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	107x	std::error_code on_set_option(
54		int fd,
55		int level,
56		int optname,
57		void const* data,
58		std::size_t size) noexcept
59		{
60	107x	if (::setsockopt(
61	107x	fd, level, optname, data, static_cast<socklen_t>(size)) !=
62		0)
63	4x	return make_err(errno);
64	103x	return {};
65		}
66	19420x	static void pre_shutdown(int) noexcept {}
67	6305x	static void pre_destroy(int) noexcept {}
68		};
69
70		struct write_policy
71		{
72	72x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
73		{
74	72x	msghdr msg{};
75	72x	msg.msg_iov = iovecs;
76	72x	msg.msg_iovlen = static_cast<std::size_t>(count);
77
78		#ifdef MSG_NOSIGNAL
79	72x	constexpr int send_flags = MSG_NOSIGNAL;
80		#else
81		constexpr int send_flags = 0;
82		#endif
83
84		ssize_t n;
85		do
86		{
87	73x	n = ::sendmsg(fd, &msg, send_flags);
88		}
89	73x	while (n < 0 && errno == EINTR);
90	72x	return n;
91		}
92
93		// Single-buffer fast path. Where MSG_NOSIGNAL exists we use
94		// send() to suppress SIGPIPE inline; otherwise fall back to
95		// write() and rely on the SO_NOSIGPIPE set in accept_policy
96		// and set_fd_options.
97		static ssize_t
98	103352x	write_one(int fd, void const* data, std::size_t size) noexcept
99		{
100		ssize_t n;
101		do
102		{
103		#ifdef MSG_NOSIGNAL
104	103353x	n = ::send(fd, data, size, MSG_NOSIGNAL);
105		#else
106		n = ::write(fd, data, size);
107		#endif
108		}
109	103353x	while (n < 0 && errno == EINTR);
110	103352x	return n;
111		}
112		};
113
114		struct accept_policy
115		{
116		static int
117	4154x	do_accept(int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
118		{
119	4154x	addrlen = sizeof(peer);
120		int new_fd;
121		do
122		{
123		new_fd =
124	4155x	::accept(fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
125		}
126	4155x	while (new_fd < 0 && errno == EINTR);
127
128	4154x	if (new_fd < 0)
129	2084x	return new_fd;
130
131	2070x	if (new_fd >= FD_SETSIZE)
132		{
133	1x	::close(new_fd);
134	1x	errno = EMFILE;
135	1x	return -1;
136		}
137
138	2069x	int flags = ::fcntl(new_fd, F_GETFL, 0);
139	2069x	if (flags == -1)
140		{
141	1x	int err = errno;
142	1x	::close(new_fd);
143	1x	errno = err;
144	1x	return -1;
145		}
146
147	2068x	if (::fcntl(new_fd, F_SETFL, flags \| O_NONBLOCK) == -1)
148		{
149	1x	int err = errno;
150	1x	::close(new_fd);
151	1x	errno = err;
152	1x	return -1;
153		}
154
155	2067x	if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
156		{
157	1x	int err = errno;
158	1x	::close(new_fd);
159	1x	errno = err;
160	1x	return -1;
161		}
162
163		#ifdef SO_NOSIGPIPE
164		// MSG_NOSIGNAL is not universal across the platforms this
165		// portable backend covers, and the write() the fast path
166		// falls back to there takes no flag at all; SO_NOSIGPIPE is
167		// the per-descriptor guard that covers both. Treat failure
168		// as fatal, matching the kqueue backend.
169		int one = 1;
170		if (::setsockopt(
171		new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)) != 0)
172		{
173		int err = errno;
174		::close(new_fd);
175		errno = err;
176		return -1;
177		}
178		#endif
179
180	2066x	return new_fd;
181		}
182		};
183
184		// Create a plain socket (no atomic flags -- select is POSIX-portable).
185	2673x	static int create_socket(int family, int type, int protocol) noexcept
186		{
187	2673x	return ::socket(family, type, protocol);
188		}
189
190		// Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
191		// Caller is responsible for closing fd on error.
192	2667x	static std::error_code set_fd_options(int fd) noexcept
193		{
194	2667x	int flags = ::fcntl(fd, F_GETFL, 0);
195	2667x	if (flags == -1)
196	2x	return make_err(errno);
197	2665x	if (::fcntl(fd, F_SETFL, flags \| O_NONBLOCK) == -1)
198	2x	return make_err(errno);
199	2663x	if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
200	2x	return make_err(errno);
201
202	2661x	if (fd >= FD_SETSIZE)
203	2x	return make_err(EMFILE);
204
205		#ifdef SO_NOSIGPIPE
206		// MSG_NOSIGNAL is not universal across the platforms this
207		// portable backend covers, and the write() the fast path falls
208		// back to there takes no flag at all; SO_NOSIGPIPE is the
209		// per-descriptor guard that covers both. Treat failure as fatal,
210		// matching the kqueue backend. Caller closes fd on error.
211		{
212		int one = 1;
213		if (::setsockopt(fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one)) !=
214		0)
215		return make_err(errno);
216		}
217		#endif
218
219	2659x	return {};
220		}
221
222		// Apply protocol-specific options after socket creation.
223		// For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
224	2283x	static std::error_code configure_ip_socket(int fd, int family) noexcept
225		{
226	2283x	if (family == AF_INET6)
227		{
228	22x	int one = 1;
229		std::ignore =
230	22x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
231		}
232
233	2283x	return set_fd_options(fd);
234		}
235
236		// Apply protocol-specific options for acceptor sockets.
237		// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
238	275x	static std::error_code configure_ip_acceptor(int fd, int family) noexcept
239		{
240	275x	if (family == AF_INET6)
241		{
242	11x	int val = 0;
243		std::ignore =
244	11x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
245		}
246
247	275x	return set_fd_options(fd);
248		}
249
250		// Apply options for local (unix) sockets.
251	109x	static std::error_code configure_local_socket(int fd) noexcept
252		{
253	109x	return set_fd_options(fd);
254		}
255
256		// Non-mutating validation for fds adopted via assign(). Select's
257		// reactor cannot handle fds above FD_SETSIZE, so reject them up
258		// front instead of letting FD_SET clobber unrelated memory.
259	155x	static std::error_code validate_assigned_fd(int fd) noexcept
260		{
261	155x	if (fd >= FD_SETSIZE)
262	2x	return make_err(EMFILE);
263	153x	return {};
264		}
265		};
266
267		} // namespace boost::corosio::detail
268
269		#endif // BOOST_COROSIO_HAS_SELECT
270
271		#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
272