[1/3] support: Change xgetline to return 0 on EOF

  The advantage is that the buffer will always contain the number
of characters as returned from the function, which allows one to use
a sequence like

  /* No more audit module output.  */
  line_length = xgetline (&buffer, &buffer_length, fp);
  TEST_COMPARE_BLOB ("", 0, buffer, line_length);

to check for an expected EOF, while also reporting any unexpected
extra data encountered.
---
 support/support_process_state.c |  2 +-
 support/xgetline.c              | 22 ++++++++++++++--------
 support/xstdio.h                |  5 ++++-
 3 files changed, 19 insertions(+), 10 deletions(-)
  

On 4/3/20 8:02 AM, Florian Weimer via Libc-alpha wrote:
> The advantage is that the buffer will always contain the number
> of characters as returned from the function, which allows one to use
> a sequence like

I agree that returning -1 is not the most useful semantic here, and
relaxing xgetline to be more like getline is better.

>   /* No more audit module output.  */
>   line_length = xgetline (&buffer, &buffer_length, fp);
>   TEST_COMPARE_BLOB ("", 0, buffer, line_length);
> 
> to check for an expected EOF, while also reporting any unexpected
> extra data encountered.

OK for master.

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

> ---
>  support/support_process_state.c |  2 +-
>  support/xgetline.c              | 22 ++++++++++++++--------
>  support/xstdio.h                |  5 ++++-
>  3 files changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/support/support_process_state.c b/support/support_process_state.c
> index 76dc798728..e303c78fc8 100644
> --- a/support/support_process_state.c
> +++ b/support/support_process_state.c
> @@ -59,7 +59,7 @@ support_process_state_wait (pid_t pid, enum support_process_state state)
>    for (;;)
>      {
>        char cur_state = -1;
> -      while (xgetline (&line, &linesiz, fstatus) != -1)
> +      while (xgetline (&line, &linesiz, fstatus) > 0)

OK.

>  	if (strncmp (line, "State:", strlen ("State:")) == 0)
>  	  {
>  	    TEST_COMPARE (sscanf (line, "%*s %c", &cur_state), 1);
> diff --git a/support/xgetline.c b/support/xgetline.c
> index 180bc2db95..d91c09ac10 100644
> --- a/support/xgetline.c
> +++ b/support/xgetline.c
> @@ -18,16 +18,22 @@
>  
>  #include <support/xstdio.h>
>  #include <support/check.h>
> -#include <errno.h>
>  
> -ssize_t
> +size_t
>  xgetline (char **lineptr, size_t *n, FILE *stream)
>  {
> -  int old_errno = errno;
> -  errno = 0;
> -  size_t ret = getline (lineptr, n, stream);
> -  if (!feof (stream) && ferror (stream))
> -    FAIL_EXIT1 ("getline failed: %m");
> -  errno = old_errno;
> +  TEST_VERIFY (!ferror (stream));
> +  ssize_t ret = getline (lineptr, n, stream);
> +  if (ferror (stream))
> +    {
> +      TEST_VERIFY (ret < 0);
> +      FAIL_EXIT1 ("getline: %m");
> +    }
> +  if (feof (stream))
> +    {
> +      TEST_VERIFY (ret <= 0);
> +      return 0;
> +    }
> +  TEST_VERIFY (ret > 0);

OK.

>    return ret;
>  }
> diff --git a/support/xstdio.h b/support/xstdio.h
> index 143957b6a8..807c3afc43 100644
> --- a/support/xstdio.h
> +++ b/support/xstdio.h
> @@ -27,7 +27,10 @@ __BEGIN_DECLS
>  FILE *xfopen (const char *path, const char *mode);
>  void xfclose (FILE *);
>  
> -ssize_t xgetline (char **lineptr, size_t *n, FILE *stream);
> +/* Read a line from FP, using getline.  *BUFFER must be NULL, or a
> +   heap-allocated pointer of *LENGTH bytes.  Return the number of
> +   bytes in the line if a line was read, or 0 on EOF.  */
> +size_t xgetline (char **lineptr, size_t *n, FILE *stream);

OK.

>  
>  __END_DECLS
>  
>