include/boost/corosio/native/detail/epoll/epoll_traits.hpp

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epoll_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_EPOLL_EPOLL_TRAITS_HPP
11		#define BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_TRAITS_HPP
12
13		#include <boost/corosio/detail/platform.hpp>
14
15		#if BOOST_COROSIO_HAS_EPOLL
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 <netinet/in.h>
25		#include <sys/socket.h>
26
27		/* epoll backend traits.
28
29		Captures the platform-specific behavior of the Linux epoll backend:
30		atomic SOCK_NONBLOCK\|SOCK_CLOEXEC on socket(), accept4() for
31		accepted connections, and sendmsg(MSG_NOSIGNAL) for writes.
32		*/
33
34		namespace boost::corosio::detail {
35
36		class epoll_scheduler;
37
38		struct epoll_traits
39		{
40		using scheduler_type = epoll_scheduler;
41		using desc_state_type = reactor_descriptor_state;
42
43		static constexpr bool needs_write_notification = false;
44
45		// No extra per-socket state or lifecycle hooks needed for epoll.
46		struct stream_socket_hook
47		{
48	191x	std::error_code on_set_option(
49		int fd,
50		int level,
51		int optname,
52		void const* data,
53		std::size_t size) noexcept
54		{
55	191x	if (::setsockopt(
56	191x	fd, level, optname, data, static_cast<socklen_t>(size)) !=
57		0)
58	5x	return make_err(errno);
59	186x	return {};
60		}
61	22977x	static void pre_shutdown(int) noexcept {}
62	7469x	static void pre_destroy(int) noexcept {}
63		};
64
65		struct write_policy
66		{
67	75x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
68		{
69	75x	msghdr msg{};
70	75x	msg.msg_iov = iovecs;
71	75x	msg.msg_iovlen = static_cast<std::size_t>(count);
72
73		ssize_t n;
74		do
75		{
76	76x	n = ::sendmsg(fd, &msg, MSG_NOSIGNAL);
77		}
78	76x	while (n < 0 && errno == EINTR);
79	75x	return n;
80		}
81
82		static ssize_t
83	98995x	write_one(int fd, void const* data, std::size_t size) noexcept
84		{
85		ssize_t n;
86		do
87		{
88	98996x	n = ::send(fd, data, size, MSG_NOSIGNAL);
89		}
90	98996x	while (n < 0 && errno == EINTR);
91	98995x	return n;
92		}
93		};
94
95		struct accept_policy
96		{
97		static int
98	4962x	do_accept(int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
99		{
100	4962x	addrlen = sizeof(peer);
101		int new_fd;
102		do
103		{
104	4963x	new_fd = ::accept4(
105		fd, reinterpret_cast<sockaddr*>(&peer), &addrlen,
106		SOCK_NONBLOCK \| SOCK_CLOEXEC);
107		}
108	4963x	while (new_fd < 0 && errno == EINTR);
109	4962x	return new_fd;
110		}
111		};
112
113		// Create a nonblocking, close-on-exec socket using Linux's atomic flags.
114	3114x	static int create_socket(int family, int type, int protocol) noexcept
115		{
116	3114x	return ::socket(family, type \| SOCK_NONBLOCK \| SOCK_CLOEXEC, protocol);
117		}
118
119		// Apply protocol-specific options after socket creation.
120		// For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
121	2647x	static std::error_code configure_ip_socket(int fd, int family) noexcept
122		{
123	2647x	if (family == AF_INET6)
124		{
125	22x	int one = 1;
126		std::ignore =
127	22x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
128		}
129	2647x	return {};
130		}
131
132		// Apply protocol-specific options for acceptor sockets.
133		// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
134	342x	static std::error_code configure_ip_acceptor(int fd, int family) noexcept
135		{
136	342x	if (family == AF_INET6)
137		{
138	11x	int val = 0;
139		std::ignore =
140	11x	::setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
141		}
142	342x	return {};
143		}
144
145		// No extra configuration needed for local (unix) sockets on epoll.
146	116x	static std::error_code configure_local_socket(int /fd/) noexcept
147		{
148	116x	return {};
149		}
150
151		// Non-mutating validation for fds adopted via assign(). Used when
152		// the caller retains fd ownership responsibility.
153	168x	static std::error_code validate_assigned_fd(int /fd/) noexcept
154		{
155	168x	return {};
156		}
157		};
158
159		} // namespace boost::corosio::detail
160
161		#endif // BOOST_COROSIO_HAS_EPOLL
162
163		#endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_TRAITS_HPP
164