signal.c

/**
 * @file
 * Signal handling
 *
 * @authors
 * Copyright (C) 1996-2000,2012 Michael R. Elkins <me@mutt.org>
 *
 * @copyright
 * 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, see <http://www.gnu.org/licenses/>.
 */

#include "config.h"
#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "globals.h"
#include "lib/lib.h"
#include "mutt_curses.h"
#include "options.h"

static sigset_t Sigset;
static sigset_t SigsetSys;
static struct sigaction SysOldInt;
static struct sigaction SysOldQuit;
static int IsEndwin = 0;

/**
 * exit_handler - Attempt to catch "ordinary" signals and shut down gracefully
 */
static void exit_handler(int sig)
{
  curs_set(1);
  endwin(); /* just to be safe */

/*
   * if sys_siglist is not defined, HAVE_DECL_SYS_SIGLIST will be set to 0
   * so we must check it with #if and not #ifdef
   */
#if HAVE_DECL_SYS_SIGLIST
  printf(_("%s...  Exiting.\n"), sys_siglist[sig]);
#elif (defined(__sun__) && defined(__svr4__))
  printf(_("Caught %s...  Exiting.\n"), _sys_siglist[sig]);
#elif (defined(__alpha) && defined(__osf__))
  printf(_("Caught %s...  Exiting.\n"), __sys_siglist[sig]);
#else
  printf(_("Caught signal %d...  Exiting.\n"), sig);
#endif
  exit(0);
}

static void chld_handler(int sig)
{
  /* empty */
}

static void sighandler(int sig)
{
  int save_errno = errno;

  switch (sig)
  {
    case SIGTSTP: /* user requested a suspend */
      if (!option(OPT_SUSPEND))
        break;
      IsEndwin = isendwin();
      curs_set(1);
      if (!IsEndwin)
        endwin();
      kill(0, SIGSTOP);

    case SIGCONT:
      if (!IsEndwin)
        refresh();
      mutt_curs_set(-1);
#if defined(USE_SLANG_CURSES) || defined(HAVE_RESIZETERM)
      /* We don't receive SIGWINCH when suspended; however, no harm is done by
       * just assuming we received one, and triggering the 'resize' anyway. */
      SigWinch = 1;
#endif
      break;

#if defined(USE_SLANG_CURSES) || defined(HAVE_RESIZETERM)
    case SIGWINCH:
      SigWinch = 1;
      break;
#endif

    case SIGINT:
      SigInt = 1;
      break;
  }
  errno = save_errno;
}

#ifdef USE_SLANG_CURSES
static int mutt_intr_hook(void)
{
  return -1;
}
#endif /* USE_SLANG_CURSES */

void mutt_signal_init(void)
{
  struct sigaction act;

  sigemptyset(&act.sa_mask);
  act.sa_flags = 0;
  act.sa_handler = SIG_IGN;
  sigaction(SIGPIPE, &act, NULL);

  act.sa_handler = exit_handler;
  sigaction(SIGTERM, &act, NULL);
  sigaction(SIGHUP, &act, NULL);
  sigaction(SIGQUIT, &act, NULL);

  /* we want to avoid race conditions */
  sigaddset(&act.sa_mask, SIGTSTP);

  act.sa_handler = sighandler;

  /* we want SIGALRM to abort the current syscall, so we do this before
   * setting the SA_RESTART flag below.  currently this is only used to
   * timeout on a connect() call in a reasonable amount of time.
   */
  sigaction(SIGALRM, &act, NULL);

/* we also don't want to mess with interrupted system calls */
#ifdef SA_RESTART
  act.sa_flags = SA_RESTART;
#endif

  sigaction(SIGCONT, &act, NULL);
  sigaction(SIGTSTP, &act, NULL);
  sigaction(SIGINT, &act, NULL);
#if defined(USE_SLANG_CURSES) || defined(HAVE_RESIZETERM)
  sigaction(SIGWINCH, &act, NULL);
#endif

  /* POSIX doesn't allow us to ignore SIGCHLD,
   * so we just install a dummy handler for it
   */
  act.sa_handler = chld_handler;
  /* don't need to block any other signals here */
  sigemptyset(&act.sa_mask);
  /* we don't want to mess with stopped children */
  act.sa_flags |= SA_NOCLDSTOP;
  sigaction(SIGCHLD, &act, NULL);

#ifdef USE_SLANG_CURSES
  /* This bit of code is required because of the implementation of
   * SLcurses_wgetch().  If a signal is received (like SIGWINCH) when we
   * are in blocking mode, SLsys_getkey() will not return an error unless
   * a handler function is defined and it returns -1.  This is needed so
   * that if the user resizes the screen while at a prompt, it will just
   * abort and go back to the main-menu.
   */
  SLang_getkey_intr_hook = mutt_intr_hook;
#endif
}

/**
 * mutt_block_signals - Block signals during critical ops
 *
 * signals which are important to block while doing critical ops
 */
void mutt_block_signals(void)
{
  if (!option(OPT_SIGNALS_BLOCKED))
  {
    sigemptyset(&Sigset);
    sigaddset(&Sigset, SIGTERM);
    sigaddset(&Sigset, SIGHUP);
    sigaddset(&Sigset, SIGTSTP);
    sigaddset(&Sigset, SIGINT);
#if defined(USE_SLANG_CURSES) || defined(HAVE_RESIZETERM)
    sigaddset(&Sigset, SIGWINCH);
#endif
    sigprocmask(SIG_BLOCK, &Sigset, 0);
    set_option(OPT_SIGNALS_BLOCKED);
  }
}

/**
 * mutt_unblock_signals - restore the previous signal mask
 */
void mutt_unblock_signals(void)
{
  if (option(OPT_SIGNALS_BLOCKED))
  {
    sigprocmask(SIG_UNBLOCK, &Sigset, 0);
    unset_option(OPT_SIGNALS_BLOCKED);
  }
}

void mutt_block_signals_system(void)
{
  struct sigaction sa;

  if (!option(OPT_SYS_SIGNALS_BLOCKED))
  {
    /* POSIX: ignore SIGINT and SIGQUIT & block SIGCHLD  before exec */
    sa.sa_handler = SIG_IGN;
    sa.sa_flags = 0;
    sigemptyset(&sa.sa_mask);
    sigaction(SIGINT, &sa, &SysOldInt);
    sigaction(SIGQUIT, &sa, &SysOldQuit);

    sigemptyset(&SigsetSys);
    sigaddset(&SigsetSys, SIGCHLD);
    sigprocmask(SIG_BLOCK, &SigsetSys, 0);
    set_option(OPT_SYS_SIGNALS_BLOCKED);
  }
}

void mutt_unblock_signals_system(int catch)
{
  if (option(OPT_SYS_SIGNALS_BLOCKED))
  {
    sigprocmask(SIG_UNBLOCK, &SigsetSys, NULL);
    if (catch)
    {
      sigaction(SIGQUIT, &SysOldQuit, NULL);
      sigaction(SIGINT, &SysOldInt, NULL);
    }
    else
    {
      struct sigaction sa;

      sa.sa_handler = SIG_DFL;
      sigemptyset(&sa.sa_mask);
      sa.sa_flags = 0;
      sigaction(SIGQUIT, &sa, NULL);
      sigaction(SIGINT, &sa, NULL);
    }

    unset_option(OPT_SYS_SIGNALS_BLOCKED);
  }
}

void mutt_allow_interrupt(int disposition)
{
  struct sigaction sa;

  memset(&sa, 0, sizeof(sa));
  sa.sa_handler = sighandler;
#ifdef SA_RESTART
  if (disposition == 0)
    sa.sa_flags |= SA_RESTART;
#endif
  sigaction(SIGINT, &sa, NULL);
}