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 //
 // buffer.hpp
 // ~~~~~~~~~~
 //
 // Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff 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)
 //
 
 #ifndef BOOST_ASIO_BUFFER_HPP
 #define BOOST_ASIO_BUFFER_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <cstddef>
 #include <cstring>
 #include <limits>
 #include <stdexcept>
 #include <string>
 #include <vector>
 #include <boost/asio/detail/array_fwd.hpp>
 #include <boost/asio/detail/memory.hpp>
 #include <boost/asio/detail/string_view.hpp>
 #include <boost/asio/detail/throw_exception.hpp>
 #include <boost/asio/detail/type_traits.hpp>
 #include <boost/asio/is_contiguous_iterator.hpp>
 
 #if defined(BOOST_ASIO_MSVC) && (BOOST_ASIO_MSVC >= 1700)
 # if defined(_HAS_ITERATOR_DEBUGGING) && (_HAS_ITERATOR_DEBUGGING != 0)
 #  if !defined(BOOST_ASIO_DISABLE_BUFFER_DEBUGGING)
 #   define BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 #  endif // !defined(BOOST_ASIO_DISABLE_BUFFER_DEBUGGING)
 # endif // defined(_HAS_ITERATOR_DEBUGGING)
 #endif // defined(BOOST_ASIO_MSVC) && (BOOST_ASIO_MSVC >= 1700)
 
 #if defined(__GNUC__)
 # if defined(_GLIBCXX_DEBUG)
 #  if !defined(BOOST_ASIO_DISABLE_BUFFER_DEBUGGING)
 #   define BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 #  endif // !defined(BOOST_ASIO_DISABLE_BUFFER_DEBUGGING)
 # endif // defined(_GLIBCXX_DEBUG)
 #endif // defined(__GNUC__)
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
 # include <boost/asio/detail/functional.hpp>
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 #if defined(BOOST_ASIO_MSVC)
 
 struct span_memfns_base
 {
   void subspan();
 };
 
 template <typename T>
 struct span_memfns_derived : T, span_memfns_base
 {
 };
 
 template <typename T, T>
 struct span_memfns_check
 {
 };
 
 template <typename>
 char (&subspan_memfn_helper(...))[2];
 
 template <typename T>
 char subspan_memfn_helper(
     span_memfns_check<
       void (span_memfns_base::*)(),
       &span_memfns_derived<T>::subspan>*);
 
 template <typename T>
 struct has_subspan_memfn :
   integral_constant<bool, sizeof(subspan_memfn_helper<T>(0)) != 1>
 {
 };
 
 #endif // defined(BOOST_ASIO_MSVC)
 
 } // namespace detail
 
 class mutable_buffer;
 class const_buffer;
 
 /// Holds a buffer that can be modified.
 /**
  * The mutable_buffer class provides a safe representation of a buffer that can
  * be modified. It does not own the underlying data, and so is cheap to copy or
  * assign.
  *
  * @par Accessing Buffer Contents
  *
  * The contents of a buffer may be accessed using the @c data() and @c size()
  * member functions:
  *
  * @code boost::asio::mutable_buffer b1 = ...;
  * std::size_t s1 = b1.size();
  * unsigned char* p1 = static_cast<unsigned char*>(b1.data());
  * @endcode
  *
  * The @c data() member function permits violations of type safety, so uses of
  * it in application code should be carefully considered.
  */
 class mutable_buffer
 {
 public:
   /// Construct an empty buffer.
   mutable_buffer() noexcept
     : data_(0),
       size_(0)
   {
   }
 
   /// Construct a buffer to represent a given memory range.
   mutable_buffer(void* data, std::size_t size) noexcept
     : data_(data),
       size_(size)
   {
   }
 
   /// Construct a buffer from a span of bytes.
   template <template <typename, std::size_t> class Span,
       typename T, std::size_t Extent>
   mutable_buffer(const Span<T, Extent>& span,
       constraint_t<
         !is_const<T>::value,
         defaulted_constraint
       > = defaulted_constraint(),
       constraint_t<
         sizeof(T) == 1,
         defaulted_constraint
       > = defaulted_constraint(),
       constraint_t<
 #if defined(BOOST_ASIO_MSVC)
         detail::has_subspan_memfn<Span<T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
         is_same<
           decltype(span.subspan(0, 0)),
           Span<T, static_cast<std::size_t>(-1)>
         >::value,
 #endif // defined(BOOST_ASIO_MSVC)
         defaulted_constraint
       > = defaulted_constraint())
     : data_(span.data()),
       size_(span.size())
   {
   }
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
   mutable_buffer(void* data, std::size_t size,
       boost::asio::detail::function<void()> debug_check)
     : data_(data),
       size_(size),
       debug_check_(debug_check)
   {
   }
 
   const boost::asio::detail::function<void()>& get_debug_check() const
   {
     return debug_check_;
   }
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 
   /// Get a pointer to the beginning of the memory range.
   void* data() const noexcept
   {
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     if (size_ && debug_check_)
       debug_check_();
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
     return data_;
   }
 
   /// Get the size of the memory range.
   std::size_t size() const noexcept
   {
     return size_;
   }
 
   /// Move the start of the buffer by the specified number of bytes.
   mutable_buffer& operator+=(std::size_t n) noexcept
   {
     std::size_t offset = n < size_ ? n : size_;
     data_ = static_cast<char*>(data_) + offset;
     size_ -= offset;
     return *this;
   }
 
 private:
   void* data_;
   std::size_t size_;
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
   boost::asio::detail::function<void()> debug_check_;
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 };
 
 /// Holds a buffer that cannot be modified.
 /**
  * The const_buffer class provides a safe representation of a buffer that cannot
  * be modified. It does not own the underlying data, and so is cheap to copy or
  * assign.
  *
  * @par Accessing Buffer Contents
  *
  * The contents of a buffer may be accessed using the @c data() and @c size()
  * member functions:
  *
  * @code boost::asio::const_buffer b1 = ...;
  * std::size_t s1 = b1.size();
  * const unsigned char* p1 = static_cast<const unsigned char*>(b1.data());
  * @endcode
  *
  * The @c data() member function permits violations of type safety, so uses of
  * it in application code should be carefully considered.
  */
 class const_buffer
 {
 public:
   /// Construct an empty buffer.
   const_buffer() noexcept
     : data_(0),
       size_(0)
   {
   }
 
   /// Construct a buffer to represent a given memory range.
   const_buffer(const void* data, std::size_t size) noexcept
     : data_(data),
       size_(size)
   {
   }
 
   /// Construct a non-modifiable buffer from a modifiable one.
   const_buffer(const mutable_buffer& b) noexcept
     : data_(b.data()),
       size_(b.size())
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , debug_check_(b.get_debug_check())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
   {
   }
 
   /// Construct a buffer from a span of bytes.
   template <template <typename, std::size_t> class Span,
       typename T, std::size_t Extent>
   const_buffer(const Span<T, Extent>& span,
       constraint_t<
         sizeof(T) == 1,
         defaulted_constraint
       > = defaulted_constraint(),
       constraint_t<
 #if defined(BOOST_ASIO_MSVC)
         detail::has_subspan_memfn<Span<T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
         is_same<
           decltype(span.subspan(0, 0)),
           Span<T, static_cast<std::size_t>(-1)>
         >::value,
 #endif // defined(BOOST_ASIO_MSVC)
         defaulted_constraint
       > = defaulted_constraint())
     : data_(span.data()),
       size_(span.size())
   {
   }
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
   const_buffer(const void* data, std::size_t size,
       boost::asio::detail::function<void()> debug_check)
     : data_(data),
       size_(size),
       debug_check_(debug_check)
   {
   }
 
   const boost::asio::detail::function<void()>& get_debug_check() const
   {
     return debug_check_;
   }
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 
   /// Get a pointer to the beginning of the memory range.
   const void* data() const noexcept
   {
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
     if (size_ && debug_check_)
       debug_check_();
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
     return data_;
   }
 
   /// Get the size of the memory range.
   std::size_t size() const noexcept
   {
     return size_;
   }
 
   /// Move the start of the buffer by the specified number of bytes.
   const_buffer& operator+=(std::size_t n) noexcept
   {
     std::size_t offset = n < size_ ? n : size_;
     data_ = static_cast<const char*>(data_) + offset;
     size_ -= offset;
     return *this;
   }
 
 private:
   const void* data_;
   std::size_t size_;
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
   boost::asio::detail::function<void()> debug_check_;
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 };
 
 /// (Deprecated: Use the socket/descriptor wait() and async_wait() member
 /// functions.) An implementation of both the ConstBufferSequence and
 /// MutableBufferSequence concepts to represent a null buffer sequence.
 class BOOST_ASIO_DEPRECATED_MSG(
   "Use the socket/descriptor wait() and async_wait() member functions")
 null_buffers
 {
 public:
   /// The type for each element in the list of buffers.
   typedef mutable_buffer value_type;
 
   /// A random-access iterator type that may be used to read elements.
   typedef const mutable_buffer* const_iterator;
 
   /// Get a random-access iterator to the first element.
   const_iterator begin() const noexcept
   {
     return &buf_;
   }
 
   /// Get a random-access iterator for one past the last element.
   const_iterator end() const noexcept
   {
     return &buf_;
   }
 
 private:
   mutable_buffer buf_;
 };
 
 /** @defgroup buffer_sequence_begin boost::asio::buffer_sequence_begin
  *
  * @brief The boost::asio::buffer_sequence_begin function returns an iterator
  * pointing to the first element in a buffer sequence.
  */
 /*@{*/
 
 /// Get an iterator to the first element in a buffer sequence.
 template <typename MutableBuffer>
 inline const mutable_buffer* buffer_sequence_begin(const MutableBuffer& b,
     constraint_t<
       is_convertible<const MutableBuffer*, const mutable_buffer*>::value
     > = 0) noexcept
 {
   return static_cast<const mutable_buffer*>(detail::addressof(b));
 }
 
 /// Get an iterator to the first element in a buffer sequence.
 template <typename ConstBuffer>
 inline const const_buffer* buffer_sequence_begin(const ConstBuffer& b,
     constraint_t<
       is_convertible<const ConstBuffer*, const const_buffer*>::value
     > = 0) noexcept
 {
   return static_cast<const const_buffer*>(detail::addressof(b));
 }
 
 /// Get an iterator to the first element in a buffer sequence.
 template <typename ConvertibleToBuffer>
 inline const ConvertibleToBuffer* buffer_sequence_begin(
     const ConvertibleToBuffer& b,
     constraint_t<
       !is_convertible<const ConvertibleToBuffer*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const ConvertibleToBuffer*, const const_buffer*>::value
     > = 0,
     constraint_t<
       is_convertible<ConvertibleToBuffer, mutable_buffer>::value
         || is_convertible<ConvertibleToBuffer, const_buffer>::value
     > = 0) noexcept
 {
   return detail::addressof(b);
 }
 
 /// Get an iterator to the first element in a buffer sequence.
 template <typename C>
 inline auto buffer_sequence_begin(C& c,
     constraint_t<
       !is_convertible<const C*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const C*, const const_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<C, mutable_buffer>::value
     > = 0,
     constraint_t<
       !is_convertible<C, const_buffer>::value
     > = 0) noexcept -> decltype(c.begin())
 {
   return c.begin();
 }
 
 /// Get an iterator to the first element in a buffer sequence.
 template <typename C>
 inline auto buffer_sequence_begin(const C& c,
     constraint_t<
       !is_convertible<const C*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const C*, const const_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<C, mutable_buffer>::value
     > = 0,
     constraint_t<
       !is_convertible<C, const_buffer>::value
     > = 0) noexcept -> decltype(c.begin())
 {
   return c.begin();
 }
 
 /*@}*/
 
 /** @defgroup buffer_sequence_end boost::asio::buffer_sequence_end
  *
  * @brief The boost::asio::buffer_sequence_end function returns an iterator
  * pointing to one past the end element in a buffer sequence.
  */
 /*@{*/
 
 /// Get an iterator to one past the end element in a buffer sequence.
 template <typename MutableBuffer>
 inline const mutable_buffer* buffer_sequence_end(const MutableBuffer& b,
     constraint_t<
       is_convertible<const MutableBuffer*, const mutable_buffer*>::value
     > = 0) noexcept
 {
   return static_cast<const mutable_buffer*>(detail::addressof(b)) + 1;
 }
 
 /// Get an iterator to one past the end element in a buffer sequence.
 template <typename ConstBuffer>
 inline const const_buffer* buffer_sequence_end(const ConstBuffer& b,
     constraint_t<
       is_convertible<const ConstBuffer*, const const_buffer*>::value
     > = 0) noexcept
 {
   return static_cast<const const_buffer*>(detail::addressof(b)) + 1;
 }
 
 /// Get an iterator to one past the end element in a buffer sequence.
 template <typename ConvertibleToBuffer>
 inline const ConvertibleToBuffer* buffer_sequence_end(
     const ConvertibleToBuffer& b,
     constraint_t<
       !is_convertible<const ConvertibleToBuffer*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const ConvertibleToBuffer*, const const_buffer*>::value
     > = 0,
     constraint_t<
       is_convertible<ConvertibleToBuffer, mutable_buffer>::value
         || is_convertible<ConvertibleToBuffer, const_buffer>::value
     > = 0) noexcept
 {
   return detail::addressof(b) + 1;
 }
 
 /// Get an iterator to one past the end element in a buffer sequence.
 template <typename C>
 inline auto buffer_sequence_end(C& c,
     constraint_t<
       !is_convertible<const C*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const C*, const const_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<C, mutable_buffer>::value
     > = 0,
     constraint_t<
       !is_convertible<C, const_buffer>::value
     > = 0) noexcept -> decltype(c.end())
 {
   return c.end();
 }
 
 /// Get an iterator to one past the end element in a buffer sequence.
 template <typename C>
 inline auto buffer_sequence_end(const C& c,
     constraint_t<
       !is_convertible<const C*, const mutable_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<const C*, const const_buffer*>::value
     > = 0,
     constraint_t<
       !is_convertible<C, mutable_buffer>::value
     > = 0,
     constraint_t<
       !is_convertible<C, const_buffer>::value
     > = 0) noexcept -> decltype(c.end())
 {
   return c.end();
 }
 
 /*@}*/
 
 namespace detail {
 
 // Tag types used to select appropriately optimised overloads.
 struct one_buffer {};
 struct multiple_buffers {};
 
 // Helper trait to detect single buffers.
 template <typename BufferSequence>
 struct buffer_sequence_cardinality :
   conditional_t<
     is_same<BufferSequence, mutable_buffer>::value
       || is_same<BufferSequence, const_buffer>::value,
     one_buffer, multiple_buffers> {};
 
 template <typename Iterator>
 inline std::size_t buffer_size(one_buffer,
     Iterator begin, Iterator) noexcept
 {
   return const_buffer(*begin).size();
 }
 
 template <typename Iterator>
 inline std::size_t buffer_size(multiple_buffers,
     Iterator begin, Iterator end) noexcept
 {
   std::size_t total_buffer_size = 0;
 
   Iterator iter = begin;
   for (; iter != end; ++iter)
   {
     const_buffer b(*iter);
     total_buffer_size += b.size();
   }
 
   return total_buffer_size;
 }
 
 } // namespace detail
 
 /// Get the total number of bytes in a buffer sequence.
 /**
  * The @c buffer_size function determines the total size of all buffers in the
  * buffer sequence, as if computed as follows:
  *
  * @code size_t total_size = 0;
  * auto i = boost::asio::buffer_sequence_begin(buffers);
  * auto end = boost::asio::buffer_sequence_end(buffers);
  * for (; i != end; ++i)
  * {
  *   const_buffer b(*i);
  *   total_size += b.size();
  * }
  * return total_size; @endcode
  *
  * The @c BufferSequence template parameter may meet either of the @c
  * ConstBufferSequence or @c MutableBufferSequence type requirements.
  */
 template <typename BufferSequence>
 inline std::size_t buffer_size(const BufferSequence& b) noexcept
 {
   return detail::buffer_size(
       detail::buffer_sequence_cardinality<BufferSequence>(),
       boost::asio::buffer_sequence_begin(b),
       boost::asio::buffer_sequence_end(b));
 }
 
 /// Create a new modifiable buffer that is offset from the start of another.
 /**
  * @relates mutable_buffer
  */
 inline mutable_buffer operator+(const mutable_buffer& b,
     std::size_t n) noexcept
 {
   std::size_t offset = n < b.size() ? n : b.size();
   char* new_data = static_cast<char*>(b.data()) + offset;
   std::size_t new_size = b.size() - offset;
   return mutable_buffer(new_data, new_size
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , b.get_debug_check()
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new modifiable buffer that is offset from the start of another.
 /**
  * @relates mutable_buffer
  */
 inline mutable_buffer operator+(std::size_t n,
     const mutable_buffer& b) noexcept
 {
   return b + n;
 }
 
 /// Create a new non-modifiable buffer that is offset from the start of another.
 /**
  * @relates const_buffer
  */
 inline const_buffer operator+(const const_buffer& b,
     std::size_t n) noexcept
 {
   std::size_t offset = n < b.size() ? n : b.size();
   const char* new_data = static_cast<const char*>(b.data()) + offset;
   std::size_t new_size = b.size() - offset;
   return const_buffer(new_data, new_size
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , b.get_debug_check()
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that is offset from the start of another.
 /**
  * @relates const_buffer
  */
 inline const_buffer operator+(std::size_t n,
     const const_buffer& b) noexcept
 {
   return b + n;
 }
 
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
 namespace detail {
 
 template <typename Iterator>
 class buffer_debug_check
 {
 public:
   buffer_debug_check(Iterator iter)
     : iter_(iter)
   {
   }
 
   ~buffer_debug_check()
   {
 #if defined(BOOST_ASIO_MSVC) && (BOOST_ASIO_MSVC == 1400)
     // MSVC 8's string iterator checking may crash in a std::string::iterator
     // object's destructor when the iterator points to an already-destroyed
     // std::string object, unless the iterator is cleared first.
     iter_ = Iterator();
 #endif // defined(BOOST_ASIO_MSVC) && (BOOST_ASIO_MSVC == 1400)
   }
 
   void operator()()
   {
     (void)*iter_;
   }
 
 private:
   Iterator iter_;
 };
 
 } // namespace detail
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
 
 /** @defgroup buffer boost::asio::buffer
  *
  * @brief The boost::asio::buffer function is used to create a buffer object to
  * represent raw memory, an array of POD elements, a vector of POD elements,
  * or a std::string.
  *
  * A buffer object represents a contiguous region of memory as a 2-tuple
  * consisting of a pointer and size in bytes. A tuple of the form <tt>{void*,
  * size_t}</tt> specifies a mutable (modifiable) region of memory. Similarly, a
  * tuple of the form <tt>{const void*, size_t}</tt> specifies a const
  * (non-modifiable) region of memory. These two forms correspond to the classes
  * mutable_buffer and const_buffer, respectively. To mirror C++'s conversion
  * rules, a mutable_buffer is implicitly convertible to a const_buffer, and the
  * opposite conversion is not permitted.
  *
  * The simplest use case involves reading or writing a single buffer of a
  * specified size:
  *
  * @code sock.send(boost::asio::buffer(data, size)); @endcode
  *
  * In the above example, the return value of boost::asio::buffer meets the
  * requirements of the ConstBufferSequence concept so that it may be directly
  * passed to the socket's write function. A buffer created for modifiable
  * memory also meets the requirements of the MutableBufferSequence concept.
  *
  * An individual buffer may be created from a builtin array, std::vector,
  * std::array or boost::array of POD elements. This helps prevent buffer
  * overruns by automatically determining the size of the buffer:
  *
  * @code char d1[128];
  * size_t bytes_transferred = sock.receive(boost::asio::buffer(d1));
  *
  * std::vector<char> d2(128);
  * bytes_transferred = sock.receive(boost::asio::buffer(d2));
  *
  * std::array<char, 128> d3;
  * bytes_transferred = sock.receive(boost::asio::buffer(d3));
  *
  * boost::array<char, 128> d4;
  * bytes_transferred = sock.receive(boost::asio::buffer(d4)); @endcode
  *
  * In all three cases above, the buffers created are exactly 128 bytes long.
  * Note that a vector is @e never automatically resized when creating or using
  * a buffer. The buffer size is determined using the vector's <tt>size()</tt>
  * member function, and not its capacity.
  *
  * @par Accessing Buffer Contents
  *
  * The contents of a buffer may be accessed using the @c data() and @c size()
  * member functions:
  *
  * @code boost::asio::mutable_buffer b1 = ...;
  * std::size_t s1 = b1.size();
  * unsigned char* p1 = static_cast<unsigned char*>(b1.data());
  *
  * boost::asio::const_buffer b2 = ...;
  * std::size_t s2 = b2.size();
  * const void* p2 = b2.data(); @endcode
  *
  * The @c data() member function permits violations of type safety, so
  * uses of it in application code should be carefully considered.
  *
  * For convenience, a @ref buffer_size function is provided that works with
  * both buffers and buffer sequences (that is, types meeting the
  * ConstBufferSequence or MutableBufferSequence type requirements). In this
  * case, the function returns the total size of all buffers in the sequence.
  *
  * @par Buffer Copying
  *
  * The @ref buffer_copy function may be used to copy raw bytes between
  * individual buffers and buffer sequences.
 *
  * In particular, when used with the @ref buffer_size function, the @ref
  * buffer_copy function can be used to linearise a sequence of buffers. For
  * example:
  *
  * @code vector<const_buffer> buffers = ...;
  *
  * vector<unsigned char> data(boost::asio::buffer_size(buffers));
  * boost::asio::buffer_copy(boost::asio::buffer(data), buffers); @endcode
  *
  * Note that @ref buffer_copy is implemented in terms of @c memcpy, and
  * consequently it cannot be used to copy between overlapping memory regions.
  *
  * @par Buffer Invalidation
  *
  * A buffer object does not have any ownership of the memory it refers to. It
  * is the responsibility of the application to ensure the memory region remains
  * valid until it is no longer required for an I/O operation. When the memory
  * is no longer available, the buffer is said to have been invalidated.
  *
  * For the boost::asio::buffer overloads that accept an argument of type
  * std::vector, the buffer objects returned are invalidated by any vector
  * operation that also invalidates all references, pointers and iterators
  * referring to the elements in the sequence (C++ Std, 23.2.4)
  *
  * For the boost::asio::buffer overloads that accept an argument of type
  * std::basic_string, the buffer objects returned are invalidated according to
  * the rules defined for invalidation of references, pointers and iterators
  * referring to elements of the sequence (C++ Std, 21.3).
  *
  * @par Buffer Arithmetic
  *
  * Buffer objects may be manipulated using simple arithmetic in a safe way
  * which helps prevent buffer overruns. Consider an array initialised as
  * follows:
  *
  * @code boost::array<char, 6> a = { 'a', 'b', 'c', 'd', 'e' }; @endcode
  *
  * A buffer object @c b1 created using:
  *
  * @code b1 = boost::asio::buffer(a); @endcode
  *
  * represents the entire array, <tt>{ 'a', 'b', 'c', 'd', 'e' }</tt>. An
  * optional second argument to the boost::asio::buffer function may be used to
  * limit the size, in bytes, of the buffer:
  *
  * @code b2 = boost::asio::buffer(a, 3); @endcode
  *
  * such that @c b2 represents the data <tt>{ 'a', 'b', 'c' }</tt>. Even if the
  * size argument exceeds the actual size of the array, the size of the buffer
  * object created will be limited to the array size.
  *
  * An offset may be applied to an existing buffer to create a new one:
  *
  * @code b3 = b1 + 2; @endcode
  *
  * where @c b3 will set to represent <tt>{ 'c', 'd', 'e' }</tt>. If the offset
  * exceeds the size of the existing buffer, the newly created buffer will be
  * empty.
  *
  * Both an offset and size may be specified to create a buffer that corresponds
  * to a specific range of bytes within an existing buffer:
  *
  * @code b4 = boost::asio::buffer(b1 + 1, 3); @endcode
  *
  * so that @c b4 will refer to the bytes <tt>{ 'b', 'c', 'd' }</tt>.
  *
  * @par Buffers and Scatter-Gather I/O
  *
  * To read or write using multiple buffers (i.e. scatter-gather I/O), multiple
  * buffer objects may be assigned into a container that supports the
  * MutableBufferSequence (for read) or ConstBufferSequence (for write) concepts:
  *
  * @code
  * char d1[128];
  * std::vector<char> d2(128);
  * boost::array<char, 128> d3;
  *
  * boost::array<mutable_buffer, 3> bufs1 = {
  *   boost::asio::buffer(d1),
  *   boost::asio::buffer(d2),
  *   boost::asio::buffer(d3) };
  * bytes_transferred = sock.receive(bufs1);
  *
  * std::vector<const_buffer> bufs2;
  * bufs2.push_back(boost::asio::buffer(d1));
  * bufs2.push_back(boost::asio::buffer(d2));
  * bufs2.push_back(boost::asio::buffer(d3));
  * bytes_transferred = sock.send(bufs2); @endcode
  *
  * @par Buffer Literals
  *
  * The `_buf` literal suffix, defined in namespace
  * <tt>boost::asio::buffer_literals</tt>, may be used to create @c const_buffer
  * objects from string, binary integer, and hexadecimal integer literals.
  * For example:
  *
  * @code
  * using namespace boost::asio::buffer_literals;
  *
  * boost::asio::const_buffer b1 = "hello"_buf;
  * boost::asio::const_buffer b2 = 0xdeadbeef_buf;
  * boost::asio::const_buffer b3 = 0x0123456789abcdef0123456789abcdef_buf;
  * boost::asio::const_buffer b4 = 0b1010101011001100_buf; @endcode
  *
  * Note that the memory associated with a buffer literal is valid for the
  * lifetime of the program. This means that the buffer can be safely used with
  * asynchronous operations.
  */
 /*@{*/
 
 /// Create a new modifiable buffer from an existing buffer.
 /**
  * @returns <tt>mutable_buffer(b)</tt>.
  */
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     const mutable_buffer& b) noexcept
 {
   return mutable_buffer(b);
 }
 
 /// Create a new modifiable buffer from an existing buffer.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     b.data(),
  *     min(b.size(), max_size_in_bytes)); @endcode
  */
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     const mutable_buffer& b,
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(
       mutable_buffer(b.data(),
         b.size() < max_size_in_bytes
         ? b.size() : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
         , b.get_debug_check()
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
         ));
 }
 
 /// Create a new non-modifiable buffer from an existing buffer.
 /**
  * @returns <tt>const_buffer(b)</tt>.
  */
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const const_buffer& b) noexcept
 {
   return const_buffer(b);
 }
 
 /// Create a new non-modifiable buffer from an existing buffer.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     b.data(),
  *     min(b.size(), max_size_in_bytes)); @endcode
  */
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const const_buffer& b,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(b.data(),
       b.size() < max_size_in_bytes
       ? b.size() : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , b.get_debug_check()
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new modifiable buffer that represents the given memory range.
 /**
  * @returns <tt>mutable_buffer(data, size_in_bytes)</tt>.
  */
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     void* data, std::size_t size_in_bytes) noexcept
 {
   return mutable_buffer(data, size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given memory range.
 /**
  * @returns <tt>const_buffer(data, size_in_bytes)</tt>.
  */
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const void* data, std::size_t size_in_bytes) noexcept
 {
   return const_buffer(data, size_in_bytes);
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     static_cast<void*>(data),
  *     N * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     PodType (&data)[N]) noexcept
 {
   return mutable_buffer(data, N * sizeof(PodType));
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     static_cast<void*>(data),
  *     min(N * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     PodType (&data)[N],
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(data,
       N * sizeof(PodType) < max_size_in_bytes
       ? N * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     static_cast<const void*>(data),
  *     N * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const PodType (&data)[N]) noexcept
 {
   return const_buffer(data, N * sizeof(PodType));
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     static_cast<const void*>(data),
  *     min(N * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const PodType (&data)[N],
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data,
       N * sizeof(PodType) < max_size_in_bytes
       ? N * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     boost::array<PodType, N>& data) noexcept
 {
   return mutable_buffer(
       data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     boost::array<PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     boost::array<const PodType, N>& data) noexcept
 {
   return const_buffer(data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     boost::array<const PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const boost::array<PodType, N>& data) noexcept
 {
   return const_buffer(data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const boost::array<PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::array<PodType, N>& data) noexcept
 {
   return mutable_buffer(data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new modifiable buffer that represents the given POD array.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::array<PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     std::array<const PodType, N>& data) noexcept
 {
   return const_buffer(data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     std::array<const PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     data.size() * sizeof(PodType)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::array<PodType, N>& data) noexcept
 {
   return const_buffer(data.data(), data.size() * sizeof(PodType));
 }
 
 /// Create a new non-modifiable buffer that represents the given POD array.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  */
 template <typename PodType, std::size_t N>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::array<PodType, N>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.data(),
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes);
 }
 
 /// Create a new modifiable buffer that represents the given POD vector.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     data.size() * sizeof(PodType)); @endcode
  *
  * @note The buffer is invalidated by any vector operation that would also
  * invalidate iterators.
  */
 template <typename PodType, typename Allocator>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::vector<PodType, Allocator>& data) noexcept
 {
   return mutable_buffer(
       data.size() ? &data[0] : 0, data.size() * sizeof(PodType)
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::vector<PodType, Allocator>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new modifiable buffer that represents the given POD vector.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  *
  * @note The buffer is invalidated by any vector operation that would also
  * invalidate iterators.
  */
 template <typename PodType, typename Allocator>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::vector<PodType, Allocator>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::vector<PodType, Allocator>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that represents the given POD vector.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     data.size() * sizeof(PodType)); @endcode
  *
  * @note The buffer is invalidated by any vector operation that would also
  * invalidate iterators.
  */
 template <typename PodType, typename Allocator>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::vector<PodType, Allocator>& data) noexcept
 {
   return const_buffer(
       data.size() ? &data[0] : 0, data.size() * sizeof(PodType)
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::vector<PodType, Allocator>::const_iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that represents the given POD vector.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(data.size() * sizeof(PodType), max_size_in_bytes)); @endcode
  *
  * @note The buffer is invalidated by any vector operation that would also
  * invalidate iterators.
  */
 template <typename PodType, typename Allocator>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::vector<PodType, Allocator>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(PodType) < max_size_in_bytes
       ? data.size() * sizeof(PodType) : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::vector<PodType, Allocator>::const_iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new modifiable buffer that represents the given string.
 /**
  * @returns <tt>mutable_buffer(data.size() ? &data[0] : 0,
  * data.size() * sizeof(Elem))</tt>.
  *
  * @note The buffer is invalidated by any non-const operation called on the
  * given string object.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::basic_string<Elem, Traits, Allocator>& data) noexcept
 {
   return mutable_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(Elem)
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::basic_string<Elem, Traits, Allocator>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new modifiable buffer that represents the given string.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(data.size() * sizeof(Elem), max_size_in_bytes)); @endcode
  *
  * @note The buffer is invalidated by any non-const operation called on the
  * given string object.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     std::basic_string<Elem, Traits, Allocator>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return mutable_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(Elem) < max_size_in_bytes
       ? data.size() * sizeof(Elem) : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::basic_string<Elem, Traits, Allocator>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that represents the given string.
 /**
  * @returns <tt>const_buffer(data.data(), data.size() * sizeof(Elem))</tt>.
  *
  * @note The buffer is invalidated by any non-const operation called on the
  * given string object.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::basic_string<Elem, Traits, Allocator>& data) noexcept
 {
   return const_buffer(data.data(), data.size() * sizeof(Elem)
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::basic_string<Elem, Traits, Allocator>::const_iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that represents the given string.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.data(),
  *     min(data.size() * sizeof(Elem), max_size_in_bytes)); @endcode
  *
  * @note The buffer is invalidated by any non-const operation called on the
  * given string object.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const std::basic_string<Elem, Traits, Allocator>& data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.data(),
       data.size() * sizeof(Elem) < max_size_in_bytes
       ? data.size() * sizeof(Elem) : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename std::basic_string<Elem, Traits, Allocator>::const_iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 #if defined(BOOST_ASIO_HAS_STRING_VIEW) \
   || defined(GENERATING_DOCUMENTATION)
 
 /// Create a new non-modifiable buffer that represents the given string_view.
 /**
  * @returns <tt>mutable_buffer(data.size() ? &data[0] : 0,
  * data.size() * sizeof(Elem))</tt>.
  */
 template <typename Elem, typename Traits>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     basic_string_view<Elem, Traits> data) noexcept
 {
   return const_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(Elem)
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename basic_string_view<Elem, Traits>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 /// Create a new non-modifiable buffer that represents the given string.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(data.size() * sizeof(Elem), max_size_in_bytes)); @endcode
  */
 template <typename Elem, typename Traits>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     basic_string_view<Elem, Traits> data,
     std::size_t max_size_in_bytes) noexcept
 {
   return const_buffer(data.size() ? &data[0] : 0,
       data.size() * sizeof(Elem) < max_size_in_bytes
       ? data.size() * sizeof(Elem) : max_size_in_bytes
 #if defined(BOOST_ASIO_ENABLE_BUFFER_DEBUGGING)
       , detail::buffer_debug_check<
           typename basic_string_view<Elem, Traits>::iterator
         >(data.begin())
 #endif // BOOST_ASIO_ENABLE_BUFFER_DEBUGGING
       );
 }
 
 #endif // defined(BOOST_ASIO_HAS_STRING_VIEW)
        //  || defined(GENERATING_DOCUMENTATION)
 
 /// Create a new modifiable buffer from a contiguous container.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     data.size() * sizeof(typename T::value_type)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     T& data,
     constraint_t<
       is_contiguous_iterator<typename T::iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_const<
         remove_reference_t<
           typename std::iterator_traits<typename T::iterator>::reference
         >
       >::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return mutable_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type));
 }
 
 /// Create a new modifiable buffer from a contiguous container.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(
  *       data.size() * sizeof(typename T::value_type),
  *       max_size_in_bytes)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     T& data, std::size_t max_size_in_bytes,
     constraint_t<
       is_contiguous_iterator<typename T::iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_const<
         remove_reference_t<
           typename std::iterator_traits<typename T::iterator>::reference
         >
       >::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return mutable_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type) < max_size_in_bytes
       ? data.size() * sizeof(typename T::value_type) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer from a contiguous container.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     data.size() * sizeof(typename T::value_type)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     T& data,
     constraint_t<
       is_contiguous_iterator<typename T::iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       is_const<
         remove_reference_t<
           typename std::iterator_traits<typename T::iterator>::reference
         >
       >::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return const_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type));
 }
 
 /// Create a new non-modifiable buffer from a contiguous container.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(
  *       data.size() * sizeof(typename T::value_type),
  *       max_size_in_bytes)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     T& data, std::size_t max_size_in_bytes,
     constraint_t<
       is_contiguous_iterator<typename T::iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       is_const<
         remove_reference_t<
           typename std::iterator_traits<typename T::iterator>::reference
         >
       >::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return const_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type) < max_size_in_bytes
       ? data.size() * sizeof(typename T::value_type) : max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer from a contiguous container.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     data.size() * sizeof(typename T::value_type)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const T& data,
     constraint_t<
       is_contiguous_iterator<typename T::const_iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return const_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type));
 }
 
 /// Create a new non-modifiable buffer from a contiguous container.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer(
  *     data.size() ? &data[0] : 0,
  *     min(
  *       data.size() * sizeof(typename T::value_type),
  *       max_size_in_bytes)); @endcode
  */
 template <typename T>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const T& data, std::size_t max_size_in_bytes,
     constraint_t<
       is_contiguous_iterator<typename T::const_iterator>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, const_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       !is_convertible<T, mutable_buffer>::value,
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return const_buffer(
       data.size() ? detail::to_address(data.begin()) : 0,
       data.size() * sizeof(typename T::value_type) < max_size_in_bytes
       ? data.size() * sizeof(typename T::value_type) : max_size_in_bytes);
 }
 
 /// Create a new modifiable buffer from a span.
 /**
  * @returns <tt>mutable_buffer(span)</tt>.
  */
 template <template <typename, std::size_t> class Span,
     typename T, std::size_t Extent>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     const Span<T, Extent>& span,
     constraint_t<
       !is_const<T>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       sizeof(T) == 1,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
 #if defined(BOOST_ASIO_MSVC)
       detail::has_subspan_memfn<Span<T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
       is_same<
         decltype(span.subspan(0, 0)),
         Span<T, static_cast<std::size_t>(-1)>
       >::value,
 #endif // defined(BOOST_ASIO_MSVC)
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return mutable_buffer(span);
 }
 
 /// Create a new modifiable buffer from a span.
 /**
  * @returns A mutable_buffer value equivalent to:
  * @code mutable_buffer b(span);
  * mutable_buffer(
  *     b.data(),
  *     min(b.size(), max_size_in_bytes)); @endcode
  */
 template <template <typename, std::size_t> class Span,
     typename T, std::size_t Extent>
 BOOST_ASIO_NODISCARD inline mutable_buffer buffer(
     const Span<T, Extent>& span,
     std::size_t max_size_in_bytes,
     constraint_t<
       !is_const<T>::value,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
       sizeof(T) == 1,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
 #if defined(BOOST_ASIO_MSVC)
       detail::has_subspan_memfn<Span<T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
       is_same<
         decltype(span.subspan(0, 0)),
         Span<T, static_cast<std::size_t>(-1)>
       >::value,
 #endif // defined(BOOST_ASIO_MSVC)
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return buffer(mutable_buffer(span), max_size_in_bytes);
 }
 
 /// Create a new non-modifiable buffer from a span.
 /**
  * @returns <tt>const_buffer(span)</tt>.
  */
 template <template <typename, std::size_t> class Span,
     typename T, std::size_t Extent>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const Span<const T, Extent>& span,
     constraint_t<
       sizeof(T) == 1,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
 #if defined(BOOST_ASIO_MSVC)
       detail::has_subspan_memfn<Span<const T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
       is_same<
         decltype(span.subspan(0, 0)),
         Span<T, static_cast<std::size_t>(-1)>
       >::value,
 #endif // defined(BOOST_ASIO_MSVC)
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return const_buffer(span);
 }
 
 /// Create a new non-modifiable buffer from a span.
 /**
  * @returns A const_buffer value equivalent to:
  * @code const_buffer b1(b);
  * const_buffer(
  *     b1.data(),
  *     min(b1.size(), max_size_in_bytes)); @endcode
  */
 template <template <typename, std::size_t> class Span,
     typename T, std::size_t Extent>
 BOOST_ASIO_NODISCARD inline const_buffer buffer(
     const Span<const T, Extent>& span,
     std::size_t max_size_in_bytes,
     constraint_t<
       sizeof(T) == 1,
       defaulted_constraint
     > = defaulted_constraint(),
     constraint_t<
 #if defined(BOOST_ASIO_MSVC)
       detail::has_subspan_memfn<Span<const T, Extent>>::value,
 #else // defined(BOOST_ASIO_MSVC)
       is_same<
         decltype(span.subspan(0, 0)),
         Span<T, static_cast<std::size_t>(-1)>
       >::value,
 #endif // defined(BOOST_ASIO_MSVC)
       defaulted_constraint
     > = defaulted_constraint()) noexcept
 {
   return buffer(const_buffer(span), max_size_in_bytes);
 }
 
 /*@}*/
 
 /// Adapt a basic_string to the DynamicBuffer requirements.
 /**
  * Requires that <tt>sizeof(Elem) == 1</tt>.
  */
 template <typename Elem, typename Traits, typename Allocator>
 class dynamic_string_buffer
 {
 public:
   /// The type used to represent a sequence of constant buffers that refers to
   /// the underlying memory.
   typedef const_buffer const_buffers_type;
 
   /// The type used to represent a sequence of mutable buffers that refers to
   /// the underlying memory.
   typedef mutable_buffer mutable_buffers_type;
 
   /// Construct a dynamic buffer from a string.
   /**
    * @param s The string to be used as backing storage for the dynamic buffer.
    * The object stores a reference to the string and the user is responsible
    * for ensuring that the string object remains valid while the
    * dynamic_string_buffer object, and copies of the object, are in use.
    *
    * @b DynamicBuffer_v1: Any existing data in the string is treated as the
    * dynamic buffer's input sequence.
    *
    * @param maximum_size Specifies a maximum size for the buffer, in bytes.
    */
   explicit dynamic_string_buffer(std::basic_string<Elem, Traits, Allocator>& s,
       std::size_t maximum_size =
         (std::numeric_limits<std::size_t>::max)()) noexcept
     : string_(s),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_((std::numeric_limits<std::size_t>::max)()),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(maximum_size)
   {
   }
 
   /// @b DynamicBuffer_v2: Copy construct a dynamic buffer.
   dynamic_string_buffer(const dynamic_string_buffer& other) noexcept
     : string_(other.string_),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_(other.size_),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(other.max_size_)
   {
   }
 
   /// Move construct a dynamic buffer.
   dynamic_string_buffer(dynamic_string_buffer&& other) noexcept
     : string_(other.string_),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_(other.size_),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(other.max_size_)
   {
   }
 
   /// @b DynamicBuffer_v1: Get the size of the input sequence.
   /// @b DynamicBuffer_v2: Get the current size of the underlying memory.
   /**
    * @returns @b DynamicBuffer_v1 The current size of the input sequence.
    * @b DynamicBuffer_v2: The current size of the underlying string if less than
    * max_size(). Otherwise returns max_size().
    */
   std::size_t size() const noexcept
   {
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     if (size_ != (std::numeric_limits<std::size_t>::max)())
       return size_;
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     return (std::min)(string_.size(), max_size());
   }
 
   /// Get the maximum size of the dynamic buffer.
   /**
    * @returns The allowed maximum size of the underlying memory.
    */
   std::size_t max_size() const noexcept
   {
     return max_size_;
   }
 
   /// Get the maximum size that the buffer may grow to without triggering
   /// reallocation.
   /**
    * @returns The current capacity of the underlying string if less than
    * max_size(). Otherwise returns max_size().
    */
   std::size_t capacity() const noexcept
   {
     return (std::min)(string_.capacity(), max_size());
   }
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   /// @b DynamicBuffer_v1: Get a list of buffers that represents the input
   /// sequence.
   /**
    * @returns An object of type @c const_buffers_type that satisfies
    * ConstBufferSequence requirements, representing the basic_string memory in
    * the input sequence.
    *
    * @note The returned object is invalidated by any @c dynamic_string_buffer
    * or @c basic_string member function that resizes or erases the string.
    */
   const_buffers_type data() const noexcept
   {
     return const_buffers_type(boost::asio::buffer(string_, size_));
   }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
   /// @b DynamicBuffer_v2: Get a sequence of buffers that represents the
   /// underlying memory.
   /**
    * @param pos Position of the first byte to represent in the buffer sequence
    *
    * @param n The number of bytes to return in the buffer sequence. If the
    * underlying memory is shorter, the buffer sequence represents as many bytes
    * as are available.
    *
    * @returns An object of type @c mutable_buffers_type that satisfies
    * MutableBufferSequence requirements, representing the basic_string memory.
    *
    * @note The returned object is invalidated by any @c dynamic_string_buffer
    * or @c basic_string member function that resizes or erases the string.
    */
   mutable_buffers_type data(std::size_t pos, std::size_t n) noexcept
   {
     return mutable_buffers_type(boost::asio::buffer(
           boost::asio::buffer(string_, max_size_) + pos, n));
   }
 
   /// @b DynamicBuffer_v2: Get a sequence of buffers that represents the
   /// underlying memory.
   /**
    * @param pos Position of the first byte to represent in the buffer sequence
    *
    * @param n The number of bytes to return in the buffer sequence. If the
    * underlying memory is shorter, the buffer sequence represents as many bytes
    * as are available.
    *
    * @note The returned object is invalidated by any @c dynamic_string_buffer
    * or @c basic_string member function that resizes or erases the string.
    */
   const_buffers_type data(std::size_t pos,
       std::size_t n) const noexcept
   {
     return const_buffers_type(boost::asio::buffer(
           boost::asio::buffer(string_, max_size_) + pos, n));
   }
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   /// @b DynamicBuffer_v1: Get a list of buffers that represents the output
   /// sequence, with the given size.
   /**
    * Ensures that the output sequence can accommodate @c n bytes, resizing the
    * basic_string object as necessary.
    *
    * @returns An object of type @c mutable_buffers_type that satisfies
    * MutableBufferSequence requirements, representing basic_string memory
    * at the start of the output sequence of size @c n.
    *
    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
    *
    * @note The returned object is invalidated by any @c dynamic_string_buffer
    * or @c basic_string member function that modifies the input sequence or
    * output sequence.
    */
   mutable_buffers_type prepare(std::size_t n)
   {
     if (size() > max_size() || max_size() - size() < n)
     {
       std::length_error ex("dynamic_string_buffer too long");
       boost::asio::detail::throw_exception(ex);
     }
 
     if (size_ == (std::numeric_limits<std::size_t>::max)())
       size_ = string_.size(); // Enable v1 behaviour.
 
     string_.resize(size_ + n);
 
     return boost::asio::buffer(boost::asio::buffer(string_) + size_, n);
   }
 
   /// @b DynamicBuffer_v1: Move bytes from the output sequence to the input
   /// sequence.
   /**
    * @param n The number of bytes to append from the start of the output
    * sequence to the end of the input sequence. The remainder of the output
    * sequence is discarded.
    *
    * Requires a preceding call <tt>prepare(x)</tt> where <tt>x >= n</tt>, and
    * no intervening operations that modify the input or output sequence.
    *
    * @note If @c n is greater than the size of the output sequence, the entire
    * output sequence is moved to the input sequence and no error is issued.
    */
   void commit(std::size_t n)
   {
     size_ += (std::min)(n, string_.size() - size_);
     string_.resize(size_);
   }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
   /// @b DynamicBuffer_v2: Grow the underlying memory by the specified number of
   /// bytes.
   /**
    * Resizes the string to accommodate an additional @c n bytes at the end.
    *
    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
    */
   void grow(std::size_t n)
   {
     if (size() > max_size() || max_size() - size() < n)
     {
       std::length_error ex("dynamic_string_buffer too long");
       boost::asio::detail::throw_exception(ex);
     }
 
     string_.resize(size() + n);
   }
 
   /// @b DynamicBuffer_v2: Shrink the underlying memory by the specified number
   /// of bytes.
   /**
    * Erases @c n bytes from the end of the string by resizing the basic_string
    * object. If @c n is greater than the current size of the string, the string
    * is emptied.
    */
   void shrink(std::size_t n)
   {
     string_.resize(n > size() ? 0 : size() - n);
   }
 
   /// @b DynamicBuffer_v1: Remove characters from the input sequence.
   /// @b DynamicBuffer_v2: Consume the specified number of bytes from the
   /// beginning of the underlying memory.
   /**
    * @b DynamicBuffer_v1: Removes @c n characters from the beginning of the
    * input sequence. @note If @c n is greater than the size of the input
    * sequence, the entire input sequence is consumed and no error is issued.
    *
    * @b DynamicBuffer_v2: Erases @c n bytes from the beginning of the string.
    * If @c n is greater than the current size of the string, the string is
    * emptied.
    */
   void consume(std::size_t n)
   {
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     if (size_ != (std::numeric_limits<std::size_t>::max)())
     {
       std::size_t consume_length = (std::min)(n, size_);
       string_.erase(0, consume_length);
       size_ -= consume_length;
       return;
     }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     string_.erase(0, n);
   }
 
 private:
   std::basic_string<Elem, Traits, Allocator>& string_;
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   std::size_t size_;
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   const std::size_t max_size_;
 };
 
 /// Adapt a vector to the DynamicBuffer requirements.
 /**
  * Requires that <tt>sizeof(Elem) == 1</tt>.
  */
 template <typename Elem, typename Allocator>
 class dynamic_vector_buffer
 {
 public:
   /// The type used to represent a sequence of constant buffers that refers to
   /// the underlying memory.
   typedef const_buffer const_buffers_type;
 
   /// The type used to represent a sequence of mutable buffers that refers to
   /// the underlying memory.
   typedef mutable_buffer mutable_buffers_type;
 
   /// Construct a dynamic buffer from a vector.
   /**
    * @param v The vector to be used as backing storage for the dynamic buffer.
    * The object stores a reference to the vector and the user is responsible
    * for ensuring that the vector object remains valid while the
    * dynamic_vector_buffer object, and copies of the object, are in use.
    *
    * @param maximum_size Specifies a maximum size for the buffer, in bytes.
    */
   explicit dynamic_vector_buffer(std::vector<Elem, Allocator>& v,
       std::size_t maximum_size =
         (std::numeric_limits<std::size_t>::max)()) noexcept
     : vector_(v),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_((std::numeric_limits<std::size_t>::max)()),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(maximum_size)
   {
   }
 
   /// @b DynamicBuffer_v2: Copy construct a dynamic buffer.
   dynamic_vector_buffer(const dynamic_vector_buffer& other) noexcept
     : vector_(other.vector_),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_(other.size_),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(other.max_size_)
   {
   }
 
   /// Move construct a dynamic buffer.
   dynamic_vector_buffer(dynamic_vector_buffer&& other) noexcept
     : vector_(other.vector_),
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       size_(other.size_),
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
       max_size_(other.max_size_)
   {
   }
 
   /// @b DynamicBuffer_v1: Get the size of the input sequence.
   /// @b DynamicBuffer_v2: Get the current size of the underlying memory.
   /**
    * @returns @b DynamicBuffer_v1 The current size of the input sequence.
    * @b DynamicBuffer_v2: The current size of the underlying vector if less than
    * max_size(). Otherwise returns max_size().
    */
   std::size_t size() const noexcept
   {
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     if (size_ != (std::numeric_limits<std::size_t>::max)())
       return size_;
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     return (std::min)(vector_.size(), max_size());
   }
 
   /// Get the maximum size of the dynamic buffer.
   /**
    * @returns @b DynamicBuffer_v1: The allowed maximum of the sum of the sizes
    * of the input sequence and output sequence. @b DynamicBuffer_v2: The allowed
    * maximum size of the underlying memory.
    */
   std::size_t max_size() const noexcept
   {
     return max_size_;
   }
 
   /// Get the maximum size that the buffer may grow to without triggering
   /// reallocation.
   /**
    * @returns @b DynamicBuffer_v1: The current total capacity of the buffer,
    * i.e. for both the input sequence and output sequence. @b DynamicBuffer_v2:
    * The current capacity of the underlying vector if less than max_size().
    * Otherwise returns max_size().
    */
   std::size_t capacity() const noexcept
   {
     return (std::min)(vector_.capacity(), max_size());
   }
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   /// @b DynamicBuffer_v1: Get a list of buffers that represents the input
   /// sequence.
   /**
    * @returns An object of type @c const_buffers_type that satisfies
    * ConstBufferSequence requirements, representing the vector memory in the
    * input sequence.
    *
    * @note The returned object is invalidated by any @c dynamic_vector_buffer
    * or @c vector member function that modifies the input sequence or output
    * sequence.
    */
   const_buffers_type data() const noexcept
   {
     return const_buffers_type(boost::asio::buffer(vector_, size_));
   }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
   /// @b DynamicBuffer_v2: Get a sequence of buffers that represents the
   /// underlying memory.
   /**
    * @param pos Position of the first byte to represent in the buffer sequence
    *
    * @param n The number of bytes to return in the buffer sequence. If the
    * underlying memory is shorter, the buffer sequence represents as many bytes
    * as are available.
    *
    * @returns An object of type @c mutable_buffers_type that satisfies
    * MutableBufferSequence requirements, representing the vector memory.
    *
    * @note The returned object is invalidated by any @c dynamic_vector_buffer
    * or @c vector member function that resizes or erases the vector.
    */
   mutable_buffers_type data(std::size_t pos, std::size_t n) noexcept
   {
     return mutable_buffers_type(boost::asio::buffer(
           boost::asio::buffer(vector_, max_size_) + pos, n));
   }
 
   /// @b DynamicBuffer_v2: Get a sequence of buffers that represents the
   /// underlying memory.
   /**
    * @param pos Position of the first byte to represent in the buffer sequence
    *
    * @param n The number of bytes to return in the buffer sequence. If the
    * underlying memory is shorter, the buffer sequence represents as many bytes
    * as are available.
    *
    * @note The returned object is invalidated by any @c dynamic_vector_buffer
    * or @c vector member function that resizes or erases the vector.
    */
   const_buffers_type data(std::size_t pos,
       std::size_t n) const noexcept
   {
     return const_buffers_type(boost::asio::buffer(
           boost::asio::buffer(vector_, max_size_) + pos, n));
   }
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   /// @b DynamicBuffer_v1: Get a list of buffers that represents the output
   /// sequence, with the given size.
   /**
    * Ensures that the output sequence can accommodate @c n bytes, resizing the
    * vector object as necessary.
    *
    * @returns An object of type @c mutable_buffers_type that satisfies
    * MutableBufferSequence requirements, representing vector memory at the
    * start of the output sequence of size @c n.
    *
    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
    *
    * @note The returned object is invalidated by any @c dynamic_vector_buffer
    * or @c vector member function that modifies the input sequence or output
    * sequence.
    */
   mutable_buffers_type prepare(std::size_t n)
   {
     if (size () > max_size() || max_size() - size() < n)
     {
       std::length_error ex("dynamic_vector_buffer too long");
       boost::asio::detail::throw_exception(ex);
     }
 
     if (size_ == (std::numeric_limits<std::size_t>::max)())
       size_ = vector_.size(); // Enable v1 behaviour.
 
     vector_.resize(size_ + n);
 
     return boost::asio::buffer(boost::asio::buffer(vector_) + size_, n);
   }
 
   /// @b DynamicBuffer_v1: Move bytes from the output sequence to the input
   /// sequence.
   /**
    * @param n The number of bytes to append from the start of the output
    * sequence to the end of the input sequence. The remainder of the output
    * sequence is discarded.
    *
    * Requires a preceding call <tt>prepare(x)</tt> where <tt>x >= n</tt>, and
    * no intervening operations that modify the input or output sequence.
    *
    * @note If @c n is greater than the size of the output sequence, the entire
    * output sequence is moved to the input sequence and no error is issued.
    */
   void commit(std::size_t n)
   {
     size_ += (std::min)(n, vector_.size() - size_);
     vector_.resize(size_);
   }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
   /// @b DynamicBuffer_v2: Grow the underlying memory by the specified number of
   /// bytes.
   /**
    * Resizes the vector to accommodate an additional @c n bytes at the end.
    *
    * @throws std::length_error If <tt>size() + n > max_size()</tt>.
    */
   void grow(std::size_t n)
   {
     if (size() > max_size() || max_size() - size() < n)
     {
       std::length_error ex("dynamic_vector_buffer too long");
       boost::asio::detail::throw_exception(ex);
     }
 
     vector_.resize(size() + n);
   }
 
   /// @b DynamicBuffer_v2: Shrink the underlying memory by the specified number
   /// of bytes.
   /**
    * Erases @c n bytes from the end of the vector by resizing the vector
    * object. If @c n is greater than the current size of the vector, the vector
    * is emptied.
    */
   void shrink(std::size_t n)
   {
     vector_.resize(n > size() ? 0 : size() - n);
   }
 
   /// @b DynamicBuffer_v1: Remove characters from the input sequence.
   /// @b DynamicBuffer_v2: Consume the specified number of bytes from the
   /// beginning of the underlying memory.
   /**
    * @b DynamicBuffer_v1: Removes @c n characters from the beginning of the
    * input sequence. @note If @c n is greater than the size of the input
    * sequence, the entire input sequence is consumed and no error is issued.
    *
    * @b DynamicBuffer_v2: Erases @c n bytes from the beginning of the vector.
    * If @c n is greater than the current size of the vector, the vector is
    * emptied.
    */
   void consume(std::size_t n)
   {
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     if (size_ != (std::numeric_limits<std::size_t>::max)())
     {
       std::size_t consume_length = (std::min)(n, size_);
       vector_.erase(vector_.begin(), vector_.begin() + consume_length);
       size_ -= consume_length;
       return;
     }
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
     vector_.erase(vector_.begin(), vector_.begin() + (std::min)(size(), n));
   }
 
 private:
   std::vector<Elem, Allocator>& vector_;
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   std::size_t size_;
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   const std::size_t max_size_;
 };
 
 /** @defgroup dynamic_buffer boost::asio::dynamic_buffer
  *
  * @brief The boost::asio::dynamic_buffer function is used to create a
  * dynamically resized buffer from a @c std::basic_string or @c std::vector.
  */
 /*@{*/
 
 /// Create a new dynamic buffer that represents the given string.
 /**
  * @returns <tt>dynamic_string_buffer<Elem, Traits, Allocator>(data)</tt>.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline
 dynamic_string_buffer<Elem, Traits, Allocator> dynamic_buffer(
     std::basic_string<Elem, Traits, Allocator>& data) noexcept
 {
   return dynamic_string_buffer<Elem, Traits, Allocator>(data);
 }
 
 /// Create a new dynamic buffer that represents the given string.
 /**
  * @returns <tt>dynamic_string_buffer<Elem, Traits, Allocator>(data,
  * max_size)</tt>.
  */
 template <typename Elem, typename Traits, typename Allocator>
 BOOST_ASIO_NODISCARD inline
 dynamic_string_buffer<Elem, Traits, Allocator> dynamic_buffer(
     std::basic_string<Elem, Traits, Allocator>& data,
     std::size_t max_size) noexcept
 {
   return dynamic_string_buffer<Elem, Traits, Allocator>(data, max_size);
 }
 
 /// Create a new dynamic buffer that represents the given vector.
 /**
  * @returns <tt>dynamic_vector_buffer<Elem, Allocator>(data)</tt>.
  */
 template <typename Elem, typename Allocator>
 BOOST_ASIO_NODISCARD inline
 dynamic_vector_buffer<Elem, Allocator> dynamic_buffer(
     std::vector<Elem, Allocator>& data) noexcept
 {
   return dynamic_vector_buffer<Elem, Allocator>(data);
 }
 
 /// Create a new dynamic buffer that represents the given vector.
 /**
  * @returns <tt>dynamic_vector_buffer<Elem, Allocator>(data, max_size)</tt>.
  */
 template <typename Elem, typename Allocator>
 BOOST_ASIO_NODISCARD inline
 dynamic_vector_buffer<Elem, Allocator> dynamic_buffer(
     std::vector<Elem, Allocator>& data,
     std::size_t max_size) noexcept
 {
   return dynamic_vector_buffer<Elem, Allocator>(data, max_size);
 }
 
 /*@}*/
 
 /** @defgroup buffer_copy boost::asio::buffer_copy
  *
  * @brief The boost::asio::buffer_copy function is used to copy bytes from a
  * source buffer (or buffer sequence) to a target buffer (or buffer sequence).
  *
  * The @c buffer_copy function is available in two forms:
  *
  * @li A 2-argument form: @c buffer_copy(target, source)
  *
  * @li A 3-argument form: @c buffer_copy(target, source, max_bytes_to_copy)
  *
  * Both forms return the number of bytes actually copied. The number of bytes
  * copied is the lesser of:
  *
  * @li @c buffer_size(target)
  *
  * @li @c buffer_size(source)
  *
  * @li @c If specified, @c max_bytes_to_copy.
  *
  * This prevents buffer overflow, regardless of the buffer sizes used in the
  * copy operation.
  *
  * Note that @ref buffer_copy is implemented in terms of @c memcpy, and
  * consequently it cannot be used to copy between overlapping memory regions.
  */
 /*@{*/
 
 namespace detail {
 
 inline std::size_t buffer_copy_1(const mutable_buffer& target,
     const const_buffer& source)
 {
   using namespace std; // For memcpy.
   std::size_t target_size = target.size();
   std::size_t source_size = source.size();
   std::size_t n = target_size < source_size ? target_size : source_size;
   if (n > 0)
     memcpy(target.data(), source.data(), n);
   return n;
 }
 
 template <typename TargetIterator, typename SourceIterator>
 inline std::size_t buffer_copy(one_buffer, one_buffer,
     TargetIterator target_begin, TargetIterator,
     SourceIterator source_begin, SourceIterator) noexcept
 {
   return (buffer_copy_1)(*target_begin, *source_begin);
 }
 
 template <typename TargetIterator, typename SourceIterator>
 inline std::size_t buffer_copy(one_buffer, one_buffer,
     TargetIterator target_begin, TargetIterator,
     SourceIterator source_begin, SourceIterator,
     std::size_t max_bytes_to_copy) noexcept
 {
   return (buffer_copy_1)(*target_begin,
       boost::asio::buffer(*source_begin, max_bytes_to_copy));
 }
 
 template <typename TargetIterator, typename SourceIterator>
 std::size_t buffer_copy(one_buffer, multiple_buffers,
     TargetIterator target_begin, TargetIterator,
     SourceIterator source_begin, SourceIterator source_end,
     std::size_t max_bytes_to_copy
       = (std::numeric_limits<std::size_t>::max)()) noexcept
 {
   std::size_t total_bytes_copied = 0;
   SourceIterator source_iter = source_begin;
 
   for (mutable_buffer target_buffer(
         boost::asio::buffer(*target_begin, max_bytes_to_copy));
       target_buffer.size() && source_iter != source_end; ++source_iter)
   {
     const_buffer source_buffer(*source_iter);
     std::size_t bytes_copied = (buffer_copy_1)(target_buffer, source_buffer);
     total_bytes_copied += bytes_copied;
     target_buffer += bytes_copied;
   }
 
   return total_bytes_copied;
 }
 
 template <typename TargetIterator, typename SourceIterator>
 std::size_t buffer_copy(multiple_buffers, one_buffer,
     TargetIterator target_begin, TargetIterator target_end,
     SourceIterator source_begin, SourceIterator,
     std::size_t max_bytes_to_copy
       = (std::numeric_limits<std::size_t>::max)()) noexcept
 {
   std::size_t total_bytes_copied = 0;
   TargetIterator target_iter = target_begin;
 
   for (const_buffer source_buffer(
         boost::asio::buffer(*source_begin, max_bytes_to_copy));
       source_buffer.size() && target_iter != target_end; ++target_iter)
   {
     mutable_buffer target_buffer(*target_iter);
     std::size_t bytes_copied = (buffer_copy_1)(target_buffer, source_buffer);
     total_bytes_copied += bytes_copied;
     source_buffer += bytes_copied;
   }
 
   return total_bytes_copied;
 }
 
 template <typename TargetIterator, typename SourceIterator>
 std::size_t buffer_copy(multiple_buffers, multiple_buffers,
     TargetIterator target_begin, TargetIterator target_end,
     SourceIterator source_begin, SourceIterator source_end) noexcept
 {
   std::size_t total_bytes_copied = 0;
 
   TargetIterator target_iter = target_begin;
   std::size_t target_buffer_offset = 0;
 
   SourceIterator source_iter = source_begin;
   std::size_t source_buffer_offset = 0;
 
   while (target_iter != target_end && source_iter != source_end)
   {
     mutable_buffer target_buffer =
       mutable_buffer(*target_iter) + target_buffer_offset;
 
     const_buffer source_buffer =
       const_buffer(*source_iter) + source_buffer_offset;
 
     std::size_t bytes_copied = (buffer_copy_1)(target_buffer, source_buffer);
     total_bytes_copied += bytes_copied;
 
     if (bytes_copied == target_buffer.size())
     {
       ++target_iter;
       target_buffer_offset = 0;
     }
     else
       target_buffer_offset += bytes_copied;
 
     if (bytes_copied == source_buffer.size())
     {
       ++source_iter;
       source_buffer_offset = 0;
     }
     else
       source_buffer_offset += bytes_copied;
   }
 
   return total_bytes_copied;
 }
 
 template <typename TargetIterator, typename SourceIterator>
 std::size_t buffer_copy(multiple_buffers, multiple_buffers,
     TargetIterator target_begin, TargetIterator target_end,
     SourceIterator source_begin, SourceIterator source_end,
     std::size_t max_bytes_to_copy) noexcept
 {
   std::size_t total_bytes_copied = 0;
 
   TargetIterator target_iter = target_begin;
   std::size_t target_buffer_offset = 0;
 
   SourceIterator source_iter = source_begin;
   std::size_t source_buffer_offset = 0;
 
   while (total_bytes_copied != max_bytes_to_copy
       && target_iter != target_end && source_iter != source_end)
   {
     mutable_buffer target_buffer =
       mutable_buffer(*target_iter) + target_buffer_offset;
 
     const_buffer source_buffer =
       const_buffer(*source_iter) + source_buffer_offset;
 
     std::size_t bytes_copied = (buffer_copy_1)(
         target_buffer, boost::asio::buffer(source_buffer,
           max_bytes_to_copy - total_bytes_copied));
     total_bytes_copied += bytes_copied;
 
     if (bytes_copied == target_buffer.size())
     {
       ++target_iter;
       target_buffer_offset = 0;
     }
     else
       target_buffer_offset += bytes_copied;
 
     if (bytes_copied == source_buffer.size())
     {
       ++source_iter;
       source_buffer_offset = 0;
     }
     else
       source_buffer_offset += bytes_copied;
   }
 
   return total_bytes_copied;
 }
 
 } // namespace detail
 
 /// Copies bytes from a source buffer sequence to a target buffer sequence.
 /**
  * @param target A modifiable buffer sequence representing the memory regions to
  * which the bytes will be copied.
  *
  * @param source A non-modifiable buffer sequence representing the memory
  * regions from which the bytes will be copied.
  *
  * @returns The number of bytes copied.
  *
  * @note The number of bytes copied is the lesser of:
  *
  * @li @c buffer_size(target)
  *
  * @li @c buffer_size(source)
  *
  * This function is implemented in terms of @c memcpy, and consequently it
  * cannot be used to copy between overlapping memory regions.
  */
 template <typename MutableBufferSequence, typename ConstBufferSequence>
 inline std::size_t buffer_copy(const MutableBufferSequence& target,
     const ConstBufferSequence& source) noexcept
 {
   return detail::buffer_copy(
       detail::buffer_sequence_cardinality<MutableBufferSequence>(),
       detail::buffer_sequence_cardinality<ConstBufferSequence>(),
       boost::asio::buffer_sequence_begin(target),
       boost::asio::buffer_sequence_end(target),
       boost::asio::buffer_sequence_begin(source),
       boost::asio::buffer_sequence_end(source));
 }
 
 /// Copies a limited number of bytes from a source buffer sequence to a target
 /// buffer sequence.
 /**
  * @param target A modifiable buffer sequence representing the memory regions to
  * which the bytes will be copied.
  *
  * @param source A non-modifiable buffer sequence representing the memory
  * regions from which the bytes will be copied.
  *
  * @param max_bytes_to_copy The maximum number of bytes to be copied.
  *
  * @returns The number of bytes copied.
  *
  * @note The number of bytes copied is the lesser of:
  *
  * @li @c buffer_size(target)
  *
  * @li @c buffer_size(source)
  *
  * @li @c max_bytes_to_copy
  *
  * This function is implemented in terms of @c memcpy, and consequently it
  * cannot be used to copy between overlapping memory regions.
  */
 template <typename MutableBufferSequence, typename ConstBufferSequence>
 inline std::size_t buffer_copy(const MutableBufferSequence& target,
     const ConstBufferSequence& source,
     std::size_t max_bytes_to_copy) noexcept
 {
   return detail::buffer_copy(
       detail::buffer_sequence_cardinality<MutableBufferSequence>(),
       detail::buffer_sequence_cardinality<ConstBufferSequence>(),
       boost::asio::buffer_sequence_begin(target),
       boost::asio::buffer_sequence_end(target),
       boost::asio::buffer_sequence_begin(source),
       boost::asio::buffer_sequence_end(source), max_bytes_to_copy);
 }
 
 /*@}*/
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 #include <boost/asio/detail/is_buffer_sequence.hpp>
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 
 /// Trait to determine whether a type satisfies the MutableBufferSequence
 /// requirements.
 template <typename T>
 struct is_mutable_buffer_sequence
 #if defined(GENERATING_DOCUMENTATION)
   : integral_constant<bool, automatically_determined>
 #else // defined(GENERATING_DOCUMENTATION)
   : boost::asio::detail::is_buffer_sequence<T, mutable_buffer>
 #endif // defined(GENERATING_DOCUMENTATION)
 {
 };
 
 /// Trait to determine whether a type satisfies the ConstBufferSequence
 /// requirements.
 template <typename T>
 struct is_const_buffer_sequence
 #if defined(GENERATING_DOCUMENTATION)
   : integral_constant<bool, automatically_determined>
 #else // defined(GENERATING_DOCUMENTATION)
   : boost::asio::detail::is_buffer_sequence<T, const_buffer>
 #endif // defined(GENERATING_DOCUMENTATION)
 {
 };
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 /// Trait to determine whether a type satisfies the DynamicBuffer_v1
 /// requirements.
 template <typename T>
 struct is_dynamic_buffer_v1
 #if defined(GENERATING_DOCUMENTATION)
   : integral_constant<bool, automatically_determined>
 #else // defined(GENERATING_DOCUMENTATION)
   : boost::asio::detail::is_dynamic_buffer_v1<T>
 #endif // defined(GENERATING_DOCUMENTATION)
 {
 };
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
 /// Trait to determine whether a type satisfies the DynamicBuffer_v2
 /// requirements.
 template <typename T>
 struct is_dynamic_buffer_v2
 #if defined(GENERATING_DOCUMENTATION)
   : integral_constant<bool, automatically_determined>
 #else // defined(GENERATING_DOCUMENTATION)
   : boost::asio::detail::is_dynamic_buffer_v2<T>
 #endif // defined(GENERATING_DOCUMENTATION)
 {
 };
 
 /// Trait to determine whether a type satisfies the DynamicBuffer requirements.
 /**
  * If @c BOOST_ASIO_NO_DYNAMIC_BUFFER_V1 is not defined, determines whether the
  * type satisfies the DynamicBuffer_v1 requirements. Otherwise, if @c
  * BOOST_ASIO_NO_DYNAMIC_BUFFER_V1 is defined, determines whether the type
  * satisfies the DynamicBuffer_v2 requirements.
  */
 template <typename T>
 struct is_dynamic_buffer
 #if defined(GENERATING_DOCUMENTATION)
   : integral_constant<bool, automatically_determined>
 #elif defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   : boost::asio::is_dynamic_buffer_v2<T>
 #else // defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
   : boost::asio::is_dynamic_buffer_v1<T>
 #endif // defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 {
 };
 
 namespace buffer_literals {
 namespace detail {
 
 template <char... Chars>
 struct chars {};
 
 template <unsigned char... Bytes>
 struct bytes {};
 
 // Literal processor that converts binary literals to an array of bytes.
 
 template <typename Bytes, char... Chars>
 struct bin_literal;
 
 template <unsigned char... Bytes>
 struct bin_literal<bytes<Bytes...>>
 {
   static const std::size_t size = sizeof...(Bytes);
   static const unsigned char data[sizeof...(Bytes)];
 };
 
 template <unsigned char... Bytes>
 const unsigned char bin_literal<bytes<Bytes...>>::data[sizeof...(Bytes)]
   = { Bytes... };
 
 template <unsigned char... Bytes, char Bit7, char Bit6, char Bit5,
     char Bit4, char Bit3, char Bit2, char Bit1, char Bit0, char... Chars>
 struct bin_literal<bytes<Bytes...>, Bit7, Bit6,
     Bit5, Bit4, Bit3, Bit2, Bit1, Bit0, Chars...> :
   bin_literal<
     bytes<Bytes...,
       static_cast<unsigned char>(
       (Bit7 == '1' ? 0x80 : 0) |
         (Bit6 == '1' ? 0x40 : 0) |
         (Bit5 == '1' ? 0x20 : 0) |
         (Bit4 == '1' ? 0x10 : 0) |
         (Bit3 == '1' ? 0x08 : 0) |
         (Bit2 == '1' ? 0x04 : 0) |
         (Bit1 == '1' ? 0x02 : 0) |
         (Bit0 == '1' ? 0x01 : 0))
     >, Chars...> {};
 
 template <unsigned char... Bytes, char... Chars>
 struct bin_literal<bytes<Bytes...>, Chars...>
 {
   static_assert(sizeof...(Chars) == 0,
       "number of digits in a binary buffer literal must be a multiple of 8");
 
   static const std::size_t size = 0;
   static const unsigned char data[1];
 };
 
 template <unsigned char... Bytes, char... Chars>
 const unsigned char bin_literal<bytes<Bytes...>, Chars...>::data[1] = {};
 
 // Literal processor that converts hexadecimal literals to an array of bytes.
 
 template <typename Bytes, char... Chars>
 struct hex_literal;
 
 template <unsigned char... Bytes>
 struct hex_literal<bytes<Bytes...>>
 {
   static const std::size_t size = sizeof...(Bytes);
   static const unsigned char data[sizeof...(Bytes)];
 };
 
 template <unsigned char... Bytes>
 const unsigned char hex_literal<bytes<Bytes...>>::data[sizeof...(Bytes)]
   = { Bytes... };
 
 template <unsigned char... Bytes, char Hi, char Lo, char... Chars>
 struct hex_literal<bytes<Bytes...>, Hi, Lo, Chars...> :
   hex_literal<
     bytes<Bytes...,
       static_cast<unsigned char>(
         Lo >= 'A' && Lo <= 'F' ? Lo - 'A' + 10 :
           (Lo >= 'a' && Lo <= 'f' ? Lo - 'a' + 10 : Lo - '0')) |
       ((static_cast<unsigned char>(
         Hi >= 'A' && Hi <= 'F' ? Hi - 'A' + 10 :
           (Hi >= 'a' && Hi <= 'f' ? Hi - 'a' + 10 : Hi - '0'))) << 4)
     >, Chars...> {};
 
 template <unsigned char... Bytes, char Char>
 struct hex_literal<bytes<Bytes...>, Char>
 {
   static_assert(!Char,
       "a hexadecimal buffer literal must have an even number of digits");
 
   static const std::size_t size = 0;
   static const unsigned char data[1];
 };
 
 template <unsigned char... Bytes, char Char>
 const unsigned char hex_literal<bytes<Bytes...>, Char>::data[1] = {};
 
 // Helper template that removes digit separators and then passes the cleaned
 // variadic pack of characters to the literal processor.
 
 template <template <typename, char...> class Literal,
     typename Clean, char... Raw>
 struct remove_separators;
 
 template <template <typename, char...> class Literal,
     char... Clean, char... Raw>
 struct remove_separators<Literal, chars<Clean...>, '\'', Raw...> :
   remove_separators<Literal, chars<Clean...>, Raw...> {};
 
 template <template <typename, char...> class Literal,
     char... Clean, char C, char... Raw>
 struct remove_separators<Literal, chars<Clean...>, C, Raw...> :
   remove_separators<Literal, chars<Clean..., C>, Raw...> {};
 
 template <template <typename, char...> class Literal, char... Clean>
 struct remove_separators<Literal, chars<Clean...>> :
   Literal<bytes<>, Clean...> {};
 
 // Helper template to determine the literal type based on the prefix.
 
 template <char... Chars>
 struct literal;
 
 template <char... Chars>
 struct literal<'0', 'b', Chars...> :
   remove_separators<bin_literal, chars<>, Chars...>{};
 
 template <char... Chars>
 struct literal<'0', 'B', Chars...> :
   remove_separators<bin_literal, chars<>, Chars...>{};
 
 template <char... Chars>
 struct literal<'0', 'x', Chars...> :
   remove_separators<hex_literal, chars<>, Chars...>{};
 
 template <char... Chars>
 struct literal<'0', 'X', Chars...> :
   remove_separators<hex_literal, chars<>, Chars...>{};
 
 } // namespace detail
 
 /// Literal operator for creating const_buffer objects from string literals.
 inline const_buffer operator ""_buf(const char* data, std::size_t n)
 {
   return const_buffer(data, n);
 }
 
 /// Literal operator for creating const_buffer objects from unbounded binary or
 /// hexadecimal integer literals.
 template <char... Chars>
 inline const_buffer operator ""_buf()
 {
   return const_buffer(
       +detail::literal<Chars...>::data,
       detail::literal<Chars...>::size);
 }
 
 } // namespace buffer_literals
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_BUFFER_HPP