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//
 
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// Copyright (c) 2026 Michael Vandeberg
 
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//
 
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
 
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 
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//
 
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// Official repository: https://github.com/cppalliance/corosio
 
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//
 
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#ifndef BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
 
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#define BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP
 
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#include <boost/corosio/detail/platform.hpp>
 
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#if BOOST_COROSIO_HAS_SELECT
 
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#include <boost/corosio/native/detail/make_err.hpp>
 
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#include <boost/corosio/native/detail/reactor/reactor_descriptor_state.hpp>
 
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#include <system_error>
 
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#include <errno.h>
 
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#include <fcntl.h>
 
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#include <netinet/in.h>
 
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#include <sys/select.h>
 
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#include <sys/socket.h>
 
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#include <unistd.h>
 
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/* select backend traits.
 
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   Captures the platform-specific behavior of the portable select() backend:
 
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   manual fcntl for O_NONBLOCK/FD_CLOEXEC, FD_SETSIZE validation,
 
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   conditional SO_NOSIGPIPE, sendmsg(MSG_NOSIGNAL) where available,
 
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   and accept()+fcntl for accepted connections.
 
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*/
 
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namespace boost::corosio::detail {
 
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class select_scheduler;
 
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struct select_traits
 
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{
 
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    using scheduler_type    = select_scheduler;
 
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    using desc_state_type   = reactor_descriptor_state;
 
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    static constexpr bool needs_write_notification = true;
 
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    // No extra per-socket state or lifecycle hooks needed for select.
 
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    struct stream_socket_hook
 
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    {
 
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        std::error_code on_set_option(
 
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            int fd, int level, int optname,
 
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            void const* data, std::size_t size) noexcept
 
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        {
 
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            if (::setsockopt(
 
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                    fd, level, optname, data,
 
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                    static_cast<socklen_t>(size)) != 0)
 
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                return make_err(errno);
 
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            return {};
 
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        }
 
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        static void pre_shutdown(int) noexcept {}
 
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        static void pre_destroy(int) noexcept {}
 
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    };
 
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    struct write_policy
 
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    {
 
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        static ssize_t write(int fd, iovec* iovecs, int count) noexcept
 
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        {
 
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            msghdr msg{};
 
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            msg.msg_iov    = iovecs;
 
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            msg.msg_iovlen = static_cast<std::size_t>(count);
 
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#ifdef MSG_NOSIGNAL
 
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            constexpr int send_flags = MSG_NOSIGNAL;
 
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#else
 
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            constexpr int send_flags = 0;
 
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#endif
 
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            ssize_t n;
 
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            do
 
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            {
 
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                n = ::sendmsg(fd, &msg, send_flags);
 
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            }
 
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            while (n < 0 && errno == EINTR);
 
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            return n;
 
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        }
 
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    };
 
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    struct accept_policy
 
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    {
 
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        static int do_accept(
 
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            int fd, sockaddr_storage& peer, socklen_t& addrlen) noexcept
 
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        {
 
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            addrlen = sizeof(peer);
 
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            int new_fd;
 
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            do
 
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            {
 
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                new_fd = ::accept(
 
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                    fd, reinterpret_cast<sockaddr*>(&peer), &addrlen);
 
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            }
 
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            while (new_fd < 0 && errno == EINTR);
 
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            if (new_fd < 0)
 
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                return new_fd;
 
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            if (new_fd >= FD_SETSIZE)
 
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            {
 
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                ::close(new_fd);
 
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                errno = EINVAL;
 
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                return -1;
 
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            }
 
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            int flags = ::fcntl(new_fd, F_GETFL, 0);
 
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            if (flags == -1)
 
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            {
 
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                int err = errno;
 
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                ::close(new_fd);
 
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                errno = err;
 
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                return -1;
 
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            }
 
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            if (::fcntl(new_fd, F_SETFL, flags | O_NONBLOCK) == -1)
 
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            {
 
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                int err = errno;
 
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                ::close(new_fd);
 
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                errno = err;
 
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                return -1;
 
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            }
 
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            if (::fcntl(new_fd, F_SETFD, FD_CLOEXEC) == -1)
 
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            {
 
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                int err = errno;
 
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                ::close(new_fd);
 
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                errno = err;
 
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                return -1;
 
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            }
 
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#ifdef SO_NOSIGPIPE
 
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            // Best-effort: SO_NOSIGPIPE is a safety net; write paths
 
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            // also use MSG_NOSIGNAL where available. Failure here
 
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            // should not prevent the accepted connection from being used.
 
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            int one = 1;
 
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            (void)::setsockopt(
 
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                new_fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
 
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#endif
 
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            return new_fd;
 
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        }
 
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    };
 
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    // Create a plain socket (no atomic flags -- select is POSIX-portable).
 
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    static int create_socket(int family, int type, int protocol) noexcept
 
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    {
 
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        return ::socket(family, type, protocol);
 
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    }
 
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    // Set O_NONBLOCK, FD_CLOEXEC; check FD_SETSIZE; optionally SO_NOSIGPIPE.
 
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    // Caller is responsible for closing fd on error.
 
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    static std::error_code set_fd_options(int fd) noexcept
 
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    {
 
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        int flags = ::fcntl(fd, F_GETFL, 0);
 
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        if (flags == -1)
 
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            return make_err(errno);
 
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        if (::fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1)
 
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            return make_err(errno);
 
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        if (::fcntl(fd, F_SETFD, FD_CLOEXEC) == -1)
 
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            return make_err(errno);
 
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        if (fd >= FD_SETSIZE)
 
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            return make_err(EMFILE);
 
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#ifdef SO_NOSIGPIPE
 
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        // Best-effort: SO_NOSIGPIPE is a safety net; write paths
 
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        // also use MSG_NOSIGNAL where available. Match develop's
 
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        // predominant behavior of ignoring failures here rather
 
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        // than failing socket creation.
 
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        {
 
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            int one = 1;
 
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            (void)::setsockopt(
 
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                fd, SOL_SOCKET, SO_NOSIGPIPE, &one, sizeof(one));
 
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        }
 
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#endif
 
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        return {};
 
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    }
 
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    // Apply protocol-specific options after socket creation.
 
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    // For IP sockets, sets IPV6_V6ONLY on AF_INET6 (best-effort).
 
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    static std::error_code
 
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    configure_ip_socket(int fd, int family) noexcept
 
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    {
 
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        if (family == AF_INET6)
 
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        {
 
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            int one = 1;
 
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            (void)::setsockopt(
 
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                fd, IPPROTO_IPV6, IPV6_V6ONLY, &one, sizeof(one));
 
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        }
 
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        return set_fd_options(fd);
 
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    }
 
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    // Apply protocol-specific options for acceptor sockets.
 
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    // For IP acceptors, sets IPV6_V6ONLY=0 (dual-stack, best-effort).
 
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    static std::error_code
 
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    configure_ip_acceptor(int fd, int family) noexcept
 
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    {
 
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        if (family == AF_INET6)
 
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        {
 
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            int val = 0;
 
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            (void)::setsockopt(
 
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                fd, IPPROTO_IPV6, IPV6_V6ONLY, &val, sizeof(val));
 
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        }
 
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        return set_fd_options(fd);
 
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    }
 
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    // Apply options for local (unix) sockets.
 
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    static std::error_code
 
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    configure_local_socket(int fd) noexcept
 
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    {
 
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        return set_fd_options(fd);
 
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    }
 
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    // Non-mutating validation for fds adopted via assign(). Select's
 
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    // reactor cannot handle fds above FD_SETSIZE, so reject them up
 
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    // front instead of letting FD_SET clobber unrelated memory.
 
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    static std::error_code
 
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    validate_assigned_fd(int fd) noexcept
 
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    {
 
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        if (fd >= FD_SETSIZE)
 
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            return make_err(EMFILE);
 
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        return {};
 
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    }
 
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};
 
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} // namespace boost::corosio::detail
 
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#endif // BOOST_COROSIO_HAS_SELECT
 
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#endif // BOOST_COROSIO_NATIVE_DETAIL_SELECT_SELECT_TRAITS_HPP