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	155x	std::error_code on_set_option(
49		int fd, int level, int optname,
50		void const* data, std::size_t size) noexcept
51		{
52	155x	if (::setsockopt(
53		fd, level, optname, data,
54	155x	static_cast<socklen_t>(size)) != 0)
55	2x	return make_err(errno);
56	153x	return {};
57		}
58	34251x	static void pre_shutdown(int) noexcept {}
59	11297x	static void pre_destroy(int) noexcept {}
60		};
61
62		struct write_policy
63		{
64	71x	static ssize_t write(int fd, iovec* iovecs, int count) noexcept
65		{
66	71x	msghdr msg{};
67	71x	msg.msg_iov = iovecs;
68	71x	msg.msg_iovlen = static_cast<std::size_t>(count);
69
70		ssize_t n;
71		do
72		{
73	71x	n = ::sendmsg(fd, &msg, MSG_NOSIGNAL);
74		}
75	71x	while (n < 0 && errno == EINTR);
76	71x	return n;
77		}
78
79	168736x	static ssize_t write_one(
80		int fd, void const* data, std::size_t size) noexcept
81		{
82		ssize_t n;
83		do
84		{
85	168736x	n = ::send(fd, data, size, MSG_NOSIGNAL);
86		}
87	168736x	while (n < 0 && errno == EINTR);
88	168736x	return n;
89		}
90		};
91
92		struct accept_policy
93		{
94	7464x	static int do_accept(
95		int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
96		{
97	7464x	addrlen = sizeof(peer);
98		int new_fd;
99		do
100		{
101	7464x	new_fd = ::accept4(
102		fd, reinterpret_cast<sockaddr*>(&peer), &addrlen,
103		SOCK_NONBLOCK \| SOCK_CLOEXEC);
104		}
105	7464x	while (new_fd < 0 && errno == EINTR);
106	7464x	return new_fd;
107		}
108		};
109
110		// Create a nonblocking, close-on-exec socket using Linux's atomic flags.
111	4223x	static int create_socket(int family, int type, int protocol) noexcept
112		{
113	4223x	return ::socket(family, type \| SOCK_NONBLOCK \| SOCK_CLOEXEC, protocol);
114		}
115
116		// Apply protocol-specific options after socket creation.
117		// For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
118		static std::error_code
119	3881x	configure_ip_socket(int fd, int family) noexcept
120		{
121	3881x	if (family == AF_INET6)
122		{
123	21x	int one = 1;
124	42x	std::ignore = ::setsockopt(
125	21x	fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
126		}
127	3881x	return {};
128		}
129
130		// Apply protocol-specific options for acceptor sockets.
131		// For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
132		static std::error_code
133	246x	configure_ip_acceptor(int fd, int family) noexcept
134		{
135	246x	if (family == AF_INET6)
136		{
137	11x	int val = 0;
138	22x	std::ignore = ::setsockopt(
139	11x	fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
140		}
141	246x	return {};
142		}
143
144		// No extra configuration needed for local (unix) sockets on epoll.
145		static std::error_code
146	96x	configure_local_socket(int /fd/) noexcept
147		{
148	96x	return {};
149		}
150
151		// Non-mutating validation for fds adopted via assign(). Used when
152		// the caller retains fd ownership responsibility.
153		static std::error_code
154	120x	validate_assigned_fd(int /fd/) noexcept
155		{
156	120x	return {};
157		}
158		};
159
160		} // namespace boost::corosio::detail
161
162		#endif // BOOST_COROSIO_HAS_EPOLL
163
164		#endif // BOOST_COROSIO_NATIVE_DETAIL_EPOLL_EPOLL_TRAITS_HPP
165