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/*
 * jmemname.c
 *
 * Copyright (C) 1992-1997, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file provides a generic implementation of the system-dependent
 * portion of the JPEG memory manager.  This implementation assumes that
 * you must explicitly construct a name for each temp file.
 * Also, the problem of determining the amount of memory available
 * is shoved onto the user.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"
#include "jmemsys.h"		/* import the system-dependent declarations */

#ifndef HAVE_STDLIB_H		/* <stdlib.h> should declare malloc(),free() */
extern void * malloc JPP((size_t size));
extern void free JPP((void *ptr));
#endif

#ifndef SEEK_SET		/* pre-ANSI systems may not define this; */
#define SEEK_SET  0		/* if not, assume 0 is correct */
#endif

#ifdef DONT_USE_B_MODE		/* define mode parameters for fopen() */
#define READ_BINARY	"r"
#define RW_BINARY	"w+"
#else
#ifdef VMS			/* VMS is very nonstandard */
#define READ_BINARY	"rb", "ctx=stm"
#define RW_BINARY	"w+b", "ctx=stm"
#else				/* standard ANSI-compliant case */
#define READ_BINARY	"rb"
#define RW_BINARY	"w+b"
#endif
#endif


/*
 * Selection of a file name for a temporary file.
 * This is system-dependent!
 *
 * The code as given is suitable for most Unix systems, and it is easily
 * modified for most non-Unix systems.  Some notes:
 *  1.  The temp file is created in the directory named by TEMP_DIRECTORY.
 *      The default value is /usr/tmp, which is the conventional place for
 *      creating large temp files on Unix.  On other systems you'll probably
 *      want to change the file location.  You can do this by editing the
 *      #define, or (preferred) by defining TEMP_DIRECTORY in jconfig.h.
 *
 *  2.  If you need to change the file name as well as its location,
 *      you can override the TEMP_FILE_NAME macro.  (Note that this is
 *      actually a printf format string; it must contain %s and %d.)
 *      Few people should need to do this.
 *
 *  3.  mktemp() is used to ensure that multiple processes running
 *      simultaneously won't select the same file names.  If your system
 *      doesn't have mktemp(), define NO_MKTEMP to do it the hard way.
 *      (If you don't have <errno.h>, also define NO_ERRNO_H.)
 *
 *  4.  You probably want to define NEED_SIGNAL_CATCHER so that cjpeg.c/djpeg.c
 *      will cause the temp files to be removed if you stop the program early.
 */

#ifndef TEMP_DIRECTORY		/* can override from jconfig.h or Makefile */
#define TEMP_DIRECTORY  "/usr/tmp/" /* recommended setting for Unix */
#endif

static int next_file_num;	/* to distinguish among several temp files */

#ifdef NO_MKTEMP

#ifndef TEMP_FILE_NAME		/* can override from jconfig.h or Makefile */
#define TEMP_FILE_NAME  "%sJPG%03d.TMP"
#endif

#ifndef NO_ERRNO_H
#include <errno.h>		/* to define ENOENT */
#endif

/* ANSI C specifies that errno is a macro, but on older systems it's more
 * likely to be a plain int variable.  And not all versions of errno.h
 * bother to declare it, so we have to in order to be most portable.  Thus:
 */
#ifndef errno
extern int errno;
#endif


LOCAL(void)
select_file_name (char * fname)
{
  FILE * tfile;

  /* Keep generating file names till we find one that's not in use */
  for (;;) {
    next_file_num++;		/* advance counter */
    sprintf(fname, TEMP_FILE_NAME, TEMP_DIRECTORY, next_file_num);
    if ((tfile = fopen(fname, READ_BINARY)) == NULL) {
      /* fopen could have failed for a reason other than the file not
       * being there; for example, file there but unreadable.
       * If <errno.h> isn't available, then we cannot test the cause.
       */
#ifdef ENOENT
      if (errno != ENOENT)
	continue;
#endif
      break;