Incorrect headers for image derivative if file stored in private filesystem

The patch #21 causes more issues since it overrides all headers returned by the hook_file_download hooks.

The attached patches take the same approach as the original patch in 🐛 Image derivative generation does not work if effect "Convert" in use and file stored in private filesystem Fixed . It directly sets headers instead of any array merging. This ensures that the content type and length are set correctly.

Bumping to 11.x so that this fix gets some visibility.
Pending: Needs tests

Updated title and description for the specific case when using the "Convert" effect.

Hiding all patch files since an MR has been created for 11.x with the https://www.drupal.org/files/issues/2023-09-26/2786763-24--D11.x.patch →

Just noticed that this still needs tests

Patch on #24 works for me.

I can still reproduce when testing manually.

phpunit tests were not showing the problem because of two problems:

• the convert effect was not saved so the file was not really converted
• ImageModuleTestHooks::fileDownload() is not adding real download headers so it does not trigger the same code path as manual testing

So looking at the summary and solution don't believe they match up, solution mentions using array_merge() but doesn't appear to be the case.

I adjusted the summary.

The tests seem to be working as expected. +1 RTBC

It's not clear from the issue summary or the comments whether this really only affects image derivatives when private files are in use, isn't it whenever an image is returned by the controller regardless of file storage? If so the issue title and summary could use an update.