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 //
 // connect.hpp
 // ~~~~~~~~~~~
 //
 // Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
 //
 // Distributed under the Boost Software License, Version 1.0. (See accompanying
 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 //
 
 #ifndef BOOST_ASIO_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;
 
   template <typename T, typename = void, typename = void>
   struct is_endpoint_sequence_helper : false_type
   {
   };
 
   template <typename T>
   struct is_endpoint_sequence_helper<T,
       void_t<
         decltype(declval<T>().begin())
       >,
       void_t<
         decltype(declval<T>().end())
       >
     > : true_type
   {
   };
 
   template <typename T, typename Iterator, typename = void>
   struct is_connect_condition_helper : false_type
   {
   };
 
   template <typename T, typename Iterator>
   struct is_connect_condition_helper<T, Iterator,
       enable_if_t<
         is_same<
           result_of_t<T(boost::system::error_code, Iterator)>,
           Iterator
         >::value
       >
     > : true_type
   {
   };
 
   template <typename T, typename Iterator>
   struct is_connect_condition_helper<T, Iterator,
       enable_if_t<
         is_same<
           result_of_t<T(boost::system::error_code,
             decltype(*declval<Iterator>()))>,
           bool
         >::value
       >
     > : true_type
   {
   };
 
   struct default_connect_condition
   {
     template <typename Endpoint>
     bool operator()(const boost::system::error_code&, const Endpoint&)
     {
       return true;
     }
   };
 } // namespace detail
 
 #if defined(GENERATING_DOCUMENTATION)
 
 /// 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
 {
   /// The value member is true if the type may be used as an endpoint sequence.
   static const bool value = automatically_determined;
 };
 
 /// Trait for determining whether a function object is a connect condition that
 /// can be used with @c connect and @c async_connect.
 template <typename T, typename Iterator>
 struct is_connect_condition
 {
   /// The value member is true if the type may be used as a connect condition.
   static constexpr bool value = automatically_determined;
 };
 
 #else // defined(GENERATING_DOCUMENTATION)
 
 template <typename T>
 struct is_endpoint_sequence : detail::is_endpoint_sequence_helper<T>
 {
 };
 
 template <typename T, typename Iterator>
 struct is_connect_condition : detail::is_connect_condition_helper<T, Iterator>
 {
 };
 
 #endif // defined(GENERATING_DOCUMENTATION)
 
 /**
  * @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.
  *
  * @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
  * @code tcp::resolver r(my_context);
  * tcp::resolver::query q("host", "service");
  * tcp::socket s(my_context);
  * boost::asio::connect(s, r.resolve(q)); @endcode
  */
 template <typename Protocol, typename Executor, typename EndpointSequence>
 typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
     const EndpointSequence& endpoints,
     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 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
  * @code tcp::resolver r(my_context);
  * tcp::resolver::query q("host", "service");
  * tcp::socket s(my_context);
  * boost::system::error_code ec;
  * boost::asio::connect(s, r.resolve(q), ec);
  * if (ec)
  * {
  *   // An error occurred.
  * } @endcode
  */
 template <typename Protocol, typename Executor, typename EndpointSequence>
 typename Protocol::endpoint connect(basic_socket<Protocol, Executor>& s,
     const EndpointSequence& endpoints, boost::system::error_code& ec,
     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 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.
  *
  * @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
  * @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::asio::connect(s, e.begin(), e.end()); @endcode
  */
 template <typename Protocol, typename Executor, typename Iterator>
 Iterator connect(basic_socket<Protocol, Executor>& s,
     Iterator begin, Iterator end);
 
 /// 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 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
  * @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;
  * boost::asio::connect(s, e.begin(), e.end(), ec);
  * if (ec)
  * {
  *   // An error occurred.
  * } @endcode
  */
 template <typename Protocol, typename Executor, typename Iterator>
 Iterator connect(basic_socket<Protocol, Executor>& s,
     Iterator begin, Iterator end, boost::system::error_code& ec);
 
 /// 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,
     constraint_t<
       is_connect_condition<ConnectCondition,
         decltype(declval<const EndpointSequence&>().begin())>::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,
     constraint_t<
       is_connect_condition<ConnectCondition,
         decltype(declval<const EndpointSequence&>().begin())>::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 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,
     constraint_t<
       is_connect_condition<ConnectCondition, Iterator>::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 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,
     constraint_t<
       is_connect_condition<ConnectCondition, Iterator>::value
     > = 0);
 
 /*@}*/
 
 /**
  * @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::async_immediate().
  *
  * @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>>
 inline 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,
     constraint_t<
       !is_connect_condition<RangeConnectToken,
         decltype(declval<const EndpointSequence&>().begin())>::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>()))
 {
   return async_initiate<RangeConnectToken,
     void (boost::system::error_code, typename Protocol::endpoint)>(
       detail::initiate_async_range_connect<Protocol, Executor>(s),
       token, endpoints, detail::default_connect_condition());
 }
 
 /// 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 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::async_immediate().
  *
  * @par Completion Signature
  * @code void(boost::system::error_code, Iterator) @endcode
  *
  * @par Example
  * @code std::vector<tcp::endpoint> endpoints = ...;
  * tcp::socket s(my_context);
  * boost::asio::async_connect(s,
  *     endpoints.begin(), endpoints.end(),
  *     connect_handler);
  *
  * // ...
  *
  * void connect_handler(
  *     const boost::system::error_code& ec,
  *     std::vector<tcp::endpoint>::iterator i)
  * {
  *   // ...
  * } @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,
     BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
       Iterator)) IteratorConnectToken = default_completion_token_t<Executor>>
 inline auto async_connect(
     basic_socket<Protocol, Executor>& s, Iterator begin, Iterator end,
     IteratorConnectToken&& token = default_completion_token_t<Executor>(),
     constraint_t<
       !is_connect_condition<IteratorConnectToken, Iterator>::value
     > = 0)
   -> decltype(
     async_initiate<IteratorConnectToken,
       void (boost::system::error_code, Iterator)>(
         declval<detail::initiate_async_iterator_connect<Protocol, Executor>>(),
         token, begin, end, declval<detail::default_connect_condition>()))
 {
   return async_initiate<IteratorConnectToken,
     void (boost::system::error_code, Iterator)>(
       detail::initiate_async_iterator_connect<Protocol, Executor>(s),
       token, begin, end, detail::default_connect_condition());
 }
 
 /// 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::async_immediate().
  *
  * @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>>
 inline 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,
     constraint_t<
       is_connect_condition<ConnectCondition,
         decltype(declval<const EndpointSequence&>().begin())>::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))
 {
   return async_initiate<RangeConnectToken,
     void (boost::system::error_code, typename Protocol::endpoint)>(
       detail::initiate_async_range_connect<Protocol, Executor>(s),
       token, endpoints, connect_condition);
 }
 
 /// 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::async_immediate().
  *
  * @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>>
 inline auto async_connect(basic_socket<Protocol, Executor>& s,
     Iterator begin, Iterator end, ConnectCondition connect_condition,
     IteratorConnectToken&& token = default_completion_token_t<Executor>(),
     constraint_t<
       is_connect_condition<ConnectCondition, Iterator>::value
     > = 0)
   -> decltype(
     async_initiate<IteratorConnectToken,
       void (boost::system::error_code, Iterator)>(
         declval<detail::initiate_async_iterator_connect<Protocol, Executor>>(),
         token, begin, end, connect_condition))
 {
   return async_initiate<IteratorConnectToken,
     void (boost::system::error_code, Iterator)>(
       detail::initiate_async_iterator_connect<Protocol, Executor>(s),
       token, begin, end, connect_condition);
 }
 
 /*@}*/
 
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #include <boost/asio/impl/connect.hpp>
 
 #endif // BOOST_ASIO_CONNECT_HPP

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