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include/boost/corosio/native/detail/posix/posix_resolver.hpp

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posix_resolver.hpp
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boost::corosio::detail::posix_resolver::resolve_op::resolve_op() :182 68x 100.0% 100.0% boost::corosio::detail::posix_resolver::reverse_resolve_op::reverse_resolve_op() :205 68x 100.0% 100.0% boost::corosio::detail::posix_resolver::reuse() :241 64x 100.0% 71.0%
Line TLA Hits Source Code
1 //
2 // Copyright (c) 2026 Steve Gerbino
3 //
4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 //
7 // Official repository: https://github.com/cppalliance/corosio
8 //
9
10 #ifndef BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_RESOLVER_HPP
11 #define BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_RESOLVER_HPP
12
13 #include <boost/corosio/detail/platform.hpp>
14
15 #if BOOST_COROSIO_POSIX
16
17 #include <boost/corosio/detail/config.hpp>
18 #include <boost/corosio/resolver.hpp>
19 #include <boost/capy/ex/execution_context.hpp>
20
21 #include <boost/corosio/native/detail/endpoint_convert.hpp>
22 #include <boost/corosio/detail/intrusive.hpp>
23 #include <boost/corosio/detail/dispatch_coro.hpp>
24 #include <boost/corosio/detail/scheduler_op.hpp>
25 #include <boost/corosio/detail/thread_pool.hpp>
26 #include <boost/corosio/native/detail/coro_op.hpp>
27
28 #include <boost/corosio/detail/scheduler.hpp>
29 #include <boost/capy/ex/executor_ref.hpp>
30 #include <coroutine>
31 #include <boost/capy/error.hpp>
32
33 #include <netdb.h>
34 #include <netinet/in.h>
35 #include <sys/socket.h>
36
37 #include <atomic>
38 #include <memory>
39 #include <optional>
40 #include <stop_token>
41 #include <string>
42
43 /*
44 POSIX Resolver Service
45 ======================
46
47 POSIX getaddrinfo() is a blocking call that cannot be monitored with
48 epoll/kqueue/io_uring. Blocking calls are dispatched to a shared
49 resolver_thread_pool service which reuses threads across operations.
50
51 Cancellation
52 ------------
53 getaddrinfo() cannot be interrupted mid-call. We use an atomic flag to
54 indicate cancellation was requested. The worker thread checks this flag
55 after getaddrinfo() returns and reports the appropriate error.
56
57 Class Hierarchy
58 ---------------
59 - posix_resolver_service (execution_context service, one per context)
60 - Owns all posix_resolver instances via a recycling object_pool
61 - Stores scheduler* for posting completions
62 - posix_resolver (one per resolver object)
63 - Contains embedded resolve_op and reverse_resolve_op for reuse
64 - Each op holds an object_ref keepalive while its pool work is
65 in flight, preventing premature destruction
66 - resolve_op (forward resolution state)
67 - Uses getaddrinfo() to resolve host/service to endpoints
68 - reverse_resolve_op (reverse resolution state)
69 - Uses getnameinfo() to resolve endpoint to host/service
70
71 Completion Flow
72 ---------------
73 Forward resolution:
74 1. resolve() sets up op_, posts work to the thread pool
75 2. Pool thread runs getaddrinfo() (blocking)
76 3. Pool thread stores results in op_.stored_results
77 4. Pool thread calls svc_.post(&op_) to queue completion
78 5. Scheduler invokes op_() which resumes the coroutine
79
80 Reverse resolution follows the same pattern using getnameinfo().
81
82 Single-Inflight Constraint
83 --------------------------
84 Each resolver has ONE embedded op_ for forward and ONE reverse_op_ for
85 reverse resolution. Concurrent operations of the same type on the same
86 resolver would corrupt state. Users must serialize operations per-resolver.
87
88 Shutdown
89 --------
90 The resolver service cancels all resolvers and releases the
91 service's own reference on each; the recycling pool frees (rather
92 than recycles) once each resolver's in-flight pool work also
93 releases its reference. The thread pool service shuts down
94 separately via execution_context service ordering, joining all
95 worker threads.
96 */
97
98 namespace boost::corosio::detail {
99
100 struct scheduler;
101
102 namespace posix_resolver_detail {
103
104 // Convert resolve_flags to addrinfo ai_flags
105 int flags_to_hints(resolve_flags flags);
106
107 // Convert reverse_flags to getnameinfo NI_* flags
108 int flags_to_ni_flags(reverse_flags flags);
109
110 // Convert addrinfo results to endpoints
111 std::vector<endpoint> convert_results(struct addrinfo* ai);
112
113 // Convert getaddrinfo error codes to std::error_code
114 std::error_code make_gai_error(int gai_err);
115
116 } // namespace posix_resolver_detail
117
118 class posix_resolver_service;
119
120 /** Resolver implementation for POSIX backends.
121
122 Each resolver instance contains a single embedded operation object (op_)
123 that is reused for each resolve() call. This design avoids per-operation
124 heap allocation but imposes a critical constraint:
125
126 @par Single-Inflight Contract
127
128 Only ONE resolve operation may be in progress at a time per resolver
129 instance. Calling resolve() while a previous resolve() is still pending
130 results in undefined behavior:
131
132 - The new call overwrites op_ fields (host, service, coroutine handle)
133 - The worker thread from the first call reads corrupted state
134 - The wrong coroutine may be resumed, or resumed multiple times
135 - Data races occur on non-atomic op_ members
136
137 @par Safe Usage Patterns
138
139 @code
140 // CORRECT: Sequential resolves
141 auto [ec1, r1] = co_await resolver.resolve("host1", "80");
142 auto [ec2, r2] = co_await resolver.resolve("host2", "80");
143
144 // CORRECT: Parallel resolves with separate resolver instances
145 resolver r1(ctx), r2(ctx);
146 auto [ec1, res1] = co_await r1.resolve("host1", "80"); // in one coroutine
147 auto [ec2, res2] = co_await r2.resolve("host2", "80"); // in another
148
149 // WRONG: Concurrent resolves on same resolver
150 // These may run concurrently if launched in parallel - UNDEFINED BEHAVIOR
151 auto f1 = resolver.resolve("host1", "80");
152 auto f2 = resolver.resolve("host2", "80"); // BAD: overlaps with f1
153 @endcode
154
155 @par Thread Safety
156 Distinct objects: Safe.
157 Shared objects: Unsafe. See single-inflight contract above.
158 */
159 class posix_resolver final
160 : public resolver::implementation
161 , public intrusive_list<posix_resolver>::node
162 {
163 friend class posix_resolver_service;
164
165 public:
166 // resolve_op - operation state for a single DNS resolution
167
168 struct resolve_op : coro_op
169 {
170 /// Where the endpoints are handed back.
171 std::vector<endpoint>* out = nullptr;
172
173 // Input parameters (owned copies for thread safety)
174 std::string host;
175 std::string service;
176 resolve_flags flags = resolve_flags::none;
177
178 // Result storage (populated by worker thread)
179 std::vector<endpoint> stored_results;
180 int gai_error = 0;
181
182 68x resolve_op() = default;
183
184 void reset() noexcept;
185 void operator()() override;
186 void destroy() override;
187 };
188
189 // reverse_resolve_op - operation state for reverse DNS resolution
190
191 struct reverse_resolve_op : coro_op
192 {
193 /// Where the name is handed back.
194 endpoint_name* result_out = nullptr;
195
196 // Input parameters
197 endpoint ep;
198 reverse_flags flags = reverse_flags::none;
199
200 // Result storage (populated by worker thread)
201 std::string stored_host;
202 std::string stored_service;
203 int gai_error = 0;
204
205 68x reverse_resolve_op() = default;
206
207 void reset() noexcept;
208 void operator()() override;
209 void destroy() override;
210 };
211
212 /// Embedded pool work item for thread pool dispatch.
213 struct pool_op : pool_work_item
214 {
215 /// Resolver that owns this work item.
216 posix_resolver* resolver_ = nullptr;
217
218 /// Prevent impl destruction while work is in flight.
219 detail::object_ref ref_;
220 };
221
222 explicit posix_resolver(posix_resolver_service& svc) noexcept;
223
224 /// Recycle into the owning service's pool. Defined out-of-line
225 /// after posix_resolver_service for its complete type.
226 void retire() noexcept override;
227
228 /** Reset for recycling.
229
230 Both ops' own `reset()` already clears `host`/`service`/
231 `stored_host`/`stored_service` via `.clear()` (preserving their
232 allocated capacity — the whole point of recycling), run at the
233 top of the next `resolve()`/`reverse_resolve()`. refs_ cannot
234 reach zero while a resolve is in flight (the pool op's
235 `object_ref` holds a reference for the duration), so asserting
236 `stop_cb` disengaged on both ops is a precondition check, not
237 a defensive one.
238
239 @pre refs_ == 0, no resolve in flight.
240 */
241 64x void reuse() noexcept
242 {
243 64x BOOST_COROSIO_ASSERT(!op_.stop_cb);
244 64x BOOST_COROSIO_ASSERT(!reverse_op_.stop_cb);
245 64x }
246
247 std::coroutine_handle<> resolve(
248 std::coroutine_handle<>,
249 capy::executor_ref,
250 std::string_view host,
251 std::string_view service,
252 resolve_flags flags,
253 std::stop_token,
254 std::error_code*,
255 std::vector<endpoint>*) override;
256
257 std::coroutine_handle<> reverse_resolve(
258 std::coroutine_handle<>,
259 capy::executor_ref,
260 endpoint const& ep,
261 reverse_flags flags,
262 std::stop_token,
263 std::error_code*,
264 endpoint_name*) override;
265
266 void cancel() noexcept override;
267
268 resolve_op op_;
269 reverse_resolve_op reverse_op_;
270
271 /// Pool work item for forward resolution.
272 pool_op resolve_pool_op_;
273
274 /// Pool work item for reverse resolution.
275 pool_op reverse_pool_op_;
276
277 /// Execute blocking `getaddrinfo()` on a pool thread.
278 static void do_resolve_work(pool_work_item*) noexcept;
279
280 /// Execute blocking `getnameinfo()` on a pool thread.
281 static void do_reverse_resolve_work(pool_work_item*) noexcept;
282
283 private:
284 posix_resolver_service& svc_;
285 };
286
287 } // namespace boost::corosio::detail
288
289 #endif // BOOST_COROSIO_POSIX
290
291 #endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_RESOLVER_HPP
292