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
22		#include <errno.h>
23		#include <netinet/in.h>
24		#include <sys/socket.h>
25
26		/* epoll backend traits.
27
28		Captures the platform-specific behavior of the Linux epoll backend:
29		atomic SOCK_NONBLOCK\|SOCK_CLOEXEC on socket(), accept4() for
30		accepted connections, and sendmsg(MSG_NOSIGNAL) for writes.
31		*/
32
33		namespace boost::corosio::detail {
34
35		class epoll_scheduler;
36
37		struct epoll_traits
38		{
39		using scheduler_type = epoll_scheduler;
40		using desc_state_type = reactor_descriptor_state;
41
42		static constexpr bool needs_write_notification = false;
43
44		// No extra per-socket state or lifecycle hooks needed for epoll.
45		struct stream_socket_hook
46		{
47	32x	std::error_code on_set_option(
48		int fd, int level, int optname,
49		void const* data, std::size_t size) noexcept
50		{
51	32x	if (::setsockopt(
52		fd, level, optname, data,
53	32x	static_cast<socklen_t>(size)) != 0)
54	✗	return make_err(errno);
55	32x	return {};
56		}
57	24581x	static void pre_shutdown(int) noexcept {}
58	8180x	static void pre_destroy(int) noexcept {}
59		};
60
61		struct write_policy
62		{
63	119129x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
64		{
65	119129x	msghdr msg{};
66	119129x	msg.msg_iov = iovecs;
67	119129x	msg.msg_iovlen = static_cast<std::size_t>(count);
68
69		ssize_t n;
70		do
71		{
72	119129x	n = ::sendmsg(fd, &msg, MSG_NOSIGNAL);
73		}
74	119129x	while (n < 0 && errno == EINTR);
75	119129x	return n;
76		}
77		};
78
79		struct accept_policy
80		{
81	5414x	static int do_accept(
82		int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
83		{
84	5414x	addrlen = sizeof(peer);
85		int new_fd;
86		do
87		{
88	5414x	new_fd = ::accept4(
89		fd, reinterpret_cast<sockaddr*>(&peer), &addrlen,
90		SOCK_NONBLOCK \| SOCK_CLOEXEC);
91		}
92	5414x	while (new_fd < 0 && errno == EINTR);
93	5414x	return new_fd;
94		}
95		};
96
97		// Create a nonblocking, close-on-exec socket using Linux's atomic flags.
98	2884x	static int create_socket(int family, int type, int protocol) noexcept
99		{
100	2884x	return ::socket(family, type \| SOCK_NONBLOCK \| SOCK_CLOEXEC, protocol);
101		}
102
103		// Apply protocol-specific options after socket creation.
104		// For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
105		static std::error_code
106	2770x	configure_ip_socket(int fd, int family) noexcept
107		{
108	2770x	if (family == AF_INET6)
109		{
110	14x	int one = 1;
111	14x	(void)::setsockopt(
112		fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
113		}
114	2770x	return {};
115		}
116
117		// Apply protocol-specific options for acceptor sockets.
118		// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
119		static std::error_code
120	94x	configure_ip_acceptor(int fd, int family) noexcept
121		{
122	94x	if (family == AF_INET6)
123		{
124	9x	int val = 0;
125	9x	(void)::setsockopt(
126		fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
127		}
128	94x	return {};
129		}
130
131		// No extra configuration needed for local (unix) sockets on epoll.
132		static std::error_code
133	20x	configure_local_socket(int /fd/) noexcept
134		{
135	20x	return {};
136		}
137
138		// Non-mutating validation for fds adopted via assign(). Used when
139		// the caller retains fd ownership responsibility.
140		static std::error_code
141	14x	validate_assigned_fd(int /fd/) noexcept
142		{
143	14x	return {};
144		}
145		};
146
147		} // namespace boost::corosio::detail
148
149		#endif // BOOST_COROSIO_HAS_EPOLL
150
151		#endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_TRAITS_HPP
152