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