. /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   21  
22   #include <errno.h> 22   #include <errno.h>
23   #include <fcntl.h> 23   #include <fcntl.h>
24   #include <netinet/in.h> 24   #include <netinet/in.h>
25   #include <sys/select.h> 25   #include <sys/select.h>
26   #include <sys/socket.h> 26   #include <sys/socket.h>
27   #include <unistd.h> 27   #include <unistd.h>
28   28  
29   /* select backend traits. 29   /* select backend traits.
30   30  
31   Captures the platform-specific behavior of the portable select() backend: 31   Captures the platform-specific behavior of the portable select() backend:
32   manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation, 32   manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation,
33   conditional SO_NOSIGPIPE, sendmsg(MSG_NOSIGNAL) where available, 33   conditional SO_NOSIGPIPE, sendmsg(MSG_NOSIGNAL) where available,
34   and accept()+fcntl for accepted connections. 34   and accept()+fcntl for accepted connections.
35   */ 35   */
36   36  
37   namespace boost::corosio::detail { 37   namespace boost::corosio::detail {
38   38  
39   class select_scheduler; 39   class select_scheduler;
40   40  
41   struct select_traits 41   struct select_traits
42   { 42   {
43   using scheduler_type = select_scheduler; 43   using scheduler_type = select_scheduler;
44   using desc_state_type = reactor_descriptor_state; 44   using desc_state_type = reactor_descriptor_state;
45   45  
46   static constexpr bool needs_write_notification = true; 46   static constexpr bool needs_write_notification = true;
47   47  
48   // No extra per-socket state or lifecycle hooks needed for select. 48   // No extra per-socket state or lifecycle hooks needed for select.
49   struct stream_socket_hook 49   struct stream_socket_hook
50   { 50   {
HITCBC 51   28 std::error_code on_set_option( 51   28 std::error_code on_set_option(
52   int fd, int level, int optname, 52   int fd, int level, int optname,
53   void const* data, std::size_t size) noexcept 53   void const* data, std::size_t size) noexcept
54   { 54   {
HITCBC 55   28 if (::setsockopt( 55   28 if (::setsockopt(
56   fd, level, optname, data, 56   fd, level, optname, data,
HITCBC 57   28 static_cast<socklen_t>(size)) != 0) 57   28 static_cast<socklen_t>(size)) != 0)
MISUBC 58   ✗ return make_err(errno); 58   ✗ return make_err(errno);
HITCBC 59   28 return {}; 59   28 return {};
60   } 60   }
HITCBC 61   23625 static void pre_shutdown(int) noexcept {} 61   14562 static void pre_shutdown(int) noexcept {}
HITCBC 62   7849 static void pre_destroy(int) noexcept {} 62   4828 static void pre_destroy(int) noexcept {}
63   }; 63   };
64   64  
65   struct write_policy 65   struct write_policy
66   { 66   {
MISLBC 67   105542 static ssize_t write(int fd, iovec* iovecs, int count) noexcept 67   ✗ static ssize_t write(int fd, iovec* iovecs, int count) noexcept
68   { 68   {
MISLBC 69   105542 msghdr msg{}; 69   ✗ msghdr msg{};
MISLBC 70   105542 msg.msg_iov = iovecs; 70   ✗ msg.msg_iov = iovecs;
MISLBC 71   105542 msg.msg_iovlen = static_cast<std::size_t>(count); 71   ✗ msg.msg_iovlen = static_cast<std::size_t>(count);
72   72  
73   #ifdef MSG_NOSIGNAL 73   #ifdef MSG_NOSIGNAL
MISLBC 74   105542 constexpr int send_flags = MSG_NOSIGNAL; 74   ✗ constexpr int send_flags = MSG_NOSIGNAL;
75   #else 75   #else
76   constexpr int send_flags = 0; 76   constexpr int send_flags = 0;
77   #endif 77   #endif
78   78  
79   ssize_t n; 79   ssize_t n;
80   do 80   do
81   { 81   {
MISLBC 82   105542 n = ::sendmsg(fd, &msg, send_flags); 82   ✗ n = ::sendmsg(fd, &msg, send_flags);
83   } 83   }
MISLBC 84   105542 while (n < 0 && errno == EINTR); 84   ✗ while (n < 0 && errno == EINTR);
MISLBC 85   105542 return n; 85   ✗ return n;
86   } 86   }
  87 +
  88 + // Single-buffer fast path. Where MSG_NOSIGNAL exists we use
  89 + // send() to suppress SIGPIPE inline; otherwise fall back to
  90 + // write() and rely on the SO_NOSIGPIPE set in accept_policy
  91 + // and set_fd_options.
HITGNC   92 + 127774 static ssize_t write_one(
  93 + int fd, void const* data, std::size_t size) noexcept
  94 + {
  95 + ssize_t n;
  96 + do
  97 + {
  98 + #ifdef MSG_NOSIGNAL
HITGNC   99 + 127774 n = ::send(fd, data, size, MSG_NOSIGNAL);
  100 + #else
  101 + n = ::write(fd, data, size);
  102 + #endif
  103 + }
HITGNC   104 + 127774 while (n < 0 && errno == EINTR);
HITGNC   105 + 127774 return n;
  106 + }
87   }; 107   };
88   108  
89   struct accept_policy 109   struct accept_policy
90   { 110   {
HITCBC 91   5212 static int do_accept( 111   3198 static int do_accept(
92   int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept 112   int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
93   { 113   {
HITCBC 94   5212 addrlen = sizeof(peer); 114   3198 addrlen = sizeof(peer);
95   int new_fd; 115   int new_fd;
96   do 116   do
97   { 117   {
HITCBC 98   5212 new_fd = ::accept( 118   3198 new_fd = ::accept(
99   fd, reinterpret_cast<sockaddr*>(&peer), &addrlen); 119   fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
100   } 120   }
HITCBC 101   5212 while (new_fd < 0 && errno == EINTR); 121   3198 while (new_fd < 0 && errno == EINTR);
102   122  
HITCBC 103   5212 if (new_fd < 0) 123   3198 if (new_fd < 0)
HITCBC 104   2606 return new_fd; 124   1599 return new_fd;
105   125  
HITCBC 106   2606 if (new_fd >= FD_SETSIZE) 126   1599 if (new_fd >= FD_SETSIZE)
107   { 127   {
MISUBC 108   ✗ ::close(new_fd); 128   ✗ ::close(new_fd);
MISUBC 109   ✗ errno = EINVAL; 129   ✗ errno = EINVAL;
MISUBC 110   ✗ return -1; 130   ✗ return -1;
111   } 131   }
112   132  
HITCBC 113   2606 int flags = ::fcntl(new_fd, F_GETFL, 0); 133   1599 int flags = ::fcntl(new_fd, F_GETFL, 0);
HITCBC 114   2606 if (flags == -1) 134   1599 if (flags == -1)
115   { 135   {
MISUBC 116   ✗ int err = errno; 136   ✗ int err = errno;
MISUBC 117   ✗ ::close(new_fd); 137   ✗ ::close(new_fd);
MISUBC 118   ✗ errno = err; 138   ✗ errno = err;
MISUBC 119   ✗ return -1; 139   ✗ return -1;
120   } 140   }
121   141  
HITCBC 122   2606 if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1) 142   1599 if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1)
123   { 143   {
MISUBC 124   ✗ int err = errno; 144   ✗ int err = errno;
MISUBC 125   ✗ ::close(new_fd); 145   ✗ ::close(new_fd);
MISUBC 126   ✗ errno = err; 146   ✗ errno = err;
MISUBC 127   ✗ return -1; 147   ✗ return -1;
128   } 148   }
129   149  
HITCBC 130   2606 if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1) 150   1599 if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
131   { 151   {
MISUBC 132   ✗ int err = errno; 152   ✗ int err = errno;
MISUBC 133   ✗ ::close(new_fd); 153   ✗ ::close(new_fd);
MISUBC 134   ✗ errno = err; 154   ✗ errno = err;
MISUBC 135   ✗ return -1; 155   ✗ return -1;
136   } 156   }
137   157  
138   #ifdef SO_NOSIGPIPE 158   #ifdef SO_NOSIGPIPE
139   // Best-effort: SO_NOSIGPIPE is a safety net; write paths 159   // Best-effort: SO_NOSIGPIPE is a safety net; write paths
140   // also use MSG_NOSIGNAL where available. Failure here 160   // also use MSG_NOSIGNAL where available. Failure here
141   // should not prevent the accepted connection from being used. 161   // should not prevent the accepted connection from being used.
142   int one = 1; 162   int one = 1;
143   (void)::setsockopt( 163   (void)::setsockopt(
144   new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)); 164   new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
145   #endif 165   #endif
146   166  
HITCBC 147   2606 return new_fd; 167   1599 return new_fd;
148   } 168   }
149   }; 169   };
150   170  
151   // Create a plain socket (no atomic flags -- select is POSIX-portable). 171   // Create a plain socket (no atomic flags -- select is POSIX-portable).
HITCBC 152   2766 static int create_socket(int family, int type, int protocol) noexcept 172   1759 static int create_socket(int family, int type, int protocol) noexcept
153   { 173   {
HITCBC 154   2766 return ::socket(family, type, protocol); 174   1759 return ::socket(family, type, protocol);
155   } 175   }
156   176  
157   // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE. 177   // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
158   // Caller is responsible for closing fd on error. 178   // Caller is responsible for closing fd on error.
HITCBC 159   2766 static std::error_code set_fd_options(int fd) noexcept 179   1759 static std::error_code set_fd_options(int fd) noexcept
160   { 180   {
HITCBC 161   2766 int flags = ::fcntl(fd, F_GETFL, 0); 181   1759 int flags = ::fcntl(fd, F_GETFL, 0);
HITCBC 162   2766 if (flags == -1) 182   1759 if (flags == -1)
MISUBC 163   ✗ return make_err(errno); 183   ✗ return make_err(errno);
HITCBC 164   2766 if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) 184   1759 if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
MISUBC 165   ✗ return make_err(errno); 185   ✗ return make_err(errno);
HITCBC 166   2766 if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) 186   1759 if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
MISUBC 167   ✗ return make_err(errno); 187   ✗ return make_err(errno);
168   188  
HITCBC 169   2766 if (fd >= FD_SETSIZE) 189   1759 if (fd >= FD_SETSIZE)
MISUBC 170   ✗ return make_err(EMFILE); 190   ✗ return make_err(EMFILE);
171   191  
172   #ifdef SO_NOSIGPIPE 192   #ifdef SO_NOSIGPIPE
173   // Best-effort: SO_NOSIGPIPE is a safety net; write paths 193   // Best-effort: SO_NOSIGPIPE is a safety net; write paths
174   // also use MSG_NOSIGNAL where available. Match develop's 194   // also use MSG_NOSIGNAL where available. Match develop's
175   // predominant behavior of ignoring failures here rather 195   // predominant behavior of ignoring failures here rather
176   // than failing socket creation. 196   // than failing socket creation.
177   { 197   {
178   int one = 1; 198   int one = 1;
179   (void)::setsockopt( 199   (void)::setsockopt(
180   fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)); 200   fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
181   } 201   }
182   #endif 202   #endif
183   203  
HITCBC 184   2766 return {}; 204   1759 return {};
185   } 205   }
186   206  
187   // Apply protocol-specific options after socket creation. 207   // Apply protocol-specific options after socket creation.
188   // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort). 208   // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
189   static std::error_code 209   static std::error_code
HITCBC 190   2672 configure_ip_socket(int fd, int family) noexcept 210   1665 configure_ip_socket(int fd, int family) noexcept
191   { 211   {
HITCBC 192   2672 if (family == AF_INET6) 212   1665 if (family == AF_INET6)
193   { 213   {
HITCBC 194   14 int one = 1; 214   14 int one = 1;
HITCBC 195   14 (void)::setsockopt( 215   14 (void)::setsockopt(
196   fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one)); 216   fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
197   } 217   }
198   218  
HITCBC 199   2672 return set_fd_options(fd); 219   1665 return set_fd_options(fd);
200   } 220   }
201   221  
202   // Apply protocol-specific options for acceptor sockets. 222   // Apply protocol-specific options for acceptor sockets.
203   // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort). 223   // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
204   static std::error_code 224   static std::error_code
HITCBC 205   74 configure_ip_acceptor(int fd, int family) noexcept 225   74 configure_ip_acceptor(int fd, int family) noexcept
206   { 226   {
HITCBC 207   74 if (family == AF_INET6) 227   74 if (family == AF_INET6)
208   { 228   {
HITCBC 209   9 int val = 0; 229   9 int val = 0;
HITCBC 210   9 (void)::setsockopt( 230   9 (void)::setsockopt(
211   fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val)); 231   fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
212   } 232   }
213   233  
HITCBC 214   74 return set_fd_options(fd); 234   74 return set_fd_options(fd);
215   } 235   }
216   236  
217   // Apply options for local (unix) sockets. 237   // Apply options for local (unix) sockets.
218   static std::error_code 238   static std::error_code
HITCBC 219   20 configure_local_socket(int fd) noexcept 239   20 configure_local_socket(int fd) noexcept
220   { 240   {
HITCBC 221   20 return set_fd_options(fd); 241   20 return set_fd_options(fd);
222   } 242   }
223   243  
224   // Non-mutating validation for fds adopted via assign(). Select's 244   // Non-mutating validation for fds adopted via assign(). Select's
225   // reactor cannot handle fds above FD_SETSIZE, so reject them up 245   // reactor cannot handle fds above FD_SETSIZE, so reject them up
226   // front instead of letting FD_SET clobber unrelated memory. 246   // front instead of letting FD_SET clobber unrelated memory.
227   static std::error_code 247   static std::error_code
HITCBC 228   14 validate_assigned_fd(int fd) noexcept 248   14 validate_assigned_fd(int fd) noexcept
229   { 249   {
HITCBC 230   14 if (fd >= FD_SETSIZE) 250   14 if (fd >= FD_SETSIZE)
MISUBC 231   ✗ return make_err(EMFILE); 251   ✗ return make_err(EMFILE);
HITCBC 232   14 return {}; 252   14 return {};
233   } 253   }
234   }; 254   };
235   255  
236   } // namespace boost::corosio::detail 256   } // namespace boost::corosio::detail
237   257  
238   #endif // BOOST_COROSIO_HAS_SELECT 258   #endif // BOOST_COROSIO_HAS_SELECT
239   259  
240   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP 260   #endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP