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