include/boost/corosio/resolver.hpp

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1		//
2		// Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com)
3		// Copyright (c) 2026 Steve Gerbino
4		// Copyright (c) 2026 Michael Vandeberg
5		//
6		// Distributed under the Boost Software License, Version 1.0. (See accompanying
7		// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
8		//
9		// Official repository: https://github.com/cppalliance/corosio
10		//
11
12		#ifndef BOOST_COROSIO_RESOLVER_HPP
13		#define BOOST_COROSIO_RESOLVER_HPP
14
15		#include <boost/corosio/detail/config.hpp>
16		#include <boost/corosio/detail/op_base.hpp>
17		#include <boost/corosio/endpoint.hpp>
18		#include <boost/corosio/io/io_object.hpp>
19		#include <boost/capy/io_result.hpp>
20		#include <boost/capy/ex/executor_ref.hpp>
21		#include <boost/capy/ex/execution_context.hpp>
22		#include <boost/capy/ex/io_env.hpp>
23		#include <boost/capy/concept/executor.hpp>
24
25		#include <system_error>
26
27		#include <cassert>
28		#include <concepts>
29		#include <coroutine>
30		#include <stop_token>
31		#include <string>
32		#include <string_view>
33		#include <vector>
34		#include <type_traits>
35
36		namespace boost::corosio {
37
38		/** Bitmask flags for resolver queries.
39
40		These flags correspond to the hints parameter of `getaddrinfo`.
41		*/
42		enum class resolve_flags : unsigned int
43		{
44		/// No flags.
45		none = 0,
46
47		/// Indicate that returned endpoint is intended for use as a locally
48		/// bound socket endpoint.
49		passive = 0x01,
50
51		/// Host name should be treated as a numeric string defining an IPv4
52		/// or IPv6 address and no name resolution should be attempted.
53		numeric_host = 0x04,
54
55		/// Service name should be treated as a numeric string defining a port
56		/// number and no name resolution should be attempted.
57		numeric_service = 0x08,
58
59		/// Only return IPv4 addresses if a non-loopback IPv4 address is
60		/// configured for the system. Only return IPv6 addresses if a
61		/// non-loopback IPv6 address is configured for the system.
62		address_configured = 0x20,
63
64		/// If the query protocol family is specified as IPv6, return
65		/// IPv4-mapped IPv6 addresses on finding no IPv6 addresses.
66		v4_mapped = 0x800,
67
68		/// If used with v4_mapped, return all matching IPv6 and IPv4 addresses.
69		all_matching = 0x100
70		};
71
72		/** Combine two `resolve_flags`. */
73		inline resolve_flags
74	17x	operator\|(resolve_flags a, resolve_flags b) noexcept
75		{
76		return static_cast<resolve_flags>(
77	17x	static_cast<unsigned int>(a) \| static_cast<unsigned int>(b));
78		}
79
80		/** Combine two `resolve_flags`. */
81		inline resolve_flags&
82	1x	operator\|=(resolve_flags& a, resolve_flags b) noexcept
83		{
84	1x	a = a \| b;
85	1x	return a;
86		}
87
88		/** Intersect two `resolve_flags`. */
89		inline resolve_flags
90	205x	operator&(resolve_flags a, resolve_flags b) noexcept
91		{
92		return static_cast<resolve_flags>(
93	205x	static_cast<unsigned int>(a) & static_cast<unsigned int>(b));
94		}
95
96		/** Intersect two `resolve_flags`. */
97		inline resolve_flags&
98	1x	operator&=(resolve_flags& a, resolve_flags b) noexcept
99		{
100	1x	a = a & b;
101	1x	return a;
102		}
103
104		/** Bitmask flags for reverse resolver queries.
105
106		These flags correspond to the flags parameter of `getnameinfo`.
107		*/
108		enum class reverse_flags : unsigned int
109		{
110		/// No flags.
111		none = 0,
112
113		/// Return the numeric form of the hostname instead of its name.
114		numeric_host = 0x01,
115
116		/// Return the numeric form of the service name instead of its name.
117		numeric_service = 0x02,
118
119		/// Return an error if the hostname cannot be resolved.
120		name_required = 0x04,
121
122		/// Lookup for datagram (UDP) service instead of stream (TCP).
123		datagram_service = 0x08
124		};
125
126		/** Combine two `reverse_flags`. */
127		inline reverse_flags
128	9x	operator\|(reverse_flags a, reverse_flags b) noexcept
129		{
130		return static_cast<reverse_flags>(
131	9x	static_cast<unsigned int>(a) \| static_cast<unsigned int>(b));
132		}
133
134		/** Combine two `reverse_flags`. */
135		inline reverse_flags&
136	1x	operator\|=(reverse_flags& a, reverse_flags b) noexcept
137		{
138	1x	a = a \| b;
139	1x	return a;
140		}
141
142		/** Intersect two `reverse_flags`. */
143		inline reverse_flags
144	75x	operator&(reverse_flags a, reverse_flags b) noexcept
145		{
146		return static_cast<reverse_flags>(
147	75x	static_cast<unsigned int>(a) & static_cast<unsigned int>(b));
148		}
149
150		/** Intersect two `reverse_flags`. */
151		inline reverse_flags&
152	1x	operator&=(reverse_flags& a, reverse_flags b) noexcept
153		{
154	1x	a = a & b;
155	1x	return a;
156		}
157
158		/** The name of an endpoint.
159
160		Reverse resolution translates an endpoint into its symbolic
161		spelling: the host name and the service name. Both fields carry
162		resolved data; the endpoint they name is the one the caller
163		passed to `resolve`.
164		*/
165		struct endpoint_name
166		{
167		/// The resolved host name.
168		std::string host_name;
169
170		/// The resolved service name.
171		std::string service_name;
172		};
173
174		/** Resolves host names and services to endpoints, from a coroutine.
175
176		This class provides asynchronous DNS resolution operations that return
177		awaitable types. Each operation participates in the affine awaitable
178		protocol, ensuring coroutines resume on the correct executor.
179
180		@par Thread Safety
181		Distinct objects: Safe.@n
182		Shared objects: Unsafe. A resolver must not have concurrent resolve
183		operations.
184
185		@par Semantics
186		Wraps platform DNS resolution (`getaddrinfo`/`getnameinfo`).
187		Operations dispatch to OS resolver APIs via the `io_context`
188		thread pool.
189
190		@par Example
191		@par !example resolver
192		*/
193		class BOOST_COROSIO_DECL resolver : public io_object
194		{
195		struct resolve_awaitable
196		: detail::value_op_base<resolve_awaitable, std::vector<endpoint>>
197		{
198		private:
199		friend resolver;
200
201	29x	resolve_awaitable(
202		resolver& r,
203		std::string_view host,
204		std::string_view service,
205		resolve_flags flags) noexcept
206	58x	: r_(r)
207	58x	, host_(host)
208	58x	, service_(service)
209	29x	, flags_(flags)
210		{
211	29x	}
212
213		friend detail::value_op_base<resolve_awaitable, std::vector<endpoint>>;
214		resolver& r_;
215		std::string host_;
216		std::string service_;
217		resolve_flags flags_;
218
219		std::coroutine_handle<>
220	28x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
221		{
222	84x	return r_.get().resolve(
223	84x	h, ex, host_, service_, flags_, token_, &ec_, &value_);
224		}
225		};
226
227		struct resolve_host_awaitable
228		: detail::value_op_base<resolve_host_awaitable, std::vector<endpoint>>
229		{
230		private:
231		friend resolver;
232
233	6x	resolve_host_awaitable(
234		resolver& r, std::string_view host, resolve_flags flags) noexcept
235	12x	: r_(r)
236	12x	, host_(host)
237	6x	, flags_(flags)
238		{
239	6x	}
240
241		friend detail::
242		value_op_base<resolve_host_awaitable, std::vector<endpoint>>;
243		resolver& r_;
244		std::string host_;
245		resolve_flags flags_;
246
247		std::coroutine_handle<>
248	5x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
249		{
250		// An empty service reaches the system resolver as null,
251		// which is the host-only query
252	15x	return r_.get().resolve(
253	15x	h, ex, host_, {}, flags_, token_, &ec_, &value_);
254		}
255
256		public:
257		// Shadows the base: the endpoint result is reshaped into
258		// the honest address list
259		[[nodiscard]] capy::io_result<std::vector<ip_address>>
260	6x	await_resume() const
261		{
262	6x	std::vector<ip_address> addrs;
263	6x	addrs.reserve(value_.size());
264	9x	for (auto const& entry : value_)
265		{
266	3x	auto a = entry.address();
267	3x	bool duplicate = false;
268	3x	for (auto const& seen : addrs)
269		{
270	✗	if (seen == a)
271		{
272	✗	duplicate = true;
273	✗	break;
274		}
275		}
276		// The same address can come back more than once
277		// (mixed name sources, repeated records); each
278		// address is reported once
279	3x	if (!duplicate)
280	3x	addrs.push_back(a);
281		}
282	12x	return {ec_, std::move(addrs)};
283	6x	}
284		};
285
286		struct reverse_resolve_awaitable
287		: detail::value_op_base<reverse_resolve_awaitable, endpoint_name>
288		{
289		private:
290		friend resolver;
291
292	20x	reverse_resolve_awaitable(
293		resolver& r, endpoint const& ep, reverse_flags flags) noexcept
294	40x	: r_(r)
295	20x	, ep_(ep)
296	20x	, flags_(flags)
297		{
298	20x	}
299
300		friend detail::value_op_base<reverse_resolve_awaitable, endpoint_name>;
301
302		resolver& r_;
303		endpoint ep_;
304		reverse_flags flags_;
305
306		std::coroutine_handle<>
307	19x	dispatch(std::coroutine_handle<> h, capy::executor_ref ex) const
308		{
309	38x	return r_.get().reverse_resolve(
310	38x	h, ex, ep_, flags_, token_, &ec_, &value_);
311		}
312		};
313
314		public:
315		/** Destructor.
316
317		Cancels any pending operations.
318		*/
319		~resolver() override;
320
321		/** Construct a resolver from an execution context.
322
323		@param ctx The execution context that owns this resolver.
324		*/
325		explicit resolver(capy::execution_context& ctx);
326
327		/** Construct a resolver from an executor.
328
329		The resolver is associated with the executor's context.
330
331		@param ex The executor whose context owns the resolver.
332		*/
333		template<class Ex>
334		requires(!std::same_as<std::remove_cvref_t<Ex>, resolver>) &&
335		capy::Executor<Ex>
336	1x	explicit resolver(Ex const& ex) : resolver(ex.context())
337		{
338	1x	}
339
340		/** Move constructor.
341
342		Transfers ownership of the resolver resources. After the move,
343		@p other is in a moved-from state and may only be destroyed or
344		assigned to.
345
346		@param other The resolver to move from.
347
348		@pre No awaitables returned by @p other's `resolve` methods
349		exist.
350		@pre The execution context associated with @p other must
351		outlive this resolver.
352		*/
353	2x	resolver(resolver&& other) noexcept : io_object(std::move(other)) {}
354
355		/** Move assignment operator.
356
357		Destroys the current implementation and transfers ownership
358		from @p other. After the move, @p other is in a moved-from
359		state and may only be destroyed or assigned to.
360
361		@param other The resolver to move from.
362
363		@pre No awaitables returned by either `*this` or @p other's
364		`resolve` methods exist.
365		@pre The execution context associated with @p other must
366		outlive this resolver.
367
368		@return Reference to this resolver.
369		*/
370	2x	resolver& operator=(resolver&& other) noexcept
371		{
372	2x	if (this != &other)
373	2x	h_ = std::move(other.h_);
374	2x	return *this;
375		}
376
377		/// Copy construction is disabled; the handle is uniquely owned.
378		resolver(resolver const&) = delete;
379		/// Copy assignment is disabled; the handle is uniquely owned.
380		resolver& operator=(resolver const&) = delete;
381
382		/** Initiate an asynchronous resolve operation.
383
384		Resolves the host and service names into a list of endpoints.
385
386		This resolver must outlive the returned awaitable.
387
388		@param host A string identifying a location. May be a descriptive
389		name or a numeric address string.
390
391		@param service A string identifying the requested service. This may
392		be a descriptive name or a numeric string corresponding to a
393		port number.
394
395		@return An awaitable that completes with
396		`io_result<std::vector<endpoint>>`.
397
398		@par Example
399		@par !example forward_resolve
400		*/
401	13x	[[nodiscard]] auto resolve(std::string_view host, std::string_view service)
402		{
403	13x	return resolve_awaitable(*this, host, service, resolve_flags::none);
404		}
405
406		/** Initiate an asynchronous host-only resolve operation.
407
408		Resolves a host name into its addresses, with no service or
409		port involved — the query `getaddrinfo` performs with a null
410		service. Use this when the host and port travel separately,
411		as they do in most configuration.
412
413		Each address appears once in the result even when the query
414		reports it more than once, and link-local results keep
415		their zone.
416
417		@param host The host name or numeric address string.
418
419		@return An awaitable that completes with
420		`io_result<std::vector<ip_address>>`.
421
422		@par Example
423		@par !example host_only_resolve
424		*/
425	3x	[[nodiscard]] auto resolve(std::string_view host)
426		{
427	3x	return resolve_host_awaitable(*this, host, resolve_flags::none);
428		}
429
430		/** Initiate an asynchronous host-only resolve operation with flags.
431
432		@param host The host name or numeric address string.
433		@param flags Resolution behavior flags.
434
435		@return An awaitable that completes with
436		`io_result<std::vector<ip_address>>`.
437		*/
438	3x	[[nodiscard]] auto resolve(std::string_view host, resolve_flags flags)
439		{
440	3x	return resolve_host_awaitable(*this, host, flags);
441		}
442
443		/** Initiate an asynchronous resolve operation with flags.
444
445		Resolves the host and service names into a list of endpoints.
446
447		This resolver must outlive the returned awaitable.
448
449		@param host A string identifying a location.
450
451		@param service A string identifying the requested service.
452
453		@param flags Flags controlling resolution behavior.
454
455		@return An awaitable that completes with
456		`io_result<std::vector<endpoint>>`.
457		*/
458	16x	[[nodiscard]] auto resolve(
459		std::string_view host, std::string_view service, resolve_flags flags)
460		{
461	16x	return resolve_awaitable(*this, host, service, flags);
462		}
463
464		/** Initiate an asynchronous reverse resolve operation.
465
466		Resolves an endpoint into a hostname and service name using
467		reverse DNS lookup (PTR record query).
468
469		This resolver must outlive the returned awaitable.
470
471		@param ep The endpoint to resolve.
472
473		@return An awaitable that completes with
474		`io_result<endpoint_name>`.
475
476		@par Example
477		@par !example reverse_resolve
478		*/
479	11x	[[nodiscard]] auto resolve(endpoint const& ep)
480		{
481	11x	return reverse_resolve_awaitable(*this, ep, reverse_flags::none);
482		}
483
484		/** Initiate an asynchronous reverse resolve operation with flags.
485
486		Resolves an endpoint into a hostname and service name using
487		reverse DNS lookup (PTR record query).
488
489		This resolver must outlive the returned awaitable.
490
491		@param ep The endpoint to resolve.
492
493		@param flags Flags controlling resolution behavior. See reverse_flags.
494
495		@return An awaitable that completes with
496		`io_result<endpoint_name>`.
497		*/
498	9x	[[nodiscard]] auto resolve(endpoint const& ep, reverse_flags flags)
499		{
500	9x	return reverse_resolve_awaitable(*this, ep, flags);
501		}
502
503		/** Cancel any pending asynchronous operations.
504
505		A resolve transfers no bytes, so a cancellation always wins. An
506		operation reports `errc::operation_canceled` even when the lookup
507		had already completed when the cancellation landed. Check
508		`ec == cond::canceled` for a portable comparison.
509		*/
510		void cancel() noexcept;
511
512		public:
513		/** Define backend hooks for DNS resolution operations.
514
515		Platform backends derive from this to implement forward and
516		reverse DNS resolution via `getaddrinfo`/`getnameinfo`.
517		*/
518		struct implementation : io_object::implementation
519		{
520		/** Initiate an asynchronous forward DNS resolution.
521
522		@param h Coroutine handle to resume on completion.
523		@param ex Executor for dispatching the completion.
524		@param host The host name or address literal to resolve.
525		@param service The service name or port number.
526		@param flags Flags controlling the lookup.
527		@param token Stop token for cancellation.
528		@param ec Output error code.
529		@param results Output resolver results.
530
531		@return Coroutine handle to resume immediately.
532		*/
533		virtual std::coroutine_handle<> resolve(
534		std::coroutine_handle<> h,
535		capy::executor_ref ex,
536		std::string_view host,
537		std::string_view service,
538		resolve_flags flags,
539		std::stop_token token,
540		std::error_code* ec,
541		std::vector<endpoint>* results) = 0;
542
543		/** Initiate an asynchronous reverse DNS resolution.
544
545		@param h Coroutine handle to resume on completion.
546		@param ex Executor for dispatching the completion.
547		@param ep The endpoint to resolve.
548		@param flags Flags controlling the lookup.
549		@param token Stop token for cancellation.
550		@param ec Output error code.
551		@param result Output reverse-resolution result.
552
553		@return Coroutine handle to resume immediately.
554		*/
555		virtual std::coroutine_handle<> reverse_resolve(
556		std::coroutine_handle<> h,
557		capy::executor_ref ex,
558		endpoint const& ep,
559		reverse_flags flags,
560		std::stop_token token,
561		std::error_code* ec,
562		endpoint_name* result) = 0;
563
564		/// Cancel pending resolve operations.
565		virtual void cancel() noexcept = 0;
566		};
567
568		protected:
569		/** Adopt an existing handle.
570
571		@param h The handle the resolver takes ownership of.
572		*/
573		explicit resolver(handle h) noexcept : io_object(std::move(h)) {}
574
575		private:
576	59x	inline implementation& get() const noexcept
577		{
578	59x	return static_cast<implementation>(h_.get());
579		}
580		};
581
582		} // namespace boost::corosio
583
584		#endif
585