Commented out WP_CACHE definition in wp-config.php being incorrectly ignored

[davidfavor]

:::: Summary

This relates specifically when moving from WP Super Cache to ZenCache. Likely also effects other caching plugins besides WP Super Cache.

A slight code modification should fix this problem. See details below.

The bottom line is this bug prohibits ZenCache from ever really being enabled, as WP_CACHE remains commented out.

This means ZenCache appears to be slow, as it's code never really executes.

:::: Detailed Explanation

ZenCache appears to sometimes missing updating wp-config.php with the WP_CACHE directive.

Here's how to reproduce this on WP-4.3.1 with all updates installed.

1. Starting point is clean wp-config.php - no caching plugins installed + no wp-config.php directives. Site speed is 45 reqs/sec

2. Install + Activate WP Super Cache. Site speed increases to 2500 reqs/sec with wp-config.php of...
   define('WP_CACHE', true); //Added by WP-Cache Manager
   define( 'WPCACHEHOME', '/sites/drf/fastseohosting.com/wordpress/wp-content/plugins/wp-super-cache/' ); //Added by WP-Cache Manager

3. Deactivate WP Super Cache + wp-config.php changes to...
   //define('WP_CACHE', true); //Added by WP-Cache Manager
   define( 'WPCACHEHOME', '/sites/drf/fastseohosting.com/wordpress/wp-content/plugins/wp-super-cache/' ); //Added by WP-Cache Manager

4. Install + Activate ZenCache + wp-config.php no changes (as expected)

5. In ZenCache settings enable + save config + wp-config.php does not change.
   //define('WP_CACHE', true); //Added by WP-Cache Manager

WP_CACHE still appears to be commented out.

:::: Suggested Fix

In zencache.inc.php it appears tests for WP_CACHE require being anchored to left, rather than unanchored (floating).

Test likely should be - ^define... - rather than - define... - which will match the commented out define cruft left over from WP Super Cache.

[raamdev]

@davidfavor Thanks for the report. This should have been addressed in v150821 (ZenCache Pro) and v150930 (ZenCache Lite). See #509

I'm going to run a few tests to see if I can reproduce this issue.

Can you tell me which version of ZenCache you are running?

[raamdev]

I have confirmed this bug following @davidfavor's steps above with both ZenCache Lite v150930 and ZenCache Pro (dev branch).

If the wp-config.php file contains the following line, Enabling ZenCache (ZenCache → Plugin Options → Enable/Disable) does not uncomment or otherwise set WP_CACHE to true in wp-config.php, so despite ZenCache being enabled, nothing on the site is actually being cached.

//define('WP_CACHE', true); //Added by WP-Cache Manager

@jaswsinc It looks like this regex is not taking into consideration that define('WP_CACHE', true); may actually be commented out in wp-config.php.

[raamdev]

The above comment only referenced the ZenCache Pro codebase. Noting here that this should also be fixed in ZenCache Lite (via this line).

[jaswrks]

@jaswsinc It looks like this regex is not taking into consideration that define('WP_CACHE', true); may actually be commented out in wp-config.php.

Good catch guys! I agree, there is room for improvement here.

@raamdev You could try playing with a negative lookbehind in that line you referenced.

i.e., (?<!\/\/\s*)

if (preg_match('/(?<!\/\/\s*)define\s*\(\s*([\'"])WP_CACHE ...

Looks like there is at least one instance of this in the removal routine also that needs to be updated.

[raamdev]

@jaswsinc Thanks! I started playing with negative lookbehinds but preg_match() (and regex101.com) complains that it must be zero-width:

Warning: preg_match(): Compilation failed: lookbehind assertion is not fixed length at offset

https://regex101.com/r/aA0yT1/2

Error: Lookbehinds need to be zero-width, thus quantifiers are not allowed

Which throws a wrench into the mix. It seems like we can check for one particular scenario (//define...) but that won't account for variations such as // define. Ideas?

[jaswrks]

Nice! I see what you mean. Well, I think it's fine to pull the \s* out of the lookbehind.

(?<!\/\/)\s*

See: https://regex101.com/r/tD0hK0/2

[jaswrks]

Ah. Nevermind. Tricky! That doesn't work either.

[raamdev]

Yep, I tried that too!

[raamdev]

Why don't we just remove define('WP_CACHE', true); if we find it in wp-config.php and then re-add it? I realize there's a slight performance hit there by doing work unnecessarily in the event that it's not commented out, but this routine is only running once when ZenCache is activated... it's not like it's running on every page load or something.

[raamdev]

In other words, just remove this entire conditional and just let the next line (removeWpCacheFromWpConfig()) remove it.

[jaswrks]

That's a decent idea. However, the reason it's like that right now, is to cover a scenario where the wp-config.php is not writable (I do that myself). So for instance, if you have this already defined in your wp-config.php file, and ZenCache finds it in there, there is no reason for us to do anything more; i.e., no reason for failure or any notice about us not being able to write to the file.

Here is a modified version of the regex that seems to work. If you can take a closer look I'd appreciate it. See: https://regex101.com/r/fD4wK5/2

(?:\n|\<\?(?:php)?|;)\s* ...

Instead of doing a lookbehind, we can be more specific about what we want to find. The define( fragment should be found right after <? or <?php, or on a new line by itself, or right after a previous statement that ends with ; ... and then followed by any amount of whitespace; i.e., \s*

[jaswrks]

Or, this might be even better. We could strip all comments from the syntax before we check. See: http://php.net/manual/en/function.php-strip-whitespace.php

[raamdev]

it's like that right now, is to cover a scenario where the wp-config.php is not writable

Ah, that makes sense. Yeah, that's an important scenario to consider.

a modified version of the regex

Yep, that seems to work. I ran it through a few tests (including directly in ZenCache) and it's working as expected.

We could strip all comments from the syntax before we check.

Hmm, that would work too. Any preference?

[jaswrks]

My preference would be to strip the comments before we do a check. That seems bulletproof in terms of us being able to accurately detect whether it's really in there or not.

You could then leave the regex as-is. However, while you're in there it's probably a good idea to change:

this:

if (preg_match('/define

to:

if (preg_match('/\bdefine

That avoids a false match on something wild like: my_define('WP_CACHE' ... by requiring that define be preceded by a word boundary.

[raamdev]

Next Pro Release Changelog:

• Bug Fix: Fixed a bug where a commented-out WP_CACHE definition in wp-config.php (such as what WP Super Cache leaves behind) was being incorrectly ignored and resulted in caching being silently disabled. Props @davidfavor. See Issue #591.

[raamdev]

Next Lite Release Changelog:

• Bug Fix: Fixed a bug where a commented-out WP_CACHE definition in wp-config.php (such as what WP Super Cache leaves behind) was being incorrectly ignored and resulted in caching being silently disabled. Props @davidfavor. See Issue #591.

[davidfavor]

Thanks for fixing this so fast!

BTW, the only reason I figured this bug out instantly is I've done the same thing in my code several times.

[raamdev]

the only reason I figured this bug out instantly is I've done the same thing in my code several times.

@davidfavor Ha! Always better to have more eyes on the bugs. 🐛 🪲 Thanks again. 😄

[raamdev]

ZenCache v151114 has been released and includes changes from this GitHub Issue. See the v151114 announcement for further details.

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This issue will now be locked to further updates. If you have something to add related to this GitHub Issue, please open a new GitHub Issue and reference this one (#591).