[4.0] Caching of headers does not work for views

[elpescador-nl]

Steps to reproduce the issue

Enable the cache (it does not matter which engine, I tested with redis and file caching). Do not use the Page caching plugin.
The easiest way with an out-of-the-box J!4 installation...
The vcf download of a contact has an extra added header Content-disposition with the card_name in the file name. For example attachment; filename="John Smith.vcf"

Expected result

The Content-disposition: attachment; filename="John Smith.vcf" header is always present. Also when delivering a cached version.

Actual result

The Content-disposition: attachment; filename="John Smith.vcf" header is only present the first time the vcf is loaded. With the cached version this header disappeared.

System information (as much as possible)

• Joomla! 4.0.0-rc6 Release Candidate
• php-fpm
• nginx

Additional comments

As I said this header is just an example. You could also test it by adding this code to a view you want to test:

Factory::getApplication()->setHeader('x-cachetest', 'hello');

[elpescador-nl]

I already found out the headers are not being stored in the cache at all.

joomla-cms/libraries/src/Cache/Cache.php

Line 748 in 72e78f4

if (isset($options['headers']) && $options['headers'])

When I force this if-clause to be true (change it to if(true)) the header is being stored. I don't think this is the solution, but it might help finding the good solution. I hope this find might help someone with more knowledge of the Caching layer to solve the problem.

In J!3.9 it all works perfectly. I tried to compare the J!4 code with it, but did not get my head around it.

[elpescador-nl]

@PhilETaylor , in my first comment I stated this works perfectly for J!3.9 (J!3.10) but I was mistaken. It doesn't work there either.
I've found a work around for this issue and using the page cache plugin on top of it prevents it from happening as it seems. So not a big priority I think.

Though it looks a bit strange to me that by activating the cache (and not the page cache) custom component headers are only sent when there is a cache miss.