wp_ob_end_flush_all bug when zlib.output_compression = On

[Matthias Reuter]

When zlib.output_compression is set to On, the function wp_ob_end_flush_all throws the following error:

Notice: ob_end_flush() [ref.outcontrol]: failed to delete buffer zlib output compression in /wp-includes/functions.php on line 2683

You can see this error e.g. when opening /wp-login.php in browser.

Critical Issue related to this bug: it also affects usage of /wp-admin/customize.php - the preview results in a blank page. Seems that the error avoids ajax snippets from getting loaded succesfully.

Hotfix is replacing in /wp-includes/functions.php

function wp_ob_end_flush_all() {
	$levels = ob_get_level();
	for ($i=0; $i<$levels; $i++)
		ob_end_flush();
}

with

function wp_ob_end_flush_all() {
	//$levels = ob_get_level();
	//for ($i=0; $i<$levels; $i++)
	//	ob_end_flush();
}

This issue occurs in all browsers (ie,ff,opera, etc) with both latest versions of WordPress, 3.4.2 and latest nightly build on a LAMP system with PHP Version 5.3.10-1~dotdeb.0.

PHP zlib settings:

Directive	Local Value	Master Value
zlib.output_compression	On	Off
zlib.output_compression_level	5	-1
zlib.output_handler	no value	no value

Related: #18239, #18525

Going to close as a duplicate of #18525, which has patches.

The same notice is mentioned in ticket:18525:9.

Hi Sergey,

thanks for relating the other tickets to this issue. Currently WordPress per default is not compatible with zlib enabled. While Server-Side-Compression is recommened by search engines and most browsers, the other tickets linked by you recommend either disabling zlib or inserting a hotfix.

I don't want to live with a hotfix over the next years which needs to be re-applied manually with every WordPress update.

I would recommend dropping support for PHP 5.2 (or even check wether PHP 5.3 is on server) to avoid that a compatibility function (wp_ob_end_flush_all()) for PHP 5.2 produces new errors on PHP 5.3 installations with zlib enabled.

So I hope that the developers of WordPress will fix this issue and don't let me hotfix that the next years until PHP 5.2 support is finally dropped.

Kind regards,

Matthias

Rather than hacking core, try this one-line plugin on for size:

remove_action( 'shutdown', 'wp_ob_end_flush_all', 1 );

We may be at the point where we can eliminate this from core. I'll look into it at the start of the 3.6 cycle. Closing this as a duplicate of #18525 makes sense, because that ticket is reporting the same problem. You disagree with the solution, and that's completely fine, but you should voice it there. (For what it's worth, I also don't like the solution, which is why I myself have not committed it.)

Wow, nacin, this fix works great and I don't need to touch the core - perfect :)