/*      $NetBSD: signal.c,v 1.6 2024/08/18 20:47:21 christos Exp $      */

/*      $OpenBSD: select.c,v 1.2 2002/06/25 15:50:15 mickey Exp $       */

/*
* Copyright 2000-2007 Niels Provos <[email protected]>
* Copyright 2007-2012 Niels Provos and Nick Mathewson
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
*    derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "event2/event-config.h"
#include "evconfig-private.h"

#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include <winsock2.h>
#include <windows.h>
#undef WIN32_LEAN_AND_MEAN
#endif
#include <sys/types.h>
#ifdef EVENT__HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#include <sys/queue.h>
#ifdef EVENT__HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef EVENT__HAVE_UNISTD_H
#include <unistd.h>
#endif
#include <errno.h>
#ifdef EVENT__HAVE_FCNTL_H
#include <fcntl.h>
#endif

#include "event2/event.h"
#include "event2/event_struct.h"
#include "event-internal.h"
#include "event2/util.h"
#include "evsignal-internal.h"
#include "log-internal.h"
#include "evmap-internal.h"
#include "evthread-internal.h"

/*
 signal.c

 This is the signal-handling implementation we use for backends that don't
 have a better way to do signal handling.  It uses sigaction() or signal()
 to set a signal handler, and a socket pair to tell the event base when

 Note that I said "the event base" : only one event base can be set up to use
 this at a time.  For historical reasons and backward compatibility, if you
 add an event for a signal to event_base A, then add an event for a signal
 (any signal!) to event_base B, event_base B will get informed about the
 signal, but event_base A won't.

 It would be neat to change this behavior in some future version of Libevent.
 kqueue already does something far more sensible.  We can make all backends
 on Linux do a reasonable thing using signalfd.
*/

#ifndef _WIN32
/* Windows wants us to call our signal handlers as __cdecl.  Nobody else
* expects you to do anything crazy like this. */
#ifndef __cdecl
#define __cdecl
#endif
#endif

static int evsig_add(struct event_base *, evutil_socket_t, short, short, void *);
static int evsig_del(struct event_base *, evutil_socket_t, short, short, void *);

static const struct eventop evsigops = {
       "signal",
       NULL,
       evsig_add,
       evsig_del,
       NULL,
       NULL,
       0, 0, 0
};

#ifndef EVENT__DISABLE_THREAD_SUPPORT
/* Lock for evsig_base and evsig_base_n_signals_added fields. */
static void *evsig_base_lock = NULL;
#endif
/* The event base that's currently getting informed about signals. */
static struct event_base *evsig_base = NULL;
/* A copy of evsig_base->sigev_n_signals_added. */
static int evsig_base_n_signals_added = 0;
static evutil_socket_t evsig_base_fd = -1;

static void __cdecl evsig_handler(int sig);

#define EVSIGBASE_LOCK() EVLOCK_LOCK(evsig_base_lock, 0)
#define EVSIGBASE_UNLOCK() EVLOCK_UNLOCK(evsig_base_lock, 0)

void
evsig_set_base_(struct event_base *base)
{
       EVSIGBASE_LOCK();
       evsig_base = base;
       evsig_base_n_signals_added = base->sig.ev_n_signals_added;
       evsig_base_fd = base->sig.ev_signal_pair[1];
       EVSIGBASE_UNLOCK();
}

/* Callback for when the signal handler write a byte to our signaling socket */
static void
evsig_cb(evutil_socket_t fd, short what, void *arg)
{
       static char signals[1024];
       ev_ssize_t n;
       int i;
       int ncaught[NSIG];
       struct event_base *base;

       base = arg;

       memset(&ncaught, 0, sizeof(ncaught));

       while (1) {
#ifdef _WIN32
               n = recv(fd, signals, sizeof(signals), 0);
#else
               n = read(fd, signals, sizeof(signals));
#endif
               if (n == -1) {
                       int err = evutil_socket_geterror(fd);
                       if (! EVUTIL_ERR_RW_RETRIABLE(err))
                               event_sock_err(1, fd, "%s: recv", __func__);
                       break;
               } else if (n == 0) {
                       /* XXX warn? */
                       break;
               }
               for (i = 0; i < n; ++i) {
                       ev_uint8_t sig = signals[i];
                       if (sig < NSIG)
                               ncaught[sig]++;
               }
       }

       EVBASE_ACQUIRE_LOCK(base, th_base_lock);
       for (i = 0; i < NSIG; ++i) {
               if (ncaught[i])
                       evmap_signal_active_(base, i, ncaught[i]);
       }
       EVBASE_RELEASE_LOCK(base, th_base_lock);
}

int
evsig_init_(struct event_base *base)
{
       /*
        * Our signal handler is going to write to one end of the socket
        * pair to wake up our event loop.  The event loop then scans for
        * signals that got delivered.
        */
       if (evutil_make_internal_pipe_(base->sig.ev_signal_pair) == -1) {
#ifdef _WIN32
               /* Make this nonfatal on win32, where sometimes people
                  have localhost firewalled. */
               event_sock_warn(-1, "%s: socketpair", __func__);
#else
               event_sock_err(1, -1, "%s: socketpair", __func__);
#endif
               return -1;
       }

       if (base->sig.sh_old) {
               mm_free(base->sig.sh_old);
       }
       base->sig.sh_old = NULL;
       base->sig.sh_old_max = 0;

       event_assign(&base->sig.ev_signal, base, base->sig.ev_signal_pair[0],
               EV_READ | EV_PERSIST, evsig_cb, base);

       base->sig.ev_signal.ev_flags |= EVLIST_INTERNAL;
       event_priority_set(&base->sig.ev_signal, 0);

       base->evsigsel = &evsigops;

       return 0;
}

/* Helper: set the signal handler for evsignal to handler in base, so that
* we can restore the original handler when we clear the current one. */
int
evsig_set_handler_(struct event_base *base,
   int evsignal, void (__cdecl *handler)(int))
{
#ifdef EVENT__HAVE_SIGACTION
       struct sigaction sa;
#else
       ev_sighandler_t sh;
#endif
       struct evsig_info *sig = &base->sig;
       void *p;

       /*
        * resize saved signal handler array up to the highest signal number.
        * a dynamic array is used to keep footprint on the low side.
        */
       if (evsignal >= sig->sh_old_max) {
               int new_max = evsignal + 1;
               event_debug(("%s: evsignal (%d) >= sh_old_max (%d), resizing",
                           __func__, evsignal, sig->sh_old_max));
               p = mm_realloc(sig->sh_old, new_max * sizeof(*sig->sh_old));
               if (p == NULL) {
                       event_warn("realloc");
                       return (-1);
               }

               memset((char *)p + sig->sh_old_max * sizeof(*sig->sh_old),
                   0, (new_max - sig->sh_old_max) * sizeof(*sig->sh_old));

               sig->sh_old_max = new_max;
               sig->sh_old = p;
       }

       /* allocate space for previous handler out of dynamic array */
       sig->sh_old[evsignal] = mm_malloc(sizeof *sig->sh_old[evsignal]);
       if (sig->sh_old[evsignal] == NULL) {
               event_warn("malloc");
               return (-1);
       }

       /* save previous handler and setup new handler */
#ifdef EVENT__HAVE_SIGACTION
       memset(&sa, 0, sizeof(sa));
       sa.sa_handler = handler;
       sa.sa_flags |= SA_RESTART;
       sigfillset(&sa.sa_mask);

       if (sigaction(evsignal, &sa, sig->sh_old[evsignal]) == -1) {
               event_warn("sigaction");
               mm_free(sig->sh_old[evsignal]);
               sig->sh_old[evsignal] = NULL;
               return (-1);
       }
#else
       if ((sh = signal(evsignal, handler)) == SIG_ERR) {
               event_warn("signal");
               mm_free(sig->sh_old[evsignal]);
               sig->sh_old[evsignal] = NULL;
               return (-1);
       }
       *sig->sh_old[evsignal] = sh;
#endif

       return (0);
}

static int
evsig_add(struct event_base *base, evutil_socket_t evsignal, short old, short events, void *p)
{
       struct evsig_info *sig = &base->sig;
       (void)p;

       EVUTIL_ASSERT(evsignal >= 0 && evsignal < NSIG);

       /* catch signals if they happen quickly */
       EVSIGBASE_LOCK();
       if (evsig_base != base && evsig_base_n_signals_added) {
               event_warnx("Added a signal to event base %p with signals "
                   "already added to event_base %p.  Only one can have "
                   "signals at a time with the %s backend.  The base with "
                   "the most recently added signal or the most recent "
                   "event_base_loop() call gets preference; do "
                   "not rely on this behavior in future Libevent versions.",
                   base, evsig_base, base->evsel->name);
       }
       evsig_base = base;
       evsig_base_n_signals_added = ++sig->ev_n_signals_added;
       evsig_base_fd = base->sig.ev_signal_pair[1];
       EVSIGBASE_UNLOCK();

       event_debug(("%s: %d: changing signal handler", __func__, (int)evsignal));
       if (evsig_set_handler_(base, (int)evsignal, evsig_handler) == -1) {
               goto err;
       }


       if (!sig->ev_signal_added) {
               if (event_add_nolock_(&sig->ev_signal, NULL, 0))
                       goto err;
               sig->ev_signal_added = 1;
       }

       return (0);

err:
       EVSIGBASE_LOCK();
       --evsig_base_n_signals_added;
       --sig->ev_n_signals_added;
       EVSIGBASE_UNLOCK();
       return (-1);
}

int
evsig_restore_handler_(struct event_base *base, int evsignal)
{
       int ret = 0;
       struct evsig_info *sig = &base->sig;
#ifdef EVENT__HAVE_SIGACTION
       struct sigaction *sh;
#else
       ev_sighandler_t *sh;
#endif

       if (evsignal >= sig->sh_old_max) {
               /* Can't actually restore. */
               /* XXXX.*/
               return 0;
       }

       /* restore previous handler */
       sh = sig->sh_old[evsignal];
       sig->sh_old[evsignal] = NULL;
#ifdef EVENT__HAVE_SIGACTION
       if (sigaction(evsignal, sh, NULL) == -1) {
               event_warn("sigaction");
               ret = -1;
       }
#else
       if (signal(evsignal, *sh) == SIG_ERR) {
               event_warn("signal");
               ret = -1;
       }
#endif

       mm_free(sh);

       return ret;
}

static int
evsig_del(struct event_base *base, evutil_socket_t evsignal, short old, short events, void *p)
{
       EVUTIL_ASSERT(evsignal >= 0 && evsignal < NSIG);

       event_debug(("%s: "EV_SOCK_FMT": restoring signal handler",
               __func__, EV_SOCK_ARG(evsignal)));

       EVSIGBASE_LOCK();
       --evsig_base_n_signals_added;
       --base->sig.ev_n_signals_added;
       EVSIGBASE_UNLOCK();

       return (evsig_restore_handler_(base, (int)evsignal));
}

static void __cdecl
evsig_handler(int sig)
{
       int save_errno = errno;
#ifdef _WIN32
       int socket_errno = EVUTIL_SOCKET_ERROR();
#endif
       ev_uint8_t msg;

       if (evsig_base == NULL) {
               event_warnx(
                       "%s: received signal %d, but have no base configured",
                       __func__, sig);
               return;
       }

#ifndef EVENT__HAVE_SIGACTION
       signal(sig, evsig_handler);
#endif

       /* Wake up our notification mechanism */
       msg = sig;
#ifdef _WIN32
       send(evsig_base_fd, (char*)&msg, 1, 0);
#else
       {
               int r = write(evsig_base_fd, (char*)&msg, 1);
               (void)r; /* Suppress 'unused return value' and 'unused var' */
       }
#endif
       errno = save_errno;
#ifdef _WIN32
       EVUTIL_SET_SOCKET_ERROR(socket_errno);
#endif
}

void
evsig_dealloc_(struct event_base *base)
{
       int i = 0;
       if (base->sig.ev_signal_added) {
               event_del(&base->sig.ev_signal);
               base->sig.ev_signal_added = 0;
       }
       /* debug event is created in evsig_init_/event_assign even when
        * ev_signal_added == 0, so unassign is required */
       event_debug_unassign(&base->sig.ev_signal);

       for (i = 0; i < NSIG; ++i) {
               if (i < base->sig.sh_old_max && base->sig.sh_old[i] != NULL)
                       evsig_restore_handler_(base, i);
       }
       EVSIGBASE_LOCK();
       if (base == evsig_base) {
               evsig_base = NULL;
               evsig_base_n_signals_added = 0;
               evsig_base_fd = -1;
       }
       EVSIGBASE_UNLOCK();

       if (base->sig.ev_signal_pair[0] != -1) {
               evutil_closesocket(base->sig.ev_signal_pair[0]);
               base->sig.ev_signal_pair[0] = -1;
       }
       if (base->sig.ev_signal_pair[1] != -1) {
               evutil_closesocket(base->sig.ev_signal_pair[1]);
               base->sig.ev_signal_pair[1] = -1;
       }
       base->sig.sh_old_max = 0;

       /* per index frees are handled in evsig_del() */
       if (base->sig.sh_old) {
               mm_free(base->sig.sh_old);
               base->sig.sh_old = NULL;
       }
}

static void
evsig_free_globals_locks(void)
{
#ifndef EVENT__DISABLE_THREAD_SUPPORT
       if (evsig_base_lock != NULL) {
               EVTHREAD_FREE_LOCK(evsig_base_lock, 0);
               evsig_base_lock = NULL;
       }
#endif
       return;
}

void
evsig_free_globals_(void)
{
       evsig_free_globals_locks();
}

#ifndef EVENT__DISABLE_THREAD_SUPPORT
int
evsig_global_setup_locks_(const int enable_locks)
{
       EVTHREAD_SETUP_GLOBAL_LOCK(evsig_base_lock, 0);
       return 0;
}

#endif