[PATCH 1 of 1] Tests: unbreak reading new stderr data after eof

[Maxim Dounin]

Hello!

On Fri, May 26, 2023 at 03:24:12PM +0400, Sergey Kandaurov wrote:

> # HG changeset patch
> # User Sergey Kandaurov <pluknet at nginx.com>
> # Date 1685100180 -14400
> #      Fri May 26 15:23:00 2023 +0400
> # Node ID dc3539be2a14a0cd0b8be9e1e9aae8c95b806828
> # Parent  4dad7cf8ebe807f9230a82dde5fc02b5e12e390b
> Tests: unbreak reading new stderr data after eof.
> 
> Tests don't expect to stop reading redirected stderr when end of file is
> reached, but rather to read new data being appended, similar to "tail -f".
> The behaviour is first changed in Ubuntu 23.04 Perl 5.36, by applying the
> upstream patch [1], and is expected for inclusion in the next Perl 5.38.
> The fix is to set filehandle's position to the end of file to clear the
> error state and allow to continue readline() further from that position.
> 
> [1] https://github.com/Perl/perl5/commit/80c1f1e45e8e
> 
> Updated mail_error_log.t and stream_error_log.t for consistency.
> 
> diff --git a/error_log.t b/error_log.t
> --- a/error_log.t
> +++ b/error_log.t
> @@ -183,7 +183,9 @@ sub lines {
>  	my ($t, $file, $pattern) = @_;
>  
>  	if ($file eq 'stderr') {
> -		return map { $_ =~ /\Q$pattern\E/ } (<$stderr>);
> +		my $value = map { $_ =~ /\Q$pattern\E/ } (<$stderr>);
> +		seek $stderr, 0, Fcntl::SEEK_END;
> +		return $value;
>  	}
>  
>  	my $path = $t->testdir() . '/' . $file;

The SEEK_END here would introduce a race: if some data are added 
after reading, SEEK_END will silently skip it.  While probably not 
important here, it might be a good idea to avoid introducing 
unneeded races when possible.  In particular, SEEK_SET might be a 
better option (untested).

Upcoming perldelta recommends $handle->clearerr() instead, which 
indeed seems to be a more explicit option (untested too).

https://github.com/Perl/perl5/blob/8db19a86dfa8408a91845da20ea7063f7646a913/pod/perldelta.pod#readline-no-longer-clears-the-stream-error-and-eof-flags


-- 
Maxim Dounin
http://mdounin.ru/