src/prompt.c

   1 /* prompt.c -- prompt routines for vlock,
   2  *             the VT locking program for linux
   3  *
   4  * This program is copyright (C) 2007 Frank Benkstein, and is free
   5  * software which is freely distributable under the terms of the
   6  * GNU General Public License version 2, included as the file COPYING in this
   7  * distribution.  It is NOT public domain software, and any
   8  * redistribution not permitted by the GNU General Public License is
   9  * expressly forbidden without prior written permission from
  10  * the author.
  11  *
  12  *
  13  * The prompt functions (prompt and prompt_echo_off) were
  14  * inspired by/copied from openpam's openpam_ttyconv.c:
  15  *
  16  * Copyright (c) 2002-2003 Networks Associates Technology, Inc.
  17  *
  18  * Redistribution and use in source and binary forms, with or without
  19  * modification, are permitted provided that the following conditions
  20  * are met:
  21  * 1. Redistributions of source code must retain the above copyright
  22  *    notice, this list of conditions and the following disclaimer.
  23  * 2. Redistributions in binary form must reproduce the above copyright
  24  *    notice, this list of conditions and the following disclaimer in the
  25  *    documentation and/or other materials provided with the distribution.
  26  * 3. The name of the author may not be used to endorse or promote
  27  *    products derived from this software without specific prior written
  28  *    permission.
  29  *
  30  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  31  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  32  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  33  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  34  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  35  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  36  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  37  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  38  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  39  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  40  * SUCH DAMAGE.
  41  *
  42  */
  43
  44 #include <stdio.h>
  45 #include <stdlib.h>
  46 #include <string.h>
  47 #include <termios.h>
  48 #include <unistd.h>
  49 #include <sys/select.h>
  50
  51 #include "vlock.h"
  52
  53 #define PROMPT_BUFFER_SIZE 512
  54
  55 char *prompt(const char *msg) {
  56   char buffer[PROMPT_BUFFER_SIZE];
  57   char *result;
  58   int len;
  59   struct termios term;
  60   tcflag_t lflag;
  61   fd_set readfds;
  62
  63   /* Write out the prompt. */
  64   (void) fputs(msg, stderr); fflush(stderr);
  65
  66   /* Get the current terminal attributes. */
  67   (void) tcgetattr(STDIN_FILENO, &term);
  68   /* Save the lflag value. */
  69   lflag = term.c_lflag;
  70   /* Enable canonical mode.  We're only interested in line buffering. */
  71   term.c_lflag |= ICANON;
  72   /* Disable terminal signals. */
  73   term.c_lflag &= ~ISIG;
  74   /* Set the terminal attributes. */
  75   (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &term);
  76   /* Discard all unread input characters. */
  77   (void) tcflush(STDIN_FILENO, TCIFLUSH);
  78
  79   /* Initialize file descriptor set. */
  80   FD_ZERO(&readfds);
  81   FD_SET(STDIN_FILENO, &readfds);
  82
  83   /* Wait until a string was entered. */
  84   if (select(STDIN_FILENO+1, &readfds, NULL, NULL, NULL) != 1) {
  85     result = NULL;
  86     goto out;
  87   }
  88
  89   /* Read the string from stdin.  At most buffer length - 1 bytes, to
  90    * leave room for the terminating zero byte. */
  91   if ((len = read(STDIN_FILENO, buffer, sizeof buffer - 1)) < 0) {
  92     result = NULL;
  93     goto out;
  94   }
  95
  96   /* Terminate the string. */
  97   buffer[len] = '\0';
  98
  99   /* Strip trailing newline characters. */
 100   for (len = strlen(buffer); len > 0; --len) {
 101     if (buffer[len-1] != '\r' && buffer[len-1] != '\n')
 102       break;
 103   }
 104
 105   /* Terminate the string, again. */
 106   buffer[len] = '\0';
 107
 108   /* Copy the string. */
 109   result = strdup(buffer);
 110
 111   /* Clear our buffer. */
 112   memset(buffer, 0, sizeof buffer);
 113
 114 out:
 115   /* Restore original terminal attributes. */
 116   term.c_lflag = lflag;
 117   (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &term);
 118
 119   return result;
 120 }
 121
 122 char *prompt_echo_off(const char *msg) {
 123   struct termios term;
 124   tcflag_t lflag;
 125   char *result;
 126
 127   (void) tcgetattr(STDIN_FILENO, &term);
 128   lflag = term.c_lflag;
 129   term.c_lflag &= ~ECHO;
 130   (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &term);
 131
 132   result = prompt(msg);
 133
 134   term.c_lflag = lflag;
 135   (void) tcsetattr(STDIN_FILENO, TCSAFLUSH, &term);
 136
 137   if (result != NULL)
 138     fputc('\n', stderr);
 139
 140   return result;
 141 }