text: //
  // basic_socket.hpp
  // ~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2017 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 ASIO_BASIC_SOCKET_HPP
  #define ASIO_BASIC_SOCKET_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include "asio/detail/config.hpp"
  #include "asio/async_result.hpp"
  #include "asio/basic_io_object.hpp"
  #include "asio/detail/handler_type_requirements.hpp"
  #include "asio/detail/throw_error.hpp"
  #include "asio/detail/type_traits.hpp"
  #include "asio/error.hpp"
  #include "asio/post.hpp"
  #include "asio/socket_base.hpp"
  
  #if defined(ASIO_HAS_MOVE)
  # include <utility>
  #endif // defined(ASIO_HAS_MOVE)
  
  #if !defined(ASIO_ENABLE_OLD_SERVICES)
  # if defined(ASIO_WINDOWS_RUNTIME)
  #  include "asio/detail/winrt_ssocket_service.hpp"
  #  define ASIO_SVC_T detail::winrt_ssocket_service<Protocol>
  # elif defined(ASIO_HAS_IOCP)
  #  include "asio/detail/win_iocp_socket_service.hpp"
  #  define ASIO_SVC_T detail::win_iocp_socket_service<Protocol>
  # else
  #  include "asio/detail/reactive_socket_service.hpp"
  #  define ASIO_SVC_T detail::reactive_socket_service<Protocol>
  # endif
  #endif // !defined(ASIO_ENABLE_OLD_SERVICES)
  
  #include "asio/detail/push_options.hpp"
  
  namespace asio {
  
  /// Provides socket functionality.
  /**
   * The basic_socket class template provides functionality that is common to both
   * stream-oriented and datagram-oriented sockets.
   *
   * @par Thread Safety
   * @e Distinct @e objects: Safe.@n
   * @e Shared @e objects: Unsafe.
   */
  template <typename Protocol ASIO_SVC_TPARAM>
  class basic_socket
    : ASIO_SVC_ACCESS basic_io_object<ASIO_SVC_T>,
      public socket_base
  {
  public:
    /// The type of the executor associated with the object.
    typedef io_context::executor_type executor_type;
  
    /// The native representation of a socket.
  #if defined(GENERATING_DOCUMENTATION)
    typedef implementation_defined native_handle_type;
  #else
    typedef typename ASIO_SVC_T::native_handle_type native_handle_type;
  #endif
  
    /// The protocol type.
    typedef Protocol protocol_type;
  
    /// The endpoint type.
    typedef typename Protocol::endpoint endpoint_type;
  
  #if !defined(ASIO_NO_EXTENSIONS)
    /// A basic_socket is always the lowest layer.
    typedef basic_socket<Protocol ASIO_SVC_TARG> lowest_layer_type;
  #endif // !defined(ASIO_NO_EXTENSIONS)
  
    /// Construct a basic_socket without opening it.
    /**
     * This constructor creates a socket without opening it.
     *
     * @param io_context The io_context object that the socket will use to
     * dispatch handlers for any asynchronous operations performed on the socket.
     */
    explicit basic_socket(asio::io_context& io_context)
      : basic_io_object<ASIO_SVC_T>(io_context)
    {
    }
  
    /// Construct and open a basic_socket.
    /**
     * This constructor creates and opens a socket.
     *
     * @param io_context The io_context object that the socket will use to
     * dispatch handlers for any asynchronous operations performed on the socket.
     *
     * @param protocol An object specifying protocol parameters to be used.
     *
     * @throws asio::system_error Thrown on failure.
     */
    basic_socket(asio::io_context& io_context,
        const protocol_type& protocol)
      : basic_io_object<ASIO_SVC_T>(io_context)
    {
      asio::error_code ec;
      this->get_service().open(this->get_implementation(), protocol, ec);
      asio::detail::throw_error(ec, "open");
    }
  
    /// Construct a basic_socket, opening it and binding it to the given local
    /// endpoint.
    /**
     * This constructor creates a socket and automatically opens it bound to the
     * specified endpoint on the local machine. The protocol used is the protocol
     * associated with the given endpoint.
     *
     * @param io_context The io_context object that the socket will use to
     * dispatch handlers for any asynchronous operations performed on the socket.
     *
     * @param endpoint An endpoint on the local machine to which the socket will
     * be bound.
     *
     * @throws asio::system_error Thrown on failure.
     */
    basic_socket(asio::io_context& io_context,
        const endpoint_type& endpoint)
      : basic_io_object<ASIO_SVC_T>(io_context)
    {
      asio::error_code ec;
      const protocol_type protocol = endpoint.protocol();
      this->get_service().open(this->get_implementation(), protocol, ec);
      asio::detail::throw_error(ec, "open");
      this->get_service().bind(this->get_implementation(), endpoint, ec);
      asio::detail::throw_error(ec, "bind");
    }
  
    /// Construct a basic_socket on an existing native socket.
    /**
     * This constructor creates a socket object to hold an existing native socket.
     *
     * @param io_context The io_context object that the socket will use to
     * dispatch handlers for any asynchronous operations performed on the socket.
     *
     * @param protocol An object specifying protocol parameters to be used.
     *
     * @param native_socket A native socket.
     *
     * @throws asio::system_error Thrown on failure.
     */
    basic_socket(asio::io_context& io_context,
        const protocol_type& protocol, const native_handle_type& native_socket)
      : basic_io_object<ASIO_SVC_T>(io_context)
    {
      asio::error_code ec;
      this->get_service().assign(this->get_implementation(),
          protocol, native_socket, ec);
      asio::detail::throw_error(ec, "assign");
    }
  
  #if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
    /// Move-construct a basic_socket from another.
    /**
     * This constructor moves a socket from one object to another.
     *
     * @param other The other basic_socket object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_socket(io_context&) constructor.
     */
    basic_socket(basic_socket&& other)
      : basic_io_object<ASIO_SVC_T>(std::move(other))
    {
    }
  
    /// Move-assign a basic_socket from another.
    /**
     * This assignment operator moves a socket from one object to another.
     *
     * @param other The other basic_socket object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_socket(io_context&) constructor.
     */
    basic_socket& operator=(basic_socket&& other)
    {
      basic_io_object<ASIO_SVC_T>::operator=(std::move(other));
      return *this;
    }
  
    // All sockets have access to each other's implementations.
    template <typename Protocol1 ASIO_SVC_TPARAM1>
    friend class basic_socket;
  
    /// Move-construct a basic_socket from a socket of another protocol type.
    /**
     * This constructor moves a socket from one object to another.
     *
     * @param other The other basic_socket object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_socket(io_context&) constructor.
     */
    template <typename Protocol1 ASIO_SVC_TPARAM1>
    basic_socket(basic_socket<Protocol1 ASIO_SVC_TARG1>&& other,
        typename enable_if<is_convertible<Protocol1, Protocol>::value>::type* = 0)
      : basic_io_object<ASIO_SVC_T>(
          other.get_service(), other.get_implementation())
    {
    }
  
    /// Move-assign a basic_socket from a socket of another protocol type.
    /**
     * This assignment operator moves a socket from one object to another.
     *
     * @param other The other basic_socket object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_socket(io_context&) constructor.
     */
    template <typename Protocol1 ASIO_SVC_TPARAM1>
    typename enable_if<is_convertible<Protocol1, Protocol>::value,
        basic_socket>::type& operator=(
          basic_socket<Protocol1 ASIO_SVC_TARG1>&& other)
    {
      basic_socket tmp(std::move(other));
      basic_io_object<ASIO_SVC_T>::operator=(std::move(tmp));
      return *this;
    }
  #endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
  
  #if defined(ASIO_ENABLE_OLD_SERVICES)
    // These functions are provided by basic_io_object<>.
  #else // defined(ASIO_ENABLE_OLD_SERVICES)
  #if !defined(ASIO_NO_DEPRECATED)
    /// (Deprecated: Use get_executor().) Get the io_context associated with the
    /// object.
    /**
     * This function may be used to obtain the io_context object that the I/O
     * object uses to dispatch handlers for asynchronous operations.
     *
     * @return A reference to the io_context object that the I/O object will use
     * to dispatch handlers. Ownership is not transferred to the caller.
     */
    asio::io_context& get_io_context()
    {
      return basic_io_object<ASIO_SVC_T>::get_io_context();
    }
  
    /// (Deprecated: Use get_executor().) Get the io_context associated with the
    /// object.
    /**
     * This function may be used to obtain the io_context object that the I/O
     * object uses to dispatch handlers for asynchronous operations.
     *
     * @return A reference to the io_context object that the I/O object will use
     * to dispatch handlers. Ownership is not transferred to the caller.
     */
    asio::io_context& get_io_service()
    {
      return basic_io_object<ASIO_SVC_T>::get_io_service();
    }
  #endif // !defined(ASIO_NO_DEPRECATED)
  
    /// Get the executor associated with the object.
    executor_type get_executor() ASIO_NOEXCEPT
    {
      return basic_io_object<ASIO_SVC_T>::get_executor();
    }
  #endif // defined(ASIO_ENABLE_OLD_SERVICES)
  
  #if !defined(ASIO_NO_EXTENSIONS)
    /// Get a reference to the lowest layer.
    /**
     * This function returns a reference to the lowest layer in a stack of
     * layers. Since a basic_socket cannot contain any further layers, it simply
     * returns a reference to itself.
     *
     * @return A reference to the lowest layer in the stack of layers. Ownership
     * is not transferred to the caller.
     */
    lowest_layer_type& lowest_layer()
    {
      return *this;
    }
  
    /// Get a const reference to the lowest layer.
    /**
     * This function returns a const reference to the lowest layer in a stack of
     * layers. Since a basic_socket cannot contain any further layers, it simply
     * returns a reference to itself.
     *
     * @return A const reference to the lowest layer in the stack of layers.
     * Ownership is not transferred to the caller.
     */
    const lowest_layer_type& lowest_layer() const
    {
      return *this;
    }
  #endif // !defined(ASIO_NO_EXTENSIONS)
  
    /// Open the socket using the specified protocol.
    /**
     * This function opens the socket so that it will use the specified protocol.
     *
     * @param protocol An object specifying protocol parameters to be used.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * socket.open(asio::ip::tcp::v4());
     * @endcode
     */
    void open(const protocol_type& protocol = protocol_type())
    {
      asio::error_code ec;
      this->get_service().open(this->get_implementation(), protocol, ec);
      asio::detail::throw_error(ec, "open");
    }
  
    /// Open the socket using the specified protocol.
    /**
     * This function opens the socket so that it will use the specified protocol.
     *
     * @param protocol An object specifying which protocol is to be used.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * asio::error_code ec;
     * socket.open(asio::ip::tcp::v4(), ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    ASIO_SYNC_OP_VOID open(const protocol_type& protocol,
        asio::error_code& ec)
    {
      this->get_service().open(this->get_implementation(), protocol, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Assign an existing native socket to the socket.
    /*
     * This function opens the socket to hold an existing native socket.
     *
     * @param protocol An object specifying which protocol is to be used.
     *
     * @param native_socket A native socket.
     *
     * @throws asio::system_error Thrown on failure.
     */
    void assign(const protocol_type& protocol,
        const native_handle_type& native_socket)
    {
      asio::error_code ec;
      this->get_service().assign(this->get_implementation(),
          protocol, native_socket, ec);
      asio::detail::throw_error(ec, "assign");
    }
  
    /// Assign an existing native socket to the socket.
    /*
     * This function opens the socket to hold an existing native socket.
     *
     * @param protocol An object specifying which protocol is to be used.
     *
     * @param native_socket A native socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     */
    ASIO_SYNC_OP_VOID assign(const protocol_type& protocol,
        const native_handle_type& native_socket, asio::error_code& ec)
    {
      this->get_service().assign(this->get_implementation(),
          protocol, native_socket, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Determine whether the socket is open.
    bool is_open() const
    {
      return this->get_service().is_open(this->get_implementation());
    }
  
    /// Close the socket.
    /**
     * This function is used to close the socket. Any asynchronous send, receive
     * or connect operations will be cancelled immediately, and will complete
     * with the asio::error::operation_aborted error.
     *
     * @throws asio::system_error Thrown on failure. Note that, even if
     * the function indicates an error, the underlying descriptor is closed.
     *
     * @note For portable behaviour with respect to graceful closure of a
     * connected socket, call shutdown() before closing the socket.
     */
    void close()
    {
      asio::error_code ec;
      this->get_service().close(this->get_implementation(), ec);
      asio::detail::throw_error(ec, "close");
    }
  
    /// Close the socket.
    /**
     * This function is used to close the socket. Any asynchronous send, receive
     * or connect operations will be cancelled immediately, and will complete
     * with the asio::error::operation_aborted error.
     *
     * @param ec Set to indicate what error occurred, if any. Note that, even if
     * the function indicates an error, the underlying descriptor is closed.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::error_code ec;
     * socket.close(ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     *
     * @note For portable behaviour with respect to graceful closure of a
     * connected socket, call shutdown() before closing the socket.
     */
    ASIO_SYNC_OP_VOID close(asio::error_code& ec)
    {
      this->get_service().close(this->get_implementation(), ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Release ownership of the underlying native socket.
    /**
     * This function causes all outstanding asynchronous connect, send and receive
     * operations to finish immediately, and the handlers for cancelled operations
     * will be passed the asio::error::operation_aborted error. Ownership
     * of the native socket is then transferred to the caller.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note This function is unsupported on Windows versions prior to Windows
     * 8.1, and will fail with asio::error::operation_not_supported on
     * these platforms.
     */
  #if defined(ASIO_MSVC) && (ASIO_MSVC >= 1400) \
    && (!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0603)
    __declspec(deprecated("This function always fails with "
          "operation_not_supported when used on Windows versions "
          "prior to Windows 8.1."))
  #endif
    native_handle_type release()
    {
      asio::error_code ec;
      native_handle_type s = this->get_service().release(
          this->get_implementation(), ec);
      asio::detail::throw_error(ec, "release");
      return s;
    }
  
    /// Release ownership of the underlying native socket.
    /**
     * This function causes all outstanding asynchronous connect, send and receive
     * operations to finish immediately, and the handlers for cancelled operations
     * will be passed the asio::error::operation_aborted error. Ownership
     * of the native socket is then transferred to the caller.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @note This function is unsupported on Windows versions prior to Windows
     * 8.1, and will fail with asio::error::operation_not_supported on
     * these platforms.
     */
  #if defined(ASIO_MSVC) && (ASIO_MSVC >= 1400) \
    && (!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0603)
    __declspec(deprecated("This function always fails with "
          "operation_not_supported when used on Windows versions "
          "prior to Windows 8.1."))
  #endif
    native_handle_type release(asio::error_code& ec)
    {
      return this->get_service().release(this->get_implementation(), ec);
    }
  
    /// Get the native socket representation.
    /**
     * This function may be used to obtain the underlying representation of the
     * socket. This is intended to allow access to native socket functionality
     * that is not otherwise provided.
     */
    native_handle_type native_handle()
    {
      return this->get_service().native_handle(this->get_implementation());
    }
  
    /// Cancel all asynchronous operations associated with the socket.
    /**
     * This function causes all outstanding asynchronous connect, send and receive
     * operations to finish immediately, and the handlers for cancelled operations
     * will be passed the asio::error::operation_aborted error.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note Calls to cancel() will always fail with
     * asio::error::operation_not_supported when run on Windows XP, Windows
     * Server 2003, and earlier versions of Windows, unless
     * ASIO_ENABLE_CANCELIO is defined. However, the CancelIo function has
     * two issues that should be considered before enabling its use:
     *
     * @li It will only cancel asynchronous operations that were initiated in the
     * current thread.
     *
     * @li It can appear to complete without error, but the request to cancel the
     * unfinished operations may be silently ignored by the operating system.
     * Whether it works or not seems to depend on the drivers that are installed.
     *
     * For portable cancellation, consider using one of the following
     * alternatives:
     *
     * @li Disable asio's I/O completion port backend by defining
     * ASIO_DISABLE_IOCP.
     *
     * @li Use the close() function to simultaneously cancel the outstanding
     * operations and close the socket.
     *
     * When running on Windows Vista, Windows Server 2008, and later, the
     * CancelIoEx function is always used. This function does not have the
     * problems described above.
     */
  #if defined(ASIO_MSVC) && (ASIO_MSVC >= 1400) \
    && (!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0600) \
    && !defined(ASIO_ENABLE_CANCELIO)
    __declspec(deprecated("By default, this function always fails with "
          "operation_not_supported when used on Windows XP, Windows Server 2003, "
          "or earlier. Consult documentation for details."))
  #endif
    void cancel()
    {
      asio::error_code ec;
      this->get_service().cancel(this->get_implementation(), ec);
      asio::detail::throw_error(ec, "cancel");
    }
  
    /// Cancel all asynchronous operations associated with the socket.
    /**
     * This function causes all outstanding asynchronous connect, send and receive
     * operations to finish immediately, and the handlers for cancelled operations
     * will be passed the asio::error::operation_aborted error.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @note Calls to cancel() will always fail with
     * asio::error::operation_not_supported when run on Windows XP, Windows
     * Server 2003, and earlier versions of Windows, unless
     * ASIO_ENABLE_CANCELIO is defined. However, the CancelIo function has
     * two issues that should be considered before enabling its use:
     *
     * @li It will only cancel asynchronous operations that were initiated in the
     * current thread.
     *
     * @li It can appear to complete without error, but the request to cancel the
     * unfinished operations may be silently ignored by the operating system.
     * Whether it works or not seems to depend on the drivers that are installed.
     *
     * For portable cancellation, consider using one of the following
     * alternatives:
     *
     * @li Disable asio's I/O completion port backend by defining
     * ASIO_DISABLE_IOCP.
     *
     * @li Use the close() function to simultaneously cancel the outstanding
     * operations and close the socket.
     *
     * When running on Windows Vista, Windows Server 2008, and later, the
     * CancelIoEx function is always used. This function does not have the
     * problems described above.
     */
  #if defined(ASIO_MSVC) && (ASIO_MSVC >= 1400) \
    && (!defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0600) \
    && !defined(ASIO_ENABLE_CANCELIO)
    __declspec(deprecated("By default, this function always fails with "
          "operation_not_supported when used on Windows XP, Windows Server 2003, "
          "or earlier. Consult documentation for details."))
  #endif
    ASIO_SYNC_OP_VOID cancel(asio::error_code& ec)
    {
      this->get_service().cancel(this->get_implementation(), ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Determine whether the socket is at the out-of-band data mark.
    /**
     * This function is used to check whether the socket input is currently
     * positioned at the out-of-band data mark.
     *
     * @return A bool indicating whether the socket is at the out-of-band data
     * mark.
     *
     * @throws asio::system_error Thrown on failure.
     */
    bool at_mark() const
    {
      asio::error_code ec;
      bool b = this->get_service().at_mark(this->get_implementation(), ec);
      asio::detail::throw_error(ec, "at_mark");
      return b;
    }
  
    /// Determine whether the socket is at the out-of-band data mark.
    /**
     * This function is used to check whether the socket input is currently
     * positioned at the out-of-band data mark.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return A bool indicating whether the socket is at the out-of-band data
     * mark.
     */
    bool at_mark(asio::error_code& ec) const
    {
      return this->get_service().at_mark(this->get_implementation(), ec);
    }
  
    /// Determine the number of bytes available for reading.
    /**
     * This function is used to determine the number of bytes that may be read
     * without blocking.
     *
     * @return The number of bytes that may be read without blocking, or 0 if an
     * error occurs.
     *
     * @throws asio::system_error Thrown on failure.
     */
    std::size_t available() const
    {
      asio::error_code ec;
      std::size_t s = this->get_service().available(
          this->get_implementation(), ec);
      asio::detail::throw_error(ec, "available");
      return s;
    }
  
    /// Determine the number of bytes available for reading.
    /**
     * This function is used to determine the number of bytes that may be read
     * without blocking.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return The number of bytes that may be read without blocking, or 0 if an
     * error occurs.
     */
    std::size_t available(asio::error_code& ec) const
    {
      return this->get_service().available(this->get_implementation(), ec);
    }
  
    /// Bind the socket to the given local endpoint.
    /**
     * This function binds the socket to the specified endpoint on the local
     * machine.
     *
     * @param endpoint An endpoint on the local machine to which the socket will
     * be bound.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * socket.open(asio::ip::tcp::v4());
     * socket.bind(asio::ip::tcp::endpoint(
     *       asio::ip::tcp::v4(), 12345));
     * @endcode
     */
    void bind(const endpoint_type& endpoint)
    {
      asio::error_code ec;
      this->get_service().bind(this->get_implementation(), endpoint, ec);
      asio::detail::throw_error(ec, "bind");
    }
  
    /// Bind the socket to the given local endpoint.
    /**
     * This function binds the socket to the specified endpoint on the local
     * machine.
     *
     * @param endpoint An endpoint on the local machine to which the socket will
     * be bound.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * socket.open(asio::ip::tcp::v4());
     * asio::error_code ec;
     * socket.bind(asio::ip::tcp::endpoint(
     *       asio::ip::tcp::v4(), 12345), ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    ASIO_SYNC_OP_VOID bind(const endpoint_type& endpoint,
        asio::error_code& ec)
    {
      this->get_service().bind(this->get_implementation(), endpoint, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Connect the socket to the specified endpoint.
    /**
     * This function is used to connect a socket to the specified remote endpoint.
     * The function call will block until the connection is successfully made or
     * an error occurs.
     *
     * The socket is automatically opened if it is not already open. If the
     * connect fails, and the socket was automatically opened, the socket is
     * not returned to the closed state.
     *
     * @param peer_endpoint The remote endpoint to which the socket will be
     * connected.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * asio::ip::tcp::endpoint endpoint(
     *     asio::ip::address::from_string("1.2.3.4"), 12345);
     * socket.connect(endpoint);
     * @endcode
     */
    void connect(const endpoint_type& peer_endpoint)
    {
      asio::error_code ec;
      if (!is_open())
      {
        this->get_service().open(this->get_implementation(),
            peer_endpoint.protocol(), ec);
        asio::detail::throw_error(ec, "connect");
      }
      this->get_service().connect(this->get_implementation(), peer_endpoint, -1, ec);
      asio::detail::throw_error(ec, "connect");
    }
  
    /// Connect the socket to the specified endpoint.
    /**
     * This function is used to connect a socket to the specified remote endpoint.
     * The function call will block until the connection is successfully made or
     * an error occurs.
     *
     * The socket is automatically opened if it is not already open. If the
     * connect fails, and the socket was automatically opened, the socket is
     * not returned to the closed state.
     *
     * @param peer_endpoint The remote endpoint to which the socket will be
     * connected.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * asio::ip::tcp::endpoint endpoint(
     *     asio::ip::address::from_string("1.2.3.4"), 12345);
     * asio::error_code ec;
     * socket.connect(endpoint, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    ASIO_SYNC_OP_VOID connect(const endpoint_type& peer_endpoint,
        asio::error_code& ec)
    {
      if (!is_open())
      {
        this->get_service().open(this->get_implementation(),
              peer_endpoint.protocol(), ec);
        if (ec)
        {
          ASIO_SYNC_OP_VOID_RETURN(ec);
        }
      }
  
      this->get_service().connect(this->get_implementation(), peer_endpoint, -1,  ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Connect the socket to the specified endpoint with a timeout.
    /**
     * This function is used to connect a socket to the specified remote endpoint.
     * The function call will block until the connection is successfully made or
     * an error occurs.
     *
     * The socket is automatically opened if it is not already open. If the
     * connect fails, and the socket was automatically opened, the socket is
     * not returned to the closed state.
     *
     * Passing a timeout of less than zero will return an invalid_argument error.
     *
     * @param peer_endpoint The remote endpoint to which the socket will be
     * connected.
     *
     * @param timeout The time to wait for the connection before failing 
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * asio::ip::tcp::endpoint endpoint(
     *     asio::ip::address::from_string("1.2.3.4"), 12345);
     * asio::error_code ec;
     * socket.connect(endpoint, std::chrono::seconds{30}, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    template <typename Duration>
    ASIO_SYNC_OP_VOID connect(const endpoint_type& peer_endpoint,
        Duration timeout, asio::error_code& ec)
    {
      if (!is_open())
      {
        this->get_service().open(this->get_implementation(),
              peer_endpoint.protocol(), ec);
        if (ec)
        {
          ASIO_SYNC_OP_VOID_RETURN(ec);
        }
      }
  
      auto timeout_ms = std::chrono::duration_cast<std::chrono::milliseconds>(timeout);
      if (timeout_ms.count() < 0)
      {
        ec = asio::error::invalid_argument;
        ASIO_SYNC_OP_VOID_RETURN(ec);
      }
      this->get_service().connect(this->get_implementation(), peer_endpoint, timeout_ms.count(), ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Start an asynchronous connect.
    /**
     * This function is used to asynchronously connect a socket to the specified
     * remote endpoint. The function call always returns immediately.
     *
     * The socket is automatically opened if it is not already open. If the
     * connect fails, and the socket was automatically opened, the socket is
     * not returned to the closed state.
     *
     * @param peer_endpoint The remote endpoint to which the socket will be
     * connected. Copies will be made of the endpoint object as required.
     *
     * @param handler The handler to be called when the connection operation
     * completes. Copies will be made of the handler as required. The function
     * signature of the handler must be:
     * @code void handler(
     *   const asio::error_code& error // Result of operation
     * ); @endcode
     * Regardless of whether the asynchronous operation completes immediately or
     * not, the handler will not be invoked from within this function. Invocation
     * of the handler will be performed in a manner equivalent to using
     * asio::io_context::post().
     *
     * @par Example
     * @code
     * void connect_handler(const asio::error_code& error)
     * {
     *   if (!error)
     *   {
     *     // Connect succeeded.
     *   }
     * }
     *
     * ...
     *
     * asio::ip::tcp::socket socket(io_context);
     * asio::ip::tcp::endpoint endpoint(
     *     asio::ip::address::from_string("1.2.3.4"), 12345);
     * socket.async_connect(endpoint, connect_handler);
     * @endcode
     */
    template <typename ConnectHandler>
    ASIO_INITFN_RESULT_TYPE(ConnectHandler,
        void (asio::error_code))
    async_connect(const endpoint_type& peer_endpoint,
        ASIO_MOVE_ARG(ConnectHandler) handler)
    {
      // If you get an error on the following line it means that your handler does
      // not meet the documented type requirements for a ConnectHandler.
      ASIO_CONNECT_HANDLER_CHECK(ConnectHandler, handler) type_check;
  
      if (!is_open())
      {
        asio::error_code ec;
        const protocol_type protocol = peer_endpoint.protocol();
        this->get_service().open(this->get_implementation(), protocol, ec);
        if (ec)
        {
          async_completion<ConnectHandler,
            void (asio::error_code)> init(handler);
  
          asio::post(this->get_executor(),
              asio::detail::bind_handler(
                ASIO_MOVE_CAST(ASIO_HANDLER_TYPE(
                  ConnectHandler, void (asio::error_code)))(
                    init.completion_handler), ec));
  
          return init.result.get();
        }
      }
  
  #if defined(ASIO_ENABLE_OLD_SERVICES)
      return this->get_service().async_connect(this->get_implementation(),
          peer_endpoint, ASIO_MOVE_CAST(ConnectHandler)(handler));
  #else // defined(ASIO_ENABLE_OLD_SERVICES)
      async_completion<ConnectHandler,
        void (asio::error_code)> init(handler);
  
      this->get_service().async_connect(
          this->get_implementation(), peer_endpoint, init.completion_handler);
  
      return init.result.get();
  #endif // defined(ASIO_ENABLE_OLD_SERVICES)
    }
  
    /// Set an option on the socket.
    /**
     * This function is used to set an option on the socket.
     *
     * @param option The new option value to be set on the socket.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @sa SettableSocketOption @n
     * asio::socket_base::broadcast @n
     * asio::socket_base::do_not_route @n
     * asio::socket_base::keep_alive @n
     * asio::socket_base::linger @n
     * asio::socket_base::receive_buffer_size @n
     * asio::socket_base::receive_low_watermark @n
     * asio::socket_base::reuse_address @n
     * asio::socket_base::send_buffer_size @n
     * asio::socket_base::send_low_watermark @n
     * asio::ip::multicast::join_group @n
     * asio::ip::multicast::leave_group @n
     * asio::ip::multicast::enable_loopback @n
     * asio::ip::multicast::outbound_interface @n
     * asio::ip::multicast::hops @n
     * asio::ip::tcp::no_delay
     *
     * @par Example
     * Setting the IPPROTO_TCP/TCP_NODELAY option:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::no_delay option(true);
     * socket.set_option(option);
     * @endcode
     */
    template <typename SettableSocketOption>
    void set_option(const SettableSocketOption& option)
    {
      asio::error_code ec;
      this->get_service().set_option(this->get_implementation(), option, ec);
      asio::detail::throw_error(ec, "set_option");
    }
  
    /// Set an option on the socket.
    /**
     * This function is used to set an option on the socket.
     *
     * @param option The new option value to be set on the socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @sa SettableSocketOption @n
     * asio::socket_base::broadcast @n
     * asio::socket_base::do_not_route @n
     * asio::socket_base::keep_alive @n
     * asio::socket_base::linger @n
     * asio::socket_base::receive_buffer_size @n
     * asio::socket_base::receive_low_watermark @n
     * asio::socket_base::reuse_address @n
     * asio::socket_base::send_buffer_size @n
     * asio::socket_base::send_low_watermark @n
     * asio::ip::multicast::join_group @n
     * asio::ip::multicast::leave_group @n
     * asio::ip::multicast::enable_loopback @n
     * asio::ip::multicast::outbound_interface @n
     * asio::ip::multicast::hops @n
     * asio::ip::tcp::no_delay
     *
     * @par Example
     * Setting the IPPROTO_TCP/TCP_NODELAY option:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::no_delay option(true);
     * asio::error_code ec;
     * socket.set_option(option, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    template <typename SettableSocketOption>
    ASIO_SYNC_OP_VOID set_option(const SettableSocketOption& option,
        asio::error_code& ec)
    {
      this->get_service().set_option(this->get_implementation(), option, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Get an option from the socket.
    /**
     * This function is used to get the current value of an option on the socket.
     *
     * @param option The option value to be obtained from the socket.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @sa GettableSocketOption @n
     * asio::socket_base::broadcast @n
     * asio::socket_base::do_not_route @n
     * asio::socket_base::keep_alive @n
     * asio::socket_base::linger @n
     * asio::socket_base::receive_buffer_size @n
     * asio::socket_base::receive_low_watermark @n
     * asio::socket_base::reuse_address @n
     * asio::socket_base::send_buffer_size @n
     * asio::socket_base::send_low_watermark @n
     * asio::ip::multicast::join_group @n
     * asio::ip::multicast::leave_group @n
     * asio::ip::multicast::enable_loopback @n
     * asio::ip::multicast::outbound_interface @n
     * asio::ip::multicast::hops @n
     * asio::ip::tcp::no_delay
     *
     * @par Example
     * Getting the value of the SOL_SOCKET/SO_KEEPALIVE option:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::socket::keep_alive option;
     * socket.get_option(option);
     * bool is_set = option.value();
     * @endcode
     */
    template <typename GettableSocketOption>
    void get_option(GettableSocketOption& option) const
    {
      asio::error_code ec;
      this->get_service().get_option(this->get_implementation(), option, ec);
      asio::detail::throw_error(ec, "get_option");
    }
  
    /// Get an option from the socket.
    /**
     * This function is used to get the current value of an option on the socket.
     *
     * @param option The option value to be obtained from the socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @sa GettableSocketOption @n
     * asio::socket_base::broadcast @n
     * asio::socket_base::do_not_route @n
     * asio::socket_base::keep_alive @n
     * asio::socket_base::linger @n
     * asio::socket_base::receive_buffer_size @n
     * asio::socket_base::receive_low_watermark @n
     * asio::socket_base::reuse_address @n
     * asio::socket_base::send_buffer_size @n
     * asio::socket_base::send_low_watermark @n
     * asio::ip::multicast::join_group @n
     * asio::ip::multicast::leave_group @n
     * asio::ip::multicast::enable_loopback @n
     * asio::ip::multicast::outbound_interface @n
     * asio::ip::multicast::hops @n
     * asio::ip::tcp::no_delay
     *
     * @par Example
     * Getting the value of the SOL_SOCKET/SO_KEEPALIVE option:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::socket::keep_alive option;
     * asio::error_code ec;
     * socket.get_option(option, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * bool is_set = option.value();
     * @endcode
     */
    template <typename GettableSocketOption>
    ASIO_SYNC_OP_VOID get_option(GettableSocketOption& option,
        asio::error_code& ec) const
    {
      this->get_service().get_option(this->get_implementation(), option, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Perform an IO control command on the socket.
    /**
     * This function is used to execute an IO control command on the socket.
     *
     * @param command The IO control command to be performed on the socket.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @sa IoControlCommand @n
     * asio::socket_base::bytes_readable @n
     * asio::socket_base::non_blocking_io
     *
     * @par Example
     * Getting the number of bytes ready to read:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::socket::bytes_readable command;
     * socket.io_control(command);
     * std::size_t bytes_readable = command.get();
     * @endcode
     */
    template <typename IoControlCommand>
    void io_control(IoControlCommand& command)
    {
      asio::error_code ec;
      this->get_service().io_control(this->get_implementation(), command, ec);
      asio::detail::throw_error(ec, "io_control");
    }
  
    /// Perform an IO control command on the socket.
    /**
     * This function is used to execute an IO control command on the socket.
     *
     * @param command The IO control command to be performed on the socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @sa IoControlCommand @n
     * asio::socket_base::bytes_readable @n
     * asio::socket_base::non_blocking_io
     *
     * @par Example
     * Getting the number of bytes ready to read:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::socket::bytes_readable command;
     * asio::error_code ec;
     * socket.io_control(command, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * std::size_t bytes_readable = command.get();
     * @endcode
     */
    template <typename IoControlCommand>
    ASIO_SYNC_OP_VOID io_control(IoControlCommand& command,
        asio::error_code& ec)
    {
      this->get_service().io_control(this->get_implementation(), command, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Gets the non-blocking mode of the socket.
    /**
     * @returns @c true if the socket's synchronous operations will fail with
     * asio::error::would_block if they are unable to perform the requested
     * operation immediately. If @c false, synchronous operations will block
     * until complete.
     *
     * @note The non-blocking mode has no effect on the behaviour of asynchronous
     * operations. Asynchronous operations will never fail with the error
     * asio::error::would_block.
     */
    bool non_blocking() const
    {
      return this->get_service().non_blocking(this->get_implementation());
    }
  
    /// Sets the non-blocking mode of the socket.
    /**
     * @param mode If @c true, the socket's synchronous operations will fail with
     * asio::error::would_block if they are unable to perform the requested
     * operation immediately. If @c false, synchronous operations will block
     * until complete.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note The non-blocking mode has no effect on the behaviour of asynchronous
     * operations. Asynchronous operations will never fail with the error
     * asio::error::would_block.
     */
    void non_blocking(bool mode)
    {
      asio::error_code ec;
      this->get_service().non_blocking(this->get_implementation(), mode, ec);
      asio::detail::throw_error(ec, "non_blocking");
    }
  
    /// Sets the non-blocking mode of the socket.
    /**
     * @param mode If @c true, the socket's synchronous operations will fail with
     * asio::error::would_block if they are unable to perform the requested
     * operation immediately. If @c false, synchronous operations will block
     * until complete.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @note The non-blocking mode has no effect on the behaviour of asynchronous
     * operations. Asynchronous operations will never fail with the error
     * asio::error::would_block.
     */
    ASIO_SYNC_OP_VOID non_blocking(
        bool mode, asio::error_code& ec)
    {
      this->get_service().non_blocking(this->get_implementation(), mode, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Gets the non-blocking mode of the native socket implementation.
    /**
     * This function is used to retrieve the non-blocking mode of the underlying
     * native socket. This mode has no effect on the behaviour of the socket
     * object's synchronous operations.
     *
     * @returns @c true if the underlying socket is in non-blocking mode and
     * direct system calls may fail with asio::error::would_block (or the
     * equivalent system error).
     *
     * @note The current non-blocking mode is cached by the socket object.
     * Consequently, the return value may be incorrect if the non-blocking mode
     * was set directly on the native socket.
     *
     * @par Example
     * This function is intended to allow the encapsulation of arbitrary
     * non-blocking system calls as asynchronous operations, in a way that is
     * transparent to the user of the socket object. The following example
     * illustrates how Linux's @c sendfile system call might be encapsulated:
     * @code template <typename Handler>
     * struct sendfile_op
     * {
     *   tcp::socket& sock_;
     *   int fd_;
     *   Handler handler_;
     *   off_t offset_;
     *   std::size_t total_bytes_transferred_;
     *
     *   // Function call operator meeting WriteHandler requirements.
     *   // Used as the handler for the async_write_some operation.
     *   void operator()(asio::error_code ec, std::size_t)
     *   {
     *     // Put the underlying socket into non-blocking mode.
     *     if (!ec)
     *       if (!sock_.native_non_blocking())
     *         sock_.native_non_blocking(true, ec);
     *
     *     if (!ec)
     *     {
     *       for (;;)
     *       {
     *         // Try the system call.
     *         errno = 0;
     *         int n = ::sendfile(sock_.native_handle(), fd_, &offset_, 65536);
     *         ec = asio::error_code(n < 0 ? errno : 0,
     *             asio::error::get_system_category());
     *         total_bytes_transferred_ += ec ? 0 : n;
     *
     *         // Retry operation immediately if interrupted by signal.
     *         if (ec == asio::error::interrupted)
     *           continue;
     *
     *         // Check if we need to run the operation again.
     *         if (ec == asio::error::would_block
     *             || ec == asio::error::try_again)
     *         {
     *           // We have to wait for the socket to become ready again.
     *           sock_.async_wait(tcp::socket::wait_write, *this);
     *           return;
     *         }
     *
     *         if (ec || n == 0)
     *         {
     *           // An error occurred, or we have reached the end of the file.
     *           // Either way we must exit the loop so we can call the handler.
     *           break;
     *         }
     *
     *         // Loop around to try calling sendfile again.
     *       }
     *     }
     *
     *     // Pass result back to user's handler.
     *     handler_(ec, total_bytes_transferred_);
     *   }
     * };
     *
     * template <typename Handler>
     * void async_sendfile(tcp::socket& sock, int fd, Handler h)
     * {
     *   sendfile_op<Handler> op = { sock, fd, h, 0, 0 };
     *   sock.async_wait(tcp::socket::wait_write, op);
     * } @endcode
     */
    bool native_non_blocking() const
    {
      return this->get_service().native_non_blocking(this->get_implementation());
    }
  
    /// Sets the non-blocking mode of the native socket implementation.
    /**
     * This function is used to modify the non-blocking mode of the underlying
     * native socket. It has no effect on the behaviour of the socket object's
     * synchronous operations.
     *
     * @param mode If @c true, the underlying socket is put into non-blocking
     * mode and direct system calls may fail with asio::error::would_block
     * (or the equivalent system error).
     *
     * @throws asio::system_error Thrown on failure. If the @c mode is
     * @c false, but the current value of @c non_blocking() is @c true, this
     * function fails with asio::error::invalid_argument, as the
     * combination does not make sense.
     *
     * @par Example
     * This function is intended to allow the encapsulation of arbitrary
     * non-blocking system calls as asynchronous operations, in a way that is
     * transparent to the user of the socket object. The following example
     * illustrates how Linux's @c sendfile system call might be encapsulated:
     * @code template <typename Handler>
     * struct sendfile_op
     * {
     *   tcp::socket& sock_;
     *   int fd_;
     *   Handler handler_;
     *   off_t offset_;
     *   std::size_t total_bytes_transferred_;
     *
     *   // Function call operator meeting WriteHandler requirements.
     *   // Used as the handler for the async_write_some operation.
     *   void operator()(asio::error_code ec, std::size_t)
     *   {
     *     // Put the underlying socket into non-blocking mode.
     *     if (!ec)
     *       if (!sock_.native_non_blocking())
     *         sock_.native_non_blocking(true, ec);
     *
     *     if (!ec)
     *     {
     *       for (;;)
     *       {
     *         // Try the system call.
     *         errno = 0;
     *         int n = ::sendfile(sock_.native_handle(), fd_, &offset_, 65536);
     *         ec = asio::error_code(n < 0 ? errno : 0,
     *             asio::error::get_system_category());
     *         total_bytes_transferred_ += ec ? 0 : n;
     *
     *         // Retry operation immediately if interrupted by signal.
     *         if (ec == asio::error::interrupted)
     *           continue;
     *
     *         // Check if we need to run the operation again.
     *         if (ec == asio::error::would_block
     *             || ec == asio::error::try_again)
     *         {
     *           // We have to wait for the socket to become ready again.
     *           sock_.async_wait(tcp::socket::wait_write, *this);
     *           return;
     *         }
     *
     *         if (ec || n == 0)
     *         {
     *           // An error occurred, or we have reached the end of the file.
     *           // Either way we must exit the loop so we can call the handler.
     *           break;
     *         }
     *
     *         // Loop around to try calling sendfile again.
     *       }
     *     }
     *
     *     // Pass result back to user's handler.
     *     handler_(ec, total_bytes_transferred_);
     *   }
     * };
     *
     * template <typename Handler>
     * void async_sendfile(tcp::socket& sock, int fd, Handler h)
     * {
     *   sendfile_op<Handler> op = { sock, fd, h, 0, 0 };
     *   sock.async_wait(tcp::socket::wait_write, op);
     * } @endcode
     */
    void native_non_blocking(bool mode)
    {
      asio::error_code ec;
      this->get_service().native_non_blocking(
          this->get_implementation(), mode, ec);
      asio::detail::throw_error(ec, "native_non_blocking");
    }
  
    /// Sets the non-blocking mode of the native socket implementation.
    /**
     * This function is used to modify the non-blocking mode of the underlying
     * native socket. It has no effect on the behaviour of the socket object's
     * synchronous operations.
     *
     * @param mode If @c true, the underlying socket is put into non-blocking
     * mode and direct system calls may fail with asio::error::would_block
     * (or the equivalent system error).
     *
     * @param ec Set to indicate what error occurred, if any. If the @c mode is
     * @c false, but the current value of @c non_blocking() is @c true, this
     * function fails with asio::error::invalid_argument, as the
     * combination does not make sense.
     *
     * @par Example
     * This function is intended to allow the encapsulation of arbitrary
     * non-blocking system calls as asynchronous operations, in a way that is
     * transparent to the user of the socket object. The following example
     * illustrates how Linux's @c sendfile system call might be encapsulated:
     * @code template <typename Handler>
     * struct sendfile_op
     * {
     *   tcp::socket& sock_;
     *   int fd_;
     *   Handler handler_;
     *   off_t offset_;
     *   std::size_t total_bytes_transferred_;
     *
     *   // Function call operator meeting WriteHandler requirements.
     *   // Used as the handler for the async_write_some operation.
     *   void operator()(asio::error_code ec, std::size_t)
     *   {
     *     // Put the underlying socket into non-blocking mode.
     *     if (!ec)
     *       if (!sock_.native_non_blocking())
     *         sock_.native_non_blocking(true, ec);
     *
     *     if (!ec)
     *     {
     *       for (;;)
     *       {
     *         // Try the system call.
     *         errno = 0;
     *         int n = ::sendfile(sock_.native_handle(), fd_, &offset_, 65536);
     *         ec = asio::error_code(n < 0 ? errno : 0,
     *             asio::error::get_system_category());
     *         total_bytes_transferred_ += ec ? 0 : n;
     *
     *         // Retry operation immediately if interrupted by signal.
     *         if (ec == asio::error::interrupted)
     *           continue;
     *
     *         // Check if we need to run the operation again.
     *         if (ec == asio::error::would_block
     *             || ec == asio::error::try_again)
     *         {
     *           // We have to wait for the socket to become ready again.
     *           sock_.async_wait(tcp::socket::wait_write, *this);
     *           return;
     *         }
     *
     *         if (ec || n == 0)
     *         {
     *           // An error occurred, or we have reached the end of the file.
     *           // Either way we must exit the loop so we can call the handler.
     *           break;
     *         }
     *
     *         // Loop around to try calling sendfile again.
     *       }
     *     }
     *
     *     // Pass result back to user's handler.
     *     handler_(ec, total_bytes_transferred_);
     *   }
     * };
     *
     * template <typename Handler>
     * void async_sendfile(tcp::socket& sock, int fd, Handler h)
     * {
     *   sendfile_op<Handler> op = { sock, fd, h, 0, 0 };
     *   sock.async_wait(tcp::socket::wait_write, op);
     * } @endcode
     */
    ASIO_SYNC_OP_VOID native_non_blocking(
        bool mode, asio::error_code& ec)
    {
      this->get_service().native_non_blocking(
          this->get_implementation(), mode, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Get the local endpoint of the socket.
    /**
     * This function is used to obtain the locally bound endpoint of the socket.
     *
     * @returns An object that represents the local endpoint of the socket.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::endpoint endpoint = socket.local_endpoint();
     * @endcode
     */
    endpoint_type local_endpoint() const
    {
      asio::error_code ec;
      endpoint_type ep = this->get_service().local_endpoint(
          this->get_implementation(), ec);
      asio::detail::throw_error(ec, "local_endpoint");
      return ep;
    }
  
    /// Get the local endpoint of the socket.
    /**
     * This function is used to obtain the locally bound endpoint of the socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @returns An object that represents the local endpoint of the socket.
     * Returns a default-constructed endpoint object if an error occurred.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::error_code ec;
     * asio::ip::tcp::endpoint endpoint = socket.local_endpoint(ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    endpoint_type local_endpoint(asio::error_code& ec) const
    {
      return this->get_service().local_endpoint(this->get_implementation(), ec);
    }
  
    /// Get the remote endpoint of the socket.
    /**
     * This function is used to obtain the remote endpoint of the socket.
     *
     * @returns An object that represents the remote endpoint of the socket.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::ip::tcp::endpoint endpoint = socket.remote_endpoint();
     * @endcode
     */
    endpoint_type remote_endpoint() const
    {
      asio::error_code ec;
      endpoint_type ep = this->get_service().remote_endpoint(
          this->get_implementation(), ec);
      asio::detail::throw_error(ec, "remote_endpoint");
      return ep;
    }
  
    /// Get the remote endpoint of the socket.
    /**
     * This function is used to obtain the remote endpoint of the socket.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @returns An object that represents the remote endpoint of the socket.
     * Returns a default-constructed endpoint object if an error occurred.
     *
     * @par Example
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::error_code ec;
     * asio::ip::tcp::endpoint endpoint = socket.remote_endpoint(ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    endpoint_type remote_endpoint(asio::error_code& ec) const
    {
      return this->get_service().remote_endpoint(this->get_implementation(), ec);
    }
  
    /// Disable sends or receives on the socket.
    /**
     * This function is used to disable send operations, receive operations, or
     * both.
     *
     * @param what Determines what types of operation will no longer be allowed.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @par Example
     * Shutting down the send side of the socket:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * socket.shutdown(asio::ip::tcp::socket::shutdown_send);
     * @endcode
     */
    void shutdown(shutdown_type what)
    {
      asio::error_code ec;
      this->get_service().shutdown(this->get_implementation(), what, ec);
      asio::detail::throw_error(ec, "shutdown");
    }
  
    /// Disable sends or receives on the socket.
    /**
     * This function is used to disable send operations, receive operations, or
     * both.
     *
     * @param what Determines what types of operation will no longer be allowed.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * Shutting down the send side of the socket:
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::error_code ec;
     * socket.shutdown(asio::ip::tcp::socket::shutdown_send, ec);
     * if (ec)
     * {
     *   // An error occurred.
     * }
     * @endcode
     */
    ASIO_SYNC_OP_VOID shutdown(shutdown_type what,
        asio::error_code& ec)
    {
      this->get_service().shutdown(this->get_implementation(), what, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Wait for the socket to become ready to read, ready to write, or to have
    /// pending error conditions.
    /**
     * This function is used to perform a blocking wait for a socket to enter
     * a ready to read, write or error condition state.
     *
     * @param w Specifies the desired socket state.
     *
     * @par Example
     * Waiting for a socket to become readable.
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * socket.wait(asio::ip::tcp::socket::wait_read);
     * @endcode
     */
    void wait(wait_type w)
    {
      asio::error_code ec;
      this->get_service().wait(this->get_implementation(), w, ec);
      asio::detail::throw_error(ec, "wait");
    }
  
    /// Wait for the socket to become ready to read, ready to write, or to have
    /// pending error conditions.
    /**
     * This function is used to perform a blocking wait for a socket to enter
     * a ready to read, write or error condition state.
     *
     * @param w Specifies the desired socket state.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @par Example
     * Waiting for a socket to become readable.
     * @code
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * asio::error_code ec;
     * socket.wait(asio::ip::tcp::socket::wait_read, ec);
     * @endcode
     */
    ASIO_SYNC_OP_VOID wait(wait_type w, asio::error_code& ec)
    {
      this->get_service().wait(this->get_implementation(), w, ec);
      ASIO_SYNC_OP_VOID_RETURN(ec);
    }
  
    /// Asynchronously wait for the socket to become ready to read, ready to
    /// write, or to have pending error conditions.
    /**
     * This function is used to perform an asynchronous wait for a socket to enter
     * a ready to read, write or error condition state.
     *
     * @param w Specifies the desired socket state.
     *
     * @param handler The handler to be called when the wait operation completes.
     * Copies will be made of the handler as required. The function signature of
     * the handler must be:
     * @code void handler(
     *   const asio::error_code& error // Result of operation
     * ); @endcode
     * Regardless of whether the asynchronous operation completes immediately or
     * not, the handler will not be invoked from within this function. Invocation
     * of the handler will be performed in a manner equivalent to using
     * asio::io_context::post().
     *
     * @par Example
     * @code
     * void wait_handler(const asio::error_code& error)
     * {
     *   if (!error)
     *   {
     *     // Wait succeeded.
     *   }
     * }
     *
     * ...
     *
     * asio::ip::tcp::socket socket(io_context);
     * ...
     * socket.async_wait(asio::ip::tcp::socket::wait_read, wait_handler);
     * @endcode
     */
    template <typename WaitHandler>
    ASIO_INITFN_RESULT_TYPE(WaitHandler,
        void (asio::error_code))
    async_wait(wait_type w, ASIO_MOVE_ARG(WaitHandler) handler)
    {
      // If you get an error on the following line it means that your handler does
      // not meet the documented type requirements for a WaitHandler.
      ASIO_WAIT_HANDLER_CHECK(WaitHandler, handler) type_check;
  
  #if defined(ASIO_ENABLE_OLD_SERVICES)
      return this->get_service().async_wait(this->get_implementation(),
          w, ASIO_MOVE_CAST(WaitHandler)(handler));
  #else // defined(ASIO_ENABLE_OLD_SERVICES)
      async_completion<WaitHandler,
        void (asio::error_code)> init(handler);
  
      this->get_service().async_wait(this->get_implementation(),
          w, init.completion_handler);
  
      return init.result.get();
  #endif // defined(ASIO_ENABLE_OLD_SERVICES)
    }
  
  protected:
    /// Protected destructor to prevent deletion through this type.
    /**
     * This function destroys the socket, cancelling any outstanding asynchronous
     * operations associated with the socket as if by calling @c cancel.
     */
    ~basic_socket()
    {
    }
  
  private:
    // Disallow copying and assignment.
    basic_socket(const basic_socket&) ASIO_DELETED;
    basic_socket& operator=(const basic_socket&) ASIO_DELETED;
  };
  
  } // namespace asio
  
  #include "asio/detail/pop_options.hpp"
  
  #if !defined(ASIO_ENABLE_OLD_SERVICES)
  # undef ASIO_SVC_T
  #endif // !defined(ASIO_ENABLE_OLD_SERVICES)
  
  #endif // ASIO_BASIC_SOCKET_HPP
  