buffer_prefix.hpp

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//
// Copyright (c) 2016-2017 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_PREFIX_HPP
#define BOOST_BEAST_BUFFER_PREFIX_HPP

#include <boost/beast/config.hpp>
#include <boost/beast/core/type_traits.hpp>
#include <boost/beast/core/detail/in_place_init.hpp>
#include <boost/asio/buffer.hpp>
#include <cstdint>
#include <type_traits>

namespace boost {
namespace beast {

template<class BufferSequence>
class buffer_prefix_view
{
    using buffers_type = typename
        std::decay<BufferSequence>::type;

    using iter_type =
        typename buffers_type::const_iterator;

    BufferSequence bs_;
    std::size_t size_;
    iter_type end_;

    template<class Deduced>
    buffer_prefix_view(
            Deduced&& other, std::size_t dist)
        : bs_(std::forward<Deduced>(other).bs_)
        , size_(other.size_)
        , end_(std::next(bs_.begin(), dist))
    {
    }

    void
    setup(std::size_t size);

public:
    using value_type = typename std::conditional<
        std::is_convertible<typename
            std::iterator_traits<iter_type>::value_type,
                boost::asio::mutable_buffer>::value,
                    boost::asio::mutable_buffer,
                        boost::asio::const_buffer>::type;

#if BOOST_BEAST_DOXYGEN
    using const_iterator = implementation_defined;

#else
    class const_iterator;

#endif

    buffer_prefix_view(buffer_prefix_view&&);

    buffer_prefix_view(buffer_prefix_view const&);

    buffer_prefix_view& operator=(buffer_prefix_view&&);

    buffer_prefix_view& operator=(buffer_prefix_view const&);

    buffer_prefix_view(
        std::size_t size,
        BufferSequence const& buffers);

    template<class... Args>
    buffer_prefix_view(
        std::size_t size,
        boost::in_place_init_t,
        Args&&... args);

    const_iterator
    begin() const;

    const_iterator
    end() const;
};

inline
boost::asio::const_buffer
buffer_prefix(std::size_t size,
    boost::asio::const_buffer buffer)
{
    using boost::asio::buffer_cast;
    using boost::asio::buffer_size;
    return { buffer_cast<void const*>(buffer),
        (std::min)(size, buffer_size(buffer)) };
}

inline
boost::asio::mutable_buffer
buffer_prefix(std::size_t size,
    boost::asio::mutable_buffer buffer)
{
    using boost::asio::buffer_cast;
    using boost::asio::buffer_size;
    return {buffer_cast<void*>(buffer),
        (std::min)(size, buffer_size(buffer))};
}

template<class BufferSequence>
#if BOOST_BEAST_DOXYGEN
buffer_prefix_view<BufferSequence>
#else
inline
typename std::enable_if<
    ! std::is_same<BufferSequence,
        boost::asio::const_buffer>::value &&
    ! std::is_same<BufferSequence,
        boost::asio::mutable_buffer>::value,
    buffer_prefix_view<BufferSequence>>::type
#endif
buffer_prefix(std::size_t size, BufferSequence const& buffers)
{
    static_assert(
        is_const_buffer_sequence<BufferSequence>::value ||
        is_mutable_buffer_sequence<BufferSequence>::value,
            "BufferSequence requirements not met");
    return buffer_prefix_view<BufferSequence>(size, buffers);
}

template<class BufferSequence>
typename std::conditional<
    is_mutable_buffer_sequence<BufferSequence>::value,
    boost::asio::mutable_buffer,
    boost::asio::const_buffer>::type
buffer_front(BufferSequence const& buffers)
{
    auto const first = buffers.begin();
    if(first == buffers.end())
        return {};
    return *first;
}

} // beast
} // boost

#include <boost/beast/core/impl/buffer_prefix.ipp>

#endif