libguile/mkstemp.c

   1 /* Copyright (C) 1991, 1992, 1996, 1998, 2001 Free Software Foundation, Inc.
   2    This file is derived from mkstemps.c from the GNU Libiberty Library
   3    which in turn is derived from the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.
  19 */
  20
  21 #if HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include "libguile/__scm.h"
  26
  27 #ifdef HAVE_STDLIB_H
  28 #include <stdlib.h>
  29 #endif
  30 #ifdef HAVE_STRING_H
  31 #include <string.h>
  32 #endif
  33 #include <errno.h>
  34 #include <stdio.h>
  35 #include <fcntl.h>
  36 #ifdef HAVE_UNISTD_H
  37 #include <unistd.h>
  38 #endif
  39 #ifdef HAVE_SYS_TIME_H
  40 #include <sys/time.h>
  41 #endif
  42 #ifdef __MINGW32__
  43 #include <process.h>
  44 #endif
  45
  46 #ifndef TMP_MAX
  47 #define TMP_MAX 16384
  48 #endif
  49
  50 /* Generate a unique temporary file name from TEMPLATE.
  51
  52    TEMPLATE has the form:
  53
  54    <path>/ccXXXXXX
  55
  56    The last six characters of TEMPLATE must be "XXXXXX"; they are
  57    replaced with a string that makes the filename unique.
  58
  59    Returns a file descriptor open on the file for reading and writing.  */
  60 int
  61 mkstemp (template)
  62      char *template;
  63 {
  64   static const char letters[]
  65     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  66   static scm_t_uint64 value;
  67 #ifdef HAVE_GETTIMEOFDAY
  68   struct timeval tv;
  69 #endif
  70   char *XXXXXX;
  71   size_t len;
  72   int count;
  73
  74   len = strlen (template);
  75
  76   if ((int) len < 6
  77       || strncmp (&template[len - 6], "XXXXXX", 6))
  78     {
  79       return -1;
  80     }
  81
  82   XXXXXX = &template[len - 6];
  83
  84 #ifdef HAVE_GETTIMEOFDAY
  85   /* Get some more or less random data.  */
  86   gettimeofday (&tv, NULL);
  87   value += ((scm_t_uint64) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
  88 #else
  89   value += getpid ();
  90 #endif
  91
  92   for (count = 0; count < TMP_MAX; ++count)
  93     {
  94       scm_t_uint64 v = value;
  95       int fd;
  96
  97       /* Fill in the random bits.  */
  98       XXXXXX[0] = letters[v % 62];
  99       v /= 62;
 100       XXXXXX[1] = letters[v % 62];
 101       v /= 62;
 102       XXXXXX[2] = letters[v % 62];
 103       v /= 62;
 104       XXXXXX[3] = letters[v % 62];
 105       v /= 62;
 106       XXXXXX[4] = letters[v % 62];
 107       v /= 62;
 108       XXXXXX[5] = letters[v % 62];
 109
 110       fd = open (template, O_RDWR|O_CREAT|O_EXCL, 0600);
 111       if (fd >= 0)
 112         /* The file does not exist.  */
 113         return fd;
 114
 115       /* This is a random value.  It is only necessary that the next
 116          TMP_MAX values generated by adding 7777 to VALUE are different
 117          with (module 2^32).  */
 118       value += 7777;
 119     }
 120
 121   /* We return the null string if we can't find a unique file name.  */
 122   template[0] = '\0';
 123   return -1;
 124 }