. /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 will be 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. `resolver_results` returned from 106   so temporaries (e.g. `resolver_results` returned from
107   `resolver::resolve`) remain alive for the coroutine's lifetime. 107   `resolver::resolve`) remain alive for the coroutine's lifetime.
108   Because the range is owned by the coroutine, passing an lvalue 108   Because the range is owned by the coroutine, passing an lvalue
109   copies it; since `resolver_results` is a 109   copies it; since `resolver_results` is a
110   `std::vector<resolver_entry>`, that is a deep copy of every entry. 110   `std::vector<resolver_entry>`, that is a deep copy of every entry.
111   Pass an rvalue (`std::move(results)`) or use the iterator overload 111   Pass an rvalue (`std::move(results)`) or use the iterator overload
112   (`connect(s, results.begin(), results.end())`) to avoid the copy. 112   (`connect(s, results.begin(), results.end())`) to avoid the copy.
113   113  
114   @return An awaitable completing with 114   @return An awaitable completing with
115   `capy::io_result<typename Socket::endpoint_type>`: 115   `capy::io_result<typename Socket::endpoint_type>`:
116   - on success: default error_code and the connected endpoint; 116   - on success: default error_code and the connected endpoint;
117   - on failure of all attempts: the error from the last attempt 117   - on failure of all attempts: the error from the last attempt
118   and a default-constructed endpoint; 118   and a default-constructed endpoint;
119   - on empty range: `std::errc::no_such_device_or_address` and a 119   - on empty range: `std::errc::no_such_device_or_address` and a
120   default-constructed endpoint. 120   default-constructed endpoint.
121   121  
122   @note The socket is closed and re-opened before each attempt, so 122   @note The socket is closed and re-opened before each attempt, so
123   any socket options set by the caller (e.g. `no_delay`, 123   any socket options set by the caller (e.g. `no_delay`,
124   `reuse_address`) are lost. Apply options after this operation 124   `reuse_address`) are lost. Apply options after this operation
125   completes. 125   completes.
126   126  
127   If auto-opening the socket fails during an attempt, that attempt 127   If auto-opening the socket fails during an attempt, that attempt
128   completes with the open error (inherits the contract of 128   completes with the open error (inherits the contract of
129   `Socket::connect`). 129   `Socket::connect`).
130   130  
131   @par Example 131   @par Example
132 - @code 132 + @par !example connect
133 - resolver r(ioc);  
134 - auto [rec, results] = co_await r.resolve("www.boost.org", "80");  
135 - if (rec) co_return;  
136 - tcp_socket s(ioc);  
137 - auto [cec, ep] = co_await corosio::connect(s, results);  
138 - @endcode  
139   */ 133   */
140   template<class Socket, std::ranges::input_range Range> 134   template<class Socket, std::ranges::input_range Range>
141   requires std::convertible_to< 135   requires std::convertible_to<
142   std::ranges::range_reference_t<Range>, 136   std::ranges::range_reference_t<Range>,
143   typename Socket::endpoint_type> 137   typename Socket::endpoint_type>
144   capy::task<capy::io_result<typename Socket::endpoint_type>> 138   capy::task<capy::io_result<typename Socket::endpoint_type>>
HITCBC 145   12 connect(Socket& s, Range endpoints) 139   12 connect(Socket& s, Range endpoints)
146   { 140   {
MISUIC 147 - detail::default_connect_condition cond; 141 + ✗ return corosio::connect(
HITCBC 148 - 12 return corosio::connect(s, std::move(endpoints), cond); 142 + 12 s, std::move(endpoints), detail::default_connect_condition{});
149   } 143   }
150   144  
151   /** Asynchronously connect a socket by trying each endpoint in a range, 145   /** Asynchronously connect a socket by trying each endpoint in a range,
152   filtered by a user-supplied condition. 146   filtered by a user-supplied condition.
153   147  
154   For each candidate the condition is invoked as 148   For each candidate the condition is invoked as
155   `cond(last_ec, ep)` where `last_ec` is the error from the most 149   `cond(last_ec, ep)` where `last_ec` is the error from the most
156   recent attempt (default-constructed before the first attempt). If 150   recent attempt (default-constructed before the first attempt). If
157   the condition returns `false` the candidate is skipped; otherwise a 151   the condition returns `false` the candidate is skipped; otherwise a
158   connect is attempted. 152   connect is attempted.
159   153  
160   @param s The socket to connect. See the non-condition overload for 154   @param s The socket to connect. See the non-condition overload for
161   requirements. 155   requirements.
162   @param endpoints A range of candidate endpoints, taken by value. See 156   @param endpoints A range of candidate endpoints, taken by value. See
163   the non-condition overload for the deep-copy caveat when passing 157   the non-condition overload for the deep-copy caveat when passing
164   an lvalue `resolver_results`. 158   an lvalue `resolver_results`.
165   @param cond A predicate invocable with 159   @param cond A predicate invocable with
166   `(std::error_code const&, typename Socket::endpoint_type const&)` 160   `(std::error_code const&, typename Socket::endpoint_type const&)`
167   returning a value contextually convertible to `bool`. 161   returning a value contextually convertible to `bool`.
168   162  
169   @return Same as the non-condition overload. If every candidate is 163   @return Same as the non-condition overload. If every candidate is
170   rejected, completes with `std::errc::no_such_device_or_address`. 164   rejected, completes with `std::errc::no_such_device_or_address`.
171   165  
172   If auto-opening the socket fails, the attempt completes with the 166   If auto-opening the socket fails, the attempt completes with the
173   open error. 167   open error.
174   */ 168   */
175   template<class Socket, std::ranges::input_range Range, class ConnectCondition> 169   template<class Socket, std::ranges::input_range Range, class ConnectCondition>
176   requires std::convertible_to< 170   requires std::convertible_to<
177   std::ranges::range_reference_t<Range>, 171   std::ranges::range_reference_t<Range>,
178   typename Socket::endpoint_type> && 172   typename Socket::endpoint_type> &&
179   std::predicate< 173   std::predicate<
180   ConnectCondition&, 174   ConnectCondition&,
181   std::error_code const&, 175   std::error_code const&,
182   typename Socket::endpoint_type const&> 176   typename Socket::endpoint_type const&>
183   capy::task<capy::io_result<typename Socket::endpoint_type>> 177   capy::task<capy::io_result<typename Socket::endpoint_type>>
HITCBC 184   16 connect(Socket& s, Range endpoints, ConnectCondition cond) 178   16 connect(Socket& s, Range endpoints, ConnectCondition cond)
185   { 179   {
186   using endpoint_type = typename Socket::endpoint_type; 180   using endpoint_type = typename Socket::endpoint_type;
187   181  
188   std::error_code last_ec; 182   std::error_code last_ec;
189   183  
190   for (auto&& e : endpoints) 184   for (auto&& e : endpoints)
191   { 185   {
192   endpoint_type ep = e; 186   endpoint_type ep = e;
193   187  
194   if (!cond(static_cast<std::error_code const&>(last_ec), 188   if (!cond(static_cast<std::error_code const&>(last_ec),
195   static_cast<endpoint_type const&>(ep))) 189   static_cast<endpoint_type const&>(ep)))
196   continue; 190   continue;
197   191  
198   if (s.is_open()) 192   if (s.is_open())
199   s.close(); 193   s.close();
200   194  
201   auto [ec] = co_await s.connect(ep); 195   auto [ec] = co_await s.connect(ep);
202   196  
203   if (!ec) 197   if (!ec)
204   co_return {std::error_code{}, std::move(ep)}; 198   co_return {std::error_code{}, std::move(ep)};
205   199  
206   if (ec == capy::cond::canceled) 200   if (ec == capy::cond::canceled)
207   co_return {ec, endpoint_type{}}; 201   co_return {ec, endpoint_type{}};
208   202  
209   last_ec = ec; 203   last_ec = ec;
210   } 204   }
211   205  
212   if (!last_ec) 206   if (!last_ec)
213   last_ec = std::make_error_code(std::errc::no_such_device_or_address); 207   last_ec = std::make_error_code(std::errc::no_such_device_or_address);
214   208  
215   co_return {last_ec, endpoint_type{}}; 209   co_return {last_ec, endpoint_type{}};
HITCBC 216   32 } 210   32 }
217   211  
218   /** Asynchronously connect a socket by trying each endpoint in an 212   /** Asynchronously connect a socket by trying each endpoint in an
219   iterator range. 213   iterator range.
220   214  
221   Behaves like the range overload, except the return value carries 215   Behaves like the range overload, except the return value carries
222   the iterator to the successfully connected endpoint on success, or 216   the iterator to the successfully connected endpoint on success, or
223   `end` on failure. This mirrors Boost.Asio's iterator-based 217   `end` on failure. This mirrors Boost.Asio's iterator-based
224   `async_connect`. 218   `async_connect`.
225   219  
226   @param s The socket to connect. 220   @param s The socket to connect.
227   @param begin The first candidate. 221   @param begin The first candidate.
228   @param end One past the last candidate. 222   @param end One past the last candidate.
229   223  
230   @return An awaitable completing with `capy::io_result<Iter>`: 224   @return An awaitable completing with `capy::io_result<Iter>`:
231   - on success: default error_code and the iterator of the 225   - on success: default error_code and the iterator of the
232   successful endpoint; 226   successful endpoint;
233   - on failure of all attempts: the error from the last attempt 227   - on failure of all attempts: the error from the last attempt
234   and `end`; 228   and `end`;
235   - on empty range: `std::errc::no_such_device_or_address` and 229   - on empty range: `std::errc::no_such_device_or_address` and
236   `end`. 230   `end`.
237   231  
238   If auto-opening the socket fails, the attempt completes with the 232   If auto-opening the socket fails, the attempt completes with the
239   open error. 233   open error.
240   */ 234   */
241   template<class Socket, std::input_iterator Iter> 235   template<class Socket, std::input_iterator Iter>
242   requires std::convertible_to< 236   requires std::convertible_to<
243   std::iter_reference_t<Iter>, 237   std::iter_reference_t<Iter>,
244   typename Socket::endpoint_type> 238   typename Socket::endpoint_type>
245   capy::task<capy::io_result<Iter>> 239   capy::task<capy::io_result<Iter>>
HITCBC 246   4 connect(Socket& s, Iter begin, Iter end) 240   4 connect(Socket& s, Iter begin, Iter end)
247   { 241   {
248   return corosio::connect( 242   return corosio::connect(
249   s, 243   s,
HITCBC 250   4 std::move(begin), 244   4 std::move(begin),
HITCBC 251   4 std::move(end), 245   4 std::move(end),
HITCBC 252   4 detail::default_connect_condition{}); 246   4 detail::default_connect_condition{});
253   } 247   }
254   248  
255   /** Asynchronously connect a socket by trying each endpoint in an 249   /** Asynchronously connect a socket by trying each endpoint in an
256   iterator range, filtered by a user-supplied condition. 250   iterator range, filtered by a user-supplied condition.
257   251  
258   @param s The socket to connect. 252   @param s The socket to connect.
259   @param begin The first candidate. 253   @param begin The first candidate.
260   @param end One past the last candidate. 254   @param end One past the last candidate.
261   @param cond A predicate invocable with 255   @param cond A predicate invocable with
262   `(std::error_code const&, typename Socket::endpoint_type const&)`. 256   `(std::error_code const&, typename Socket::endpoint_type const&)`.
263   257  
264   @return Same as the plain iterator overload. If every candidate is 258   @return Same as the plain iterator overload. If every candidate is
265   rejected, completes with `std::errc::no_such_device_or_address`. 259   rejected, completes with `std::errc::no_such_device_or_address`.
266   260  
267   If auto-opening the socket fails, the attempt completes with the 261   If auto-opening the socket fails, the attempt completes with the
268   open error. 262   open error.
269   */ 263   */
270   template<class Socket, std::input_iterator Iter, class ConnectCondition> 264   template<class Socket, std::input_iterator Iter, class ConnectCondition>
271   requires std::convertible_to< 265   requires std::convertible_to<
272   std::iter_reference_t<Iter>, 266   std::iter_reference_t<Iter>,
273   typename Socket::endpoint_type> && 267   typename Socket::endpoint_type> &&
274   std::predicate< 268   std::predicate<
275   ConnectCondition&, 269   ConnectCondition&,
276   std::error_code const&, 270   std::error_code const&,
277   typename Socket::endpoint_type const&> 271   typename Socket::endpoint_type const&>
278   capy::task<capy::io_result<Iter>> 272   capy::task<capy::io_result<Iter>>
HITCBC 279   4 connect(Socket& s, Iter begin, Iter end, ConnectCondition cond) 273   4 connect(Socket& s, Iter begin, Iter end, ConnectCondition cond)
280   { 274   {
281   using endpoint_type = typename Socket::endpoint_type; 275   using endpoint_type = typename Socket::endpoint_type;
282   276  
283   std::error_code last_ec; 277   std::error_code last_ec;
284   278  
285   for (Iter it = begin; it != end; ++it) 279   for (Iter it = begin; it != end; ++it)
286   { 280   {
287   endpoint_type ep = *it; 281   endpoint_type ep = *it;
288   282  
289   if (!cond(static_cast<std::error_code const&>(last_ec), 283   if (!cond(static_cast<std::error_code const&>(last_ec),
290   static_cast<endpoint_type const&>(ep))) 284   static_cast<endpoint_type const&>(ep)))
291   continue; 285   continue;
292   286  
293   if (s.is_open()) 287   if (s.is_open())
294   s.close(); 288   s.close();
295   289  
296   auto [ec] = co_await s.connect(ep); 290   auto [ec] = co_await s.connect(ep);
297   291  
298   if (!ec) 292   if (!ec)
299   co_return {std::error_code{}, std::move(it)}; 293   co_return {std::error_code{}, std::move(it)};
300   294  
301   if (ec == capy::cond::canceled) 295   if (ec == capy::cond::canceled)
302   co_return {ec, std::move(end)}; 296   co_return {ec, std::move(end)};
303   297  
304   last_ec = ec; 298   last_ec = ec;
305   } 299   }
306   300  
307   if (!last_ec) 301   if (!last_ec)
308   last_ec = std::make_error_code(std::errc::no_such_device_or_address); 302   last_ec = std::make_error_code(std::errc::no_such_device_or_address);
309   303  
310   co_return {last_ec, std::move(end)}; 304   co_return {last_ec, std::move(end)};
HITCBC 311   8 } 305   8 }
312   306  
313   } // namespace boost::corosio 307   } // namespace boost::corosio
314   308  
315   #endif 309   #endif