text: /* 
   * Original: readpassphrase.c in OpenSSH portable
   */
  /*
   * Copyright (c) 2000-2002, 2007, 2010
   *	Todd C. Miller <millert@openbsd.org>
   *
   * Permission to use, copy, modify, and distribute this software for any
   * purpose with or without fee is hereby granted, provided that the above
   * copyright notice and this permission notice appear in all copies.
   *
   * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
   * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
   * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
   * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
   *
   * Sponsored in part by the Defense Advanced Research Projects
   * Agency (DARPA) and Air Force Research Laboratory, Air Force
   * Materiel Command, USAF, under agreement number F39502-99-1-0512.
   */
  
  #include <ctype.h>
  #include <errno.h>
  #include <fcntl.h>
  #include <paths.h>
  #include <pwd.h>
  #include <signal.h>
  #include <string.h>
  #include <termios.h>
  #include <unistd.h>
  
  #if !defined(_NSIG) && defined(NSIG)
  # define _NSIG NSIG
  #endif
  
  static volatile sig_atomic_t readpassphrase_signo[_NSIG];
  
  static void
  readpassphrase_handler(int s)
  {
  
  	readpassphrase_signo[s] = 1;
  }
  
  char *
  readpassphrase(const char *prompt, char *buf, size_t bufsiz, int flags)
  {
  	ssize_t nr;
  	int input, output, save_errno, i, need_restart;
  	char ch, *p, *end;
  	struct termios term, oterm;
  	struct sigaction sa, savealrm, saveint, savehup, savequit, saveterm;
  	struct sigaction savetstp, savettin, savettou, savepipe;
  /* If we don't have TCSASOFT define it so that ORing it it below is a no-op. */
  #ifndef TCSASOFT
  	const int tcasoft = 0;
  #else
  	const int tcasoft = TCSASOFT;
  #endif
  
  	/* I suppose we could alloc on demand in this case (XXX). */
  	if (bufsiz == 0) {
  		errno = EINVAL;
  		return(NULL);
  	}
  
  restart:
  	for (i = 0; i < _NSIG; i++)
  		readpassphrase_signo[i] = 0;
  	nr = -1;
  	save_errno = 0;
  	need_restart = 0;
  	/*
  	 * Read and write to /dev/tty if available.  If not, read from
  	 * stdin and write to stderr unless a tty is required.
  	 */
  	if ((flags & RPP_STDIN) ||
  	    (input = output = open(_PATH_TTY, O_RDWR)) == -1) {
  		if (flags & RPP_REQUIRE_TTY) {
  			errno = ENOTTY;
  			return(NULL);
  		}
  		input = STDIN_FILENO;
  		output = STDERR_FILENO;
  	}
  
  	/*
  	 * Turn off echo if possible.
  	 * If we are using a tty but are not the foreground pgrp this will
  	 * generate SIGTTOU, so do it *before* installing the signal handlers.
  	 */
  	if (input != STDIN_FILENO && tcgetattr(input, &oterm) == 0) {
  		memcpy(&term, &oterm, sizeof(term));
  		if (!(flags & RPP_ECHO_ON))
  			term.c_lflag &= ~(ECHO | ECHONL);
  #ifdef VSTATUS
  		if (term.c_cc[VSTATUS] != _POSIX_VDISABLE)
  			term.c_cc[VSTATUS] = _POSIX_VDISABLE;
  #endif
  		(void)tcsetattr(input, TCSAFLUSH|tcasoft, &term);
  	} else {
  		memset(&term, 0, sizeof(term));
  		term.c_lflag |= ECHO;
  		memset(&oterm, 0, sizeof(oterm));
  		oterm.c_lflag |= ECHO;
  	}
  
  	/*
  	 * Catch signals that would otherwise cause the user to end
  	 * up with echo turned off in the shell.  Don't worry about
  	 * things like SIGXCPU and SIGVTALRM for now.
  	 */
  	sigemptyset(&sa.sa_mask);
  	sa.sa_flags = 0;		/* don't restart system calls */
  	sa.sa_handler = readpassphrase_handler;
  	(void)sigaction(SIGALRM, &sa, &savealrm);
  	(void)sigaction(SIGHUP, &sa, &savehup);
  	(void)sigaction(SIGINT, &sa, &saveint);
  	(void)sigaction(SIGPIPE, &sa, &savepipe);
  	(void)sigaction(SIGQUIT, &sa, &savequit);
  	(void)sigaction(SIGTERM, &sa, &saveterm);
  	(void)sigaction(SIGTSTP, &sa, &savetstp);
  	(void)sigaction(SIGTTIN, &sa, &savettin);
  	(void)sigaction(SIGTTOU, &sa, &savettou);
  
  	if (!(flags & RPP_STDIN))
  		(void)write(output, prompt, strlen(prompt));
  	end = buf + bufsiz - 1;
  	p = buf;
  	while ((nr = read(input, &ch, 1)) == 1 && ch != '\n' && ch != '\r') {
  		if (p < end) {
  			if ((flags & RPP_SEVENBIT))
  				ch &= 0x7f;
  			if (isalpha((unsigned char)ch)) {
  				if ((flags & RPP_FORCELOWER))
  					ch = (char)tolower((unsigned char)ch);
  				if ((flags & RPP_FORCEUPPER))
  					ch = (char)toupper((unsigned char)ch);
  			}
  			*p++ = ch;
  		}
  	}
  	*p = '\0';
  	save_errno = errno;
  	if (!(term.c_lflag & ECHO))
  		(void)write(output, "\n", 1);
  
  	/* Restore old terminal settings and signals. */
  	if (memcmp(&term, &oterm, sizeof(term)) != 0) {
  		const int sigttou = readpassphrase_signo[SIGTTOU];
  
  		/* Ignore SIGTTOU generated when we are not the fg pgrp. */
  		while (tcsetattr(input, TCSAFLUSH|tcasoft, &oterm) == -1 &&
  		    errno == EINTR && !readpassphrase_signo[SIGTTOU])
  			continue;
  		readpassphrase_signo[SIGTTOU] = sigttou;
  	}
  	(void)sigaction(SIGALRM, &savealrm, NULL);
  	(void)sigaction(SIGHUP, &savehup, NULL);
  	(void)sigaction(SIGINT, &saveint, NULL);
  	(void)sigaction(SIGQUIT, &savequit, NULL);
  	(void)sigaction(SIGPIPE, &savepipe, NULL);
  	(void)sigaction(SIGTERM, &saveterm, NULL);
  	(void)sigaction(SIGTSTP, &savetstp, NULL);
  	(void)sigaction(SIGTTIN, &savettin, NULL);
  	(void)sigaction(SIGTTOU, &savettou, NULL);
  	if (input != STDIN_FILENO)
  		(void)close(input);
  
  	/*
  	 * If we were interrupted by a signal, resend it to ourselves
  	 * now that we have restored the signal handlers.
  	 */
  	for (i = 0; i < _NSIG; i++) {
  		if (readpassphrase_signo[i]) {
  			kill(getpid(), i);
  			switch (i) {
  			case SIGTSTP:
  			case SIGTTIN:
  			case SIGTTOU:
  				need_restart = 1;
  			}
  		}
  	}
  	if (need_restart)
  		goto restart;
  
  	if (save_errno)
  		errno = save_errno;
  	return(nr == -1 ? NULL : buf);
  }
  