. /include/boost/corosio /connect.hpp
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1   // 1   //
2   // Copyright (c) 2026 Michael Vandeberg 2   // Copyright (c) 2026 Michael Vandeberg
3   // 3   //
4   // Distributed under the Boost Software License, Version 1.0. (See accompanying 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) 5   // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6   // 6   //
7   // Official repository: https://github.com/cppalliance/corosio 7   // Official repository: https://github.com/cppalliance/corosio
8   // 8   //
9   9  
10   #ifndef BOOST_COROSIO_CONNECT_HPP 10   #ifndef BOOST_COROSIO_CONNECT_HPP
11   #define BOOST_COROSIO_CONNECT_HPP 11   #define BOOST_COROSIO_CONNECT_HPP
12   12  
13   #include <boost/corosio/detail/config.hpp> 13   #include <boost/corosio/detail/config.hpp>
14   14  
15   #include <boost/capy/cond.hpp> 15   #include <boost/capy/cond.hpp>
16   #include <boost/capy/io_result.hpp> 16   #include <boost/capy/io_result.hpp>
17   #include <boost/capy/task.hpp> 17   #include <boost/capy/task.hpp>
18   18  
19   #include <concepts> 19   #include <concepts>
20   #include <iterator> 20   #include <iterator>
21   #include <ranges> 21   #include <ranges>
22   #include <system_error> 22   #include <system_error>
23   #include <utility> 23   #include <utility>
24   24  
25   /* 25   /*
26   Range-based composed connect operation. 26   Range-based composed connect operation.
27   27  
28   These free functions try each endpoint in a range (or iterator pair) 28   These free functions try each endpoint in a range (or iterator pair)
29   in order, returning on the first successful connect. Between attempts 29   in order, returning on the first successful connect. Between attempts
30   the socket is closed so that the next attempt can auto-open with the 30   the socket is closed so that the next attempt can auto-open with the
31   correct address family (e.g. going from IPv4 to IPv6 candidates). 31   correct address family (e.g. going from IPv4 to IPv6 candidates).
32   32  
33   The iteration semantics follow Boost.Asio's range/iterator async_connect: 33   The iteration semantics follow Boost.Asio's range/iterator async_connect:
34   on success, the successful endpoint (or its iterator) is returned; on 34   on success, the successful endpoint (or its iterator) is returned; on
35   all-fail, the last attempt's error code is returned; on an empty range 35   all-fail, the last attempt's error code is returned; on an empty range
36   (or when a connect_condition rejects every candidate), 36   (or when a connect_condition rejects every candidate),
37   std::errc::no_such_device_or_address is returned, matching the error 37   std::errc::no_such_device_or_address is returned, matching the error
38   the resolver uses for "no results" in posix_resolver_service. 38   the resolver uses for "no results" in posix_resolver_service.
39   39  
40   The operation is a plain coroutine; cancellation is propagated to the 40   The operation is a plain coroutine; cancellation is propagated to the
41   inner per-endpoint connect via the affine awaitable protocol on io_env. 41   inner per-endpoint connect via the affine awaitable protocol on io_env.
42   */ 42   */
43   43  
44   namespace boost::corosio { 44   namespace boost::corosio {
45   45  
46   namespace detail { 46   namespace detail {
47   47  
48   /* Always-true connect condition used by the overloads that take no 48   /* Always-true connect condition used by the overloads that take no
49   user-supplied predicate. Kept at namespace-detail scope so it has a 49   user-supplied predicate. Kept at namespace-detail scope so it has a
50   stable linkage name across translation units. */ 50   stable linkage name across translation units. */
51   struct default_connect_condition 51   struct default_connect_condition
52   { 52   {
53   template<class Endpoint> 53   template<class Endpoint>
HITCBC 54   20 bool operator()(std::error_code const&, Endpoint const&) const noexcept 54   20 bool operator()(std::error_code const&, Endpoint const&) const noexcept
55   { 55   {
HITCBC 56   20 return true; 56   20 return true;
57   } 57   }
58   }; 58   };
59   59  
60   } // namespace detail 60   } // namespace detail
61   61  
62   /* Forward declarations so the non-condition overloads can delegate 62   /* Forward declarations so the non-condition overloads can delegate
63   to the condition overloads via qualified lookup (qualified calls 63   to the condition overloads via qualified lookup (qualified calls
64   bind to the overload set visible at definition, not instantiation). */ 64   bind to the overload set visible at definition, not instantiation). */
65   65  
66   template<class Socket, std::ranges::input_range Range, class ConnectCondition> 66   template<class Socket, std::ranges::input_range Range, class ConnectCondition>
67   requires std::convertible_to< 67   requires std::convertible_to<
68   std::ranges::range_reference_t<Range>, 68   std::ranges::range_reference_t<Range>,
69   typename Socket::endpoint_type> && 69   typename Socket::endpoint_type> &&
70   std::predicate< 70   std::predicate<
71   ConnectCondition&, 71   ConnectCondition&,
72   std::error_code const&, 72   std::error_code const&,
73   typename Socket::endpoint_type const&> 73   typename Socket::endpoint_type const&>
74   capy::task<capy::io_result<typename Socket::endpoint_type>> 74   capy::task<capy::io_result<typename Socket::endpoint_type>>
75   connect(Socket& s, Range endpoints, ConnectCondition cond); 75   connect(Socket& s, Range endpoints, ConnectCondition cond);
76   76  
77   template<class Socket, std::input_iterator Iter, class ConnectCondition> 77   template<class Socket, std::input_iterator Iter, class ConnectCondition>
78   requires std::convertible_to< 78   requires std::convertible_to<
79   std::iter_reference_t<Iter>, 79   std::iter_reference_t<Iter>,
80   typename Socket::endpoint_type> && 80   typename Socket::endpoint_type> &&
81   std::predicate< 81   std::predicate<
82   ConnectCondition&, 82   ConnectCondition&,
83   std::error_code const&, 83   std::error_code const&,
84   typename Socket::endpoint_type const&> 84   typename Socket::endpoint_type const&>
85   capy::task<capy::io_result<Iter>> 85   capy::task<capy::io_result<Iter>>
86   connect(Socket& s, Iter begin, Iter end, ConnectCondition cond); 86   connect(Socket& s, Iter begin, Iter end, ConnectCondition cond);
87   87  
88   /** Asynchronously connect a socket by trying each endpoint in a range. 88   /** Asynchronously connect a socket by trying each endpoint in a range.
89   89  
90   Each candidate is tried in order. Before each attempt the socket is 90   Each candidate is tried in order. Before each attempt the socket is
91   closed (so the next `connect` auto-opens with the candidate's 91   closed (so the next `connect` auto-opens with the candidate's
92   address family). On first successful connect, the operation 92   address family). On first successful connect, the operation
93   completes with the connected endpoint. 93   completes with the connected endpoint.
94   94  
95   @par Cancellation 95   @par Cancellation
96   Supports cancellation via the affine awaitable protocol. If a 96   Supports cancellation via the affine awaitable protocol. If a
97   per-endpoint connect completes with `capy::cond::canceled` the 97   per-endpoint connect completes with `capy::cond::canceled` the
98   operation completes immediately with that error and does not try 98   operation completes immediately with that error and does not try
99   further endpoints. 99   further endpoints.
100   100  
101   @param s The socket to connect. Must have a `connect(endpoint)` 101   @param s The socket to connect. Must have a `connect(endpoint)`
102   member returning an awaitable, plus `close()` and `is_open()`. 102   member returning an awaitable, plus `close()` and `is_open()`.
103 - If the socket is already open, it is closed before the 103 + If the socket is already open, it will be closed before the
104   first attempt. 104   first attempt.
105   @param endpoints A range of candidate endpoints. Taken by value 105   @param endpoints A range of candidate endpoints. Taken by value
106   so temporaries (e.g. the `std::vector<endpoint>` returned from 106   so temporaries (e.g. the `std::vector<endpoint>` returned from
107 - Passing an lvalue copies the range; pass an rvalue  
108 - (`std::move(endpoints)`) or use the iterator overload  
109 - (`connect(s, begin, end)`) to avoid the copy.  
110   `resolver::resolve`) remain alive for the coroutine's lifetime. 107   `resolver::resolve`) remain alive for the coroutine's lifetime.
111   108  
112   @return An awaitable completing with 109   @return An awaitable completing with
113   `capy::io_result<typename Socket::endpoint_type>`: 110   `capy::io_result<typename Socket::endpoint_type>`:
114 - - on success: default `error_code` and the connected endpoint; 111 + - on success: default error_code and the connected endpoint;
115   - on failure of all attempts: the error from the last attempt 112   - on failure of all attempts: the error from the last attempt
116   and a default-constructed endpoint; 113   and a default-constructed endpoint;
117   - on empty range: `std::errc::no_such_device_or_address` and a 114   - on empty range: `std::errc::no_such_device_or_address` and a
118   default-constructed endpoint. 115   default-constructed endpoint.
119 - @throws std::bad_alloc if copying an lvalue `endpoints` fails to  
120 - allocate.  
121 -  
122   116  
123   @note The socket is closed and re-opened before each attempt, so 117   @note The socket is closed and re-opened before each attempt, so
124   any socket options set by the caller (e.g. `no_delay`, 118   any socket options set by the caller (e.g. `no_delay`,
125   `reuse_address`) are lost. Apply options after this operation 119   `reuse_address`) are lost. Apply options after this operation
126   completes. 120   completes.
127   121  
128   If auto-opening the socket fails during an attempt, that attempt 122   If auto-opening the socket fails during an attempt, that attempt
129   completes with the open error (inherits the contract of 123   completes with the open error (inherits the contract of
130   `Socket::connect`). 124   `Socket::connect`).
131   125  
132   @par Example 126   @par Example
133   @par !example connect 127   @par !example connect
134   */ 128   */
135   template<class Socket, std::ranges::input_range Range> 129   template<class Socket, std::ranges::input_range Range>
136   requires std::convertible_to< 130   requires std::convertible_to<
137   std::ranges::range_reference_t<Range>, 131   std::ranges::range_reference_t<Range>,
138   typename Socket::endpoint_type> 132   typename Socket::endpoint_type>
139   capy::task<capy::io_result<typename Socket::endpoint_type>> 133   capy::task<capy::io_result<typename Socket::endpoint_type>>
HITCBC 140   12 connect(Socket& s, Range endpoints) 134   12 connect(Socket& s, Range endpoints)
141   { 135   {
142   detail::default_connect_condition cond; 136   detail::default_connect_condition cond;
HITCBC 143   12 return corosio::connect(s, std::move(endpoints), cond); 137   12 return corosio::connect(s, std::move(endpoints), cond);
144   } 138   }
145   139  
146   /** Asynchronously connect a socket by trying each endpoint in a range, 140   /** Asynchronously connect a socket by trying each endpoint in a range,
147   filtered by a user-supplied condition. 141   filtered by a user-supplied condition.
148   142  
149   For each candidate the condition is invoked as 143   For each candidate the condition is invoked as
150   `cond(last_ec, ep)` where `last_ec` is the error from the most 144   `cond(last_ec, ep)` where `last_ec` is the error from the most
151   recent attempt (default-constructed before the first attempt). If 145   recent attempt (default-constructed before the first attempt). If
152 - the condition returns `false`, the candidate is skipped. Otherwise, 146 + the condition returns `false` the candidate is skipped; otherwise a
153 - a connect is attempted. 147 + connect is attempted.
154   148  
155   @param s The socket to connect. See the non-condition overload for 149   @param s The socket to connect. See the non-condition overload for
156   requirements. 150   requirements.
157   @param endpoints A range of candidate endpoints, taken by value. 151   @param endpoints A range of candidate endpoints, taken by value.
158   @param cond A predicate invocable with 152   @param cond A predicate invocable with
159   `(std::error_code const&, typename Socket::endpoint_type const&)` 153   `(std::error_code const&, typename Socket::endpoint_type const&)`
160   returning a value contextually convertible to `bool`. 154   returning a value contextually convertible to `bool`.
161   155  
162   @return Same as the non-condition overload. If every candidate is 156   @return Same as the non-condition overload. If every candidate is
163   rejected, completes with `std::errc::no_such_device_or_address`. 157   rejected, completes with `std::errc::no_such_device_or_address`.
164   158  
165   If auto-opening the socket fails, the attempt completes with the 159   If auto-opening the socket fails, the attempt completes with the
166   open error. 160   open error.
167   */ 161   */
168   template<class Socket, std::ranges::input_range Range, class ConnectCondition> 162   template<class Socket, std::ranges::input_range Range, class ConnectCondition>
169   requires std::convertible_to< 163   requires std::convertible_to<
170   std::ranges::range_reference_t<Range>, 164   std::ranges::range_reference_t<Range>,
171   typename Socket::endpoint_type> && 165   typename Socket::endpoint_type> &&
172   std::predicate< 166   std::predicate<
173   ConnectCondition&, 167   ConnectCondition&,
174   std::error_code const&, 168   std::error_code const&,
175   typename Socket::endpoint_type const&> 169   typename Socket::endpoint_type const&>
176   capy::task<capy::io_result<typename Socket::endpoint_type>> 170   capy::task<capy::io_result<typename Socket::endpoint_type>>
HITCBC 177   16 connect(Socket& s, Range endpoints, ConnectCondition cond) 171   16 connect(Socket& s, Range endpoints, ConnectCondition cond)
178   { 172   {
179   using endpoint_type = typename Socket::endpoint_type; 173   using endpoint_type = typename Socket::endpoint_type;
180   174  
181   std::error_code last_ec; 175   std::error_code last_ec;
182   176  
183   for (auto&& e : endpoints) 177   for (auto&& e : endpoints)
184   { 178   {
185   endpoint_type ep = e; 179   endpoint_type ep = e;
186   180  
187   if (!cond( 181   if (!cond(
188   static_cast<std::error_code const&>(last_ec), 182   static_cast<std::error_code const&>(last_ec),
189   static_cast<endpoint_type const&>(ep))) 183   static_cast<endpoint_type const&>(ep)))
190   continue; 184   continue;
191   185  
192   if (s.is_open()) 186   if (s.is_open())
193   s.close(); 187   s.close();
194   188  
195   auto [ec] = co_await s.connect(ep); 189   auto [ec] = co_await s.connect(ep);
196   190  
197   if (!ec) 191   if (!ec)
198   co_return {std::error_code{}, std::move(ep)}; 192   co_return {std::error_code{}, std::move(ep)};
199   193  
200   if (ec == capy::cond::canceled) 194   if (ec == capy::cond::canceled)
201   co_return {ec, endpoint_type{}}; 195   co_return {ec, endpoint_type{}};
202   196  
203   last_ec = ec; 197   last_ec = ec;
204   } 198   }
205   199  
206   if (!last_ec) 200   if (!last_ec)
207   last_ec = std::make_error_code(std::errc::no_such_device_or_address); 201   last_ec = std::make_error_code(std::errc::no_such_device_or_address);
208   202  
209   co_return {last_ec, endpoint_type{}}; 203   co_return {last_ec, endpoint_type{}};
HITCBC 210   32 } 204   32 }
211   205  
212   /** Asynchronously connect a socket by trying each endpoint in an 206   /** Asynchronously connect a socket by trying each endpoint in an
213   iterator range. 207   iterator range.
214   208  
215   Behaves like the range overload, except the return value carries 209   Behaves like the range overload, except the return value carries
216   the iterator to the successfully connected endpoint on success, or 210   the iterator to the successfully connected endpoint on success, or
217   `end` on failure. This mirrors Boost.Asio's iterator-based 211   `end` on failure. This mirrors Boost.Asio's iterator-based
218   `async_connect`. 212   `async_connect`.
219   213  
220   @param s The socket to connect. 214   @param s The socket to connect.
221   @param begin The first candidate. 215   @param begin The first candidate.
222   @param end One past the last candidate. 216   @param end One past the last candidate.
223   217  
224   @return An awaitable completing with `capy::io_result<Iter>`: 218   @return An awaitable completing with `capy::io_result<Iter>`:
225 - - on success: default `error_code` and the iterator of the 219 + - on success: default error_code and the iterator of the
226   successful endpoint; 220   successful endpoint;
227   - on failure of all attempts: the error from the last attempt 221   - on failure of all attempts: the error from the last attempt
228   and `end`; 222   and `end`;
229   - on empty range: `std::errc::no_such_device_or_address` and 223   - on empty range: `std::errc::no_such_device_or_address` and
230   `end`. 224   `end`.
231   225  
232   If auto-opening the socket fails, the attempt completes with the 226   If auto-opening the socket fails, the attempt completes with the
233   open error. 227   open error.
234   */ 228   */
235   template<class Socket, std::input_iterator Iter> 229   template<class Socket, std::input_iterator Iter>
236   requires std::convertible_to< 230   requires std::convertible_to<
237   std::iter_reference_t<Iter>, 231   std::iter_reference_t<Iter>,
238   typename Socket::endpoint_type> 232   typename Socket::endpoint_type>
239   capy::task<capy::io_result<Iter>> 233   capy::task<capy::io_result<Iter>>
HITCBC 240   4 connect(Socket& s, Iter begin, Iter end) 234   4 connect(Socket& s, Iter begin, Iter end)
241   { 235   {
242   return corosio::connect( 236   return corosio::connect(
HITCBC 243   4 s, std::move(begin), std::move(end), 237   4 s, std::move(begin), std::move(end),
HITCBC 244   4 detail::default_connect_condition{}); 238   4 detail::default_connect_condition{});
245   } 239   }
246   240  
247   /** Asynchronously connect a socket by trying each endpoint in an 241   /** Asynchronously connect a socket by trying each endpoint in an
248 -  
249 - @par Cancellation  
250 - Supports cancellation via the affine awaitable protocol. If a  
251 - per-endpoint connect completes with `capy::cond::canceled` the  
252 - operation completes immediately with that error and `end`, without  
253 - trying further endpoints.  
254   iterator range, filtered by a user-supplied condition. 242   iterator range, filtered by a user-supplied condition.
255   243  
256   @param s The socket to connect. 244   @param s The socket to connect.
257   @param begin The first candidate. 245   @param begin The first candidate.
258   @param end One past the last candidate. 246   @param end One past the last candidate.
259   @param cond A predicate invocable with 247   @param cond A predicate invocable with
260   `(std::error_code const&, typename Socket::endpoint_type const&)`. 248   `(std::error_code const&, typename Socket::endpoint_type const&)`.
261   249  
262   @return Same as the plain iterator overload. If every candidate is 250   @return Same as the plain iterator overload. If every candidate is
263   rejected, completes with `std::errc::no_such_device_or_address`. 251   rejected, completes with `std::errc::no_such_device_or_address`.
264   252  
265   If auto-opening the socket fails, the attempt completes with the 253   If auto-opening the socket fails, the attempt completes with the
266   open error. 254   open error.
267   */ 255   */
268   template<class Socket, std::input_iterator Iter, class ConnectCondition> 256   template<class Socket, std::input_iterator Iter, class ConnectCondition>
269   requires std::convertible_to< 257   requires std::convertible_to<
270   std::iter_reference_t<Iter>, 258   std::iter_reference_t<Iter>,
271   typename Socket::endpoint_type> && 259   typename Socket::endpoint_type> &&
272   std::predicate< 260   std::predicate<
273   ConnectCondition&, 261   ConnectCondition&,
274   std::error_code const&, 262   std::error_code const&,
275   typename Socket::endpoint_type const&> 263   typename Socket::endpoint_type const&>
276   capy::task<capy::io_result<Iter>> 264   capy::task<capy::io_result<Iter>>
HITCBC 277   4 connect(Socket& s, Iter begin, Iter end, ConnectCondition cond) 265   4 connect(Socket& s, Iter begin, Iter end, ConnectCondition cond)
278   { 266   {
279   using endpoint_type = typename Socket::endpoint_type; 267   using endpoint_type = typename Socket::endpoint_type;
280   268  
281   std::error_code last_ec; 269   std::error_code last_ec;
282   270  
283   for (Iter it = begin; it != end; ++it) 271   for (Iter it = begin; it != end; ++it)
284   { 272   {
285   endpoint_type ep = *it; 273   endpoint_type ep = *it;
286   274  
287   if (!cond( 275   if (!cond(
288   static_cast<std::error_code const&>(last_ec), 276   static_cast<std::error_code const&>(last_ec),
289   static_cast<endpoint_type const&>(ep))) 277   static_cast<endpoint_type const&>(ep)))
290   continue; 278   continue;
291   279  
292   if (s.is_open()) 280   if (s.is_open())
293   s.close(); 281   s.close();
294   282  
295   auto [ec] = co_await s.connect(ep); 283   auto [ec] = co_await s.connect(ep);
296   284  
297   if (!ec) 285   if (!ec)
298   co_return {std::error_code{}, std::move(it)}; 286   co_return {std::error_code{}, std::move(it)};
299   287  
300   if (ec == capy::cond::canceled) 288   if (ec == capy::cond::canceled)
301   co_return {ec, std::move(end)}; 289   co_return {ec, std::move(end)};
302   290  
303   last_ec = ec; 291   last_ec = ec;
304   } 292   }
305   293  
306   if (!last_ec) 294   if (!last_ec)
307   last_ec = std::make_error_code(std::errc::no_such_device_or_address); 295   last_ec = std::make_error_code(std::errc::no_such_device_or_address);
308   296  
309   co_return {last_ec, std::move(end)}; 297   co_return {last_ec, std::move(end)};
HITCBC 310   8 } 298   8 }
311   299  
312   } // namespace boost::corosio 300   } // namespace boost::corosio
313   301  
314   #endif 302   #endif