libguile/mkstemp.c

   1 /* Copyright (C) 1991, 1992, 1996, 1998 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 #include "scmconfig.h"
  21
  22 #ifdef HAVE_STDLIB_H
  23 #include <stdlib.h>
  24 #endif
  25 #ifdef HAVE_STRING_H
  26 #include <string.h>
  27 #endif
  28 #include <errno.h>
  29 #include <stdio.h>
  30 #include <fcntl.h>
  31 #ifdef HAVE_UNISTD_H
  32 #include <unistd.h>
  33 #endif
  34 #ifdef HAVE_SYS_TIME_H
  35 #include <sys/time.h>
  36 #endif
  37
  38 /* We need to provide a type for gcc_uint64_t.  */
  39 #ifdef __GNUC__
  40 typedef unsigned long long gcc_uint64_t;
  41 #else
  42 typedef unsigned long gcc_uint64_t;
  43 #endif
  44
  45 #ifndef TMP_MAX
  46 #define TMP_MAX 16384
  47 #endif
  48
  49 /* Generate a unique temporary file name from TEMPLATE.
  50
  51    TEMPLATE has the form:
  52
  53    <path>/ccXXXXXX
  54
  55    The last six characters of TEMPLATE must be "XXXXXX"; they are
  56    replaced with a string that makes the filename unique.
  57
  58    Returns a file descriptor open on the file for reading and writing.  */
  59 int
  60 mkstemp (template)
  61      char *template;
  62 {
  63   static const char letters[]
  64     = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  65   static gcc_uint64_t value;
  66 #ifdef HAVE_GETTIMEOFDAY
  67   struct timeval tv;
  68 #endif
  69   char *XXXXXX;
  70   size_t len;
  71   int count;
  72
  73   len = strlen (template);
  74
  75   if ((int) len < 6
  76       || strncmp (&template[len - 6], "XXXXXX", 6))
  77     {
  78       return -1;
  79     }
  80
  81   XXXXXX = &template[len - 6];
  82
  83 #ifdef HAVE_GETTIMEOFDAY
  84   /* Get some more or less random data.  */
  85   gettimeofday (&tv, NULL);
  86   value += ((gcc_uint64_t) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
  87 #else
  88   value += getpid ();
  89 #endif
  90
  91   for (count = 0; count < TMP_MAX; ++count)
  92     {
  93       gcc_uint64_t v = value;
  94       int fd;
  95
  96       /* Fill in the random bits.  */
  97       XXXXXX[0] = letters[v % 62];
  98       v /= 62;
  99       XXXXXX[1] = letters[v % 62];
 100       v /= 62;
 101       XXXXXX[2] = letters[v % 62];
 102       v /= 62;
 103       XXXXXX[3] = letters[v % 62];
 104       v /= 62;
 105       XXXXXX[4] = letters[v % 62];
 106       v /= 62;
 107       XXXXXX[5] = letters[v % 62];
 108
 109       fd = open (template, O_RDWR|O_CREAT|O_EXCL, 0600);
 110       if (fd >= 0)
 111         /* The file does not exist.  */
 112         return fd;
 113
 114       /* This is a random value.  It is only necessary that the next
 115          TMP_MAX values generated by adding 7777 to VALUE are different
 116          with (module 2^32).  */
 117       value += 7777;
 118     }
 119
 120   /* We return the null string if we can't find a unique file name.  */
 121   template[0] = '\0';
 122   return -1;
 123 }