include/boost/corosio/native/detail/select/select_traits.hpp

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select_traits.hpp

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1		//
2		// Copyright (c) 2026 Michael Vandeberg
3		//
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)
6		//
7		// Official repository: https://github.com/cppalliance/corosio
8		//
9
10		#ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
12
13		#include <boost/corosio/detail/platform.hpp>
14
15		#if BOOST_COROSIO_HAS_SELECT
16
17		#include <boost/corosio/native/detail/make_err.hpp>
18		#include <boost/corosio/native/detail/reactor/reactor_descriptor_state.hpp>
19
20		#include <system_error>
21		#include <tuple>
22
23		#include <errno.h>
24		#include <fcntl.h>
25		#include <netinet/in.h>
26		#include <sys/select.h>
27		#include <sys/socket.h>
28		#include <unistd.h>
29
30		/* select backend traits.
31
32		Captures the platform-specific behavior of the portable select() backend:
33		manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation,
34		mandatory SO_NOSIGPIPE where the platform defines it,
35		sendmsg(MSG_NOSIGNAL) where available, and accept()+fcntl for
36		accepted connections.
37		*/
38
39		namespace boost::corosio::detail {
40
41		class select_scheduler;
42
43		struct select_traits
44		{
45		using scheduler_type = select_scheduler;
46		using desc_state_type = reactor_descriptor_state;
47
48		static constexpr bool needs_write_notification = true;
49
50		// No extra per-socket state or lifecycle hooks needed for select.
51		struct stream_socket_hook
52		{
53	74x	std::error_code on_set_option(
54		int fd, int level, int optname,
55		void const* data, std::size_t size) noexcept
56		{
57	74x	if (::setsockopt(
58		fd, level, optname, data,
59	74x	static_cast<socklen_t>(size)) != 0)
60	2x	return make_err(errno);
61	72x	return {};
62		}
63	30265x	static void pre_shutdown(int) noexcept {}
64	9968x	static void pre_destroy(int) noexcept {}
65		};
66
67		struct write_policy
68		{
69	67x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
70		{
71	67x	msghdr msg{};
72	67x	msg.msg_iov = iovecs;
73	67x	msg.msg_iovlen = static_cast<std::size_t>(count);
74
75		#ifdef MSG_NOSIGNAL
76	67x	constexpr int send_flags = MSG_NOSIGNAL;
77		#else
78		constexpr int send_flags = 0;
79		#endif
80
81		ssize_t n;
82		do
83		{
84	67x	n = ::sendmsg(fd, &msg, send_flags);
85		}
86	67x	while (n < 0 && errno == EINTR);
87	67x	return n;
88		}
89
90		// Single-buffer fast path. Where MSG_NOSIGNAL exists we use
91		// send() to suppress SIGPIPE inline; otherwise fall back to
92		// write() and rely on the SO_NOSIGPIPE set in accept_policy
93		// and set_fd_options.
94	168342x	static ssize_t write_one(
95		int fd, void const* data, std::size_t size) noexcept
96		{
97		ssize_t n;
98		do
99		{
100		#ifdef MSG_NOSIGNAL
101	168342x	n = ::send(fd, data, size, MSG_NOSIGNAL);
102		#else
103		n = ::write(fd, data, size);
104		#endif
105		}
106	168342x	while (n < 0 && errno == EINTR);
107	168342x	return n;
108		}
109		};
110
111		struct accept_policy
112		{
113	6605x	static int do_accept(
114		int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
115		{
116	6605x	addrlen = sizeof(peer);
117		int new_fd;
118		do
119		{
120	6605x	new_fd = ::accept(
121		fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
122		}
123	6605x	while (new_fd < 0 && errno == EINTR);
124
125	6605x	if (new_fd < 0)
126	3306x	return new_fd;
127
128	3299x	if (new_fd >= FD_SETSIZE)
129		{
130	✗	::close(new_fd);
131	✗	errno = EINVAL;
132	✗	return -1;
133		}
134
135	3299x	int flags = ::fcntl(new_fd, F_GETFL, 0);
136	3299x	if (flags == -1)
137		{
138	✗	int err = errno;
139	✗	::close(new_fd);
140	✗	errno = err;
141	✗	return -1;
142		}
143
144	3299x	if (::fcntl(new_fd, F_SETFL, flags \| O_NONBLOCK) == -1)
145		{
146	✗	int err = errno;
147	✗	::close(new_fd);
148	✗	errno = err;
149	✗	return -1;
150		}
151
152	3299x	if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
153		{
154	✗	int err = errno;
155	✗	::close(new_fd);
156	✗	errno = err;
157	✗	return -1;
158		}
159
160		#ifdef SO_NOSIGPIPE
161		// SO_NOSIGPIPE is the only SIGPIPE guard on platforms that
162		// lack MSG_NOSIGNAL (macOS/BSD). Treat failure as fatal,
163		// matching the kqueue backend and Boost.Asio.
164		int one = 1;
165		if (::setsockopt(
166		new_fd, SOL_SOCKET, SO_NOSIGPIPE,
167		&one, sizeof(one)) != 0)
168		{
169		int err = errno;
170		::close(new_fd);
171		errno = err;
172		return -1;
173		}
174		#endif
175
176	3299x	return new_fd;
177		}
178		};
179
180		// Create a plain socket (no atomic flags -- select is POSIX-portable).
181	3694x	static int create_socket(int family, int type, int protocol) noexcept
182		{
183	3694x	return ::socket(family, type, protocol);
184		}
185
186		// Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
187		// Caller is responsible for closing fd on error.
188	3694x	static std::error_code set_fd_options(int fd) noexcept
189		{
190	3694x	int flags = ::fcntl(fd, F_GETFL, 0);
191	3694x	if (flags == -1)
192	✗	return make_err(errno);
193	3694x	if (::fcntl(fd, F_SETFL, flags \| O_NONBLOCK) == -1)
194	✗	return make_err(errno);
195	3694x	if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
196	✗	return make_err(errno);
197
198	3694x	if (fd >= FD_SETSIZE)
199	✗	return make_err(EMFILE);
200
201		#ifdef SO_NOSIGPIPE
202		// SO_NOSIGPIPE is the only SIGPIPE guard on platforms that lack
203		// MSG_NOSIGNAL (macOS/BSD). Treat failure as fatal, matching the
204		// kqueue backend and Boost.Asio. Caller closes fd on error.
205		{
206		int one = 1;
207		if (::setsockopt(
208		fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)) != 0)
209		return make_err(errno);
210		}
211		#endif
212
213	3694x	return {};
214		}
215
216		// Apply protocol-specific options after socket creation.
217		// For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
218		static std::error_code
219	3432x	configure_ip_socket(int fd, int family) noexcept
220		{
221	3432x	if (family == AF_INET6)
222		{
223	21x	int one = 1;
224	42x	std::ignore = ::setsockopt(
225	21x	fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
226		}
227
228	3432x	return set_fd_options(fd);
229		}
230
231		// Apply protocol-specific options for acceptor sockets.
232		// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
233		static std::error_code
234	171x	configure_ip_acceptor(int fd, int family) noexcept
235		{
236	171x	if (family == AF_INET6)
237		{
238	11x	int val = 0;
239	22x	std::ignore = ::setsockopt(
240	11x	fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
241		}
242
243	171x	return set_fd_options(fd);
244		}
245
246		// Apply options for local (unix) sockets.
247		static std::error_code
248	91x	configure_local_socket(int fd) noexcept
249		{
250	91x	return set_fd_options(fd);
251		}
252
253		// Non-mutating validation for fds adopted via assign(). Select's
254		// reactor cannot handle fds above FD_SETSIZE, so reject them up
255		// front instead of letting FD_SET clobber unrelated memory.
256		static std::error_code
257	114x	validate_assigned_fd(int fd) noexcept
258		{
259	114x	if (fd >= FD_SETSIZE)
260	✗	return make_err(EMFILE);
261	114x	return {};
262		}
263		};
264
265		} // namespace boost::corosio::detail
266
267		#endif // BOOST_COROSIO_HAS_SELECT
268
269		#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
270