include/boost/corosio/udp_socket.hpp

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udp_socket.hpp

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1		//
2		// Copyright (c) 2026 Steve Gerbino
3		// Copyright (c) 2026 Michael Vandeberg
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_UDP_SOCKET_HPP
12		#define BOOST_COROSIO_UDP_SOCKET_HPP
13
14		#include <boost/corosio/detail/config.hpp>
15		#include <boost/corosio/detail/platform.hpp>
16		#include <boost/corosio/detail/except.hpp>
17		#include <boost/corosio/detail/native_handle.hpp>
18		#include <boost/corosio/detail/op_base.hpp>
19		#include <boost/corosio/io/io_object.hpp>
20		#include <boost/capy/io_result.hpp>
21		#include <boost/corosio/detail/buffer_param.hpp>
22		#include <boost/corosio/endpoint.hpp>
23		#include <boost/corosio/message_flags.hpp>
24		#include <boost/corosio/shutdown_type.hpp>
25		#include <boost/corosio/udp.hpp>
26		#include <boost/corosio/wait_type.hpp>
27		#include <boost/capy/ex/executor_ref.hpp>
28		#include <boost/capy/ex/execution_context.hpp>
29		#include <boost/capy/ex/io_env.hpp>
30		#include <boost/capy/concept/executor.hpp>
31
32		#include <system_error>
33
34		#include <concepts>
35		#include <coroutine>
36		#include <cstddef>
37		#include <stop_token>
38		#include <type_traits>
39
40		namespace boost::corosio {
41
42		/** An asynchronous UDP socket for coroutine I/O.
43
44		This class provides asynchronous UDP datagram operations that
45		return awaitable types. Each operation participates in the affine
46		awaitable protocol, ensuring coroutines resume on the correct
47		executor.
48
49		Supports two modes of operation:
50
51		Connectionless mode: each `send_to` specifies a destination
52		endpoint, and each `recv_from` captures the source endpoint.
53		The socket must be opened (and optionally bound) before I/O.
54
55		Connected mode: call `connect()` to set a default peer,
56		then use `send()`/`recv()` without endpoint arguments.
57		The kernel filters incoming datagrams to those from the
58		connected peer.
59
60		@par Thread Safety
61		Distinct objects: Safe.@n
62		Shared objects: Unsafe. A socket must not have concurrent
63		operations of the same type (e.g., two simultaneous recv_from).
64		One send_to and one recv_from may be in flight simultaneously.
65
66		@par Example
67		@par !example udp_socket
68		*/
69		class BOOST_COROSIO_DECL udp_socket : public io_object
70		{
71		public:
72		using shutdown_type = corosio::shutdown_type;
73		using enum corosio::shutdown_type;
74
75		/** Define backend hooks for UDP socket operations.
76
77		Platform backends (epoll, kqueue, select) derive from
78		this to implement datagram I/O and option management.
79		*/
80		struct implementation : io_object::implementation
81		{
82		/** Initiate an asynchronous send_to operation.
83
84		@param h Coroutine handle to resume on completion.
85		@param ex Executor for dispatching the completion.
86		@param buf The buffer data to send.
87		@param dest The destination endpoint.
88		@param flags Platform message flags (e.g. `MSG_DONTWAIT`).
89		@param token Stop token for cancellation.
90		@param ec Output error code.
91		@param bytes_out Output bytes transferred.
92
93		@return Coroutine handle to resume immediately.
94		*/
95		virtual std::coroutine_handle<> send_to(
96		std::coroutine_handle<> h,
97		capy::executor_ref ex,
98		buffer_param buf,
99		endpoint dest,
100		int flags,
101		std::stop_token token,
102		std::error_code* ec,
103		std::size_t* bytes_out) = 0;
104
105		/** Initiate an asynchronous recv_from operation.
106
107		@param h Coroutine handle to resume on completion.
108		@param ex Executor for dispatching the completion.
109		@param buf The buffer to receive into.
110		@param source Output endpoint for the sender's address.
111		@param flags Platform message flags (e.g. `MSG_PEEK`).
112		@param token Stop token for cancellation.
113		@param ec Output error code.
114		@param bytes_out Output bytes transferred.
115
116		@return Coroutine handle to resume immediately.
117		*/
118		virtual std::coroutine_handle<> recv_from(
119		std::coroutine_handle<> h,
120		capy::executor_ref ex,
121		buffer_param buf,
122		endpoint* source,
123		int flags,
124		std::stop_token token,
125		std::error_code* ec,
126		std::size_t* bytes_out) = 0;
127
128		/// Return the platform socket descriptor.
129		virtual native_handle_type native_handle() const noexcept = 0;
130
131		/** Release ownership of the native socket handle.
132
133		Deregisters the socket from the backend and cancels
134		pending operations without closing the descriptor. The
135		caller takes ownership.
136
137		@return The native handle.
138		*/
139		virtual native_handle_type release_socket() noexcept = 0;
140
141		/** Request cancellation of pending asynchronous operations.
142
143		All outstanding operations complete with operation_canceled
144		error. Check `ec == cond::canceled` for portable comparison.
145		*/
146		virtual void cancel() noexcept = 0;
147
148		/// Shut down the socket in one or both directions.
149		virtual std::error_code shutdown(shutdown_type what) noexcept = 0;
150
151		/** Set a socket option.
152
153		@param level The protocol level (e.g. `SOL_SOCKET`).
154		@param optname The option name.
155		@param data Pointer to the option value.
156		@param size Size of the option value in bytes.
157		@return Error code on failure, empty on success.
158		*/
159		virtual std::error_code set_option(
160		int level,
161		int optname,
162		void const* data,
163		std::size_t size) noexcept = 0;
164
165		/** Get a socket option.
166
167		@param level The protocol level (e.g. `SOL_SOCKET`).
168		@param optname The option name.
169		@param data Pointer to receive the option value.
170		@param size On entry, the size of the buffer. On exit,
171		the size of the option value.
172		@return Error code on failure, empty on success.
173		*/
174		virtual std::error_code
175		get_option(int level, int optname, void* data, std::size_t* size)
176		const noexcept = 0;
177
178		/// Return the cached local endpoint.
179		virtual endpoint local_endpoint() const noexcept = 0;
180
181		/// Return the cached remote endpoint (connected mode).
182		virtual endpoint remote_endpoint() const noexcept = 0;
183
184		/** Initiate an asynchronous connect to set the default peer.
185
186		@param h Coroutine handle to resume on completion.
187		@param ex Executor for dispatching the completion.
188		@param ep The remote endpoint to connect to.
189		@param token Stop token for cancellation.
190		@param ec Output error code.
191
192		@return Coroutine handle to resume immediately.
193		*/
194		virtual std::coroutine_handle<> connect(
195		std::coroutine_handle<> h,
196		capy::executor_ref ex,
197		endpoint ep,
198		std::stop_token token,
199		std::error_code* ec) = 0;
200
201		/** Initiate an asynchronous connected send operation.
202
203		@param h Coroutine handle to resume on completion.
204		@param ex Executor for dispatching the completion.
205		@param buf The buffer data to send.
206		@param flags Platform message flags (e.g. `MSG_DONTWAIT`).
207		@param token Stop token for cancellation.
208		@param ec Output error code.
209		@param bytes_out Output bytes transferred.
210
211		@return Coroutine handle to resume immediately.
212		*/
213		virtual std::coroutine_handle<> send(
214		std::coroutine_handle<> h,
215		capy::executor_ref ex,
216		buffer_param buf,
217		int flags,
218		std::stop_token token,
219		std::error_code* ec,
220		std::size_t* bytes_out) = 0;
221
222		/** Initiate an asynchronous connected recv operation.
223
224		@param h Coroutine handle to resume on completion.
225		@param ex Executor for dispatching the completion.
226		@param buf The buffer to receive into.
227		@param flags Platform message flags (e.g. `MSG_PEEK`).
228		@param token Stop token for cancellation.
229		@param ec Output error code.
230		@param bytes_out Output bytes transferred.
231
232		@return Coroutine handle to resume immediately.
233		*/
234		virtual std::coroutine_handle<> recv(
235		std::coroutine_handle<> h,
236		capy::executor_ref ex,
237		buffer_param buf,
238		int flags,
239		std::stop_token token,
240		std::error_code* ec,
241		std::size_t* bytes_out) = 0;
242
243		/** Initiate an asynchronous wait for socket readiness.
244
245		Completes when the socket becomes ready for the
246		specified direction, or an error condition is
247		reported. No bytes are transferred.
248
249		@param h Coroutine handle to resume on completion.
250		@param ex Executor for dispatching the completion.
251		@param w The direction to wait on.
252		@param token Stop token for cancellation.
253		@param ec Output error code.
254
255		@return Coroutine handle to resume immediately.
256		*/
257		virtual std::coroutine_handle<> wait(
258		std::coroutine_handle<> h,
259		capy::executor_ref ex,
260		wait_type w,
261		std::stop_token token,
262		std::error_code* ec) = 0;
263		};
264
265		/** Represent the awaitable returned by @ref send_to.
266
267		Captures the destination endpoint and buffer, then dispatches
268		to the backend implementation on suspension.
269		*/
270		struct send_to_awaitable : detail::bytes_op_base<send_to_awaitable>
271		{
272		udp_socket& s_;
273		buffer_param buf_;
274		endpoint dest_;
275		int flags_;
276
277	71x	send_to_awaitable(
278		udp_socket& s,
279		buffer_param buf,
280		endpoint dest,
281		int flags = 0) noexcept
282	142x	: s_(s)
283	71x	, buf_(buf)
284	71x	, dest_(dest)
285	71x	, flags_(flags)
286		{
287	71x	}
288
289		std::coroutine_handle<>
290	69x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
291		{
292	138x	return s_.get().send_to(
293	138x	h, ex, buf_, dest_, flags_, token_, &ec_, &bytes_);
294		}
295		};
296
297		/** Represent the awaitable returned by @ref recv_from.
298
299		Captures the source endpoint reference and buffer, then
300		dispatches to the backend implementation on suspension.
301		*/
302		struct recv_from_awaitable : detail::bytes_op_base<recv_from_awaitable>
303		{
304		udp_socket& s_;
305		buffer_param buf_;
306		endpoint& source_;
307		int flags_;
308
309	91x	recv_from_awaitable(
310		udp_socket& s,
311		buffer_param buf,
312		endpoint& source,
313		int flags = 0) noexcept
314	182x	: s_(s)
315	91x	, buf_(buf)
316	91x	, source_(source)
317	91x	, flags_(flags)
318		{
319	91x	}
320
321		std::coroutine_handle<>
322	89x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
323		{
324	178x	return s_.get().recv_from(
325	178x	h, ex, buf_, &source_, flags_, token_, &ec_, &bytes_);
326		}
327		};
328
329		/// Represent the awaitable returned by @ref connect.
330		struct connect_awaitable : detail::void_op_base<connect_awaitable>
331		{
332		udp_socket& s_;
333		endpoint endpoint_;
334
335	40x	connect_awaitable(udp_socket& s, endpoint ep) noexcept
336	80x	: s_(s)
337	40x	, endpoint_(ep)
338		{
339	40x	}
340
341		std::coroutine_handle<>
342	40x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
343		{
344	40x	return s_.get().connect(h, ex, endpoint_, token_, &ec_);
345		}
346		};
347
348		/// Represent the awaitable returned by @ref wait.
349		struct wait_awaitable : detail::void_op_base<wait_awaitable>
350		{
351		udp_socket& s_;
352		wait_type w_;
353
354	30x	wait_awaitable(udp_socket& s, wait_type w) noexcept : s_(s), w_(w) {}
355
356		std::coroutine_handle<>
357	30x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
358		{
359	30x	return s_.get().wait(h, ex, w_, token_, &ec_);
360		}
361		};
362
363		/// Represent the awaitable returned by @ref send.
364		struct send_awaitable : detail::bytes_op_base<send_awaitable>
365		{
366		udp_socket& s_;
367		buffer_param buf_;
368		int flags_;
369
370	26x	send_awaitable(udp_socket& s, buffer_param buf, int flags = 0) noexcept
371	52x	: s_(s)
372	26x	, buf_(buf)
373	26x	, flags_(flags)
374		{
375	26x	}
376
377		std::coroutine_handle<>
378	24x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
379		{
380	24x	return s_.get().send(h, ex, buf_, flags_, token_, &ec_, &bytes_);
381		}
382		};
383
384		/// Represent the awaitable returned by @ref recv.
385		struct recv_awaitable : detail::bytes_op_base<recv_awaitable>
386		{
387		udp_socket& s_;
388		buffer_param buf_;
389		int flags_;
390
391	61x	recv_awaitable(udp_socket& s, buffer_param buf, int flags = 0) noexcept
392	122x	: s_(s)
393	61x	, buf_(buf)
394	61x	, flags_(flags)
395		{
396	61x	}
397
398		std::coroutine_handle<>
399	59x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
400		{
401	59x	return s_.get().recv(h, ex, buf_, flags_, token_, &ec_, &bytes_);
402		}
403		};
404
405		public:
406		/** Destructor.
407
408		Closes the socket if open, cancelling any pending operations.
409		*/
410		~udp_socket() override;
411
412		/** Construct a socket from an execution context.
413
414		@param ctx The execution context that will own this socket.
415		*/
416		explicit udp_socket(capy::execution_context& ctx);
417
418		/** Construct a socket from an executor.
419
420		The socket is associated with the executor's context.
421
422		@param ex The executor whose context will own the socket.
423		*/
424		template<class Ex>
425		requires(!std::same_as<std::remove_cvref_t<Ex>, udp_socket>) &&
426		capy::Executor<Ex>
427		explicit udp_socket(Ex const& ex) : udp_socket(ex.context())
428		{
429		}
430
431		/** Move constructor.
432
433		Transfers ownership of the socket resources.
434
435		@param other The socket to move from.
436		*/
437	4x	udp_socket(udp_socket&& other) noexcept : io_object(std::move(other)) {}
438
439		/** Move assignment operator.
440
441		Closes any existing socket and transfers ownership.
442
443		@param other The socket to move from.
444		@return Reference to this socket.
445		*/
446	2x	udp_socket& operator=(udp_socket&& other) noexcept
447		{
448	2x	if (this != &other)
449		{
450	2x	close();
451	2x	h_ = std::move(other.h_);
452		}
453	2x	return *this;
454		}
455
456		udp_socket(udp_socket const&) = delete;
457		udp_socket& operator=(udp_socket const&) = delete;
458
459		/** Open the socket.
460
461		Creates a UDP socket and associates it with the platform
462		reactor.
463
464		Failures such as descriptor exhaustion are normal runtime
465		conditions and are reported through the returned error code.
466		Opening an already-open socket is a no-op that reports
467		success.
468
469		@param proto The protocol (IPv4 or IPv6). Defaults to
470		`udp::v4()`.
471
472		@return The error code, empty on success.
473		*/
474		[[nodiscard]] std::error_code open(udp proto = udp::v4()) noexcept;
475
476		/** Close the socket.
477
478		Releases socket resources. Any pending operations complete
479		with `errc::operation_canceled`.
480		*/
481		void close() noexcept;
482
483		/** Check if the socket is open.
484
485		@return `true` if the socket is open and ready for operations.
486		*/
487	1712x	bool is_open() const noexcept
488		{
489		#if BOOST_COROSIO_HAS_IOCP && !defined(BOOST_COROSIO_MRDOCS)
490		return h_ && get().native_handle() != ~native_handle_type(0);
491		#else
492	1712x	return h_ && get().native_handle() >= 0;
493		#endif
494		}
495
496		/** Bind the socket to a local endpoint.
497
498		Associates the socket with a local address and port.
499		Required before calling `recv_from`.
500
501		@param ep The local endpoint to bind to.
502
503		@return Error code on failure, empty on success.
504
505		A closed socket reports `errc::bad_file_descriptor`.
506		*/
507		[[nodiscard]] std::error_code bind(endpoint ep) noexcept;
508
509		/** Disable sends or receives on the socket.
510
511		Failures such as an unconnected socket are normal runtime
512		conditions and are reported through the returned error
513		code. A closed socket reports `errc::bad_file_descriptor`.
514
515		@param what Determines what operations will no longer be
516		allowed.
517
518		@return The error code, empty on success.
519		*/
520		[[nodiscard]] std::error_code shutdown(shutdown_type what) noexcept;
521
522		/** Cancel any pending asynchronous operations.
523
524		All outstanding operations complete with
525		`errc::operation_canceled`. Check `ec == cond::canceled`
526		for portable comparison.
527		*/
528		void cancel() noexcept;
529
530		/** Get the native socket handle.
531
532		@return The native socket handle, or -1 if not open.
533		*/
534		native_handle_type native_handle() const noexcept;
535
536		/** Assign an existing native socket to this object.
537
538		Adopts a UDP socket created outside the library — received
539		from another process, inherited, or made natively — and
540		registers it with the backend. The socket must be a datagram
541		socket in the `AF_INET` or `AF_INET6` family. Adoption never
542		alters the descriptor's flags or options: on POSIX the fd
543		must already be non-blocking, and on Windows the socket must
544		be overlapped-capable.
545
546		If this object is already open, pending operations complete
547		with `errc::operation_canceled` and the held socket is
548		closed before the new one is adopted.
549
550		@par Exception Safety
551		Strong guarantee on validation failure: the object is
552		unchanged. If backend registration fails, the object either
553		retains its previous socket or is left closed, depending on
554		the backend. In all failure cases the caller retains
555		ownership of `fd`.
556
557		@param fd The native socket to adopt. On success the object
558		owns it and will close it.
559
560		@return The error code, empty on success. Validation and
561		registration failures are normal runtime conditions when
562		adopting foreign descriptors.
563		*/
564		[[nodiscard]] std::error_code assign(native_handle_type fd) noexcept;
565
566		/** Release ownership of the native socket handle.
567
568		Deregisters the socket from the backend and cancels pending
569		operations without closing the descriptor. The caller takes
570		ownership of the returned handle.
571
572		@return The native handle.
573
574		@throws std::system_error `errc::bad_file_descriptor` if the
575		socket is not open.
576
577		@post is_open() == false
578		*/
579		native_handle_type release();
580
581		/** Set a socket option.
582
583		@param opt The option to set.
584
585		@throws std::system_error `errc::bad_file_descriptor` if the
586		socket is not open; otherwise thrown on failure.
587		*/
588		template<class Option>
589	91x	void set_option(Option const& opt)
590		{
591	91x	if (!is_open())
592	2x	detail::throw_system_error(
593	4x	make_error_code(std::errc::bad_file_descriptor),
594		"udp_socket::set_option");
595	89x	std::error_code ec = get().set_option(
596		Option::level(), Option::name(), opt.data(), opt.size());
597	89x	if (ec)
598	6x	detail::throw_system_error(ec, "udp_socket::set_option");
599	83x	}
600
601		/** Get a socket option.
602
603		@return The current option value.
604
605		@throws std::system_error `errc::bad_file_descriptor` if the
606		socket is not open; otherwise thrown on failure.
607		*/
608		template<class Option>
609	57x	Option get_option() const
610		{
611	57x	if (!is_open())
612	2x	detail::throw_system_error(
613	4x	make_error_code(std::errc::bad_file_descriptor),
614		"udp_socket::get_option");
615	55x	Option opt{};
616	55x	std::size_t sz = opt.size();
617		std::error_code ec =
618	55x	get().get_option(Option::level(), Option::name(), opt.data(), &sz);
619	55x	if (ec)
620	2x	detail::throw_system_error(ec, "udp_socket::get_option");
621	53x	opt.resize(sz);
622	53x	return opt;
623		}
624
625		/** Get the local endpoint of the socket.
626
627		@return The local endpoint, or a default endpoint if not bound.
628		*/
629		endpoint local_endpoint() const noexcept;
630
631		/** Send a datagram to the specified destination.
632
633		@param buf The buffer containing data to send.
634		@param dest The destination endpoint.
635		@param flags Message flags (e.g. message_flags::dont_route).
636
637		@return An awaitable that completes with
638		`io_result<std::size_t>`.
639
640		A closed socket reports `errc::bad_file_descriptor`.
641		*/
642		template<capy::ConstBufferSequence Buffers>
643		[[nodiscard]] auto
644	71x	send_to(Buffers const& buf, endpoint dest, corosio::message_flags flags)
645		{
646	71x	send_to_awaitable aw(*this, buf, dest, static_cast<int>(flags));
647	71x	if (!is_open())
648	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
649	71x	return aw;
650		}
651
652		/// @overload
653		template<capy::ConstBufferSequence Buffers>
654	71x	[[nodiscard]] auto send_to(Buffers const& buf, endpoint dest)
655		{
656	71x	return send_to(buf, dest, corosio::message_flags::none);
657		}
658
659		/** Receive a datagram and capture the sender's endpoint.
660
661		@param buf The buffer to receive data into.
662		@param source Reference to an endpoint that will be set to
663		the sender's address on successful completion.
664		@param flags Message flags (e.g. message_flags::peek).
665
666		@return An awaitable that completes with
667		`io_result<std::size_t>`.
668
669		A closed socket reports `errc::bad_file_descriptor`.
670		*/
671		template<capy::MutableBufferSequence Buffers>
672	91x	[[nodiscard]] auto recv_from(
673		Buffers const& buf, endpoint& source, corosio::message_flags flags)
674		{
675	91x	recv_from_awaitable aw(*this, buf, source, static_cast<int>(flags));
676	91x	if (!is_open())
677	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
678	91x	return aw;
679		}
680
681		/// @overload
682		template<capy::MutableBufferSequence Buffers>
683	90x	[[nodiscard]] auto recv_from(Buffers const& buf, endpoint& source)
684		{
685	90x	return recv_from(buf, source, corosio::message_flags::none);
686		}
687
688		/** Initiate an asynchronous connect to set the default peer.
689
690		If the socket is not already open, it is opened automatically
691		using the address family of @p ep.
692
693		@param ep The remote endpoint to connect to.
694
695		@return An awaitable that completes with `io_result<>`.
696
697		If the socket needs to be opened and the open fails, the
698		awaitable completes immediately with that error.
699		*/
700	40x	[[nodiscard]] auto connect(endpoint ep)
701		{
702	40x	connect_awaitable aw(*this, ep);
703	40x	if (!is_open())
704	8x	aw.ec_ = open(ep.is_v6() ? udp::v6() : udp::v4());
705	40x	return aw;
706		}
707
708		/** Wait for the socket to become ready in a given direction.
709
710		Suspends until the socket is ready for the requested
711		direction, or an error condition is reported. No bytes
712		are transferred.
713
714		The operation supports cancellation via `std::stop_token`.
715
716		@param w The wait direction (read, write, or error).
717
718		@return An awaitable that completes with `io_result<>`.
719
720		A closed socket completes with `errc::bad_file_descriptor`.
721
722		@par Preconditions
723		This socket must outlive the returned awaitable.
724		*/
725	30x	[[nodiscard]] auto wait(wait_type w)
726		{
727	30x	return wait_awaitable(*this, w);
728		}
729
730		/** Send a datagram to the connected peer.
731
732		@param buf The buffer containing data to send.
733		@param flags Message flags.
734
735		@return An awaitable that completes with
736		`io_result<std::size_t>`.
737
738		A closed socket reports `errc::bad_file_descriptor`.
739		*/
740		template<capy::ConstBufferSequence Buffers>
741	26x	[[nodiscard]] auto send(Buffers const& buf, corosio::message_flags flags)
742		{
743	26x	send_awaitable aw(*this, buf, static_cast<int>(flags));
744	26x	if (!is_open())
745	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
746	26x	return aw;
747		}
748
749		/// @overload
750		template<capy::ConstBufferSequence Buffers>
751	26x	[[nodiscard]] auto send(Buffers const& buf)
752		{
753	26x	return send(buf, corosio::message_flags::none);
754		}
755
756		/** Receive a datagram from the connected peer.
757
758		@param buf The buffer to receive data into.
759		@param flags Message flags (e.g. message_flags::peek).
760
761		@return An awaitable that completes with
762		`io_result<std::size_t>`.
763
764		A closed socket reports `errc::bad_file_descriptor`.
765		*/
766		template<capy::MutableBufferSequence Buffers>
767	61x	[[nodiscard]] auto recv(Buffers const& buf, corosio::message_flags flags)
768		{
769	61x	recv_awaitable aw(*this, buf, static_cast<int>(flags));
770	61x	if (!is_open())
771	2x	aw.ec_ = make_error_code(std::errc::bad_file_descriptor);
772	61x	return aw;
773		}
774
775		/// @overload
776		template<capy::MutableBufferSequence Buffers>
777	61x	[[nodiscard]] auto recv(Buffers const& buf)
778		{
779	61x	return recv(buf, corosio::message_flags::none);
780		}
781
782		/** Get the remote endpoint of the socket.
783
784		Returns the address and port of the connected peer.
785
786		@return The remote endpoint, or a default endpoint if
787		not connected.
788		*/
789		endpoint remote_endpoint() const noexcept;
790
791		protected:
792		/// Construct from a pre-built handle (for native_udp_socket).
793	42x	explicit udp_socket(io_object::handle h) noexcept : io_object(std::move(h))
794		{
795	42x	}
796
797		private:
798		/// Open the socket for the given protocol triple.
799		[[nodiscard]] std::error_code
800		open_for_family(int family, int type, int protocol) noexcept;
801
802	2365x	inline implementation& get() const noexcept
803		{
804	2365x	return static_cast<implementation>(h_.get());
805		}
806		};
807
808		} // namespace boost::corosio
809
810		#endif // BOOST_COROSIO_UDP_SOCKET_HPP
811