buffer type for
    a list of buffer sequence. The equivalent type of the alias will vary
    depending on the template type argument:

    @li If every type in the list is a <em>MutableBufferSequence</em>,
        the resulting type alias will be `net::mutable_buffer`, otherwise

    @li The resulting type alias will be `net::const_buffer`.

    @par Example
    The following code returns the first buffer in a buffer sequence,
    or generates a compilation error if the argument is not a buffer
    sequence:
    @code
    template <class BufferSequence>
    buffers_type <BufferSequence>
    buffers_front (BufferSequence const& buffers)
    {
        static_assert(
            net::is_const_buffer_sequence<BufferSequence>::value,
            "BufferSequence type requirements not met");
        auto const first = net::buffer_sequence_begin (buffers);
        if (first == net::buffer_sequence_end (buffers))
            return {};
        return *first;
    }
    @endcode

    @tparam BufferSequence A list of zero or more types to check. If this
    list is empty, the resulting type alias will be `net::mutable_buffer`.
*/
template<class... BufferSequence>
#if BOOST_BEAST_DOXYGEN
using buffers_type = __see_below__;
#else
using buffers_type = typename std::conditional<
    is_mutable_buffer_sequence<BufferSequence...>::value,
    net::mutable_buffer, net::const_buffer>::type;
#endif

/** Type alias for the iterator type of a buffer sequence type.

    This metafunction is used to determine the type of iterator
    used by a particular buffer sequence.

    @tparam T The buffer sequence type to use. The resulting
    type alias will be equal to the iterator type used by
    the buffer sequence.
*/
template <class BufferSequence>
#if BOOST_BEAST_DOXYGEN
using buffers_iterator_type = __see_below__;
#elif BOOST_WORKAROUND(BOOST_MSVC, < 1910)
using buffers_iterator_type = typename
    detail::buffers_iterator_type_helper<
        typename std::decay<BufferSequence>::type>::type;
#else
using buffers_iterator_type =
    decltype(net::buffer_sequence_begin(
        std::declval<BufferSequence const&>()));
#endif

/** Return the total number of bytes in a buffer or buffer sequence

    This function returns the total number of bytes in a buffer,
    buffer sequence, or object convertible to a buffer. Specifically
    it may be passed:

    @li A <em>ConstBufferSequence</em> or <em>MutableBufferSequence</em>

    @li A `net::const_buffer` or `net::mutable_buffer`

    @li An object convertible to `net::const_buffer`

    This function is designed as an easier-to-use replacement for
    `net::buffer_size`. It recognizes customization points found through
    argument-dependent lookup. The call `beast::buffer_bytes(b)` is
    equivalent to performing:
    @code
    using namespace net;
    buffer_bytes(b);
    @endcode
    In addition this handles types which are convertible to
    `net::const_buffer`; these are not handled by `net::buffer_size`.

    @param buffers The buffer or buffer sequence to calculate the size of.

    @return The total number of bytes in the buffer or sequence.
*/
#if BOOST_BEAST_DOXYGEN
template<class BufferSequence>
std::size_t
buffer_bytes(BufferSequence const& buffers);
#else
BOOST_BEAST_INLINE_VARIABLE(buffer_bytes, detail::buffer_bytes_impl)
#endif

} // beast
} // boost

#endif