Incompatibility with CDN Linker plugin (white screen cached)

[Slobork]

Hi,

a couple of times white screen was cached for the homepage of a site I have mapped over the Multisite. Sure, when I clear the cache it will catch the page normally after that.

Would be possible to come with a solution that Quick Cache detects when this kind of incident happens and that it clears itself?

I don't know is this Multisite specific, but I noticed it only on the Multisite. Maybe because regular WP installations I have are small sites which I've set with caching - 6 months, so it doesn't get a chance to rebuild itself and get into the issue.

Thanks.

[raamdev]

@SBOQ thank you for reporting this important issue.

The next time this happens, can you confirm that what's actually happening is that a blank cache file is being written for the home page? I don't see how this would be possible, but if a blank cache file is in fact being written and subsequently loaded (resulting in a blank white page), this needs to be fixed.

However, as I said I don't see how this could be possible looking at the code. If a blank cache file is not being written and loaded but something else is happening, we'll need to track that down.

In short, unless I can reproduce this issue I have no way of debugging and fixing it.

[Slobork]

yes, I thought it would be tough. I'll try to gather more info the next time it happens, but it may take a while since it happened just 2 times until now.

[Slobork]

@raamdev Hi buddy.
I found that the problem here is the conflict with the CDN Linker plugin.

When the white screen was cached I've looked into the cache file and I see that the html comment of the CDN Linker plugin intersect the code in the place where usually is the <!DOCTYPE> declaration positioned, i.e. after the comment. So Instead of
the code looks like this:

After the CDN Linker intersect nothing else appears in the file except the usual Quick Cache's comment (when the file is cached and expiration time).
When the file is normally cached the CDN Linker's comment appears at the bottom of the file, right before the Quick Cache's comment.

Since the white screen has happened again, I've decided to test it more intensively by setting low caching expiration time. I see that white screen will be cached quite often (about 2 in 5 times). Also it's not Multisite related, since I've tested it on the regular WP installation and the issue is the same.

When the CDN Linker plugin is disabled, the problem won't appear, but I need that plugin :(

[raamdev]

@SBOQ Thanks so much for reporting your findings!

Could you get in touch with the CDN Linker developers and ask them if this might be a bug in CDN Linker? If it's a compatibility issue with Quick Cache that we can work out, I'd love to make the necessary changes to Quick Cache to resolve the conflict.

[Slobork]

@raamdev I've opened a support thread at CDN-Linker regarding this.
Can you please join the conversation at https://github.com/wmark/CDN-Linker/issues/33
I would try to be of help, but unless one of you aren't able to reproduce the error I'm afraid that this cannot evolve further.

[raamdev]

@SBOQ Would you mind testing a development copy of Quick Cache Pro to see if you still experience this issue with CDN Linker? I can provide you with a ZIP file with a development copy of Quick Cache Pro via email; please open a trouble ticket and I will send it.

[Slobork]

Ticket submitted (Ticket ID: 2482).
It's quite late here, and whenever you send it I'm not sure will I be able to test it in the next 24h.
But I hope to come back with the results as soon as possible.
Cheers!

[Slobork]

Unfortunately nothing is changed with the new development version, the white screen is still cached occasionally in my testing.

I see that Mark, CDN-Linker author, has opened a new issue thread for the Quick Cache with references that may be a cause for this issue. So I suppose you'll continue from there - #97

[raamdev]

@SBOQ Thank you for testing that for me. I've left some comments on the issue that Mark opened. I'll leave this issue open for now until I reach some conclusion on the issue.

[raamdev]

Please see #97 for related discussion. Closing this issue for now, as it appears we've taken this issue as far as possible for now.