PHP errors since upgrade to WP 5.3 ‘Cannot modify header information’

I’m seeing exactly the same.

But the code in Comet Cache itself is unchanged and looks normal, just trying to add some cache-suppressing headers at that point. Which up until recently worked fine. So for some reason, the headers are now being sent too early.

See here.

Yup, normally this happens when some file has a BOM, or has white space beyond the closing ?> (which in general should therefore be omitted).

So the problem is in general hard to find – WHICH of the many PHP files executed before HTML output actually should happen is the culprit? Is it in the theme (unchanged in my WP, so no), or a recently updated plugin, or in WP Core (the latter seems unlikely or there would have been a huge outcry).

Anyone know how to find the cause quickly and easily?

Tim

Well, I did find some old ISO-8859-1 characters in my wp-config.php, but removing them has not solved this problem, It’s somewhere else )-:

On further inspection: This should be easy to fix, see here, and many other places.
Our common problem is, that the subclause ” (output started at…” – which would tell us which file is the culprit – is missing in our error messages.

Howcome? I’m using (Plesk) PHP 7.3.11, via Nginx (directly) and PHP-FPM.

This was reported on their official support forums earlier this year:
https://forums.wpsharks.com/t/debug-log-php-warning-cannot-modify-header-information-headers-already-sent/5902

@jumbo thanks for the pointer, but I do not see any answer there…

On further research and reflection, what I can say is that I do NOT see this problem with the Weaver Xtreme theme (from Bruce Wampler, which I use a lot). But I do see it with some older themes: Edin, DI-Basis, Tatami (Elma Studios) and Customizr. So maybe it really is ultimately to do with the theme calling some old functions at thwe wrong point in the process?

I did find a way to get rid of the error: Deactivate and Delete Comet Cache )-: What is not exactly want I wanted to do.

Any ideas, anyone?

Tim

Similarly there seems to be a problem with W3TC.

So something has changed under the hood of WP 5.3 which is causing grief for some of us.

And it does seem – at least in some cases – to be the theme, see here.

I am having this issue as well. I don’t think it is a whitespace issue. The all the lines in this function fire the warning. It is probably an execution order thing:

/**
* Sends no-cache headers.
*
* @since 151220 Enhancing no-cache headers.
*/
public function sendNoCacheHeaders()
{
header_remove(‘Last-Modified’);
header(‘Expires: Wed, 11 Jan 1984 05:00:00 GMT’);
header(‘Cache-Control: no-cache, must-revalidate, max-age=0’);
header(‘Pragma: no-cache’);
}

Hi, I have the same issue, log flooded with such messages.
What’s the status? Is there a fix coming, by any chance?

Regards
Franco

No response in a week for me. Might want to just start a new thread on it. Pretty sure it is execution order of that sendNoCacheHeaders function

Having the same issue. Any solution? Our logs are flooded.

Is a fix foreseen? Can we have a ETA, please?

had to delete Comet ?? no solution from devs…

Give a try to Rapid Cache, it’s newly created fork of this plugin.

This is still an issue and plugin saw no updates for ages.
Is it dead?