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/*
* Copyright (c) 1987 Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that: (1) source distributions retain this entire copyright
* notice and comment, and (2) distributions including binaries display
* the following acknowledgement: ``This product includes software
* developed by the University of California, Berkeley and its contributors''
* in the documentation or other materials provided with the distribution.
* Neither the name of the University nor the names of its
* contributors may be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/
/* This is file MKTEMP.C */
/* This file may have been modified by DJ Delorie (Jan 1991). If so,
** these modifications are Copyright (C) 1991 DJ Delorie.
*/
/*
FUNCTION
<<mktemp>>, <<mkstemp>>, <<mkstemps>>,
<<mkostemps>>---generate unused file name
INDEX
mktemp
INDEX
mkstemp
INDEX
mkstemps
INDEX
mkostemps
SYNOPSIS
#include <stdlib.h>
char *mktemp(char *<[path]>);
int mkstemp(char *<[path]>);
int mkstemps(char *<[path]>, int suffixlen);
int mkostemps(char *<[path]>, int suffixlen, int flags);
DESCRIPTION
<<mktemp>>, <<mkstemp>>, <<mkstemps>>, and <<mkostemps>> attempt to
generate a file name that is not yet in use for any existing file.
<<mkstemp>>, <<mkstemps>> and <mkostemps>> create the file and open it
for reading and writing; <<mktemp>> simply generates the file name
(making <<mktemp>> a security risk). <<mkostemps>> allow the addition
of other <<open>> flags, such as <<O_CLOEXEC>>, <<O_APPEND>>, or
<<O_SYNC>>. On platforms with a separate text mode, <<mkstemp>>
forces <<O_BINARY>>, while <<mkostemp>> allows the choice between
<<O_BINARY>>, <<O_TEXT>>, or 0 for default.
You supply a simple pattern for the generated file name, as the string
at <[path]>. The pattern should be a valid filename (including path
information if you wish) ending with at least six `<<X>>' characters.
The generated filename will match the leading part of the name you
supply, with the trailing `<<X>>' characters replaced by some
combination of digits and letters. With <<mkstemps>> and
<mkostemps>>, the `<<X>>' characters end <[suffixlen]> bytes before
the end of the string.
RETURNS
<<mktemp>> returns the pointer <[path]> to the modified string
representing an unused filename, unless it could not generate one, or
the pattern you provided is not suitable for a filename; in that case,
it returns <<NULL>>. Be aware that there is an inherent race between
generating the name and attempting to create a file by that name;
you are advised to use <<O_EXCL|O_CREAT>>.
<<mkstemp>>, <<mkstemps>> and <<mkostemps>> return a file descriptor
to the newly created file, unless it could not generate an unused
filename, or the pattern you provided is not suitable for a filename;
in that case, it returns <<-1>>.
NOTES
Never use <<mktemp>>. The generated filenames are easy to guess and
there's a race between the test if the file exists and the creation
of the file. In combination this makes <<mktemp>> prone to attacks
and using it is a security risk. Whenever possible use <<mkstemp>>
instead. It doesn't suffer the race condition.
PORTABILITY
ANSI C does not require either <<mktemp>> or <<mkstemp>>; the System V
Interface Definition requires <<mktemp>> as of Issue 2. POSIX 2001
requires <<mkstemp>> while deprecating <<mktemp>>. <<mkstemps>>, and
<<mkostemps>> are not standardized.
Supporting OS subroutines required: <<open>>
*/
#include "stdio_private.h"
/* Our names are six characters from [0-9a-z] */
#define NUM_NAMES (36UL * 36UL * 36UL * 36UL * 36UL * 36UL)
/* Attempts */
#define NUM_ATTEMPT (36UL * 36UL * 36UL)
static int
_gettemp(char *path, int suffixlen, int *doopen, int flags)
{
char *start, *trv;
char *end;
uint32_t attempt;
end = path + strlen(path) - suffixlen;
trv = end;
/* Replace 'X' with 'a' */
while (path < trv && *--trv == 'X')
*trv = 'a';
/* Make sure we got six Xs */
if (end - trv < 6) {
errno = EINVAL;
return 0;
}
start = trv + 1;
for (attempt = 0; attempt < NUM_ATTEMPT; attempt++) {
/* Generate a random filename index */
long filename = random() % NUM_NAMES;
size_t i;
/* Convert the random index into characters */
for (i = 0; i < 6; i++) {
char c = filename % 36;
filename /= 36;
if (c < 10)
c += '0';
else
c += 'a' - 10;
start[i] = c;
}
/*
* Use open to check if the file exists to avoid depending on
* stat or access. Don't rely on O_EXCL working, although if it
* doesn't, this introduces a race condition
*/
int fd = open(path, O_RDONLY);
if (fd < 0) {
if (errno != EACCES) {
if (errno != ENOENT)
return 0;
if (doopen) {
fd = open(path, flags | O_CREAT | O_EXCL | O_RDWR, 0600);
if (fd >= 0) {
*doopen = fd;
return 1;
}
if (errno != EEXIST)
return 0;
} else {
return 1;
}
}
} else
close(fd);
}
return 0;
}
int
mkstemp(char *template)
{
int fd;
return (_gettemp(template, 0, &fd, 0) ? fd : -1);
}
char *
mktemp(char *template)
{
return (_gettemp(template, 0, (int *)NULL, 0) ? template : (char *)NULL);
}
#ifndef O_BINARY
#define O_BINARY 0
#endif
#ifndef O_TEXT
#define O_TEXT 0
#endif
int
mkstemps(char *template, int suffixlen)
{
int fd;
return (_gettemp(template, suffixlen, &fd, O_BINARY) ? fd : -1);
}
int
mkostemps(char *template, int suffixlen, int flags)
{
int fd;
flags &= (O_APPEND | O_CLOEXEC | O_SYNC | O_BINARY | O_TEXT);
return (_gettemp(template, suffixlen, &fd, flags) ? fd : -1);
}