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편집 파일: connect.hpp

//
// connect.hpp
// ~~~~~~~~~~~
//
// Copyright (c) 2003-2024 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_CONNECT_HPP
#define BOOST_ASIO_CONNECT_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/config.hpp>
#include <boost/asio/async_result.hpp>
#include <boost/asio/basic_socket.hpp>
#include <boost/asio/detail/type_traits.hpp>
#include <boost/asio/error.hpp>

#include <boost/asio/detail/push_options.hpp>

namespace boost {
namespace asio {

namespace detail
{
  struct default_connect_condition;
  template <typename, typename> class initiate_async_range_connect;
  template <typename, typename> class initiate_async_iterator_connect;

char (&has_iterator_helper(...))[2];

template <typename T>
  char has_iterator_helper(T*, typename T::iterator* = 0);

template <typename T>
  struct has_iterator_typedef
  {
    enum { value = (sizeof((has_iterator_helper)((T*)(0))) == 1) };
  };
} // namespace detail

/// Type trait used to determine whether a type is an endpoint sequence that can
/// be used with with @c connect and @c async_connect.
template <typename T>
struct is_endpoint_sequence
{
#if defined(GENERATING_DOCUMENTATION)
  /// The value member is true if the type may be used as an endpoint sequence.
  static const bool value;
#else
  enum
  {
    value = detail::has_iterator_typedef<T>::value
  };
#endif
};

/**
 * @defgroup connect boost::asio::connect
 *
 * @brief The @c connect function is a composed operation that establishes a
 * socket connection by trying each endpoint in a sequence.
 */
/*@{*/

/// Establishes a socket connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param endpoints A sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @returns The successfully connected endpoint.
 *
 * @throws boost::system::system_error Thrown on failure. If the sequence is
 * empty, the associated @c error_code is boost::asio::error::not_found.
 * Otherwise, contains the error from the last connection attempt.
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::socket s(my_context);
 * tcp::endpoint e = boost::asio::connect(s,
 *     r.resolve(q), my_connect_condition());
 * std::cout << "Connected to: " << e << std::endl; @endcode
 */
template <typename Protocol, typename Executor,
    typename EndpointSequence, typename ConnectCondition>
typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
    const EndpointSequence& endpoints, ConnectCondition connect_condition,
    constraint_t<is_endpoint_sequence<EndpointSequence>::value> = 0);

/// Establishes a socket connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param endpoints A sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param ec Set to indicate what error occurred, if any. If the sequence is
 * empty, set to boost::asio::error::not_found. Otherwise, contains the error
 * from the last connection attempt.
 *
 * @returns On success, the successfully connected endpoint. Otherwise, a
 * default-constructed endpoint.
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::socket s(my_context);
 * boost::system::error_code ec;
 * tcp::endpoint e = boost::asio::connect(s,
 *     r.resolve(q), my_connect_condition(), ec);
 * if (ec)
 * {
 *   // An error occurred.
 * }
 * else
 * {
 *   std::cout << "Connected to: " << e << std::endl;
 * } @endcode
 */
template <typename Protocol, typename Executor,
    typename EndpointSequence, typename ConnectCondition>
typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
    const EndpointSequence& endpoints, ConnectCondition connect_condition,
    boost::system::error_code& ec,
    constraint_t<is_endpoint_sequence<EndpointSequence>::value> = 0);

#if !defined(BOOST_ASIO_NO_DEPRECATED)
/// (Deprecated: Use range overload.) Establishes a socket connection by trying
/// each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @returns On success, an iterator denoting the successfully connected
 * endpoint. Otherwise, the end iterator.
 *
 * @throws boost::system::system_error Thrown on failure. If the sequence is
 * empty, the associated @c error_code is boost::asio::error::not_found.
 * Otherwise, contains the error from the last connection attempt.
 *
 * @note This overload assumes that a default constructed object of type @c
 * Iterator represents the end of the sequence. This is a valid assumption for
 * iterator types such as @c boost::asio::ip::tcp::resolver::iterator.
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition>
Iterator connect(basic_socket<Protocol, Executor>& s,
    Iterator begin, ConnectCondition connect_condition,
    constraint_t<!is_endpoint_sequence<Iterator>::value> = 0);

/// (Deprecated: Use range overload.) Establishes a socket connection by trying
/// each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param ec Set to indicate what error occurred, if any. If the sequence is
 * empty, set to boost::asio::error::not_found. Otherwise, contains the error
 * from the last connection attempt.
 *
 * @returns On success, an iterator denoting the successfully connected
 * endpoint. Otherwise, the end iterator.
 *
 * @note This overload assumes that a default constructed object of type @c
 * Iterator represents the end of the sequence. This is a valid assumption for
 * iterator types such as @c boost::asio::ip::tcp::resolver::iterator.
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition>
Iterator connect(basic_socket<Protocol, Executor>& s, Iterator begin,
    ConnectCondition connect_condition, boost::system::error_code& ec,
    constraint_t<!is_endpoint_sequence<Iterator>::value> = 0);
#endif // !defined(BOOST_ASIO_NO_DEPRECATED)

/// Establishes a socket connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param end An iterator pointing to the end of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @returns An iterator denoting the successfully connected endpoint.
 *
 * @throws boost::system::system_error Thrown on failure. If the sequence is
 * empty, the associated @c error_code is boost::asio::error::not_found.
 * Otherwise, contains the error from the last connection attempt.
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::resolver::results_type e = r.resolve(q);
 * tcp::socket s(my_context);
 * tcp::resolver::results_type::iterator i = boost::asio::connect(
 *     s, e.begin(), e.end(), my_connect_condition());
 * std::cout << "Connected to: " << i->endpoint() << std::endl; @endcode
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition>
Iterator connect(basic_socket<Protocol, Executor>& s, Iterator begin,
    Iterator end, ConnectCondition connect_condition);

/// Establishes a socket connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c connect member
 * function, once for each endpoint in the sequence, until a connection is
 * successfully established.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param end An iterator pointing to the end of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param ec Set to indicate what error occurred, if any. If the sequence is
 * empty, set to boost::asio::error::not_found. Otherwise, contains the error
 * from the last connection attempt.
 *
 * @returns On success, an iterator denoting the successfully connected
 * endpoint. Otherwise, the end iterator.
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::resolver::results_type e = r.resolve(q);
 * tcp::socket s(my_context);
 * boost::system::error_code ec;
 * tcp::resolver::results_type::iterator i = boost::asio::connect(
 *     s, e.begin(), e.end(), my_connect_condition());
 * if (ec)
 * {
 *   // An error occurred.
 * }
 * else
 * {
 *   std::cout << "Connected to: " << i->endpoint() << std::endl;
 * } @endcode
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition>
Iterator connect(basic_socket<Protocol, Executor>& s,
    Iterator begin, Iterator end, ConnectCondition connect_condition,
    boost::system::error_code& ec);

/*@}*/

/**
 * @defgroup async_connect boost::asio::async_connect
 *
 * @brief The @c async_connect function is a composed asynchronous operation
 * that establishes a socket connection by trying each endpoint in a sequence.
 */
/*@{*/

/// Asynchronously establishes a socket connection by trying each endpoint in a
/// sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c async_connect
 * member function, once for each endpoint in the sequence, until a connection
 * is successfully established. It is an initiating function for an @ref
 * asynchronous_operation, and always returns immediately.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param endpoints A sequence of endpoints.
 *
 * @param token The @ref completion_token that will be used to produce a
 * completion handler, which will be called when the connect 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. if the sequence is empty, set to
 *   // boost::asio::error::not_found. Otherwise, contains the
 *   // error from the last connection attempt.
 *   const boost::system::error_code& error,
 *
 *   // On success, the successfully connected endpoint.
 *   // Otherwise, a default-constructed endpoint.
 *   const typename Protocol::endpoint& endpoint
 * ); @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, typename Protocol::endpoint) @endcode
 *
 * @par Example
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::socket s(my_context);
 *
 * // ...
 *
 * r.async_resolve(q, resolve_handler);
 *
 * // ...
 *
 * void resolve_handler(
 *     const boost::system::error_code& ec,
 *     tcp::resolver::results_type results)
 * {
 *   if (!ec)
 *   {
 *     boost::asio::async_connect(s, results, connect_handler);
 *   }
 * }
 *
 * // ...
 *
 * void connect_handler(
 *     const boost::system::error_code& ec,
 *     const tcp::endpoint& endpoint)
 * {
 *   // ...
 * } @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 socket's @c async_connect operation.
 */
template <typename Protocol, typename Executor, typename EndpointSequence,
    BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
      typename Protocol::endpoint)) RangeConnectToken
        = default_completion_token_t<Executor>>
auto async_connect(basic_socket<Protocol, Executor>& s,
    const EndpointSequence& endpoints,
    RangeConnectToken&& token = default_completion_token_t<Executor>(),
    constraint_t<is_endpoint_sequence<EndpointSequence>::value> = 0)
  -> decltype(
    async_initiate<RangeConnectToken,
      void (boost::system::error_code, typename Protocol::endpoint)>(
        declval<detail::initiate_async_range_connect<Protocol, Executor>>(),
        token, endpoints, declval<detail::default_connect_condition>()));

#if !defined(BOOST_ASIO_NO_DEPRECATED)
/// (Deprecated: Use range overload.) Asynchronously establishes a socket
/// connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c async_connect
 * member function, once for each endpoint in the sequence, until a connection
 * is successfully established. It is an initiating function for an @ref
 * asynchronous_operation, and always returns immediately.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param token The @ref completion_token that will be used to produce a
 * completion handler, which will be called when the connect 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. if the sequence is empty, set to
 *   // boost::asio::error::not_found. Otherwise, contains the
 *   // error from the last connection attempt.
 *   const boost::system::error_code& error,
 *
 *   // On success, an iterator denoting the successfully
 *   // connected endpoint. Otherwise, the end iterator.
 *   Iterator iterator
 * ); @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, Iterator) @endcode
 *
 * @note This overload assumes that a default constructed object of type @c
 * Iterator represents the end of the sequence. This is a valid assumption for
 * iterator types such as @c boost::asio::ip::tcp::resolver::iterator.
 *
 * @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 socket's @c async_connect operation.
 */
template <typename Protocol, typename Executor, typename Iterator,
    BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
      Iterator)) IteratorConnectToken = default_completion_token_t<Executor>>
auto async_connect(basic_socket<Protocol, Executor>& s, Iterator begin,
    IteratorConnectToken&& token = default_completion_token_t<Executor>(),
    constraint_t<!is_endpoint_sequence<Iterator>::value> = 0)
  -> decltype(
    async_initiate<IteratorConnectToken,
      void (boost::system::error_code, Iterator)>(
        declval<detail::initiate_async_iterator_connect<Protocol, Executor>>(),
        token, begin, Iterator(),
        declval<detail::default_connect_condition>()));
#endif // !defined(BOOST_ASIO_NO_DEPRECATED)

/// Asynchronously establishes a socket connection by trying each endpoint in a
/// sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c async_connect
 * member function, once for each endpoint in the sequence, until a connection
 * is successfully established. It is an initiating function for an @ref
 * asynchronous_operation, and always returns immediately.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param endpoints A sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param token The @ref completion_token that will be used to produce a
 * completion handler, which will be called when the connect 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. if the sequence is empty, set to
 *   // boost::asio::error::not_found. Otherwise, contains the
 *   // error from the last connection attempt.
 *   const boost::system::error_code& error,
 *
 *   // On success, an iterator denoting the successfully
 *   // connected endpoint. Otherwise, the end iterator.
 *   Iterator iterator
 * ); @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, typename Protocol::endpoint) @endcode
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::socket s(my_context);
 *
 * // ...
 *
 * r.async_resolve(q, resolve_handler);
 *
 * // ...
 *
 * void resolve_handler(
 *     const boost::system::error_code& ec,
 *     tcp::resolver::results_type results)
 * {
 *   if (!ec)
 *   {
 *     boost::asio::async_connect(s, results,
 *         my_connect_condition(),
 *         connect_handler);
 *   }
 * }
 *
 * // ...
 *
 * void connect_handler(
 *     const boost::system::error_code& ec,
 *     const tcp::endpoint& endpoint)
 * {
 *   if (ec)
 *   {
 *     // An error occurred.
 *   }
 *   else
 *   {
 *     std::cout << "Connected to: " << endpoint << std::endl;
 *   }
 * } @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 socket's @c async_connect operation.
 */
template <typename Protocol, typename Executor,
    typename EndpointSequence, typename ConnectCondition,
    BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
      typename Protocol::endpoint)) RangeConnectToken
        = default_completion_token_t<Executor>>
auto async_connect(basic_socket<Protocol, Executor>& s,
    const EndpointSequence& endpoints, ConnectCondition connect_condition,
    RangeConnectToken&& token = default_completion_token_t<Executor>(),
    constraint_t<is_endpoint_sequence<EndpointSequence>::value> = 0)
  -> decltype(
    async_initiate<RangeConnectToken,
      void (boost::system::error_code, typename Protocol::endpoint)>(
        declval<detail::initiate_async_range_connect<Protocol, Executor>>(),
        token, endpoints, connect_condition));

#if !defined(BOOST_ASIO_NO_DEPRECATED)
/// (Deprecated: Use range overload.) Asynchronously establishes a socket
/// connection by trying each endpoint in a sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c async_connect
 * member function, once for each endpoint in the sequence, until a connection
 * is successfully established. It is an initiating function for an @ref
 * asynchronous_operation, and always returns immediately.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param token The @ref completion_token that will be used to produce a
 * completion handler, which will be called when the connect 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. if the sequence is empty, set to
 *   // boost::asio::error::not_found. Otherwise, contains the
 *   // error from the last connection attempt.
 *   const boost::system::error_code& error,
 *
 *   // On success, an iterator denoting the successfully
 *   // connected endpoint. Otherwise, the end iterator.
 *   Iterator iterator
 * ); @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, Iterator) @endcode
 *
 * @note This overload assumes that a default constructed object of type @c
 * Iterator represents the end of the sequence. This is a valid assumption for
 * iterator types such as @c boost::asio::ip::tcp::resolver::iterator.
 *
 * @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 socket's @c async_connect operation.
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition,
    BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
      Iterator)) IteratorConnectToken = default_completion_token_t<Executor>>
auto async_connect(basic_socket<Protocol, Executor>& s,
    Iterator begin, ConnectCondition connect_condition,
    IteratorConnectToken&& token = default_completion_token_t<Executor>(),
    constraint_t<!is_endpoint_sequence<Iterator>::value> = 0)
  -> decltype(
    async_initiate<IteratorConnectToken,
      void (boost::system::error_code, Iterator)>(
        declval<detail::initiate_async_iterator_connect<Protocol, Executor>>(),
        token, begin, Iterator(), connect_condition));
#endif // !defined(BOOST_ASIO_NO_DEPRECATED)

/// Asynchronously establishes a socket connection by trying each endpoint in a
/// sequence.
/**
 * This function attempts to connect a socket to one of a sequence of
 * endpoints. It does this by repeated calls to the socket's @c async_connect
 * member function, once for each endpoint in the sequence, until a connection
 * is successfully established. It is an initiating function for an @ref
 * asynchronous_operation, and always returns immediately.
 *
 * @param s The socket to be connected. If the socket is already open, it will
 * be closed.
 *
 * @param begin An iterator pointing to the start of a sequence of endpoints.
 *
 * @param end An iterator pointing to the end of a sequence of endpoints.
 *
 * @param connect_condition A function object that is called prior to each
 * connection attempt. The signature of the function object must be:
 * @code bool connect_condition(
 *     const boost::system::error_code& ec,
 *     const typename Protocol::endpoint& next); @endcode
 * The @c ec parameter contains the result from the most recent connect
 * operation. Before the first connection attempt, @c ec is always set to
 * indicate success. The @c next parameter is the next endpoint to be tried.
 * The function object should return true if the next endpoint should be tried,
 * and false if it should be skipped.
 *
 * @param token The @ref completion_token that will be used to produce a
 * completion handler, which will be called when the connect 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. if the sequence is empty, set to
 *   // boost::asio::error::not_found. Otherwise, contains the
 *   // error from the last connection attempt.
 *   const boost::system::error_code& error,
 *
 *   // On success, an iterator denoting the successfully
 *   // connected endpoint. Otherwise, the end iterator.
 *   Iterator iterator
 * ); @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, Iterator) @endcode
 *
 * @par Example
 * The following connect condition function object can be used to output
 * information about the individual connection attempts:
 * @code struct my_connect_condition
 * {
 *   bool operator()(
 *       const boost::system::error_code& ec,
 *       const::tcp::endpoint& next)
 *   {
 *     if (ec) std::cout << "Error: " << ec.message() << std::endl;
 *     std::cout << "Trying: " << next << std::endl;
 *     return true;
 *   }
 * }; @endcode
 * It would be used with the boost::asio::connect function as follows:
 * @code tcp::resolver r(my_context);
 * tcp::resolver::query q("host", "service");
 * tcp::socket s(my_context);
 *
 * // ...
 *
 * r.async_resolve(q, resolve_handler);
 *
 * // ...
 *
 * void resolve_handler(
 *     const boost::system::error_code& ec,
 *     tcp::resolver::iterator i)
 * {
 *   if (!ec)
 *   {
 *     tcp::resolver::iterator end;
 *     boost::asio::async_connect(s, i, end,
 *         my_connect_condition(),
 *         connect_handler);
 *   }
 * }
 *
 * // ...
 *
 * void connect_handler(
 *     const boost::system::error_code& ec,
 *     tcp::resolver::iterator i)
 * {
 *   if (ec)
 *   {
 *     // An error occurred.
 *   }
 *   else
 *   {
 *     std::cout << "Connected to: " << i->endpoint() << std::endl;
 *   }
 * } @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 socket's @c async_connect operation.
 */
template <typename Protocol, typename Executor,
    typename Iterator, typename ConnectCondition,
    BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
      Iterator)) IteratorConnectToken = default_completion_token_t<Executor>>
auto async_connect(basic_socket<Protocol, Executor>& s,
    Iterator begin, Iterator end, ConnectCondition connect_condition,
    IteratorConnectToken&& token = default_completion_token_t<Executor>())
  -> decltype(
    async_initiate<IteratorConnectToken,
      void (boost::system::error_code, Iterator)>(
        declval<detail::initiate_async_iterator_connect<Protocol, Executor>>(),
        token, begin, end, connect_condition));

/*@}*/

} // namespace asio
} // namespace boost

#include <boost/asio/detail/pop_options.hpp>

#include <boost/asio/impl/connect.hpp>

#endif