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/op_base.hpp>
17		#include <boost/corosio/wait_type.hpp>
18		#include <boost/corosio/io/io_object.hpp>
19		#include <boost/capy/io_result.hpp>
20		#include <boost/corosio/endpoint.hpp>
21		#include <boost/corosio/tcp.hpp>
22		#include <boost/corosio/tcp_socket.hpp>
23		#include <boost/capy/ex/executor_ref.hpp>
24		#include <boost/capy/ex/execution_context.hpp>
25		#include <boost/capy/ex/io_env.hpp>
26		#include <boost/capy/concept/executor.hpp>
27
28		#include <system_error>
29
30		#include <concepts>
31		#include <coroutine>
32		#include <cstddef>
33		#include <stop_token>
34		#include <type_traits>
35
36		namespace boost::corosio {
37
38		/** An asynchronous TCP acceptor for coroutine I/O.
39
40		This class provides asynchronous TCP accept operations that return
41		awaitable types. The acceptor binds to a local endpoint and listens
42		for incoming connections.
43
44		Each accept operation participates in the affine awaitable protocol,
45		ensuring coroutines resume on the correct executor.
46
47		@par Thread Safety
48		Distinct objects: Safe.@n
49		Shared objects: Unsafe. An acceptor must not have concurrent accept
50		operations.
51
52		@par Semantics
53		Wraps the platform TCP listener. Operations dispatch to
54		OS accept APIs via the io_context reactor.
55
56		@par Example
57		@code
58		// Convenience constructor: open + SO_REUSEADDR + bind + listen
59		io_context ioc;
60		tcp_acceptor acc( ioc, endpoint( 8080 ) );
61
62		tcp_socket peer( ioc );
63		auto [ec] = co_await acc.accept( peer );
64		if ( !ec ) {
65		// peer is now a connected socket
66		auto [ec2, n] = co_await peer.read_some( buf );
67		}
68		@endcode
69
70		@par Example
71		@code
72		// Fine-grained setup
73		tcp_acceptor acc( ioc );
74		acc.open( tcp::v6() );
75		acc.set_option( socket_option::reuse_address( true ) );
76		acc.set_option( socket_option::v6_only( true ) );
77		if ( auto ec = acc.bind( endpoint( ipv6_address::any(), 8080 ) ) )
78		return ec;
79		if ( auto ec = acc.listen() )
80		return ec;
81		@endcode
82		*/
83		class BOOST_COROSIO_DECL tcp_acceptor : public io_object
84		{
85		struct wait_awaitable
86		: detail::void_op_base<wait_awaitable>
87		{
88		tcp_acceptor& acc_;
89		wait_type w_;
90
91	2x	wait_awaitable(tcp_acceptor& acc, wait_type w) noexcept
92	2x	: acc_(acc), w_(w) {}
93
94	2x	std::coroutine_handle<> dispatch(
95		std::coroutine_handle<> h, capy::executor_ref ex) const
96		{
97	2x	return acc_.get().wait(h, ex, w_, token_, &ec_);
98		}
99		};
100
101		struct accept_awaitable
102		{
103		tcp_acceptor& acc_;
104		tcp_socket& peer_;
105		std::stop_token token_;
106		mutable std::error_code ec_;
107		mutable io_object::implementation* peer_impl_ = nullptr;
108
109	8415x	accept_awaitable(tcp_acceptor& acc, tcp_socket& peer) noexcept
110	8415x	: acc_(acc)
111	8415x	, peer_(peer)
112		{
113	8415x	}
114
115	8415x	bool await_ready() const noexcept
116		{
117	8415x	return token_.stop_requested();
118		}
119
120	8415x	capy::io_result<> await_resume() const noexcept
121		{
122	8415x	if (token_.stop_requested())
123	6x	return {make_error_code(std::errc::operation_canceled)};
124
125	8409x	if (!ec_ && peer_impl_)
126	8403x	peer_.h_.reset(peer_impl_);
127	8409x	return {ec_};
128		}
129
130	8415x	auto await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
131		-> std::coroutine_handle<>
132		{
133	8415x	token_ = env->stop_token;
134	25245x	return acc_.get().accept(
135	25245x	h, env->executor, token_, &ec_, &peer_impl_);
136		}
137		};
138
139		public:
140		/** Destructor.
141
142		Closes the acceptor if open, cancelling any pending operations.
143		*/
144		~tcp_acceptor() override;
145
146		/** Construct an acceptor from an execution context.
147
148		@param ctx The execution context that will own this acceptor.
149		*/
150		explicit tcp_acceptor(capy::execution_context& ctx);
151
152		/** Convenience constructor: open + SO_REUSEADDR + bind + listen.
153
154		Creates a fully-bound listening acceptor in a single
155		expression. The address family is deduced from @p ep.
156
157		@param ctx The execution context that will own this acceptor.
158		@param ep The local endpoint to bind to.
159		@param backlog The maximum pending connection queue length.
160
161		@throws std::system_error on bind or listen failure.
162		*/
163		tcp_acceptor(capy::execution_context& ctx, endpoint ep, int backlog = 128);
164
165		/** Construct an acceptor from an executor.
166
167		The acceptor is associated with the executor's context.
168
169		@param ex The executor whose context will own the acceptor.
170		*/
171		template<class Ex>
172		requires(!std::same_as<std::remove_cvref_t<Ex>, tcp_acceptor>) &&
173		capy::Executor<Ex>
174		explicit tcp_acceptor(Ex const& ex) : tcp_acceptor(ex.context())
175		{
176		}
177
178		/** Convenience constructor from an executor.
179
180		@param ex The executor whose context will own the acceptor.
181		@param ep The local endpoint to bind to.
182		@param backlog The maximum pending connection queue length.
183
184		@throws std::system_error on bind or listen failure.
185		*/
186		template<class Ex>
187		requires capy::Executor<Ex>
188		tcp_acceptor(Ex const& ex, endpoint ep, int backlog = 128)
189		: tcp_acceptor(ex.context(), ep, backlog)
190		{
191		}
192
193		/** Move constructor.
194
195		Transfers ownership of the acceptor resources.
196
197		@param other The acceptor to move from.
198
199		@pre No awaitables returned by @p other's methods exist.
200		@pre The execution context associated with @p other must
201		outlive this acceptor.
202		*/
203	2x	tcp_acceptor(tcp_acceptor&& other) noexcept : io_object(std::move(other)) {}
204
205		/** Move assignment operator.
206
207		Closes any existing acceptor and transfers ownership.
208
209		@param other The acceptor to move from.
210
211		@pre No awaitables returned by either `*this` or @p other's
212		methods exist.
213		@pre The execution context associated with @p other must
214		outlive this acceptor.
215
216		@return Reference to this acceptor.
217		*/
218	2x	tcp_acceptor& operator=(tcp_acceptor&& other) noexcept
219		{
220	2x	if (this != &other)
221		{
222	2x	close();
223	2x	h_ = std::move(other.h_);
224		}
225	2x	return *this;
226		}
227
228		tcp_acceptor(tcp_acceptor const&) = delete;
229		tcp_acceptor& operator=(tcp_acceptor const&) = delete;
230
231		/** Create the acceptor socket without binding or listening.
232
233		Creates a TCP socket with dual-stack enabled for IPv6.
234		Does not set SO_REUSEADDR — call `set_option` explicitly
235		if needed.
236
237		If the acceptor is already open, this function is a no-op.
238
239		@param proto The protocol (IPv4 or IPv6). Defaults to
240		`tcp::v4()`.
241
242		@throws std::system_error on failure.
243
244		@par Example
245		@code
246		acc.open( tcp::v6() );
247		acc.set_option( socket_option::reuse_address( true ) );
248		acc.bind( endpoint( ipv6_address::any(), 8080 ) );
249		acc.listen();
250		@endcode
251
252		@see bind, listen
253		*/
254		void open(tcp proto = tcp::v4());
255
256		/** Bind to a local endpoint.
257
258		The acceptor must be open. Binds the socket to @p ep and
259		caches the resolved local endpoint (useful when port 0 is
260		used to request an ephemeral port).
261
262		@param ep The local endpoint to bind to.
263
264		@return An error code indicating success or the reason for
265		failure.
266
267		@par Error Conditions
268		@li `errc::address_in_use`: The endpoint is already in use.
269		@li `errc::address_not_available`: The address is not available
270		on any local interface.
271		@li `errc::permission_denied`: Insufficient privileges to bind
272		to the endpoint (e.g., privileged port).
273
274		@throws std::logic_error if the acceptor is not open.
275		*/
276		[[nodiscard]] std::error_code bind(endpoint ep);
277
278		/** Start listening for incoming connections.
279
280		The acceptor must be open and bound. Registers the acceptor
281		with the platform reactor.
282
283		@param backlog The maximum length of the queue of pending
284		connections. Defaults to 128.
285
286		@return An error code indicating success or the reason for
287		failure.
288
289		@throws std::logic_error if the acceptor is not open.
290		*/
291		[[nodiscard]] std::error_code listen(int backlog = 128);
292
293		/** Close the acceptor.
294
295		Releases acceptor resources. Any pending operations complete
296		with `errc::operation_canceled`.
297		*/
298		void close();
299
300		/** Check if the acceptor is listening.
301
302		@return `true` if the acceptor is open and listening.
303		*/
304	9641x	bool is_open() const noexcept
305		{
306	9641x	return h_ && get().is_open();
307		}
308
309		/** Initiate an asynchronous accept operation.
310
311		Accepts an incoming connection and initializes the provided
312		socket with the new connection. The acceptor must be listening
313		before calling this function.
314
315		The operation supports cancellation via `std::stop_token` through
316		the affine awaitable protocol. If the associated stop token is
317		triggered, the operation completes immediately with
318		`errc::operation_canceled`.
319
320		@param peer The socket to receive the accepted connection. Any
321		existing connection on this socket will be closed.
322
323		@return An awaitable that completes with `io_result<>`.
324		Returns success on successful accept, or an error code on
325		failure including:
326		- operation_canceled: Cancelled via stop_token or cancel().
327		Check `ec == cond::canceled` for portable comparison.
328
329		@par Preconditions
330		The acceptor must be listening (`is_open() == true`).
331		The peer socket must be associated with the same execution context.
332
333		Both this acceptor and @p peer must outlive the returned
334		awaitable.
335
336		@par Example
337		@code
338		tcp_socket peer(ioc);
339		auto [ec] = co_await acc.accept(peer);
340		if (!ec) {
341		// Use peer socket
342		}
343		@endcode
344		*/
345	8415x	auto accept(tcp_socket& peer)
346		{
347	8415x	if (!is_open())
348	✗	detail::throw_logic_error("accept: acceptor not listening");
349	8415x	return accept_awaitable(*this, peer);
350		}
351
352		/** Wait for an incoming connection or readiness condition.
353
354		Suspends until the listen socket is ready in the
355		requested direction, or an error condition is reported.
356		For `wait_type::read`, completion signals that a
357		subsequent @ref accept will succeed without blocking.
358		No connection is consumed.
359
360		@param w The wait direction.
361
362		@return An awaitable that completes with `io_result<>`.
363
364		@par Preconditions
365		The acceptor must be listening. This acceptor must
366		outlive the returned awaitable.
367		*/
368	2x	[[nodiscard]] auto wait(wait_type w)
369		{
370	2x	if (!is_open())
371	✗	detail::throw_logic_error("wait: acceptor not listening");
372	2x	return wait_awaitable(*this, w);
373		}
374
375		/** Cancel any pending asynchronous operations.
376
377		All outstanding operations complete with `errc::operation_canceled`.
378		Check `ec == cond::canceled` for portable comparison.
379		*/
380		void cancel();
381
382		/** Get the local endpoint of the acceptor.
383
384		Returns the local address and port to which the acceptor is bound.
385		This is useful when binding to port 0 (ephemeral port) to discover
386		the OS-assigned port number. The endpoint is cached when listen()
387		is called.
388
389		@return The local endpoint, or a default endpoint (0.0.0.0:0) if
390		the acceptor is not listening.
391
392		@par Thread Safety
393		The cached endpoint value is set during listen() and cleared
394		during close(). This function may be called concurrently with
395		accept operations, but must not be called concurrently with
396		listen() or close().
397		*/
398		endpoint local_endpoint() const noexcept;
399
400		/** Set a socket option on the acceptor.
401
402		Applies a type-safe socket option to the underlying listening
403		socket. The socket must be open (via `open()` or `listen()`).
404		This is useful for setting options between `open()` and
405		`listen()`, such as `socket_option::reuse_port`.
406
407		@par Example
408		@code
409		acc.open( tcp::v6() );
410		acc.set_option( socket_option::reuse_port( true ) );
411		acc.bind( endpoint( ipv6_address::any(), 8080 ) );
412		acc.listen();
413		@endcode
414
415		@param opt The option to set.
416
417		@throws std::logic_error if the acceptor is not open.
418		@throws std::system_error on failure.
419		*/
420		template<class Option>
421	171x	void set_option(Option const& opt)
422		{
423	171x	if (!is_open())
424	✗	detail::throw_logic_error("set_option: acceptor not open");
425	171x	std::error_code ec = get().set_option(
426		Option::level(), Option::name(), opt.data(), opt.size());
427	171x	if (ec)
428	✗	detail::throw_system_error(ec, "tcp_acceptor::set_option");
429	171x	}
430
431		/** Get a socket option from the acceptor.
432
433		Retrieves the current value of a type-safe socket option.
434
435		@par Example
436		@code
437		auto opt = acc.get_option<socket_option::reuse_address>();
438		@endcode
439
440		@return The current option value.
441
442		@throws std::logic_error if the acceptor is not open.
443		@throws std::system_error on failure.
444		*/
445		template<class Option>
446		Option get_option() const
447		{
448		if (!is_open())
449		detail::throw_logic_error("get_option: acceptor not open");
450		Option opt{};
451		std::size_t sz = opt.size();
452		std::error_code ec =
453		get().get_option(Option::level(), Option::name(), opt.data(), &sz);
454		if (ec)
455		detail::throw_system_error(ec, "tcp_acceptor::get_option");
456		opt.resize(sz);
457		return opt;
458		}
459
460		/** Define backend hooks for TCP acceptor operations.
461
462		Platform backends derive from this to implement
463		accept, endpoint query, open-state checks, cancellation,
464		and socket-option management.
465		*/
466		struct implementation : io_object::implementation
467		{
468		/// Initiate an asynchronous accept operation.
469		virtual std::coroutine_handle<> accept(
470		std::coroutine_handle<>,
471		capy::executor_ref,
472		std::stop_token,
473		std::error_code*,
474		io_object::implementation**) = 0;
475
476		/** Initiate an asynchronous wait for acceptor readiness.
477
478		Completes when the listen socket becomes ready for
479		the specified direction (typically `wait_type::read`
480		for an incoming connection), or an error condition is
481		reported. No connection is consumed.
482		*/
483		virtual std::coroutine_handle<> wait(
484		std::coroutine_handle<> h,
485		capy::executor_ref ex,
486		wait_type w,
487		std::stop_token token,
488		std::error_code* ec) = 0;
489
490		/// Returns the cached local endpoint.
491		virtual endpoint local_endpoint() const noexcept = 0;
492
493		/// Return true if the acceptor has a kernel resource open.
494		virtual bool is_open() const noexcept = 0;
495
496		/** Cancel any pending asynchronous operations.
497
498		All outstanding operations complete with operation_canceled error.
499		*/
500		virtual void cancel() noexcept = 0;
501
502		/** Set a socket option.
503
504		@param level The protocol level.
505		@param optname The option name.
506		@param data Pointer to the option value.
507		@param size Size of the option value in bytes.
508		@return Error code on failure, empty on success.
509		*/
510		virtual std::error_code set_option(
511		int level,
512		int optname,
513		void const* data,
514		std::size_t size) noexcept = 0;
515
516		/** Get a socket option.
517
518		@param level The protocol level.
519		@param optname The option name.
520		@param data Pointer to receive the option value.
521		@param size On entry, the size of the buffer. On exit,
522		the size of the option value.
523		@return Error code on failure, empty on success.
524		*/
525		virtual std::error_code
526		get_option(int level, int optname, void* data, std::size_t* size)
527		const noexcept = 0;
528		};
529
530		protected:
531	4x	explicit tcp_acceptor(handle h) noexcept : io_object(std::move(h)) {}
532
533		/// Transfer accepted peer impl to the peer socket.
534		static void
535	4x	reset_peer_impl(tcp_socket& peer, io_object::implementation* impl) noexcept
536		{
537	4x	if (impl)
538	4x	peer.h_.reset(impl);
539	4x	}
540
541		private:
542	18389x	inline implementation& get() const noexcept
543		{
544	18389x	return static_cast<implementation>(h_.get());
545		}
546		};
547
548		} // namespace boost::corosio
549
550		#endif
551