guile/libguile/mkstemp.c

/* Copyright (C) 1991, 1992, 1996, 1998, 2001, 2006, 2013,
     2014 Free Software Foundation, Inc.

   This file is derived from mkstemps.c from the GNU Libiberty Library
   which in turn is derived from the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
   Boston, MA 02110-1301, USA. 
*/

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include "libguile/__scm.h"

#ifdef HAVE_STDLIB_H
#include <stdlib.h>
#endif
#ifdef HAVE_STRING_H
#include <string.h>
#endif
#include <errno.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#ifdef __MINGW32__
#include <process.h>
#endif

#ifndef TMP_MAX
#define TMP_MAX 16384
#endif

/* We provide this prototype to avoid compiler warnings.  If this ever
   conflicts with a declaration in a system header file, we'll find
   out, because we should include that header file here.  */
int mkstemp (char *);

/* Generate a unique temporary file name from TEMPLATE.

   TEMPLATE has the form:

   <path>/ccXXXXXX

   The last six characters of TEMPLATE must be "XXXXXX"; they are
   replaced with a string that makes the filename unique.

   Returns a file descriptor open on the file for reading and writing.  */
int
mkstemp (template)
     char *template;
{
  static const char letters[]
    = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
  static scm_t_uint64 value;
#ifdef HAVE_GETTIMEOFDAY
  struct timeval tv;
#endif
  char *XXXXXX;
  size_t len;
  int count;

  len = strlen (template);

  if ((int) len < 6
      || strncmp (&template[len - 6], "XXXXXX", 6))
    {
      return -1;
    }

  XXXXXX = &template[len - 6];

#ifdef HAVE_GETTIMEOFDAY
  /* Get some more or less random data.  */
  gettimeofday (&tv, NULL);
  value += ((scm_t_uint64) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
#else
  value += getpid ();
#endif

  for (count = 0; count < TMP_MAX; ++count)
    {
      scm_t_uint64 v = value;
      int fd;

      /* Fill in the random bits.  */
      XXXXXX[0] = letters[v % 62];
      v /= 62;
      XXXXXX[1] = letters[v % 62];
      v /= 62;
      XXXXXX[2] = letters[v % 62];
      v /= 62;
      XXXXXX[3] = letters[v % 62];
      v /= 62;
      XXXXXX[4] = letters[v % 62];
      v /= 62;
      XXXXXX[5] = letters[v % 62];

      fd = open (template, O_RDWR|O_CREAT|O_EXCL|O_BINARY, 0600);
      if (fd >= 0)
	/* The file does not exist.  */
	return fd;

      /* This is a random value.  It is only necessary that the next
	 TMP_MAX values generated by adding 7777 to VALUE are different
	 with (module 2^32).  */
      value += 7777;
    }

  /* We return the null string if we can't find a unique file name.  */
  template[0] = '\0';
  return -1;
}