Subject: Re: bug#57129: 29.0.50; Improve behavior of conditionals in Eshell

From: Bruno Haible <[email-masked]>
Date: Tue, 16 Aug 2022 15:35:17 +0200

Eli Zaretskii wrote:
> The problem is that callers of
> make-temp-file reasonably expect it to return a new name every call.
> And evidently, it does that on GNU/Linux (not sure how, given that the
> tempname.c code is supposed to be in glibc?).  So if there's no
> intention to change gen_tempname on non-glibc platforms so that it
> doesn't repeat the same "random characters" upon each call, I think
> Emacs should call a different function to generate "random" names of
> temporary files, for consistency across platforms if not for other
> reasons.

You are making incorrect assumptions or hypotheses. I am adding the unit
test below. It proves that (at least) on Linux, FreeBSD 11, NetBSD 7,
OpenBSD 6.0, macOS, AIX 7.1, Solaris 10, Cygwin, and native Windows,
gen_tempname *does* return a new file name on each call, with a very high
probability.

So, gen_tempname does *not* repeat the same "random characters" upon each call.

2022-08-16  Bruno Haible  <[email-masked]>

	tempname: Add tests.
	* tests/test-tempname.c: New file.
	* modules/tempname-tests: New file.

=========================== tests/test-tempname.c ==========================
/* Test of creating a temporary file.
   Copyright (C) 2022 Free Software Foundation, Inc.

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program 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 General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */

/* Written by Bruno Haible <[email-masked]>, 2022.  */

#include <config.h>

#include "tempname.h"

#include <string.h>
#include <unistd.h>

#include "macros.h"

int
main ()
{
  /* Verify that two consecutive calls to gen_tempname return two different
     file names, with a high probability.  */
  const char *templ18 = "gl-temp-XXXXXX.xyz";
  char filename1[18 + 1];
  char filename2[18 + 1];

  strcpy (filename1, templ18);
  int fd1 = gen_tempname (filename1, strlen (".xyz"), 0, GT_FILE);
  ASSERT (fd1 >= 0);

  strcpy (filename2, templ18);
  int fd2 = gen_tempname (filename2, strlen (".xyz"), 0, GT_FILE);
  ASSERT (fd2 >= 0);

  /* With 6 'X' and a good pseudo-random number generator behind the scenes,
     the probability of getting the same file name twice in a row should be
     1/62^6 < 1/10^10.  */
  ASSERT (strcmp (filename1, filename2) != 0);

  /* Clean up.  */
  close (fd1);
  close (fd2);
  unlink (filename1);
  unlink (filename2);

  return 0;
}
=========================== modules/tempname-tests =========================
Files:
tests/test-tempname.c
tests/macros.h

Depends-on:
unlink

configure.ac:

Makefile.am:
TESTS += test-tempname
check_PROGRAMS += test-tempname
test_tempname_LDADD = $(LDADD) $(LIB_GETRANDOM) $(LIB_CLOCK_GETTIME)
============================================================================