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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() :179 64x 100.0% 100.0% boost::corosio::detail::posix_resolver::reverse_resolve_op::reverse_resolve_op() :202 64x 100.0% 100.0%
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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 shared_ptr
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 - Uses shared_from_this to prevent premature destruction
65 - resolve_op (forward resolution state)
66 - Uses getaddrinfo() to resolve host/service to endpoints
67 - reverse_resolve_op (reverse resolution state)
68 - Uses getnameinfo() to resolve endpoint to host/service
69
70 Completion Flow
71 ---------------
72 Forward resolution:
73 1. resolve() sets up op_, posts work to the thread pool
74 2. Pool thread runs getaddrinfo() (blocking)
75 3. Pool thread stores results in op_.stored_results
76 4. Pool thread calls svc_.post(&op_) to queue completion
77 5. Scheduler invokes op_() which resumes the coroutine
78
79 Reverse resolution follows the same pattern using getnameinfo().
80
81 Single-Inflight Constraint
82 --------------------------
83 Each resolver has ONE embedded op_ for forward and ONE reverse_op_ for
84 reverse resolution. Concurrent operations of the same type on the same
85 resolver would corrupt state. Users must serialize operations per-resolver.
86
87 Shutdown
88 --------
89 The resolver service cancels all resolvers and clears the impl map.
90 The thread pool service shuts down separately via execution_context
91 service ordering, joining all worker threads.
92 */
93
94 namespace boost::corosio::detail {
95
96 struct scheduler;
97
98 namespace posix_resolver_detail {
99
100 // Convert resolve_flags to addrinfo ai_flags
101 int flags_to_hints(resolve_flags flags);
102
103 // Convert reverse_flags to getnameinfo NI_* flags
104 int flags_to_ni_flags(reverse_flags flags);
105
106 // Convert addrinfo results to endpoints
107 std::vector<endpoint> convert_results(struct addrinfo* ai);
108
109 // Convert getaddrinfo error codes to std::error_code
110 std::error_code make_gai_error(int gai_err);
111
112 } // namespace posix_resolver_detail
113
114 class posix_resolver_service;
115
116 /** Resolver implementation for POSIX backends.
117
118 Each resolver instance contains a single embedded operation object (op_)
119 that is reused for each resolve() call. This design avoids per-operation
120 heap allocation but imposes a critical constraint:
121
122 @par Single-Inflight Contract
123
124 Only ONE resolve operation may be in progress at a time per resolver
125 instance. Calling resolve() while a previous resolve() is still pending
126 results in undefined behavior:
127
128 - The new call overwrites op_ fields (host, service, coroutine handle)
129 - The worker thread from the first call reads corrupted state
130 - The wrong coroutine may be resumed, or resumed multiple times
131 - Data races occur on non-atomic op_ members
132
133 @par Safe Usage Patterns
134
135 @code
136 // CORRECT: Sequential resolves
137 auto [ec1, r1] = co_await resolver.resolve("host1", "80");
138 auto [ec2, r2] = co_await resolver.resolve("host2", "80");
139
140 // CORRECT: Parallel resolves with separate resolver instances
141 resolver r1(ctx), r2(ctx);
142 auto [ec1, res1] = co_await r1.resolve("host1", "80"); // in one coroutine
143 auto [ec2, res2] = co_await r2.resolve("host2", "80"); // in another
144
145 // WRONG: Concurrent resolves on same resolver
146 // These may run concurrently if launched in parallel - UNDEFINED BEHAVIOR
147 auto f1 = resolver.resolve("host1", "80");
148 auto f2 = resolver.resolve("host2", "80"); // BAD: overlaps with f1
149 @endcode
150
151 @par Thread Safety
152 Distinct objects: Safe.
153 Shared objects: Unsafe. See single-inflight contract above.
154 */
155 class posix_resolver final
156 : public resolver::implementation
157 , public std::enable_shared_from_this<posix_resolver>
158 , public intrusive_list<posix_resolver>::node
159 {
160 friend class posix_resolver_service;
161
162 public:
163 // resolve_op - operation state for a single DNS resolution
164
165 struct resolve_op : coro_op
166 {
167 /// Where the endpoints are handed back.
168 std::vector<endpoint>* out = nullptr;
169
170 // Input parameters (owned copies for thread safety)
171 std::string host;
172 std::string service;
173 resolve_flags flags = resolve_flags::none;
174
175 // Result storage (populated by worker thread)
176 std::vector<endpoint> stored_results;
177 int gai_error = 0;
178
179 64x resolve_op() = default;
180
181 void reset() noexcept;
182 void operator()() override;
183 void destroy() override;
184 };
185
186 // reverse_resolve_op - operation state for reverse DNS resolution
187
188 struct reverse_resolve_op : coro_op
189 {
190 /// Where the name is handed back.
191 endpoint_name* result_out = nullptr;
192
193 // Input parameters
194 endpoint ep;
195 reverse_flags flags = reverse_flags::none;
196
197 // Result storage (populated by worker thread)
198 std::string stored_host;
199 std::string stored_service;
200 int gai_error = 0;
201
202 64x reverse_resolve_op() = default;
203
204 void reset() noexcept;
205 void operator()() override;
206 void destroy() override;
207 };
208
209 /// Embedded pool work item for thread pool dispatch.
210 struct pool_op : pool_work_item
211 {
212 /// Resolver that owns this work item.
213 posix_resolver* resolver_ = nullptr;
214
215 /// Prevent impl destruction while work is in flight.
216 std::shared_ptr<posix_resolver> ref_;
217 };
218
219 explicit posix_resolver(posix_resolver_service& svc) noexcept;
220
221 std::coroutine_handle<> resolve(
222 std::coroutine_handle<>,
223 capy::executor_ref,
224 std::string_view host,
225 std::string_view service,
226 resolve_flags flags,
227 std::stop_token,
228 std::error_code*,
229 std::vector<endpoint>*) override;
230
231 std::coroutine_handle<> reverse_resolve(
232 std::coroutine_handle<>,
233 capy::executor_ref,
234 endpoint const& ep,
235 reverse_flags flags,
236 std::stop_token,
237 std::error_code*,
238 endpoint_name*) override;
239
240 void cancel() noexcept override;
241
242 resolve_op op_;
243 reverse_resolve_op reverse_op_;
244
245 /// Pool work item for forward resolution.
246 pool_op resolve_pool_op_;
247
248 /// Pool work item for reverse resolution.
249 pool_op reverse_pool_op_;
250
251 /// Execute blocking `getaddrinfo()` on a pool thread.
252 static void do_resolve_work(pool_work_item*) noexcept;
253
254 /// Execute blocking `getnameinfo()` on a pool thread.
255 static void do_reverse_resolve_work(pool_work_item*) noexcept;
256
257 private:
258 posix_resolver_service& svc_;
259 };
260
261 } // namespace boost::corosio::detail
262
263 #endif // BOOST_COROSIO_POSIX
264
265 #endif // BOOST_COROSIO_NATIVE_DETAIL_POSIX_POSIX_RESOLVER_HPP
266