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 //
 // read.hpp
 // ~~~~~~~~
 //
 // Copyright (c) 2003-2023 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_READ_HPP
 #define BOOST_ASIO_READ_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 <boost/asio/async_result.hpp>
 #include <boost/asio/buffer.hpp>
 #include <boost/asio/completion_condition.hpp>
 #include <boost/asio/error.hpp>
 
 #if !defined(BOOST_ASIO_NO_EXTENSIONS)
 # include <boost/asio/basic_streambuf_fwd.hpp>
 #endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace detail {
 
 template <typename> class initiate_async_read;
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 template <typename> class initiate_async_read_dynbuf_v1;
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 template <typename> class initiate_async_read_dynbuf_v2;
 
 } // namespace detail
 
 /**
  * @defgroup read boost::asio::read
  *
  * @brief The @c read function is a composed operation that reads a certain
  * amount of data from a stream before returning.
  */
 /*@{*/
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  *
  * @par Example
  * To read into a single data buffer use the @ref buffer function as follows:
  * @code boost::asio::read(s, boost::asio::buffer(data, size)); @endcode
  * See the @ref buffer documentation for information on reading into multiple
  * buffers in one go, and how to use it with arrays, boost::array or
  * std::vector.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all()); @endcode
  */
 template <typename SyncReadStream, typename MutableBufferSequence>
 std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes transferred.
  *
  * @par Example
  * To read into a single data buffer use the @ref buffer function as follows:
  * @code boost::asio::read(s, boost::asio::buffer(data, size), ec); @endcode
  * See the @ref buffer documentation for information on reading into multiple
  * buffers in one go, and how to use it with arrays, boost::array or
  * std::vector.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all(), ec); @endcode
  */
 template <typename SyncReadStream, typename MutableBufferSequence>
 std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
     boost::system::error_code& ec,
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  *
  * @par Example
  * To read into a single data buffer use the @ref buffer function as follows:
  * @code boost::asio::read(s, boost::asio::buffer(data, size),
  *     boost::asio::transfer_at_least(32)); @endcode
  * See the @ref buffer documentation for information on reading into multiple
  * buffers in one go, and how to use it with arrays, boost::array or
  * std::vector.
  */
 template <typename SyncReadStream, typename MutableBufferSequence,
   typename CompletionCondition>
 std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
     CompletionCondition completion_condition,
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes read. If an error occurs, returns the total
  * number of bytes successfully transferred prior to the error.
  */
 template <typename SyncReadStream, typename MutableBufferSequence,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s, const MutableBufferSequence& buffers,
     CompletionCondition completion_condition, boost::system::error_code& ec,
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0);
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all()); @endcode
  */
 template <typename SyncReadStream, typename DynamicBuffer_v1>
 std::size_t read(SyncReadStream& s,
     DynamicBuffer_v1&& buffers,
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes transferred.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all(), ec); @endcode
  */
 template <typename SyncReadStream, typename DynamicBuffer_v1>
 std::size_t read(SyncReadStream& s,
     DynamicBuffer_v1&& buffers,
     boost::system::error_code& ec,
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  */
 template <typename SyncReadStream, typename DynamicBuffer_v1,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s,
     DynamicBuffer_v1&& buffers,
     CompletionCondition completion_condition,
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes read. If an error occurs, returns the total
  * number of bytes successfully transferred prior to the error.
  */
 template <typename SyncReadStream, typename DynamicBuffer_v1,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s,
     DynamicBuffer_v1&& buffers,
     CompletionCondition completion_condition, boost::system::error_code& ec,
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0);
 
 #if !defined(BOOST_ASIO_NO_EXTENSIONS)
 #if !defined(BOOST_ASIO_NO_IOSTREAM)
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param b The basic_streambuf object into which the data will be read.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, b,
  *     boost::asio::transfer_all()); @endcode
  */
 template <typename SyncReadStream, typename Allocator>
 std::size_t read(SyncReadStream& s, basic_streambuf<Allocator>& b);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param b The basic_streambuf object into which the data will be read.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes transferred.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, b,
  *     boost::asio::transfer_all(), ec); @endcode
  */
 template <typename SyncReadStream, typename Allocator>
 std::size_t read(SyncReadStream& s, basic_streambuf<Allocator>& b,
     boost::system::error_code& ec);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param b The basic_streambuf object into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  */
 template <typename SyncReadStream, typename Allocator,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s, basic_streambuf<Allocator>& b,
     CompletionCondition completion_condition);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param b The basic_streambuf object into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes read. If an error occurs, returns the total
  * number of bytes successfully transferred prior to the error.
  */
 template <typename SyncReadStream, typename Allocator,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s, basic_streambuf<Allocator>& b,
     CompletionCondition completion_condition, boost::system::error_code& ec);
 
 #endif // !defined(BOOST_ASIO_NO_IOSTREAM)
 #endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all()); @endcode
  */
 template <typename SyncReadStream, typename DynamicBuffer_v2>
 std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes transferred.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::read(
  *     s, buffers,
  *     boost::asio::transfer_all(), ec); @endcode
  */
 template <typename SyncReadStream, typename DynamicBuffer_v2>
 std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
     boost::system::error_code& ec,
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @returns The number of bytes transferred.
  *
  * @throws boost::system::system_error Thrown on failure.
  */
 template <typename SyncReadStream, typename DynamicBuffer_v2,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
     CompletionCondition completion_condition,
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0);
 
 /// Attempt to read a certain amount of data from a stream before returning.
 /**
  * This function is used to read a certain number of bytes of data from a
  * stream. The call will block until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * read_some function.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the SyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's read_some function.
  *
  * @param ec Set to indicate what error occurred, if any.
  *
  * @returns The number of bytes read. If an error occurs, returns the total
  * number of bytes successfully transferred prior to the error.
  */
 template <typename SyncReadStream, typename DynamicBuffer_v2,
     typename CompletionCondition>
 std::size_t read(SyncReadStream& s, DynamicBuffer_v2 buffers,
     CompletionCondition completion_condition, boost::system::error_code& ec,
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0);
 
 /*@}*/
 /**
  * @defgroup async_read boost::asio::async_read
  *
  * @brief The @c async_read function is a composed asynchronous operation that
  * reads a certain amount of data from a stream before completion.
  */
 /*@{*/
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream. Although the buffers object may be copied as necessary, ownership of
  * the underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @par Example
  * To read into a single data buffer use the @ref buffer function as follows:
  * @code
  * boost::asio::async_read(s, boost::asio::buffer(data, size), handler);
  * @endcode
  * See the @ref buffer documentation for information on reading into multiple
  * buffers in one go, and how to use it with arrays, boost::array or
  * std::vector.
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::async_read(
  *     s, buffers,
  *     boost::asio::transfer_all(),
  *     handler); @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream, typename MutableBufferSequence,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read<AsyncReadStream>>(),
         token, buffers, transfer_all()));
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The supplied buffers are full. That is, the bytes transferred is equal to
  * the sum of the buffer sizes.
  *
  * @li The completion_condition function object returns 0.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers One or more buffers into which the data will be read. The sum
  * of the buffer sizes indicates the maximum number of bytes to read from the
  * stream. Although the buffers object may be copied as necessary, ownership of
  * the underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest async_read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's async_read_some function.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @par Example
  * To read into a single data buffer use the @ref buffer function as follows:
  * @code boost::asio::async_read(s,
  *     boost::asio::buffer(data, size),
  *     boost::asio::transfer_at_least(32),
  *     handler); @endcode
  * See the @ref buffer documentation for information on reading into multiple
  * buffers in one go, and how to use it with arrays, boost::array or
  * std::vector.
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream,
     typename MutableBufferSequence, typename CompletionCondition,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, const MutableBufferSequence& buffers,
     CompletionCondition completion_condition,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_mutable_buffer_sequence<MutableBufferSequence>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read<AsyncReadStream>>(),
         token, buffers,
         static_cast<CompletionCondition&&>(completion_condition)));
 
 #if !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  * Although the buffers object may be copied as necessary, ownership of the
  * underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::async_read(
  *     s, buffers,
  *     boost::asio::transfer_all(),
  *     handler); @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream, typename DynamicBuffer_v1,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, DynamicBuffer_v1&& buffers,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v1<AsyncReadStream>>(),
         token, static_cast<DynamicBuffer_v1&&>(buffers), transfer_all()));
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  * Although the buffers object may be copied as necessary, ownership of the
  * underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest async_read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's async_read_some function.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream,
     typename DynamicBuffer_v1, typename CompletionCondition,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, DynamicBuffer_v1&& buffers,
     CompletionCondition completion_condition,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_dynamic_buffer_v1<decay_t<DynamicBuffer_v1>>::value
     > = 0,
     constraint_t<
       !is_dynamic_buffer_v2<decay_t<DynamicBuffer_v1>>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v1<AsyncReadStream>>(),
         token, static_cast<DynamicBuffer_v1&&>(buffers),
         static_cast<CompletionCondition&&>(completion_condition)));
 
 #if !defined(BOOST_ASIO_NO_EXTENSIONS)
 #if !defined(BOOST_ASIO_NO_IOSTREAM)
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param b A basic_streambuf object into which the data will be read. Ownership
  * of the streambuf is retained by the caller, which must guarantee that it
  * remains valid until the completion handler is called.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::async_read(
  *     s, b,
  *     boost::asio::transfer_all(),
  *     handler); @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream, typename Allocator,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, basic_streambuf<Allocator>& b,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>())
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v1<AsyncReadStream>>(),
         token, basic_streambuf_ref<Allocator>(b), transfer_all()));
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The supplied buffer is full (that is, it has reached maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param b A basic_streambuf object into which the data will be read. Ownership
  * of the streambuf is retained by the caller, which must guarantee that it
  * remains valid until the completion handler is called.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest async_read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's async_read_some function.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream,
     typename Allocator, typename CompletionCondition,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, basic_streambuf<Allocator>& b,
     CompletionCondition completion_condition,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>())
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v1<AsyncReadStream>>(),
         token, basic_streambuf_ref<Allocator>(b),
         static_cast<CompletionCondition&&>(completion_condition)));
 
 #endif // !defined(BOOST_ASIO_NO_IOSTREAM)
 #endif // !defined(BOOST_ASIO_NO_EXTENSIONS)
 #endif // !defined(BOOST_ASIO_NO_DYNAMIC_BUFFER_V1)
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li An error occurred.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  * Although the buffers object may be copied as necessary, ownership of the
  * underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @note This overload is equivalent to calling:
  * @code boost::asio::async_read(
  *     s, buffers,
  *     boost::asio::transfer_all(),
  *     handler); @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream, typename DynamicBuffer_v2,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, DynamicBuffer_v2 buffers,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v2<AsyncReadStream>>(),
         token, static_cast<DynamicBuffer_v2&&>(buffers), transfer_all()));
 
 /// Start an asynchronous operation to read a certain amount of data from a
 /// stream.
 /**
  * This function is used to asynchronously read a certain number of bytes of
  * data from a stream. It is an initiating function for an @ref
  * asynchronous_operation, and always returns immediately. The asynchronous
  * operation will continue until one of the following conditions is true:
  *
  * @li The specified dynamic buffer sequence is full (that is, it has reached
  * maximum size).
  *
  * @li The completion_condition function object returns 0.
  *
  * This operation is implemented in terms of zero or more calls to the stream's
  * async_read_some function, and is known as a <em>composed operation</em>. The
  * program must ensure that the stream performs no other read operations (such
  * as async_read, the stream's async_read_some function, or any other composed
  * operations that perform reads) until this operation completes.
  *
  * @param s The stream from which the data is to be read. The type must support
  * the AsyncReadStream concept.
  *
  * @param buffers The dynamic buffer sequence into which the data will be read.
  * Although the buffers object may be copied as necessary, ownership of the
  * underlying memory blocks is retained by the caller, which must guarantee
  * that they remain valid until the completion handler is called.
  *
  * @param completion_condition The function object to be called to determine
  * whether the read operation is complete. The signature of the function object
  * must be:
  * @code std::size_t completion_condition(
  *   // Result of latest async_read_some operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes transferred so far.
  *   std::size_t bytes_transferred
  * ); @endcode
  * A return value of 0 indicates that the read operation is complete. A non-zero
  * return value indicates the maximum number of bytes to be read on the next
  * call to the stream's async_read_some function.
  *
  * @param token The @ref completion_token that will be used to produce a
  * completion handler, which will be called when the read completes.
  * Potential completion tokens include @ref use_future, @ref use_awaitable,
  * @ref yield_context, or a function object with the correct completion
  * signature. The function signature of the completion handler must be:
  * @code void handler(
  *   // Result of operation.
  *   const boost::system::error_code& error,
  *
  *   // Number of bytes copied into the buffers. If an error
  *   // occurred, this will be the number of bytes successfully
  *   // transferred prior to the error.
  *   std::size_t bytes_transferred
  * ); @endcode
  * Regardless of whether the asynchronous operation completes immediately or
  * not, the completion handler will not be invoked from within this function.
  * On immediate completion, invocation of the handler will be performed in a
  * manner equivalent to using boost::asio::post().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, std::size_t) @endcode
  *
  * @par Per-Operation Cancellation
  * This asynchronous operation supports cancellation for the following
  * boost::asio::cancellation_type values:
  *
  * @li @c cancellation_type::terminal
  *
  * @li @c cancellation_type::partial
  *
  * if they are also supported by the @c AsyncReadStream type's
  * @c async_read_some operation.
  */
 template <typename AsyncReadStream,
     typename DynamicBuffer_v2, typename CompletionCondition,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       std::size_t)) ReadToken = default_completion_token_t<
         typename AsyncReadStream::executor_type>>
 auto async_read(AsyncReadStream& s, DynamicBuffer_v2 buffers,
     CompletionCondition completion_condition,
     ReadToken&& token = default_completion_token_t<
       typename AsyncReadStream::executor_type>(),
     constraint_t<
       is_dynamic_buffer_v2<DynamicBuffer_v2>::value
     > = 0)
   -> decltype(
     async_initiate<ReadToken,
       void (boost::system::error_code, std::size_t)>(
         declval<detail::initiate_async_read_dynbuf_v2<AsyncReadStream>>(),
         token, static_cast<DynamicBuffer_v2&&>(buffers),
         static_cast<CompletionCondition&&>(completion_condition)));
 
 /*@}*/
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #include <boost/asio/impl/read.hpp>
 
 #endif // BOOST_ASIO_READ_HPP

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