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