libguile/mkstemp.c

   1 /* Copyright (C) 1991, 1992, 1996, 1998, 2001, 2006, 2013,
   2      2014 Free Software Foundation, Inc.
   3
   4    This file is derived from mkstemps.c from the GNU Libiberty Library
   5    which in turn is derived from the GNU C Library.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Library General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Library General Public License for more details.
  16
  17    You should have received a copy of the GNU Library General Public
  18    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  19    write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  20    Boston, MA 02110-1301, USA.
  21 */
  22
  23 #ifdef HAVE_CONFIG_H
  24 #  include <config.h>
  25 #endif
  26
  27 #include "libguile/__scm.h"
  28
  29 #ifdef HAVE_STDLIB_H
  30 #include <stdlib.h>
  31 #endif
  32 #ifdef HAVE_STRING_H
  33 #include <string.h>
  34 #endif
  35 #include <errno.h>
  36 #include <stdio.h>
  37 #include <fcntl.h>
  38 #include <unistd.h>
  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 /* We provide this prototype to avoid compiler warnings.  If this ever
  51    conflicts with a declaration in a system header file, we'll find
  52    out, because we should include that header file here.  */
  53 int mkstemp (char *);
  54
  55 /* Generate a unique temporary file name from TEMPLATE.
  56
  57    TEMPLATE has the form:
  58
  59    <path>/ccXXXXXX
  60
  61    The last six characters of TEMPLATE must be "XXXXXX"; they are
  62    replaced with a string that makes the filename unique.
  63
  64    Returns a file descriptor open on the file for reading and writing.  */
  65 int
  66 mkstemp (template)
  67      char *template;
  68 {
  69   static const char letters[]
  70     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  71   static scm_t_uint64 value;
  72 #ifdef HAVE_GETTIMEOFDAY
  73   struct timeval tv;
  74 #endif
  75   char *XXXXXX;
  76   size_t len;
  77   int count;
  78
  79   len = strlen (template);
  80
  81   if ((int) len < 6
  82       || strncmp (&template[len - 6], "XXXXXX", 6))
  83     {
  84       return -1;
  85     }
  86
  87   XXXXXX = &template[len - 6];
  88
  89 #ifdef HAVE_GETTIMEOFDAY
  90   /* Get some more or less random data.  */
  91   gettimeofday (&tv, NULL);
  92   value += ((scm_t_uint64) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
  93 #else
  94   value += getpid ();
  95 #endif
  96
  97   for (count = 0; count < TMP_MAX; ++count)
  98     {
  99       scm_t_uint64 v = value;
 100       int fd;
 101
 102       /* Fill in the random bits.  */
 103       XXXXXX[0] = letters[v % 62];
 104       v /= 62;
 105       XXXXXX[1] = letters[v % 62];
 106       v /= 62;
 107       XXXXXX[2] = letters[v % 62];
 108       v /= 62;
 109       XXXXXX[3] = letters[v % 62];
 110       v /= 62;
 111       XXXXXX[4] = letters[v % 62];
 112       v /= 62;
 113       XXXXXX[5] = letters[v % 62];
 114
 115       fd = open (template, O_RDWR|O_CREAT|O_EXCL|O_BINARY, 0600);
 116       if (fd >= 0)
 117         /* The file does not exist.  */
 118         return fd;
 119
 120       /* This is a random value.  It is only necessary that the next
 121          TMP_MAX values generated by adding 7777 to VALUE are different
 122          with (module 2^32).  */
 123       value += 7777;
 124     }
 125
 126   /* We return the null string if we can't find a unique file name.  */
 127   template[0] = '\0';
 128   return -1;
 129 }