New file, slightly modified from libiberties

[bpt/guile.git] / libguile / mkstemp.c

/* Copyright (C) 1991, 1992, 1996, 1998 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., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include "scmconfig.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>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

/* We need to provide a type for gcc_uint64_t.  */
#ifdef __GNUC__
typedef unsigned long long gcc_uint64_t;
#else
typedef unsigned long gcc_uint64_t;
#endif

#ifndef TMP_MAX
#define TMP_MAX 16384
#endif

/* 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 gcc_uint64_t 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 += ((gcc_uint64_t) tv.tv_usec << 16) ^ tv.tv_sec ^ getpid ();
#else
  value += getpid ();
#endif

  for (count = 0; count < TMP_MAX; ++count)
    {
      gcc_uint64_t 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, 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;
}