CSS crashing YUI-CSS-compressor-PHP-port

[futtta]

Hi Túbal;
I'm using your YUI-CSS port in my WordPress plugin (Autoptimize).

A user filed a bugreport that my plugin was generating internal server errors. After investigating the problem is due to YUI-CSS-compressor-PHP-port not being able to optimize specific CSS of All In One Buttons, another WordPress plugin. The YUI-CSS port's GUI on my healthy Linux-VPS doesn't succeed in optimizing that CSS either, so this indeed seems like a bug?

Looking forward to your feedback, let me know if I can help in any way!

frank

[futtta]

So I've been looking into this a lot more over the last couple of days, assisted by two Autoptmize-users who had similar problems. They were on Xampp by the way, which due to default Apache config on Windows exhibits this problem a lot sooner, as mentioned here by others before as well.

The issue is specifically with line 294, which tries to hide colons before stripping whitespace (297);

$css = preg_replace_callback('/(?:^|\})(?:(?:[^\{\:])+\:)+(?:[^\{]*\{)/', array($this, 'replace_colon'), $css);

When processing long css-strings (my tests worked until 10396 bytes but failed the CSS-string was bigger, this happens for CSS that could not be chunked securely earlier in the code, e.g. when you have a long list of selectors for a declaration block), this line of code causes a stack overflow in PCRE (regex-lib used by PHP) which in turn makes Apache segfault. There are a lot of bug-reports about this disruptive behavior on bugs.php.net, all of which are closed stating this is a problem in PCRE that is also discussed in that bug-db.

Possible solutions in order of (personal) preference;

1. simplify regex, making it use less space on the stack (example by PCRE-team here)
2. replace the regex on line 297 (which removes the whitespace) with another -less efficient?- one, removing the need to apply the colon-magic just before and after
3. check str_len($css) and don't replace colons if lenght > chunck_size (or chunk_size*1.5 or *2)
4. ask users to increase Apache's threadstacksize
   5. leave as is

I tried both (2), (3) and (4) successfully, but I'm not smart enough to do (1). So who is?

frank

[futtta]

As not being smart enough is no excuse, I came up with the following alternative approach;

$css = preg_replace_callback('/(?:(?:^|\})([^\{]*\s:))/', array($this, 'replace_colon'), $css);

Based on tests with un-chunkable large CSS-strings this (see here for a visual representation of the regex) works while it does seem to replace the colon where needed and the test-suite indeed reports an identical success rate.

This got released today as part of Autoptimize 1.8.

[tubalmartin]

I'll look into this ASAP. Thanks for your work!

[futtta]

Any news Túbal?

[tubalmartin]

I have already fixed this issue. Thank you for your work! Appreciated! I'll release a new version of the lib today.

[tubalmartin]

Fixed in v2.4.8-3