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diff --git a/boost/beast/core/detail/stream_traits.hpp b/boost/beast/core/detail/stream_traits.hpp
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+++ b/boost/beast/core/detail/stream_traits.hpp
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+//
+// 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_DETAIL_STREAM_TRAITS_HPP
+#define BOOST_BEAST_DETAIL_STREAM_TRAITS_HPP
+
+#include <boost/beast/core/error.hpp>
+#include <boost/asio/buffer.hpp>
+#include <boost/type_traits/make_void.hpp>
+#include <type_traits>
+
+namespace boost {
+namespace beast {
+namespace detail {
+
+//------------------------------------------------------------------------------
+//
+// get_lowest_layer
+// lowest_layer_type
+// detail::has_next_layer
+//
+
+template <class T>
+std::false_type has_next_layer_impl(void*);
+
+template <class T>
+auto has_next_layer_impl(decltype(nullptr)) ->
+    decltype(std::declval<T&>().next_layer(), std::true_type{});
+
+template <class T>
+using has_next_layer = decltype(has_next_layer_impl<T>(nullptr));
+
+template<class T, bool = has_next_layer<T>::value>
+struct lowest_layer_type_impl
+{
+    using type = typename std::remove_reference<T>::type;
+};
+
+template<class T>
+struct lowest_layer_type_impl<T, true>
+{
+    using type = typename lowest_layer_type_impl<
+        decltype(std::declval<T&>().next_layer())>::type;
+};
+
+template<class T>
+using lowest_layer_type = typename
+    lowest_layer_type_impl<T>::type;
+
+template<class T>
+T&
+get_lowest_layer_impl(
+    T& t, std::false_type) noexcept
+{
+    return t;
+}
+
+template<class T>
+lowest_layer_type<T>&
+get_lowest_layer_impl(
+    T& t, std::true_type) noexcept
+{
+    return get_lowest_layer_impl(t.next_layer(),
+        has_next_layer<typename std::decay<
+            decltype(t.next_layer())>::type>{});
+}
+
+//------------------------------------------------------------------------------
+
+// Types that meet the requirements,
+// for use with std::declval only.
+template<class BufferType>
+struct BufferSequence
+{
+    using value_type = BufferType;
+    using const_iterator = BufferType const*;
+    ~BufferSequence() = default;
+    BufferSequence(BufferSequence const&) = default;
+    const_iterator begin() const noexcept { return {}; }
+    const_iterator end() const noexcept { return {}; }
+};
+using ConstBufferSequence =
+    BufferSequence<net::const_buffer>;
+using MutableBufferSequence =
+    BufferSequence<net::mutable_buffer>;
+
+//
+
+// Types that meet the requirements,
+// for use with std::declval only.
+struct StreamHandler
+{
+    StreamHandler(StreamHandler const&) = default;
+    void operator()(error_code, std::size_t) {}
+};
+using ReadHandler = StreamHandler;
+using WriteHandler = StreamHandler;
+
+//------------------------------------------------------------------------------
+
+} // detail
+} // beast
+} // boost
+
+#endif