. /include/boost/corosio /native /detail /select /select_traits.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_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP 10   #ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
11   #define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP 11   #define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
12   12  
13   #include <boost/corosio/detail/platform.hpp> 13   #include <boost/corosio/detail/platform.hpp>
14   14  
15   #if BOOST_COROSIO_HAS_SELECT 15   #if BOOST_COROSIO_HAS_SELECT
16   16  
17   #include <boost/corosio/native/detail/make_err.hpp> 17   #include <boost/corosio/native/detail/make_err.hpp>
18   #include <boost/corosio/native/detail/reactor/reactor_descriptor_state.hpp> 18   #include <boost/corosio/native/detail/reactor/reactor_descriptor_state.hpp>
19   19  
20   #include <system_error> 20   #include <system_error>
21   #include <tuple> 21   #include <tuple>
22   22  
23   #include <errno.h> 23   #include <errno.h>
24   #include <fcntl.h> 24   #include <fcntl.h>
25   #include <netinet/in.h> 25   #include <netinet/in.h>
26   #include <sys/select.h> 26   #include <sys/select.h>
27   #include <sys/socket.h> 27   #include <sys/socket.h>
28   #include <unistd.h> 28   #include <unistd.h>
29   29  
30   /* select backend traits. 30   /* select backend traits.
31   31  
32   Captures the platform-specific behavior of the portable select() backend: 32   Captures the platform-specific behavior of the portable select() backend:
33   manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation, 33   manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation,
34   mandatory SO_NOSIGPIPE where the platform defines it, 34   mandatory SO_NOSIGPIPE where the platform defines it,
35   sendmsg(MSG_NOSIGNAL) where available, and accept()+fcntl for 35   sendmsg(MSG_NOSIGNAL) where available, and accept()+fcntl for
36   accepted connections. 36   accepted connections.
37   */ 37   */
38   38  
39   namespace boost::corosio::detail { 39   namespace boost::corosio::detail {
40   40  
41   class select_scheduler; 41   class select_scheduler;
42   42  
43   struct select_traits 43   struct select_traits
44   { 44   {
45   using scheduler_type = select_scheduler; 45   using scheduler_type = select_scheduler;
46   using desc_state_type = reactor_descriptor_state; 46   using desc_state_type = reactor_descriptor_state;
47   47  
48   static constexpr bool needs_write_notification = true; 48   static constexpr bool needs_write_notification = true;
49   49  
50   // No extra per-socket state or lifecycle hooks needed for select. 50   // No extra per-socket state or lifecycle hooks needed for select.
51   struct stream_socket_hook 51   struct stream_socket_hook
52   { 52   {
HITCBC 53   100 std::error_code on_set_option( 53   107 std::error_code on_set_option(
54   int fd, int level, int optname, 54   int fd, int level, int optname,
55   void const* data, std::size_t size) noexcept 55   void const* data, std::size_t size) noexcept
56   { 56   {
HITCBC 57   100 if (::setsockopt( 57   107 if (::setsockopt(
58   fd, level, optname, data, 58   fd, level, optname, data,
HITCBC 59   100 static_cast<socklen_t>(size)) != 0) 59   107 static_cast<socklen_t>(size)) != 0)
HITCBC 60   4 return make_err(errno); 60   4 return make_err(errno);
HITCBC 61   96 return {}; 61   103 return {};
62   } 62   }
HITCBC 63   28893 static void pre_shutdown(int) noexcept {} 63   20968 static void pre_shutdown(int) noexcept {}
HITCBC 64   9468 static void pre_destroy(int) noexcept {} 64   6821 static void pre_destroy(int) noexcept {}
65   }; 65   };
66   66  
67   struct write_policy 67   struct write_policy
68   { 68   {
HITCBC 69   72 static ssize_t write(int fd, iovec* iovecs, int count) noexcept 69   72 static ssize_t write(int fd, iovec* iovecs, int count) noexcept
70   { 70   {
HITCBC 71   72 msghdr msg{}; 71   72 msghdr msg{};
HITCBC 72   72 msg.msg_iov = iovecs; 72   72 msg.msg_iov = iovecs;
HITCBC 73   72 msg.msg_iovlen = static_cast<std::size_t>(count); 73   72 msg.msg_iovlen = static_cast<std::size_t>(count);
74   74  
75   #ifdef MSG_NOSIGNAL 75   #ifdef MSG_NOSIGNAL
HITCBC 76   72 constexpr int send_flags = MSG_NOSIGNAL; 76   72 constexpr int send_flags = MSG_NOSIGNAL;
77   #else 77   #else
78   constexpr int send_flags = 0; 78   constexpr int send_flags = 0;
79   #endif 79   #endif
80   80  
81   ssize_t n; 81   ssize_t n;
82   do 82   do
83   { 83   {
HITCBC 84   73 n = ::sendmsg(fd, &msg, send_flags); 84   73 n = ::sendmsg(fd, &msg, send_flags);
85   } 85   }
HITCBC 86   73 while (n < 0 && errno == EINTR); 86   73 while (n < 0 && errno == EINTR);
HITCBC 87   72 return n; 87   72 return n;
88   } 88   }
89   89  
90   // Single-buffer fast path. Where MSG_NOSIGNAL exists we use 90   // Single-buffer fast path. Where MSG_NOSIGNAL exists we use
91   // send() to suppress SIGPIPE inline; otherwise fall back to 91   // send() to suppress SIGPIPE inline; otherwise fall back to
92   // write() and rely on the SO_NOSIGPIPE set in accept_policy 92   // write() and rely on the SO_NOSIGPIPE set in accept_policy
93   // and set_fd_options. 93   // and set_fd_options.
HITCBC 94   99460 static ssize_t write_one( 94   116842 static ssize_t write_one(
95   int fd, void const* data, std::size_t size) noexcept 95   int fd, void const* data, std::size_t size) noexcept
96   { 96   {
97   ssize_t n; 97   ssize_t n;
98   do 98   do
99   { 99   {
100   #ifdef MSG_NOSIGNAL 100   #ifdef MSG_NOSIGNAL
HITCBC 101   99461 n = ::send(fd, data, size, MSG_NOSIGNAL); 101   116843 n = ::send(fd, data, size, MSG_NOSIGNAL);
102   #else 102   #else
103   n = ::write(fd, data, size); 103   n = ::write(fd, data, size);
104   #endif 104   #endif
105   } 105   }
HITCBC 106   99461 while (n < 0 && errno == EINTR); 106   116843 while (n < 0 && errno == EINTR);
HITCBC 107   99460 return n; 107   116842 return n;
108   } 108   }
109   }; 109   };
110   110  
111   struct accept_policy 111   struct accept_policy
112   { 112   {
HITCBC 113   6254 static int do_accept( 113   4496 static int do_accept(
114   int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept 114   int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
115   { 115   {
HITCBC 116   6254 addrlen = sizeof(peer); 116   4496 addrlen = sizeof(peer);
117   int new_fd; 117   int new_fd;
118   do 118   do
119   { 119   {
HITCBC 120   6255 new_fd = ::accept( 120   4497 new_fd = ::accept(
121   fd, reinterpret_cast<sockaddr*>(&peer), &addrlen); 121   fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
122   } 122   }
HITCBC 123   6255 while (new_fd < 0 && errno == EINTR); 123   4497 while (new_fd < 0 && errno == EINTR);
124   124  
HITCBC 125   6254 if (new_fd < 0) 125   4496 if (new_fd < 0)
HITCBC 126   3128 return new_fd; 126   2254 return new_fd;
127   127  
HITCBC 128   3126 if (new_fd >= FD_SETSIZE) 128   2242 if (new_fd >= FD_SETSIZE)
129   { 129   {
HITCBC 130   1 ::close(new_fd); 130   1 ::close(new_fd);
HITCBC 131   1 errno = EMFILE; 131   1 errno = EMFILE;
HITCBC 132   1 return -1; 132   1 return -1;
133   } 133   }
134   134  
HITCBC 135   3125 int flags = ::fcntl(new_fd, F_GETFL, 0); 135   2241 int flags = ::fcntl(new_fd, F_GETFL, 0);
HITCBC 136   3125 if (flags == -1) 136   2241 if (flags == -1)
137   { 137   {
HITCBC 138   1 int err = errno; 138   1 int err = errno;
HITCBC 139   1 ::close(new_fd); 139   1 ::close(new_fd);
HITCBC 140   1 errno = err; 140   1 errno = err;
HITCBC 141   1 return -1; 141   1 return -1;
142   } 142   }
143   143  
HITCBC 144   3124 if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1) 144   2240 if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1)
145   { 145   {
HITCBC 146   1 int err = errno; 146   1 int err = errno;
HITCBC 147   1 ::close(new_fd); 147   1 ::close(new_fd);
HITCBC 148   1 errno = err; 148   1 errno = err;
HITCBC 149   1 return -1; 149   1 return -1;
150   } 150   }
151   151  
HITCBC 152   3123 if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1) 152   2239 if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
153   { 153   {
HITCBC 154   1 int err = errno; 154   1 int err = errno;
HITCBC 155   1 ::close(new_fd); 155   1 ::close(new_fd);
HITCBC 156   1 errno = err; 156   1 errno = err;
HITCBC 157   1 return -1; 157   1 return -1;
158   } 158   }
159   159  
160   #ifdef SO_NOSIGPIPE 160   #ifdef SO_NOSIGPIPE
161   // MSG_NOSIGNAL is not universal across the platforms this 161   // MSG_NOSIGNAL is not universal across the platforms this
162   // portable backend covers, and the write() the fast path 162   // portable backend covers, and the write() the fast path
163   // falls back to there takes no flag at all; SO_NOSIGPIPE is 163   // falls back to there takes no flag at all; SO_NOSIGPIPE is
164   // the per-descriptor guard that covers both. Treat failure 164   // the per-descriptor guard that covers both. Treat failure
165   // as fatal, matching the kqueue backend. 165   // as fatal, matching the kqueue backend.
166   int one = 1; 166   int one = 1;
167   if (::setsockopt( 167   if (::setsockopt(
168   new_fd, SOL_SOCKET, SO_NOSIGPIPE, 168   new_fd, SOL_SOCKET, SO_NOSIGPIPE,
169   &one, sizeof(one)) != 0) 169   &one, sizeof(one)) != 0)
170   { 170   {
171   int err = errno; 171   int err = errno;
172   ::close(new_fd); 172   ::close(new_fd);
173   errno = err; 173   errno = err;
174   return -1; 174   return -1;
175   } 175   }
176   #endif 176   #endif
177   177  
HITCBC 178   3122 return new_fd; 178   2238 return new_fd;
179   } 179   }
180   }; 180   };
181   181  
182   // Create a plain socket (no atomic flags -- select is POSIX-portable). 182   // Create a plain socket (no atomic flags -- select is POSIX-portable).
HITCBC 183   3600 static int create_socket(int family, int type, int protocol) noexcept 183   2841 static int create_socket(int family, int type, int protocol) noexcept
184   { 184   {
HITCBC 185   3600 return ::socket(family, type, protocol); 185   2841 return ::socket(family, type, protocol);
186   } 186   }
187   187  
188   // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE. 188   // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
189   // Caller is responsible for closing fd on error. 189   // Caller is responsible for closing fd on error.
HITCBC 190   3594 static std::error_code set_fd_options(int fd) noexcept 190   2835 static std::error_code set_fd_options(int fd) noexcept
191   { 191   {
HITCBC 192   3594 int flags = ::fcntl(fd, F_GETFL, 0); 192   2835 int flags = ::fcntl(fd, F_GETFL, 0);
HITCBC 193   3594 if (flags == -1) 193   2835 if (flags == -1)
HITCBC 194   2 return make_err(errno); 194   2 return make_err(errno);
HITCBC 195   3592 if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) 195   2833 if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
HITCBC 196   2 return make_err(errno); 196   2 return make_err(errno);
HITCBC 197   3590 if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) 197   2831 if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
HITCBC 198   2 return make_err(errno); 198   2 return make_err(errno);
199   199  
HITCBC 200   3588 if (fd >= FD_SETSIZE) 200   2829 if (fd >= FD_SETSIZE)
HITCBC 201   2 return make_err(EMFILE); 201   2 return make_err(EMFILE);
202   202  
203   #ifdef SO_NOSIGPIPE 203   #ifdef SO_NOSIGPIPE
204   // MSG_NOSIGNAL is not universal across the platforms this 204   // MSG_NOSIGNAL is not universal across the platforms this
205   // portable backend covers, and the write() the fast path falls 205   // portable backend covers, and the write() the fast path falls
206   // back to there takes no flag at all; SO_NOSIGPIPE is the 206   // back to there takes no flag at all; SO_NOSIGPIPE is the
207   // per-descriptor guard that covers both. Treat failure as fatal, 207   // per-descriptor guard that covers both. Treat failure as fatal,
208   // matching the kqueue backend. Caller closes fd on error. 208   // matching the kqueue backend. Caller closes fd on error.
209   { 209   {
210   int one = 1; 210   int one = 1;
211   if (::setsockopt( 211   if (::setsockopt(
212   fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)) != 0) 212   fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)) != 0)
213   return make_err(errno); 213   return make_err(errno);
214   } 214   }
215   #endif 215   #endif
216   216  
HITCBC 217   3586 return {}; 217   2827 return {};
218   } 218   }
219   219  
220   // Apply protocol-specific options after socket creation. 220   // Apply protocol-specific options after socket creation.
221   // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort). 221   // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
222   static std::error_code 222   static std::error_code
HITCBC 223   3284 configure_ip_socket(int fd, int family) noexcept 223   2455 configure_ip_socket(int fd, int family) noexcept
224   { 224   {
HITCBC 225   3284 if (family == AF_INET6) 225   2455 if (family == AF_INET6)
226   { 226   {
HITCBC 227   22 int one = 1; 227   22 int one = 1;
HITCBC 228   44 std::ignore = ::setsockopt( 228   44 std::ignore = ::setsockopt(
HITCBC 229   22 fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one)); 229   22 fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
230   } 230   }
231   231  
HITCBC 232   3284 return set_fd_options(fd); 232   2455 return set_fd_options(fd);
233   } 233   }
234   234  
235   // Apply protocol-specific options for acceptor sockets. 235   // Apply protocol-specific options for acceptor sockets.
236   // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort). 236   // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
237   static std::error_code 237   static std::error_code
HITCBC 238   212 configure_ip_acceptor(int fd, int family) noexcept 238   274 configure_ip_acceptor(int fd, int family) noexcept
239   { 239   {
HITCBC 240   212 if (family == AF_INET6) 240   274 if (family == AF_INET6)
241   { 241   {
HITCBC 242   11 int val = 0; 242   11 int val = 0;
HITCBC 243   22 std::ignore = ::setsockopt( 243   22 std::ignore = ::setsockopt(
HITCBC 244   11 fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val)); 244   11 fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
245   } 245   }
246   246  
HITCBC 247   212 return set_fd_options(fd); 247   274 return set_fd_options(fd);
248   } 248   }
249   249  
250   // Apply options for local (unix) sockets. 250   // Apply options for local (unix) sockets.
251   static std::error_code 251   static std::error_code
HITCBC 252   98 configure_local_socket(int fd) noexcept 252   106 configure_local_socket(int fd) noexcept
253   { 253   {
HITCBC 254   98 return set_fd_options(fd); 254   106 return set_fd_options(fd);
255   } 255   }
256   256  
257   // Non-mutating validation for fds adopted via assign(). Select's 257   // Non-mutating validation for fds adopted via assign(). Select's
258   // reactor cannot handle fds above FD_SETSIZE, so reject them up 258   // reactor cannot handle fds above FD_SETSIZE, so reject them up
259   // front instead of letting FD_SET clobber unrelated memory. 259   // front instead of letting FD_SET clobber unrelated memory.
260   static std::error_code 260   static std::error_code
HITCBC 261   146 validate_assigned_fd(int fd) noexcept 261   155 validate_assigned_fd(int fd) noexcept
262   { 262   {
HITCBC 263   146 if (fd >= FD_SETSIZE) 263   155 if (fd >= FD_SETSIZE)
HITCBC 264   2 return make_err(EMFILE); 264   2 return make_err(EMFILE);
HITCBC 265   144 return {}; 265   153 return {};
266   } 266   }
267   }; 267   };
268   268  
269   } // namespace boost::corosio::detail 269   } // namespace boost::corosio::detail
270   270  
271   #endif // BOOST_COROSIO_HAS_SELECT 271   #endif // BOOST_COROSIO_HAS_SELECT
272   272  
273   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP 273   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP