safesyssocket.h

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/* Copyright (C) 2012,2013,2014,2018,2019 Olly Betts
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
 */

#ifndef XAPIAN_INCLUDED_SAFESYSSOCKET_H
#define XAPIAN_INCLUDED_SAFESYSSOCKET_H

// Some older BSDs require sys/types.h to be included first.  Also seems to
// be needed for some mingw versions.
#include <sys/types.h>
#ifndef __WIN32__
# include <sys/socket.h>
#else
# include "safewinsock2.h"
#endif

#ifdef __WIN32__
# include <type_traits>
# if defined SOCK_CLOEXEC
static_assert(!SOCK_CLOEXEC, "__WIN32__ doesn't support SOCK_CLOEXEC");
# endif
# define SOCK_CLOEXEC 0

static_assert(std::is_unsigned<SOCKET>::value, "SOCKET is unsigned");

inline int xapian_convert_socket_to_int_(SOCKET sock) {
    // Winsock2 function socket() and accept() return the unsigned type SOCKET,
    // which is a 32-bit type for WIN32 and a 64-bit type for WIN64.
    //
    // https://learn.microsoft.com/en-us/windows/win32/winprog64/interprocess-communication
    // says that only the lower 32 bits are significant and one can
    // truncate to 32 bits or sign-extend to 64 bits.
    //
    // We make a slight additional assumption that valid socket values fit
    // in 31 bits (with INVALID_SOCKET being all bits set), which seems to
    // be true in practice.  This means we can cast SOCKET to int and treat
    // the result like a file descriptor (and INVALID_SOCKET casts to -1
    // which matches file descriptor semantics).
    //
    // Ours is not the only code to assume this since it makes it much easier
    // to write code that deals with BSD sockets and winsock2's bastardised
    // version of them) so hopefully Microsoft are unlikely to arbitrarily
    // change this.
    //
    // We check this assumption rather than quietly mangling the value.
    if (rare(sock > SOCKET(0x7fffffff) && sock != INVALID_SOCKET)) {
        closesocket(sock);
        sock = INVALID_SOCKET;
        // "Too many open sockets" seems the most appropriate error to fake.
        WSASetLastError(WSAEMFILE);
    }
    return int(sock);
}

inline int socket_(int domain, int type, int protocol) {
    return xapian_convert_socket_to_int_(socket(domain, type, protocol));
}

# ifdef socket
#  undef socket
# endif
# define socket(D,T,P) socket_(D,T,P)

inline int accept_(int sockfd, struct sockaddr* addr, SOCKLEN_T* addrlen) {
    return xapian_convert_socket_to_int_(accept(sockfd, addr, addrlen));
}

# ifdef accept
#  undef accept
# endif
# define accept(S,A,L) accept_(S,A,L)

#elif !defined SOCK_CLOEXEC
# define SOCK_CLOEXEC 0
#else
// On Linux at least, sometimes SOCK_CLOEXEC is defined but the kernel doesn't
// handle it in socket() or socketpair():

# include <cerrno>

inline int socket_(int domain, int type, int protocol) {
    // Usually type is passed a constant, so we'll collapse to one branch or
    // the other here.  The case where SOCK_CLOEXEC == 0 is handled suitably.
    if (type & SOCK_CLOEXEC) {
        int save_errno = errno;
        int r = socket(domain, type, protocol);
        if (r < 0 && errno == EINVAL) {
            errno = save_errno;
            r = socket(domain, type &~ SOCK_CLOEXEC, protocol);
        }
        return r;
    } else {
        return socket(domain, type, protocol);
    }
}

inline int socketpair_(int domain, int type, int protocol, int *sv) {
    // Usually type is passed a constant, so we'll collapse to one branch or
    // the other here.  The case where SOCK_CLOEXEC == 0 is handled suitably.
    if (type & SOCK_CLOEXEC) {
        int save_errno = errno;
        int r = socketpair(domain, type, protocol, sv);
        if (r != 0 && errno == EINVAL) {
            errno = save_errno;
            r = socketpair(domain, type &~ SOCK_CLOEXEC, protocol, sv);
        }
        return r;
    } else {
        return socketpair(domain, type, protocol, sv);
    }
}

# ifdef socket
#  undef socket
# endif
# define socket(D,T,P) socket_(D,T,P)
# ifdef socketpair
#  undef socketpair
# endif
# define socketpair(D,T,P,S) socketpair_(D,T,P,S)
#endif

#endif // XAPIAN_INCLUDED_SAFESYSSOCKET_H