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)
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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//
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// Official repository: https://github.com/cppalliance/corosio
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// Official repository: https://github.com/cppalliance/corosio
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//
8   
//
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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   
    {
51   
        std::error_code on_set_option(
51   
        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   
        {
55   
            if (::setsockopt(
55   
            if (::setsockopt(
56   
                    fd, level, optname, data,
56   
                    fd, level, optname, data,
57   
                    static_cast<socklen_t>(size)) != 0)
57   
                    static_cast<socklen_t>(size)) != 0)
58   
                return make_err(errno);
58   
                return make_err(errno);
59   
            return {};
59   
            return {};
60   
        }
60   
        }
61   
        static void pre_shutdown(int) noexcept {}
61   
        static void pre_shutdown(int) noexcept {}
62   
        static void pre_destroy(int) noexcept {}
62   
        static void pre_destroy(int) noexcept {}
63   
    };
63   
    };
64  
64  
65   
    struct write_policy
65   
    struct write_policy
66   
    {
66   
    {
67   
        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   
        {
69   
            msghdr msg{};
69   
            msghdr msg{};
70   
            msg.msg_iov    = iovecs;
70   
            msg.msg_iov    = iovecs;
71   
            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
74   
            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   
            {
82   
                n = ::sendmsg(fd, &msg, send_flags);
82   
                n = ::sendmsg(fd, &msg, send_flags);
83   
            }
83   
            }
84   
            while (n < 0 && errno == EINTR);
84   
            while (n < 0 && errno == EINTR);
85   
            return n;
85   
            return n;
86   
        }
86   
        }
87   
    };
87   
    };
88  
88  
89   
    struct accept_policy
89   
    struct accept_policy
90   
    {
90   
    {
91   
        static int do_accept(
91   
        static int do_accept(
92   
            int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
92   
            int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
93   
        {
93   
        {
94   
            addrlen = sizeof(peer);
94   
            addrlen = sizeof(peer);
95   
            int new_fd;
95   
            int new_fd;
96   
            do
96   
            do
97   
            {
97   
            {
98   
                new_fd = ::accept(
98   
                new_fd = ::accept(
99   
                    fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
99   
                    fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
100   
            }
100   
            }
101   
            while (new_fd < 0 && errno == EINTR);
101   
            while (new_fd < 0 && errno == EINTR);
102  
102  
103   
            if (new_fd < 0)
103   
            if (new_fd < 0)
104   
                return new_fd;
104   
                return new_fd;
105  
105  
106   
            if (new_fd >= FD_SETSIZE)
106   
            if (new_fd >= FD_SETSIZE)
107   
            {
107   
            {
108   
                ::close(new_fd);
108   
                ::close(new_fd);
109   
                errno = EINVAL;
109   
                errno = EINVAL;
110   
                return -1;
110   
                return -1;
111   
            }
111   
            }
112  
112  
113   
            int flags = ::fcntl(new_fd, F_GETFL, 0);
113   
            int flags = ::fcntl(new_fd, F_GETFL, 0);
114   
            if (flags == -1)
114   
            if (flags == -1)
115   
            {
115   
            {
116   
                int err = errno;
116   
                int err = errno;
117   
                ::close(new_fd);
117   
                ::close(new_fd);
118   
                errno = err;
118   
                errno = err;
119   
                return -1;
119   
                return -1;
120   
            }
120   
            }
121  
121  
122   
            if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1)
122   
            if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1)
123   
            {
123   
            {
124   
                int err = errno;
124   
                int err = errno;
125   
                ::close(new_fd);
125   
                ::close(new_fd);
126   
                errno = err;
126   
                errno = err;
127   
                return -1;
127   
                return -1;
128   
            }
128   
            }
129  
129  
130   
            if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
130   
            if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
131   
            {
131   
            {
132   
                int err = errno;
132   
                int err = errno;
133   
                ::close(new_fd);
133   
                ::close(new_fd);
134   
                errno = err;
134   
                errno = err;
135   
                return -1;
135   
                return -1;
136   
            }
136   
            }
137  
137  
138   
#ifdef SO_NOSIGPIPE
138   
#ifdef SO_NOSIGPIPE
139   
            // Best-effort: SO_NOSIGPIPE is a safety net; write paths
139   
            // Best-effort: SO_NOSIGPIPE is a safety net; write paths
140   
            // also use MSG_NOSIGNAL where available. Failure here
140   
            // also use MSG_NOSIGNAL where available. Failure here
141   
            // should not prevent the accepted connection from being used.
141   
            // should not prevent the accepted connection from being used.
142   
            int one = 1;
142   
            int one = 1;
143   
            (void)::setsockopt(
143   
            (void)::setsockopt(
144   
                new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
144   
                new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
145   
#endif
145   
#endif
146  
146  
147   
            return new_fd;
147   
            return new_fd;
148   
        }
148   
        }
149   
    };
149   
    };
150  
150  
151   
    // Create a plain socket (no atomic flags -- select is POSIX-portable).
151   
    // Create a plain socket (no atomic flags -- select is POSIX-portable).
152   
    static int create_socket(int family, int type, int protocol) noexcept
152   
    static int create_socket(int family, int type, int protocol) noexcept
153   
    {
153   
    {
154   
        return ::socket(family, type, protocol);
154   
        return ::socket(family, type, protocol);
155   
    }
155   
    }
156  
156  
157   
    // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
157   
    // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
158   
    // Caller is responsible for closing fd on error.
158   
    // Caller is responsible for closing fd on error.
159   
    static std::error_code set_fd_options(int fd) noexcept
159   
    static std::error_code set_fd_options(int fd) noexcept
160   
    {
160   
    {
161   
        int flags = ::fcntl(fd, F_GETFL, 0);
161   
        int flags = ::fcntl(fd, F_GETFL, 0);
162   
        if (flags == -1)
162   
        if (flags == -1)
163   
            return make_err(errno);
163   
            return make_err(errno);
164   
        if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
164   
        if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
165   
            return make_err(errno);
165   
            return make_err(errno);
166   
        if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
166   
        if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
167   
            return make_err(errno);
167   
            return make_err(errno);
168  
168  
169   
        if (fd >= FD_SETSIZE)
169   
        if (fd >= FD_SETSIZE)
170   
            return make_err(EMFILE);
170   
            return make_err(EMFILE);
171  
171  
172   
#ifdef SO_NOSIGPIPE
172   
#ifdef SO_NOSIGPIPE
173   
        // Best-effort: SO_NOSIGPIPE is a safety net; write paths
173   
        // Best-effort: SO_NOSIGPIPE is a safety net; write paths
174   
        // also use MSG_NOSIGNAL where available. Match develop's
174   
        // also use MSG_NOSIGNAL where available. Match develop's
175   
        // predominant behavior of ignoring failures here rather
175   
        // predominant behavior of ignoring failures here rather
176   
        // than failing socket creation.
176   
        // than failing socket creation.
177   
        {
177   
        {
178   
            int one = 1;
178   
            int one = 1;
179   
            (void)::setsockopt(
179   
            (void)::setsockopt(
180   
                fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
180   
                fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
181   
        }
181   
        }
182   
#endif
182   
#endif
183  
183  
184   
        return {};
184   
        return {};
185   
    }
185   
    }
186  
186  
187   
    // Apply protocol-specific options after socket creation.
187   
    // Apply protocol-specific options after socket creation.
188   
    // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
188   
    // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
189   
    static std::error_code
189   
    static std::error_code
190   
    configure_ip_socket(int fd, int family) noexcept
190   
    configure_ip_socket(int fd, int family) noexcept
191   
    {
191   
    {
192   
        if (family == AF_INET6)
192   
        if (family == AF_INET6)
193   
        {
193   
        {
194   
            int one = 1;
194   
            int one = 1;
195   
            (void)::setsockopt(
195   
            (void)::setsockopt(
196   
                fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
196   
                fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
197   
        }
197   
        }
198  
198  
199   
        return set_fd_options(fd);
199   
        return set_fd_options(fd);
200   
    }
200   
    }
201  
201  
202   
    // Apply protocol-specific options for acceptor sockets.
202   
    // Apply protocol-specific options for acceptor sockets.
203   
    // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
203   
    // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
204   
    static std::error_code
204   
    static std::error_code
205   
    configure_ip_acceptor(int fd, int family) noexcept
205   
    configure_ip_acceptor(int fd, int family) noexcept
206   
    {
206   
    {
207   
        if (family == AF_INET6)
207   
        if (family == AF_INET6)
208   
        {
208   
        {
209   
            int val = 0;
209   
            int val = 0;
210   
            (void)::setsockopt(
210   
            (void)::setsockopt(
211   
                fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
211   
                fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
212   
        }
212   
        }
213  
213  
214   
        return set_fd_options(fd);
214   
        return set_fd_options(fd);
215   
    }
215   
    }
216  
216  
217   
    // Apply options for local (unix) sockets.
217   
    // Apply options for local (unix) sockets.
218   
    static std::error_code
218   
    static std::error_code
219   
    configure_local_socket(int fd) noexcept
219   
    configure_local_socket(int fd) noexcept
220   
    {
220   
    {
221   
        return set_fd_options(fd);
221   
        return set_fd_options(fd);
222   
    }
222   
    }
223  
223  
224   
    // Non-mutating validation for fds adopted via assign(). Select's
224   
    // Non-mutating validation for fds adopted via assign(). Select's
225   
    // reactor cannot handle fds above FD_SETSIZE, so reject them up
225   
    // reactor cannot handle fds above FD_SETSIZE, so reject them up
226   
    // front instead of letting FD_SET clobber unrelated memory.
226   
    // front instead of letting FD_SET clobber unrelated memory.
227   
    static std::error_code
227   
    static std::error_code
228   
    validate_assigned_fd(int fd) noexcept
228   
    validate_assigned_fd(int fd) noexcept
229   
    {
229   
    {
230   
        if (fd >= FD_SETSIZE)
230   
        if (fd >= FD_SETSIZE)
231   
            return make_err(EMFILE);
231   
            return make_err(EMFILE);
232   
        return {};
232   
        return {};
233   
    }
233   
    }
234   
};
234   
};
235  
235  
236   
} // namespace boost::corosio::detail
236   
} // namespace boost::corosio::detail
237  
237  
238   
#endif // BOOST_COROSIO_HAS_SELECT
238   
#endif // BOOST_COROSIO_HAS_SELECT
239  
239  
240   
#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
240   
#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP