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 //
 // ip/basic_resolver.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_IP_BASIC_RESOLVER_HPP
 #define BOOST_ASIO_IP_BASIC_RESOLVER_HPP
 
 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
 # pragma once
 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
 
 #include <boost/asio/detail/config.hpp>
 #include <string>
 #include <utility>
 #include <boost/asio/any_io_executor.hpp>
 #include <boost/asio/async_result.hpp>
 #include <boost/asio/detail/handler_type_requirements.hpp>
 #include <boost/asio/detail/io_object_impl.hpp>
 #include <boost/asio/detail/non_const_lvalue.hpp>
 #include <boost/asio/detail/string_view.hpp>
 #include <boost/asio/detail/throw_error.hpp>
 #include <boost/asio/error.hpp>
 #include <boost/asio/execution_context.hpp>
 #include <boost/asio/ip/basic_resolver_iterator.hpp>
 #include <boost/asio/ip/basic_resolver_query.hpp>
 #include <boost/asio/ip/basic_resolver_results.hpp>
 #include <boost/asio/ip/resolver_base.hpp>
 #if defined(BOOST_ASIO_WINDOWS_RUNTIME)
 # include <boost/asio/detail/winrt_resolver_service.hpp>
 #else
 # include <boost/asio/detail/resolver_service.hpp>
 #endif
 
 #include <boost/asio/detail/push_options.hpp>
 
 namespace boost {
 namespace asio {
 namespace ip {
 
 #if !defined(BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL)
 #define BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL
 
 // Forward declaration with defaulted arguments.
 template <typename InternetProtocol, typename Executor = any_io_executor>
 class basic_resolver;
 
 #endif // !defined(BOOST_ASIO_IP_BASIC_RESOLVER_FWD_DECL)
 
 /// Provides endpoint resolution functionality.
 /**
  * The basic_resolver class template provides the ability to resolve a query
  * to a list of endpoints.
  *
  * @par Thread Safety
  * @e Distinct @e objects: Safe.@n
  * @e Shared @e objects: Unsafe.
  */
 template <typename InternetProtocol, typename Executor>
 class basic_resolver
   : public resolver_base
 {
 private:
   class initiate_async_resolve;
 
 public:
   /// The type of the executor associated with the object.
   typedef Executor executor_type;
 
   /// Rebinds the resolver type to another executor.
   template <typename Executor1>
   struct rebind_executor
   {
     /// The resolver type when rebound to the specified executor.
     typedef basic_resolver<InternetProtocol, Executor1> other;
   };
 
   /// The protocol type.
   typedef InternetProtocol protocol_type;
 
   /// The endpoint type.
   typedef typename InternetProtocol::endpoint endpoint_type;
 
   /// The results type.
   typedef basic_resolver_results<InternetProtocol> results_type;
 
   /// Construct with executor.
   /**
    * This constructor creates a basic_resolver.
    *
    * @param ex The I/O executor that the resolver will use, by default, to
    * dispatch handlers for any asynchronous operations performed on the
    * resolver.
    */
   explicit basic_resolver(const executor_type& ex)
     : impl_(0, ex)
   {
   }
 
   /// Construct with execution context.
   /**
    * This constructor creates a basic_resolver.
    *
    * @param context An execution context which provides the I/O executor that
    * the resolver will use, by default, to dispatch handlers for any
    * asynchronous operations performed on the resolver.
    */
   template <typename ExecutionContext>
   explicit basic_resolver(ExecutionContext& context,
       constraint_t<
         is_convertible<ExecutionContext&, execution_context&>::value
       > = 0)
     : impl_(0, 0, context)
   {
   }
 
   /// Move-construct a basic_resolver from another.
   /**
    * This constructor moves a resolver from one object to another.
    *
    * @param other The other basic_resolver 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_resolver(const executor_type&) constructor.
    */
   basic_resolver(basic_resolver&& other)
     : impl_(std::move(other.impl_))
   {
   }
 
   // All resolvers have access to each other's implementations.
   template <typename InternetProtocol1, typename Executor1>
   friend class basic_resolver;
 
   /// Move-construct a basic_resolver from another.
   /**
    * This constructor moves a resolver from one object to another.
    *
    * @param other The other basic_resolver 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_resolver(const executor_type&) constructor.
    */
   template <typename Executor1>
   basic_resolver(basic_resolver<InternetProtocol, Executor1>&& other,
       constraint_t<
           is_convertible<Executor1, Executor>::value
       > = 0)
     : impl_(std::move(other.impl_))
   {
   }
 
   /// Move-assign a basic_resolver from another.
   /**
    * This assignment operator moves a resolver from one object to another.
    * Cancels any outstanding asynchronous operations associated with the target
    * object.
    *
    * @param other The other basic_resolver 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_resolver(const executor_type&) constructor.
    */
   basic_resolver& operator=(basic_resolver&& other)
   {
     impl_ = std::move(other.impl_);
     return *this;
   }
 
   /// Move-assign a basic_resolver from another.
   /**
    * This assignment operator moves a resolver from one object to another.
    * Cancels any outstanding asynchronous operations associated with the target
    * object.
    *
    * @param other The other basic_resolver 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_resolver(const executor_type&) constructor.
    */
   template <typename Executor1>
   constraint_t<
     is_convertible<Executor1, Executor>::value,
     basic_resolver&
   > operator=(basic_resolver<InternetProtocol, Executor1>&& other)
   {
     basic_resolver tmp(std::move(other));
     impl_ = std::move(tmp.impl_);
     return *this;
   }
 
   /// Destroys the resolver.
   /**
    * This function destroys the resolver, cancelling any outstanding
    * asynchronous wait operations associated with the resolver as if by calling
    * @c cancel.
    */
   ~basic_resolver()
   {
   }
 
   /// Get the executor associated with the object.
   executor_type get_executor() noexcept
   {
     return impl_.get_executor();
   }
 
   /// Cancel any asynchronous operations that are waiting on the resolver.
   /**
    * This function forces the completion of any pending asynchronous
    * operations on the host resolver. The handler for each cancelled operation
    * will be invoked with the boost::asio::error::operation_aborted error code.
    */
   void cancel()
   {
     return impl_.get_service().cancel(impl_.get_implementation());
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @returns A range object representing the list of endpoint entries. A
    * successful call to this function is guaranteed to return a non-empty
    * range.
    *
    * @throws boost::system::system_error Thrown on failure.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service)
   {
     return resolve(host, service, resolver_base::flags());
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param ec Set to indicate what error occurred, if any.
    *
    * @returns A range object representing the list of endpoint entries. An
    * empty range is returned if an error occurs. A successful call to this
    * function is guaranteed to return a non-empty range.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service, boost::system::error_code& ec)
   {
     return resolve(host, service, resolver_base::flags(), ec);
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @returns A range object representing the list of endpoint entries. A
    * successful call to this function is guaranteed to return a non-empty
    * range.
    *
    * @throws boost::system::system_error Thrown on failure.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service, resolver_base::flags resolve_flags)
   {
     boost::system::error_code ec;
     basic_resolver_query<protocol_type> q(static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
     results_type r = impl_.get_service().resolve(
         impl_.get_implementation(), q, ec);
     boost::asio::detail::throw_error(ec, "resolve");
     return r;
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @param ec Set to indicate what error occurred, if any.
    *
    * @returns A range object representing the list of endpoint entries. An
    * empty range is returned if an error occurs. A successful call to this
    * function is guaranteed to return a non-empty range.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service, resolver_base::flags resolve_flags,
       boost::system::error_code& ec)
   {
     basic_resolver_query<protocol_type> q(static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
     return impl_.get_service().resolve(impl_.get_implementation(), q, ec);
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @returns A range object representing the list of endpoint entries. A
    * successful call to this function is guaranteed to return a non-empty
    * range.
    *
    * @throws boost::system::system_error Thrown on failure.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service)
   {
     return resolve(protocol, host, service, resolver_base::flags());
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param ec Set to indicate what error occurred, if any.
    *
    * @returns A range object representing the list of endpoint entries. An
    * empty range is returned if an error occurs. A successful call to this
    * function is guaranteed to return a non-empty range.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service,
       boost::system::error_code& ec)
   {
     return resolve(protocol, host, service, resolver_base::flags(), ec);
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @returns A range object representing the list of endpoint entries. A
    * successful call to this function is guaranteed to return a non-empty
    * range.
    *
    * @throws boost::system::system_error Thrown on failure.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service,
       resolver_base::flags resolve_flags)
   {
     boost::system::error_code ec;
     basic_resolver_query<protocol_type> q(
         protocol, static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
     results_type r = impl_.get_service().resolve(
         impl_.get_implementation(), q, ec);
     boost::asio::detail::throw_error(ec, "resolve");
     return r;
   }
 
   /// Perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @param ec Set to indicate what error occurred, if any.
    *
    * @returns A range object representing the list of endpoint entries. An
    * empty range is returned if an error occurs. A successful call to this
    * function is guaranteed to return a non-empty range.
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   results_type resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service,
       resolver_base::flags resolve_flags, boost::system::error_code& ec)
   {
     basic_resolver_query<protocol_type> q(
         protocol, static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
     return impl_.get_service().resolve(impl_.get_implementation(), q, ec);
   }
 
   /// Asynchronously perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param token The @ref completion_token that will be used to produce a
    * completion handler, which will be called when the resolve 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(
    *   const boost::system::error_code& error, // Result of operation.
    *   resolver::results_type results // Resolved endpoints as a range.
    * ); @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().
    *
    * A successful resolve operation is guaranteed to pass a non-empty range to
    * the handler.
    *
    * @par Completion Signature
    * @code void(boost::system::error_code, results_type) @endcode
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   template <
       BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
         results_type)) ResolveToken = default_completion_token_t<executor_type>>
   auto async_resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service,
       ResolveToken&& token = default_completion_token_t<executor_type>())
     -> decltype(
       boost::asio::async_initiate<ResolveToken,
         void (boost::system::error_code, results_type)>(
           declval<initiate_async_resolve>(), token,
           declval<basic_resolver_query<protocol_type>&>()))
   {
     return async_resolve(host, service, resolver_base::flags(),
         static_cast<ResolveToken&&>(token));
   }
 
   /// Asynchronously perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries. It is an initiating function for an @ref
    * asynchronous_operation, and always returns immediately.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @param token The @ref completion_token that will be used to produce a
    * completion handler, which will be called when the resolve 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(
    *   const boost::system::error_code& error, // Result of operation.
    *   resolver::results_type results // Resolved endpoints as a range.
    * ); @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().
    *
    * A successful resolve operation is guaranteed to pass a non-empty range to
    * the handler.
    *
    * @par Completion Signature
    * @code void(boost::system::error_code, results_type) @endcode
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   template <
       BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
         results_type)) ResolveToken = default_completion_token_t<executor_type>>
   auto async_resolve(BOOST_ASIO_STRING_VIEW_PARAM host,
       BOOST_ASIO_STRING_VIEW_PARAM service, resolver_base::flags resolve_flags,
       ResolveToken&& token = default_completion_token_t<executor_type>())
     -> decltype(
       boost::asio::async_initiate<ResolveToken,
         void (boost::system::error_code, results_type)>(
           declval<initiate_async_resolve>(), token,
           declval<basic_resolver_query<protocol_type>&>()))
   {
     basic_resolver_query<protocol_type> q(static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
 
     return boost::asio::async_initiate<ResolveToken,
       void (boost::system::error_code, results_type)>(
         initiate_async_resolve(this), token, q);
   }
 
   /// Asynchronously perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries. It is an initiating function for an @ref
    * asynchronous_operation, and always returns immediately.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param token The @ref completion_token that will be used to produce a
    * completion handler, which will be called when the resolve 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(
    *   const boost::system::error_code& error, // Result of operation.
    *   resolver::results_type results // Resolved endpoints as a range.
    * ); @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().
    *
    * A successful resolve operation is guaranteed to pass a non-empty range to
    * the handler.
    *
    * @par Completion Signature
    * @code void(boost::system::error_code, results_type) @endcode
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   template <
       BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
         results_type)) ResolveToken = default_completion_token_t<executor_type>>
   auto async_resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service,
       ResolveToken&& token = default_completion_token_t<executor_type>())
     -> decltype(
       boost::asio::async_initiate<ResolveToken,
         void (boost::system::error_code, results_type)>(
           declval<initiate_async_resolve>(), token,
           declval<basic_resolver_query<protocol_type>&>()))
   {
     return async_resolve(protocol, host, service, resolver_base::flags(),
         static_cast<ResolveToken&&>(token));
   }
 
   /// Asynchronously perform forward resolution of a query to a list of entries.
   /**
    * This function is used to resolve host and service names into a list of
    * endpoint entries. It is an initiating function for an @ref
    * asynchronous_operation, and always returns immediately.
    *
    * @param protocol A protocol object, normally representing either the IPv4 or
    * IPv6 version of an internet protocol.
    *
    * @param host A string identifying a location. May be a descriptive name or
    * a numeric address string. If an empty string and the passive flag has been
    * specified, the resolved endpoints are suitable for local service binding.
    * If an empty string and passive is not specified, the resolved endpoints
    * will use the loopback address.
    *
    * @param service A string identifying the requested service. This may be a
    * descriptive name or a numeric string corresponding to a port number. May
    * be an empty string, in which case all resolved endpoints will have a port
    * number of 0.
    *
    * @param resolve_flags A set of flags that determine how name resolution
    * should be performed. The default flags are suitable for communication with
    * remote hosts. See the @ref resolver_base documentation for the set of
    * available flags.
    *
    * @param token The @ref completion_token that will be used to produce a
    * completion handler, which will be called when the resolve 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(
    *   const boost::system::error_code& error, // Result of operation.
    *   resolver::results_type results // Resolved endpoints as a range.
    * ); @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().
    *
    * A successful resolve operation is guaranteed to pass a non-empty range to
    * the handler.
    *
    * @par Completion Signature
    * @code void(boost::system::error_code, results_type) @endcode
    *
    * @note On POSIX systems, host names may be locally defined in the file
    * <tt>/etc/hosts</tt>. On Windows, host names may be defined in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\hosts</tt>. Remote host name
    * resolution is performed using DNS. Operating systems may use additional
    * locations when resolving host names (such as NETBIOS names on Windows).
    *
    * On POSIX systems, service names are typically defined in the file
    * <tt>/etc/services</tt>. On Windows, service names may be found in the file
    * <tt>c:\\windows\\system32\\drivers\\etc\\services</tt>. Operating systems
    * may use additional locations when resolving service names.
    */
   template <
       BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
         results_type)) ResolveToken = default_completion_token_t<executor_type>>
   auto async_resolve(const protocol_type& protocol,
       BOOST_ASIO_STRING_VIEW_PARAM host, BOOST_ASIO_STRING_VIEW_PARAM service,
       resolver_base::flags resolve_flags,
       ResolveToken&& token = default_completion_token_t<executor_type>())
     -> decltype(
       boost::asio::async_initiate<ResolveToken,
         void (boost::system::error_code, results_type)>(
           declval<initiate_async_resolve>(), token,
           declval<basic_resolver_query<protocol_type>&>()))
   {
     basic_resolver_query<protocol_type> q(
         protocol, static_cast<std::string>(host),
         static_cast<std::string>(service), resolve_flags);
 
     return boost::asio::async_initiate<ResolveToken,
       void (boost::system::error_code, results_type)>(
         initiate_async_resolve(this), token, q);
   }
 
   /// Perform reverse resolution of an endpoint to a list of entries.
   /**
    * This function is used to resolve an endpoint into a list of endpoint
    * entries.
    *
    * @param e An endpoint object that determines what endpoints will be
    * returned.
    *
    * @returns A range object representing the list of endpoint entries. A
    * successful call to this function is guaranteed to return a non-empty
    * range.
    *
    * @throws boost::system::system_error Thrown on failure.
    */
   results_type resolve(const endpoint_type& e)
   {
     boost::system::error_code ec;
     results_type i = impl_.get_service().resolve(
         impl_.get_implementation(), e, ec);
     boost::asio::detail::throw_error(ec, "resolve");
     return i;
   }
 
   /// Perform reverse resolution of an endpoint to a list of entries.
   /**
    * This function is used to resolve an endpoint into a list of endpoint
    * entries.
    *
    * @param e An endpoint object that determines what endpoints will be
    * returned.
    *
    * @param ec Set to indicate what error occurred, if any.
    *
    * @returns A range object representing the list of endpoint entries. An
    * empty range is returned if an error occurs. A successful call to this
    * function is guaranteed to return a non-empty range.
    */
   results_type resolve(const endpoint_type& e, boost::system::error_code& ec)
   {
     return impl_.get_service().resolve(impl_.get_implementation(), e, ec);
   }
 
   /// Asynchronously perform reverse resolution of an endpoint to a list of
   /// entries.
   /**
    * This function is used to asynchronously resolve an endpoint into a list of
    * endpoint entries. It is an initiating function for an @ref
    * asynchronous_operation, and always returns immediately.
    *
    * @param e An endpoint object that determines what endpoints will be
    * returned.
    *
    * @param token The @ref completion_token that will be used to produce a
    * completion handler, which will be called when the resolve 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(
    *   const boost::system::error_code& error, // Result of operation.
    *   resolver::results_type results // Resolved endpoints as a range.
    * ); @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().
    *
    * A successful resolve operation is guaranteed to pass a non-empty range to
    * the handler.
    *
    * @par Completion Signature
    * @code void(boost::system::error_code, results_type) @endcode
    */
   template <
       BOOST_ASIO_COMPLETION_TOKEN_FOR(void (boost::system::error_code,
         results_type)) ResolveToken = default_completion_token_t<executor_type>>
   auto async_resolve(const endpoint_type& e,
       ResolveToken&& token = default_completion_token_t<executor_type>())
     -> decltype(
       boost::asio::async_initiate<ResolveToken,
         void (boost::system::error_code, results_type)>(
           declval<initiate_async_resolve>(), token, e))
   {
     return boost::asio::async_initiate<ResolveToken,
       void (boost::system::error_code, results_type)>(
         initiate_async_resolve(this), token, e);
   }
 
 private:
   // Disallow copying and assignment.
   basic_resolver(const basic_resolver&) = delete;
   basic_resolver& operator=(const basic_resolver&) = delete;
 
   class initiate_async_resolve
   {
   public:
     typedef Executor executor_type;
 
     explicit initiate_async_resolve(basic_resolver* self)
       : self_(self)
     {
     }
 
     executor_type get_executor() const noexcept
     {
       return self_->get_executor();
     }
 
     template <typename ResolveHandler, typename Query>
     void operator()(ResolveHandler&& handler,
         const Query& q) const
     {
       // If you get an error on the following line it means that your handler
       // does not meet the documented type requirements for a ResolveHandler.
       BOOST_ASIO_RESOLVE_HANDLER_CHECK(
           ResolveHandler, handler, results_type) type_check;
 
       boost::asio::detail::non_const_lvalue<ResolveHandler> handler2(handler);
       self_->impl_.get_service().async_resolve(
           self_->impl_.get_implementation(), q,
           handler2.value, self_->impl_.get_executor());
     }
 
   private:
     basic_resolver* self_;
   };
 
 # if defined(BOOST_ASIO_WINDOWS_RUNTIME)
   boost::asio::detail::io_object_impl<
     boost::asio::detail::winrt_resolver_service<InternetProtocol>,
     Executor> impl_;
 # else
   boost::asio::detail::io_object_impl<
     boost::asio::detail::resolver_service<InternetProtocol>,
     Executor> impl_;
 # endif
 };
 
 } // namespace ip
 } // namespace asio
 } // namespace boost
 
 #include <boost/asio/detail/pop_options.hpp>
 
 #endif // BOOST_ASIO_IP_BASIC_RESOLVER_HPP

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