[PATCH v2] lineedit: fix some tab completions written to stdout

[Natanael Copa]

On Fri, 01 Nov 2024 23:07:31 +0000
"Sertonix" <sertonix at posteo.net> wrote:

> In fd47f056765 (lineedit: print prompt and editing operations to stderr)
> some output was left printing to stdout. This causes a race condition
> between stderr and stdout which in some cases leads to output written in
> the wrong places.
> 
> Downstream issue: https://gitlab.alpinelinux.org/alpine/aports/-/issues/16566
> Fixes: fd47f056765
> 
> Signed-off-by: Sertonix <sertonix at posteo.net>
> ---
>  The implicit '\n' doesn't apply to stderr so it needed to be explicit.
> 
>  libbb/lineedit.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/libbb/lineedit.c b/libbb/lineedit.c
> index 151208c1c..26f47f043 100644
> --- a/libbb/lineedit.c
> +++ b/libbb/lineedit.c
> @@ -451,7 +451,7 @@ static void put_cur_glyph_and_inc_cursor(void)
>  		 * have automargin (IOW: it is moving cursor to next line
>  		 * by itself (which is wrong for VT-10x terminals)),
>  		 * this will break things: there will be one extra empty line */
> -		puts("\r"); /* + implicit '\n' */
> +		fprintf(stderr, "\r\n");

You could use fputs here.

>  #else
>  		/* VT-10x terminals don't wrap cursor to next line when last char
>  		 * on the line is printed - cursor stays "over" this char.
> @@ -1170,9 +1170,9 @@ static void showfiles(void)
>  			);
>  		}
>  		if (ENABLE_UNICODE_SUPPORT)
> -			puts(printable_string(matches[n]));
> +			fprintf(stderr, "%s\n", printable_string(matches[n]));

You could use fputs here as well.

>  		else
> -			puts(matches[n]);
> +			fprintf(stderr, "%s\n", matches[n]);

Also here. And at this point you could probably save a few bytes by
creating a fputs_stderr function.

>  	}
>  }
>  

Thanks for working on this. It has annoyed me every day since we updated to busybox 1.37.

-nc