[PATCH v2] Add a new fwrite test for read-only streams

[Carlos O'Donell]

On 9/5/24 2:34 PM, Tulio Magno Quites Machado Filho wrote:
> From: Tulio Magno Quites Machado Filho <tuliom@redhat.com>
> 
> Changes since v1:
> 
> - Rebased the commit on top of the latest code;
> - Removed implicit checks when using TEST_VERIFY_EXIT ();
> - Fixed check for return code from create_temp_file ();
> - Added a check that guarantees the file was not modified;

Passed pre-commit CI so that's good.

Fixes Adhemerval's review comments.

LGTM.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> 
> -- >8 --
> 
> Ensure that fwrite() behaves correctly even when the stream is
> read-only.
> ---
>  stdio-common/Makefile        |  1 +
>  stdio-common/tst-fwrite-ro.c | 69 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 70 insertions(+)
>  create mode 100644 stdio-common/tst-fwrite-ro.c
> 
> diff --git a/stdio-common/Makefile b/stdio-common/Makefile
> index d99e0cbfeb..0e18045038 100644
> --- a/stdio-common/Makefile
> +++ b/stdio-common/Makefile
> @@ -223,6 +223,7 @@ tests := \
>    tst-freopen64-3 \
>    tst-fseek \
>    tst-fwrite \
> +  tst-fwrite-ro \

OK.

>    tst-getline \
>    tst-getline-enomem \
>    tst-gets \
> diff --git a/stdio-common/tst-fwrite-ro.c b/stdio-common/tst-fwrite-ro.c
> new file mode 100644
> index 0000000000..b15753d4c4
> --- /dev/null
> +++ b/stdio-common/tst-fwrite-ro.c
> @@ -0,0 +1,69 @@
> +/* Test fwrite on a read-only stream.

OK.

> +   Copyright (C) 2024 Free Software Foundation, Inc.
> +   This file is part of 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 Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 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
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +#include <stdio.h>
> +#include <support/check.h>
> +#include <support/temp_file.h>
> +#include <support/xstdio.h>
> +#include <support/xunistd.h>
> +
> +/* A small buffer size is enough to run this test.  */
> +#define BUFSIZE 4
> +
> +static int
> +do_test (void)
> +{
> +  int fd;
> +  FILE *f;
> +  char buffer[BUFSIZE];
> +
> +  /* Create a temporary file and open it in read-only mode.  */
> +  fd = create_temp_file ("tst-fwrite-ro", NULL);
> +  TEST_VERIFY_EXIT (fd != -1);

OK. Good, no implicit check.

> +  f = fdopen (fd, "r");

OK. Read only.

> +  TEST_VERIFY_EXIT (f != NULL);

OK. Good, no implicit check.

> +
> +  /* Try to write to the temporary file with nmemb = 0, then check that
> +     fwrite returns 0.  No errors are expected from this.  */
> +  TEST_COMPARE (fwrite ("a", 1, 0, f), 0);
> +  TEST_COMPARE (ferror (f), 0);
> +
> +  /* Try to write to the temporary file with size = 0, then check that
> +     fwrite returns 0.  No errors are expected from this.  */
> +  TEST_COMPARE (fwrite ("a", 0, 1, f), 0);
> +  TEST_COMPARE (ferror (f), 0);
> +
> +  /* Try to write a single byte to the temporary file, then check that
> +     fwrite returns 0.  Check if an error was reported.  */
> +  TEST_COMPARE (fwrite ("a", 1, 1, f), 0);
> +  TEST_COMPARE (ferror (f), 1);
> +  clearerr (f);
> +
> +  /* Ensure that we are at the beginning of the file.  */
> +  rewind (f);
> +  /* Check if the file was not modified.  That means there is nothing to be
> +     read.  EOF must be reached.  */
> +  TEST_COMPARE (fread(buffer, 1, BUFSIZE, f), 0);
> +  TEST_COMPARE (feof (f), 1);

OK. Agreed, for a read-only empty buffer it must set EOF right away after reading nothing.

> +
> +  xfclose (f);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>