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
22		#include <errno.h>
23		#include <fcntl.h>
24		#include <netinet/in.h>
25		#include <sys/select.h>
26		#include <sys/socket.h>
27		#include <unistd.h>
28
29		/* select backend traits.
30
31		Captures the platform-specific behavior of the portable select() backend:
32		manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation,
33		conditional SO_NOSIGPIPE, sendmsg(MSG_NOSIGNAL) where available,
34		and accept()+fcntl for accepted connections.
35		*/
36
37		namespace boost::corosio::detail {
38
39		class select_scheduler;
40		struct select_descriptor_state;
41
42		struct select_traits
43		{
44		using scheduler_type = select_scheduler;
45		using desc_state_type = select_descriptor_state;
46
47		static constexpr bool needs_write_notification = true;
48
49		/// No extra per-socket state or lifecycle hooks needed for select.
50		struct stream_socket_hook
51		{
52	28x	std::error_code on_set_option(
53		int fd, int level, int optname,
54		void const* data, std::size_t size) noexcept
55		{
56	28x	if (::setsockopt(
57		fd, level, optname, data,
58	28x	static_cast<socklen_t>(size)) != 0)
59	✗	return make_err(errno);
60	28x	return {};
61		}
62	✗	static void pre_shutdown(int) noexcept {}
63	4038x	static void pre_destroy(int) noexcept {}
64		};
65
66		struct write_policy
67		{
68	131116x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
69		{
70	131116x	msghdr msg{};
71	131116x	msg.msg_iov = iovecs;
72	131116x	msg.msg_iovlen = static_cast<std::size_t>(count);
73
74		#ifdef MSG_NOSIGNAL
75	131116x	constexpr int send_flags = MSG_NOSIGNAL;
76		#else
77		constexpr int send_flags = 0;
78		#endif
79
80		ssize_t n;
81		do
82		{
83	131116x	n = ::sendmsg(fd, &msg, send_flags);
84		}
85	131116x	while (n < 0 && errno == EINTR);
86	131116x	return n;
87		}
88		};
89
90		struct accept_policy
91		{
92	2674x	static int do_accept(
93		int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
94		{
95	2674x	addrlen = sizeof(peer);
96		int new_fd;
97		do
98		{
99	2674x	new_fd = ::accept(
100		fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
101		}
102	2674x	while (new_fd < 0 && errno == EINTR);
103
104	2674x	if (new_fd < 0)
105	1337x	return new_fd;
106
107	1337x	if (new_fd >= FD_SETSIZE)
108		{
109	✗	::close(new_fd);
110	✗	errno = EINVAL;
111	✗	return -1;
112		}
113
114	1337x	int flags = ::fcntl(new_fd, F_GETFL, 0);
115	1337x	if (flags == -1)
116		{
117	✗	int err = errno;
118	✗	::close(new_fd);
119	✗	errno = err;
120	✗	return -1;
121		}
122
123	1337x	if (::fcntl(new_fd, F_SETFL, flags \| O_NONBLOCK) == -1)
124		{
125	✗	int err = errno;
126	✗	::close(new_fd);
127	✗	errno = err;
128	✗	return -1;
129		}
130
131	1337x	if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
132		{
133	✗	int err = errno;
134	✗	::close(new_fd);
135	✗	errno = err;
136	✗	return -1;
137		}
138
139		#ifdef SO_NOSIGPIPE
140		int one = 1;
141		if (::setsockopt(
142		new_fd, SOL_SOCKET, SO_NOSIGPIPE,
143		&one, sizeof(one)) == -1)
144		{
145		int err = errno;
146		::close(new_fd);
147		errno = err;
148		return -1;
149		}
150		#endif
151
152	1337x	return new_fd;
153		}
154		};
155
156		/// Create a plain socket (no atomic flags — select is POSIX-portable).
157	1481x	static int create_socket(int family, int type, int protocol) noexcept
158		{
159	1481x	return ::socket(family, type, protocol);
160		}
161
162		/// Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
163		/// Caller is responsible for closing fd on error.
164	1495x	static std::error_code set_fd_options(int fd) noexcept
165		{
166	1495x	int flags = ::fcntl(fd, F_GETFL, 0);
167	1495x	if (flags == -1)
168	✗	return make_err(errno);
169	1495x	if (::fcntl(fd, F_SETFL, flags \| O_NONBLOCK) == -1)
170	✗	return make_err(errno);
171	1495x	if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
172	✗	return make_err(errno);
173
174	1495x	if (fd >= FD_SETSIZE)
175	✗	return make_err(EMFILE);
176
177		#ifdef SO_NOSIGPIPE
178		{
179		int one = 1;
180		::setsockopt(fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
181		}
182		#endif
183
184	1495x	return {};
185		}
186
187		/// Apply protocol-specific options after socket creation.
188		/// For IP sockets, sets IPV6_V6ONLY on AF_INET6.
189		static std::error_code
190	1398x	configure_ip_socket(int fd, int family) noexcept
191		{
192	1398x	if (family == AF_INET6)
193		{
194	13x	int one = 1;
195	13x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
196		}
197
198	1398x	return set_fd_options(fd);
199		}
200
201		/// Apply protocol-specific options for acceptor sockets.
202		/// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack).
203		static std::error_code
204	63x	configure_ip_acceptor(int fd, int family) noexcept
205		{
206	63x	if (family == AF_INET6)
207		{
208	8x	int val = 0;
209	8x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
210		}
211
212	63x	return set_fd_options(fd);
213		}
214
215		/// Apply options for local (unix) sockets.
216		static std::error_code
217	34x	configure_local_socket(int fd) noexcept
218		{
219	34x	return set_fd_options(fd);
220		}
221		};
222
223		} // namespace boost::corosio::detail
224
225		#endif // BOOST_COROSIO_HAS_SELECT
226
227		#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
228