From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Wong <normalperson@yhbt.net>
Subject: Re: [PATCH 3/7] Extract, test and enhance the logic to collapse
 ../foo paths.
Date: Mon, 30 Jul 2012 19:51:08 +0000
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To: "Michael G. Schwern" <schwern@pobox.com>
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"Michael G. Schwern" <schwern@pobox.com> wrote:
> From: "Michael G. Schwern" <schwern@pobox.com>
> 
> The SVN API functions will not accept ../foo but their canonicalization
> functions will not collapse it.  So we'll have to do it ourselves.
> 
> _collapse_dotdot() works better than the existing regex did.

I don't dispute it's better, but it's worth explaining in the commit
message to reviewers why something is "better".

> This will be used shortly when canonicalize_path() starts using the
> SVN API.
> ---

> +# Turn foo/../bar into bar
> +sub _collapse_dotdot {
> +	my $path = shift;
> +
> +	1 while $path =~ s{/[^/]+/+\.\.}{};
> +	1 while $path =~ s{[^/]+/+\.\./}{};
> +	1 while $path =~ s{[^/]+/+\.\.}{};

This is a bug that's gone unnoticed[1] for over 5 years now,
but I've just noticed this doesn' handle "foo/..bar"  or "foo/...bar"
cases correctly.

>  sub canonicalize_path {
>  	my ($path) = @_;
>  	my $dot_slash_added = 0;
> @@ -83,7 +95,7 @@ sub canonicalize_path {
>  	# good reason), so let's do this manually.
>  	$path =~ s#/+#/#g;
>  	$path =~ s#/\.(?:/|$)#/#g;
> -	$path =~ s#/[^/]+/\.\.##g;
> +	$path = _collapse_dotdot($path);

[1] - I doubt anybody uses paths like these, though...