include/boost/corosio/tcp_acceptor.hpp

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tcp_acceptor.hpp

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1		//
2		// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3		// Copyright (c) 2026 Steve Gerbino
4		//
5		// Distributed under the Boost Software License, Version 1.0. (See accompanying
6		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7		//
8		// Official repository: https://github.com/cppalliance/corosio
9		//
10
11		#ifndef BOOST_COROSIO_TCP_ACCEPTOR_HPP
12		#define BOOST_COROSIO_TCP_ACCEPTOR_HPP
13
14		#include <boost/corosio/detail/config.hpp>
15		#include <boost/corosio/detail/except.hpp>
16		#include <boost/corosio/detail/native_handle.hpp>
17		#include <boost/corosio/detail/op_base.hpp>
18		#include <boost/corosio/wait_type.hpp>
19		#include <boost/corosio/io/io_object.hpp>
20		#include <boost/capy/io_result.hpp>
21		#include <boost/corosio/endpoint.hpp>
22		#include <boost/corosio/tcp.hpp>
23		#include <boost/corosio/tcp_socket.hpp>
24		#include <boost/capy/ex/executor_ref.hpp>
25		#include <boost/capy/ex/execution_context.hpp>
26		#include <boost/capy/ex/io_env.hpp>
27		#include <boost/capy/concept/executor.hpp>
28
29		#include <system_error>
30
31		#include <concepts>
32		#include <coroutine>
33		#include <cstddef>
34		#include <stop_token>
35		#include <type_traits>
36
37		namespace boost::corosio {
38
39		/** An asynchronous TCP acceptor for coroutine I/O.
40
41		This class provides asynchronous TCP accept operations that return
42		awaitable types. The acceptor binds to a local endpoint and listens
43		for incoming connections.
44
45		Each accept operation participates in the affine awaitable protocol,
46		ensuring coroutines resume on the correct executor.
47
48		@par Thread Safety
49		Distinct objects: Safe.@n
50		Shared objects: Unsafe. An acceptor must not have concurrent accept
51		operations.
52
53		@par Semantics
54		Wraps the platform TCP listener. Operations dispatch to
55		OS accept APIs via the io_context reactor.
56
57		@par Example
58		@code
59		// Convenience constructor: open + configure + bind + listen
60		io_context ioc;
61		tcp_acceptor acc( ioc, endpoint( 8080 ) );
62
63		tcp_socket peer( ioc );
64		auto [ec] = co_await acc.accept( peer );
65		if ( !ec ) {
66		// peer is now a connected socket
67		auto [ec2, n] = co_await peer.read_some( buf );
68		}
69		@endcode
70
71		@par Example
72		@code
73		// Fine-grained setup
74		tcp_acceptor acc( ioc );
75		if ( auto ec = acc.open( tcp::v6() ) )
76		return ec;
77		acc.set_option( socket_option::reuse_address( true ) );
78		acc.set_option( socket_option::v6_only( true ) );
79		if ( auto ec = acc.bind( endpoint( ipv6_address::any(), 8080 ) ) )
80		return ec;
81		if ( auto ec = acc.listen() )
82		return ec;
83		@endcode
84		*/
85		class BOOST_COROSIO_DECL tcp_acceptor : public io_object
86		{
87		struct wait_awaitable
88		: detail::void_op_base<wait_awaitable>
89		{
90		tcp_acceptor& acc_;
91		wait_type w_;
92
93	19x	wait_awaitable(tcp_acceptor& acc, wait_type w) noexcept
94	19x	: acc_(acc), w_(w) {}
95
96	17x	std::coroutine_handle<> dispatch(
97		std::coroutine_handle<> h, capy::executor_ref ex) const
98		{
99	17x	return acc_.get().wait(h, ex, w_, token_, &ec_);
100		}
101		};
102
103		struct accept_awaitable
104		{
105		tcp_acceptor& acc_;
106		tcp_socket& peer_;
107		std::stop_token token_;
108		mutable std::error_code ec_;
109		mutable io_object::implementation* peer_impl_ = nullptr;
110
111	7002x	accept_awaitable(tcp_acceptor& acc, tcp_socket& peer) noexcept
112	7002x	: acc_(acc)
113	7002x	, peer_(peer)
114		{
115	7002x	}
116
117	7002x	bool await_ready() const noexcept
118		{
119		// A pre-set ec_ means the initiator failed before
120		// dispatch (e.g. a closed object).
121	7002x	return static_cast<bool>(ec_) \|\| token_.stop_requested();
122		}
123
124	7000x	[[nodiscard]] capy::io_result<> await_resume() const noexcept
125		{
126	7000x	if (token_.stop_requested())
127	27x	return {make_error_code(std::errc::operation_canceled)};
128
129	6973x	if (!ec_ && peer_impl_)
130	6962x	peer_.h_.reset(peer_impl_);
131	6973x	return {ec_};
132		}
133
134	7000x	auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
135		-> std::coroutine_handle<>
136		{
137	7000x	token_ = env->stop_token;
138	21000x	return acc_.get().accept(
139	21000x	h, env->executor, token_, &ec_, &peer_impl_);
140		}
141		};
142
143		struct accept_value_awaitable
144		{
145		tcp_acceptor& acc_;
146		std::stop_token token_;
147		mutable std::error_code ec_;
148		mutable io_object::implementation* peer_impl_ = nullptr;
149
150	31x	explicit accept_value_awaitable(tcp_acceptor& acc) noexcept
151	31x	: acc_(acc)
152		{
153	31x	}
154
155	31x	bool await_ready() const noexcept
156		{
157		// A pre-set ec_ means the initiator failed before
158		// dispatch (e.g. a closed object).
159	31x	return static_cast<bool>(ec_) \|\| token_.stop_requested();
160		}
161
162	31x	[[nodiscard]] capy::io_result<tcp_socket> await_resume() noexcept
163		{
164		// The peer is built only on success: error paths must not
165		// touch acc_.context(), which a moved-from acceptor lacks.
166	31x	if (token_.stop_requested())
167	✗	return {make_error_code(std::errc::operation_canceled),
168	✗	tcp_socket()};
169
170	31x	if (ec_ \|\| !peer_impl_)
171	4x	return {ec_, tcp_socket()};
172
173	27x	tcp_socket peer(acc_.context());
174	27x	peer.h_.reset(peer_impl_);
175	27x	return {ec_, std::move(peer)};
176	27x	}
177
178	27x	auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
179		-> std::coroutine_handle<>
180		{
181	27x	token_ = env->stop_token;
182	81x	return acc_.get().accept(
183	81x	h, env->executor, token_, &ec_, &peer_impl_);
184		}
185		};
186
187		public:
188		/** Destructor.
189
190		Closes the acceptor if open, cancelling any pending operations.
191		*/
192		~tcp_acceptor() override;
193
194		/** Construct an acceptor from an execution context.
195
196		@param ctx The execution context that will own this acceptor.
197		*/
198		explicit tcp_acceptor(capy::execution_context& ctx);
199
200		/** Convenience constructor: open + configure + bind + listen.
201
202		Creates a fully-bound listening acceptor in a single
203		expression, throwing the codes the piecewise `open()` +
204		`set_option()` + `bind()` + `listen()` path reports. The
205		address family is deduced from @p ep.
206
207		Before binding, the constructor configures address reuse so
208		a server can rebind its port immediately after a restart:
209		`SO_REUSEADDR` on POSIX, `SO_EXCLUSIVEADDRUSE` on Windows
210		( where `SO_REUSEADDR` instead grants other sockets
211		bind-over rights ). A second listener on an occupied
212		endpoint therefore throws `errc::address_in_use` on every
213		platform.
214
215		@param ctx The execution context that will own this acceptor.
216		@param ep The local endpoint to bind to.
217		@param backlog The maximum pending connection queue length.
218
219		@throws std::system_error on open, configuration, bind, or
220		listen failure.
221		*/
222		tcp_acceptor(capy::execution_context& ctx, endpoint ep, int backlog = 128);
223
224		/** Construct an acceptor from an executor.
225
226		The acceptor is associated with the executor's context.
227
228		@param ex The executor whose context will own the acceptor.
229		*/
230		template<class Ex>
231		requires(!std::same_as<std::remove_cvref_t<Ex>, tcp_acceptor>) &&
232		capy::Executor<Ex>
233	1x	explicit tcp_acceptor(Ex const& ex) : tcp_acceptor(ex.context())
234		{
235	1x	}
236
237		/** Convenience constructor from an executor.
238
239		@param ex The executor whose context will own the acceptor.
240		@param ep The local endpoint to bind to.
241		@param backlog The maximum pending connection queue length.
242
243		@throws std::system_error on open, configuration, bind, or
244		listen failure.
245		*/
246		template<class Ex>
247		requires capy::Executor<Ex>
248		tcp_acceptor(Ex const& ex, endpoint ep, int backlog = 128)
249		: tcp_acceptor(ex.context(), ep, backlog)
250		{
251		}
252
253		/** Move constructor.
254
255		Transfers ownership of the acceptor resources.
256
257		@param other The acceptor to move from.
258
259		@pre No awaitables returned by @p other's methods exist.
260		@pre The execution context associated with @p other must
261		outlive this acceptor.
262		*/
263	9x	tcp_acceptor(tcp_acceptor&& other) noexcept : io_object(std::move(other)) {}
264
265		/** Move assignment operator.
266
267		Closes any existing acceptor and transfers ownership.
268
269		@param other The acceptor to move from.
270
271		@pre No awaitables returned by either `*this` or @p other's
272		methods exist.
273		@pre The execution context associated with @p other must
274		outlive this acceptor.
275
276		@return Reference to this acceptor.
277		*/
278	3x	tcp_acceptor& operator=(tcp_acceptor&& other) noexcept
279		{
280	3x	if (this != &other)
281		{
282	3x	close();
283	3x	h_ = std::move(other.h_);
284		}
285	3x	return *this;
286		}
287
288		tcp_acceptor(tcp_acceptor const&) = delete;
289		tcp_acceptor& operator=(tcp_acceptor const&) = delete;
290
291		/** Create the acceptor socket without binding or listening.
292
293		Creates a TCP socket with dual-stack enabled for IPv6.
294		Does not set SO_REUSEADDR — call `set_option` explicitly
295		if needed.
296
297		If the acceptor is already open, this function is a no-op.
298
299		Failures such as descriptor exhaustion are normal runtime
300		conditions and are reported through the returned error code.
301
302		@param proto The protocol (IPv4 or IPv6). Defaults to
303		`tcp::v4()`.
304
305		@par Example
306		@code
307		if (auto ec = acc.open( tcp::v6() ))
308		return; // report the error
309		acc.set_option( socket_option::reuse_address( true ) );
310		if (auto ec = acc.bind( endpoint( ipv6_address::any(), 8080 ) ))
311		return;
312		if (auto ec = acc.listen())
313		return;
314		@endcode
315
316		@see bind, listen
317
318		@return The error code, empty on success.
319		*/
320		[[nodiscard]] std::error_code open(tcp proto = tcp::v4()) noexcept;
321
322		/** Bind to a local endpoint.
323
324		The acceptor must be open. Binds the socket to @p ep and
325		caches the resolved local endpoint (useful when port 0 is
326		used to request an ephemeral port).
327
328		@param ep The local endpoint to bind to.
329
330		@return An error code indicating success or the reason for
331		failure.
332
333		@par Error Conditions
334		@li `errc::address_in_use`: The endpoint is already in use.
335		@li `errc::address_not_available`: The address is not available
336		on any local interface.
337		@li `errc::permission_denied`: Insufficient privileges to bind
338		to the endpoint (e.g., privileged port).
339
340		A closed acceptor reports `errc::bad_file_descriptor`.
341		*/
342		[[nodiscard]] std::error_code bind(endpoint ep) noexcept;
343
344		/** Start listening for incoming connections.
345
346		The acceptor must be open and bound. Registers the acceptor
347		with the platform reactor.
348
349		@param backlog The maximum length of the queue of pending
350		connections. Defaults to 128.
351
352		@return An error code indicating success or the reason for
353		failure.
354
355		A closed acceptor reports `errc::bad_file_descriptor`.
356		*/
357		[[nodiscard]] std::error_code listen(int backlog = 128) noexcept;
358
359		/** Close the acceptor.
360
361		Releases acceptor resources. Any pending operations complete
362		with `errc::operation_canceled`.
363		*/
364		void close() noexcept;
365
366		/** Check if the acceptor is listening.
367
368		@return `true` if the acceptor is open and listening.
369		*/
370	9926x	bool is_open() const noexcept
371		{
372	9926x	return h_ && get().is_open();
373		}
374
375		/** Initiate an asynchronous accept operation.
376
377		Accepts an incoming connection and initializes the provided
378		socket with the new connection. The acceptor must be listening
379		before calling this function.
380
381		The operation supports cancellation via `std::stop_token` through
382		the affine awaitable protocol. If the associated stop token is
383		triggered, the operation completes immediately with
384		`errc::operation_canceled`.
385
386		@param peer The socket to receive the accepted connection. Any
387		existing connection on this socket will be closed.
388
389		@return An awaitable that completes with `io_result<>`.
390		Returns success on successful accept, or an error code on
391		failure including:
392		- operation_canceled: Cancelled via stop_token or cancel().
393		Check `ec == cond::canceled` for portable comparison.
394
395		A closed acceptor completes with `errc::bad_file_descriptor`.
396
397		@par Preconditions
398		The peer socket must be associated with the same execution context.
399
400		Both this acceptor and @p peer must outlive the returned
401		awaitable.
402
403		@par Example
404		@code
405		tcp_socket peer(ioc);
406		auto [ec] = co_await acc.accept(peer);
407		if (ec)
408		co_return;
409		auto [wec, n] = co_await peer.write_some(buffer);
410		@endcode
411
412		@see accept()
413		*/
414	7002x	[[nodiscard]] auto accept(tcp_socket& peer)
415		{
416	7002x	accept_awaitable aw(*this, peer);
417	7002x	if (!is_open())
418	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
419	7002x	return aw;
420		}
421
422		/** Initiate an asynchronous accept operation, returning the peer.
423
424		Accepts an incoming connection and returns a newly constructed
425		socket for it, associated with this acceptor's execution context.
426		The acceptor must be listening before calling this function.
427
428		The caller does not pre-construct the peer socket; the returned
429		socket shares this acceptor's execution context.
430
431		The operation supports cancellation via `std::stop_token` through
432		the affine awaitable protocol. If the associated stop token is
433		triggered, the operation completes immediately with
434		`errc::operation_canceled`.
435
436		@return An awaitable that completes with `io_result<tcp_socket>`.
437		On success the payload is the connected peer socket; on failure
438		(including cancellation) the error code is set and the payload
439		socket is unconnected. Errors include:
440		- operation_canceled: Cancelled via stop_token or cancel().
441		Check `ec == cond::canceled` for portable comparison.
442
443		A closed acceptor completes with `errc::bad_file_descriptor`.
444		On failure the returned socket is default-constructed and
445		may only be destroyed or assigned.
446
447		@par Preconditions
448		This acceptor must outlive the returned awaitable.
449
450		@par Example
451		@code
452		auto [ec, peer] = co_await acc.accept();
453		if (ec)
454		co_return;
455		auto [wec, n] = co_await peer.write_some(buffer);
456		@endcode
457
458		@see accept(tcp_socket&)
459		*/
460	31x	[[nodiscard]] auto accept()
461		{
462	31x	accept_value_awaitable aw(*this);
463	31x	if (!is_open())
464	4x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
465	31x	return aw;
466		}
467
468		/** Wait for an incoming connection or readiness condition.
469
470		Suspends until the listen socket is ready in the
471		requested direction, or an error condition is reported.
472		For `wait_type::read`, completion signals that a
473		subsequent @ref accept will succeed without blocking; a
474		connection already queued when the wait begins completes
475		it immediately. No connection is consumed.
476
477		@note `wait_type::write` is not usable on an acceptor:
478		writability carries no meaning for a listening socket, so
479		the wait fails with `errc::operation_not_supported` on
480		every backend.
481
482		@param w The wait direction.
483
484		@return An awaitable that completes with `io_result<>`.
485
486		A closed acceptor completes with `errc::bad_file_descriptor`.
487
488		@par Preconditions
489		This acceptor must outlive the returned awaitable.
490		*/
491	19x	[[nodiscard]] auto wait(wait_type w)
492		{
493	19x	wait_awaitable aw(*this, w);
494	19x	if (!is_open())
495	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
496	19x	return aw;
497		}
498
499		/** Cancel any pending asynchronous operations.
500
501		All outstanding operations complete with `errc::operation_canceled`.
502		Check `ec == cond::canceled` for portable comparison.
503		*/
504		void cancel() noexcept;
505
506		/** Get the native socket handle.
507
508		Returns the underlying platform-specific socket descriptor.
509		On POSIX systems this is an `int` file descriptor.
510		On Windows this is a `SOCKET` handle.
511
512		@return The native socket handle, or -1/INVALID_SOCKET if not open.
513
514		@par Preconditions
515		None. May be called on closed acceptors.
516		*/
517		native_handle_type native_handle() const noexcept;
518
519		/** Assign an existing native socket to this acceptor.
520
521		Adopts a listening socket created outside the library —
522		received from a service manager, inherited, or made natively —
523		and registers it with the backend. The socket must be a
524		listening stream socket in the `AF_INET` or `AF_INET6` family.
525		Adoption never alters the descriptor's flags or options: on
526		POSIX the fd must already be non-blocking, and on Windows the
527		socket must be overlapped-capable.
528
529		Adoption does not verify listen state; @ref accept reports the
530		error if the socket is not listening.
531
532		If this object is already open, pending operations complete
533		with `errc::operation_canceled` and the held socket is
534		closed before the new one is adopted.
535
536		@par Exception Safety
537		Strong guarantee on validation failure: the object is
538		unchanged. If backend registration fails, the object either
539		retains its previous socket or is left closed, depending on
540		the backend. In all failure cases the caller retains
541		ownership of `fd`.
542
543		@param fd The native socket to adopt. On success the object
544		owns it and will close it.
545
546		@return The error code, empty on success. Validation and
547		registration failures are normal runtime conditions when
548		adopting foreign descriptors.
549		*/
550		[[nodiscard]] std::error_code assign(native_handle_type fd) noexcept;
551
552		/** Release ownership of the native socket handle.
553
554		Deregisters the socket from the backend and cancels pending
555		operations without closing the descriptor. The caller takes
556		ownership of the returned handle.
557
558		@return The native handle.
559
560		@throws std::system_error `errc::bad_file_descriptor` if the
561		acceptor is not open.
562
563		@post is_open() == false
564		*/
565		native_handle_type release();
566
567		/** Get the local endpoint of the acceptor.
568
569		Returns the local address and port to which the acceptor is bound.
570		This is useful when binding to port 0 (ephemeral port) to discover
571		the OS-assigned port number. The endpoint is cached when bind()
572		is called.
573
574		@return The local endpoint, or a default endpoint (0.0.0.0:0) if
575		the acceptor is not open.
576
577		@par Thread Safety
578		The cached endpoint value is set during bind() and cleared
579		during close(). This function may be called concurrently with
580		accept operations, but must not be called concurrently with
581		bind() or close().
582		*/
583		endpoint local_endpoint() const noexcept;
584
585		/** Set a socket option on the acceptor.
586
587		Applies a type-safe socket option to the underlying listening
588		socket. The socket must be open (via `open()` or `listen()`).
589		This is useful for setting options between `open()` and
590		`listen()`, such as `socket_option::reuse_port`.
591
592		@par Example
593		@code
594		if ( auto ec = acc.open( tcp::v6() ) )
595		return ec;
596		acc.set_option( socket_option::reuse_port( true ) );
597		if ( auto ec = acc.bind( endpoint( ipv6_address::any(), 8080 ) ) )
598		return ec;
599		if ( auto ec = acc.listen() )
600		return ec;
601		@endcode
602
603		@param opt The option to set.
604
605		@throws std::system_error `errc::bad_file_descriptor` if the
606		acceptor is not open; otherwise thrown on failure.
607		*/
608		template<class Option>
609	404x	void set_option(Option const& opt)
610		{
611	404x	if (!is_open())
612	2x	detail::throw_system_error(
613	4x	make_error_code(std::errc::bad_file_descriptor),
614		"tcp_acceptor::set_option");
615	402x	std::error_code ec = get().set_option(
616		Option::level(), Option::name(), opt.data(), opt.size());
617	402x	if (ec)
618	2x	detail::throw_system_error(ec, "tcp_acceptor::set_option");
619	400x	}
620
621		/** Get a socket option from the acceptor.
622
623		Retrieves the current value of a type-safe socket option.
624
625		@par Example
626		@code
627		auto opt = acc.get_option<socket_option::reuse_address>();
628		@endcode
629
630		@return The current option value.
631
632		@throws std::system_error `errc::bad_file_descriptor` if the
633		acceptor is not open; otherwise thrown on failure.
634		*/
635		template<class Option>
636	10x	Option get_option() const
637		{
638	10x	if (!is_open())
639	2x	detail::throw_system_error(
640	4x	make_error_code(std::errc::bad_file_descriptor),
641		"tcp_acceptor::get_option");
642	8x	Option opt{};
643	8x	std::size_t sz = opt.size();
644		std::error_code ec =
645	8x	get().get_option(Option::level(), Option::name(), opt.data(), &sz);
646	8x	if (ec)
647	2x	detail::throw_system_error(ec, "tcp_acceptor::get_option");
648	6x	opt.resize(sz);
649	6x	return opt;
650		}
651
652		/** Define backend hooks for TCP acceptor operations.
653
654		Platform backends derive from this to implement
655		accept, endpoint query, open-state checks, cancellation,
656		and socket-option management.
657		*/
658		struct implementation : io_object::implementation
659		{
660		/// Initiate an asynchronous accept operation.
661		virtual std::coroutine_handle<> accept(
662		std::coroutine_handle<>,
663		capy::executor_ref,
664		std::stop_token,
665		std::error_code*,
666		io_object::implementation**) = 0;
667
668		/** Initiate an asynchronous wait for acceptor readiness.
669
670		Completes when the listen socket becomes ready for
671		the specified direction (typically `wait_type::read`
672		for an incoming connection), or an error condition is
673		reported. No connection is consumed.
674		*/
675		virtual std::coroutine_handle<> wait(
676		std::coroutine_handle<> h,
677		capy::executor_ref ex,
678		wait_type w,
679		std::stop_token token,
680		std::error_code* ec) = 0;
681
682		/// Returns the cached local endpoint.
683		virtual endpoint local_endpoint() const noexcept = 0;
684
685		/// Return true if the acceptor has a kernel resource open.
686		virtual bool is_open() const noexcept = 0;
687
688		/// Return the native handle, or the platform sentinel if closed.
689		virtual native_handle_type native_handle() const noexcept = 0;
690
691		/// Release and return the native handle without closing.
692		virtual native_handle_type release_socket() noexcept = 0;
693
694		/** Cancel any pending asynchronous operations.
695
696		All outstanding operations complete with operation_canceled error.
697		*/
698		virtual void cancel() noexcept = 0;
699
700		/** Set a socket option.
701
702		@param level The protocol level.
703		@param optname The option name.
704		@param data Pointer to the option value.
705		@param size Size of the option value in bytes.
706		@return Error code on failure, empty on success.
707		*/
708		virtual std::error_code set_option(
709		int level,
710		int optname,
711		void const* data,
712		std::size_t size) noexcept = 0;
713
714		/** Get a socket option.
715
716		@param level The protocol level.
717		@param optname The option name.
718		@param data Pointer to receive the option value.
719		@param size On entry, the size of the buffer. On exit,
720		the size of the option value.
721		@return Error code on failure, empty on success.
722		*/
723		virtual std::error_code
724		get_option(int level, int optname, void* data, std::size_t* size)
725		const noexcept = 0;
726		};
727
728		protected:
729	27x	explicit tcp_acceptor(handle h) noexcept : io_object(std::move(h)) {}
730
731		/// Transfer accepted peer impl to the peer socket.
732		static void
733	11x	reset_peer_impl(tcp_socket& peer, io_object::implementation* impl) noexcept
734		{
735	11x	if (impl)
736	11x	peer.h_.reset(impl);
737	11x	}
738
739		private:
740	17766x	inline implementation& get() const noexcept
741		{
742	17766x	return static_cast<implementation>(h_.get());
743		}
744		};
745
746		} // namespace boost::corosio
747
748		#endif
749