sysdeps/posix/mkstemp.c

   1 /* Copyright (C) 1991, 1992, 1996, 1998 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 #include <stdlib.h>
  20 #include <string.h>
  21 #include <errno.h>
  22 #include <stdint.h>
  23 #include <stdio.h>
  24 #include <fcntl.h>
  25 #include <unistd.h>
  26 #include <sys/time.h>
  27
  28 /* Generate a unique temporary file name from TEMPLATE.
  29    The last six characters of TEMPLATE must be "XXXXXX";
  30    they are replaced with a string that makes the filename unique.
  31    Returns a file descriptor open on the file for reading and writing.  */
  32 int
  33 mkstemp (template)
  34      char *template;
  35 {
  36   static const char letters[]
  37     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  38   static uint64_t value;
  39   struct timeval tv;
  40   char *XXXXXX;
  41   size_t len;
  42   int count;
  43
  44   len = strlen (template);
  45   if (len < 6 || strcmp (&template[len - 6], "XXXXXX"))
  46     {
  47       __set_errno (EINVAL);
  48       return -1;
  49     }
  50
  51   /* This is where the Xs start.  */
  52   XXXXXX = &template[len - 6];
  53
  54   /* Get some more or less random data.  */
  55   __gettimeofday (&tv, NULL);
  56   value += ((uint64_t) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
  57
  58   for (count = 0; count < TMP_MAX; ++count)
  59     {
  60       uint64_t v = value;
  61       int fd;
  62
  63       /* Fill in the random bits.  */
  64       XXXXXX[0] = letters[v % 62];
  65       v /= 62;
  66       XXXXXX[1] = letters[v % 62];
  67       v /= 62;
  68       XXXXXX[2] = letters[v % 62];
  69       v /= 62;
  70       XXXXXX[3] = letters[v % 62];
  71       v /= 62;
  72       XXXXXX[4] = letters[v % 62];
  73       v /= 62;
  74       XXXXXX[5] = letters[v % 62];
  75
  76       fd = open (template, O_RDWR|O_CREAT|O_EXCL, 0600);
  77       if (fd >= 0)
  78         /* The file does not exist.  */
  79         return fd;
  80
  81       /* This is a random value.  It is only necessary that the next
  82          TMP_MAX values generated by adding 7777 to VALUE are different
  83          with (module 2^32).  */
  84       value += 7777;
  85     }
  86
  87   /* We return the null string if we can't find a unique file name.  */
  88   template[0] = '\0';
  89   return -1;
  90 }