/*
 * getpass.c
 * Pieter Droogendijk
 */
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <termios.h>

/*
 * Suitable to read a password from the controlling terminal. 
 * Takes a prompt, a buffer and that buffer's length.
 * Returns the length of the password.
 */
size_t safegetpass (const char *prompt, char *buf, size_t buflen)
{
  FILE *fp;
  char *cterminal;
  struct termios temptermopt, oldtermopt;
  sigset_t tempsigset, oldsigset;
  int input;
  size_t obuflen = buflen;
 
  /* Open controlling terminal. */
  cterminal = ctermid (NULL);
  fp = fopen (cterminal, "r+");
  if (fp == NULL)
    return -1;

  /* Disable stdio buffering. */
  setbuf (fp, NULL);

  /* Block SIGINT, SIGQUIT, SIGSTOP and SIGTSTP. */
  sigemptyset (&tempsigset);
  sigaddset (&tempsigset, SIGINT);
  sigaddset (&tempsigset, SIGQUIT);
  sigaddset (&tempsigset, SIGSTOP);
  sigaddset (&tempsigset, SIGTSTP);
  sigprocmask (SIG_BLOCK, &tempsigset, &oldsigset);

  /* Disable echoing on controlling terminal. */
  tcgetattr (fileno (fp), &oldtermopt);
  temptermopt = oldtermopt;
  temptermopt.c_lflag &= ~(ECHO|ECHOE|ECHOK|ECHONL);
  tcsetattr (fileno (fp), TCSAFLUSH, &temptermopt);

  fputs (prompt, fp);

  /* Get the password. */
  while ( (input = getc(fp)) != EOF && input != '\n' ) {
    if (buflen <= 1)
      break;
    buflen --;
    *buf++ = input;
  }
  *buf = '\0';

  putc ('\n', fp);

  /* Restore terminal and signal settings. */
  tcsetattr (fileno (fp), TCSAFLUSH, &oldtermopt);
  sigprocmask (SIG_SETMASK, &oldsigset, NULL);

  /* We're done with the terminal now. */
  fclose (fp);

  return obuflen - buflen;
}

int main (void)
{
  char buf[5];
  size_t len = safegetpass ("Password", buf, sizeof buf);
  printf ("%u '%s'\n", (unsigned) len, buf);
}