feat(nextcloud): add support of imaginary an externalPreviewProvider

[wrenix]

Description of the change

Benefits

• faster image rendering for preview
• nextcloud container is not killed (e.g. OOM) if big and much preview images are generated

Possible drawbacks

Works for me.

TODO:

• write CI test

Checklist

• I have read the CONTRIBUTING.md doc.
• DCO has been signed off on the commit.
• Chart version bumped in Chart.yaml according to semver.
• (optional) Parameters are documented in the README.md

[wrenix]

ping @jessebot / @provokateurin do you like to review?

[provokateurin]

Sorry, I don't have the time for that atm. I hope I can do it at some point, but only at the beginning of next month the earliest.

[jessebot]

oh this is neat! May I ask what the difference between this and the preview generator app are? (I'm not against it btw, just want to learn more) I will review this more thoroughly as soon as I have a moment 🙏

[jessebot]

Looks good to me. Thanks for this! Perhaps we can add another PR for adding a CI test of some sort in the future?

[SIMULATAN]

Thank you for working on this 🚀
Just wanted to point out that, with Nextcloud 30, the OC\Preview\Imaginary provider no longer generates PDF previews. It may be worth considering adding the new ImaginaryPDF provider to the Imaginary notes in the README.md file.
See https://docs.nextcloud.com/server/latest/admin_manual/release_notes/upgrade_to_30.html#previews-for-pdf-files-with-imaginary
Thanks again, looking forward to using it to speed up my (terribly slow) Nextcloud media previewing ❤️

[wrenix]

rebased on main and add docu in e393d90 like @SIMULATAN suggested

[wrenix]

rebased, squashed und test added

[wrenix]

rebased - Does i interprate you @jessebot last comment correct, that i could merge it?

[provokateurin]

LGTM, just one question

[provokateurin]

Given that this is required for imaginary to be utilized, should it just be part of the defaultConfig?

[wrenix]

I am not sure which other PreviewProvider are default.
And which we should enable after enable Imaginary (like for office/collabora and txt files).

[provokateurin]

I don't remember if the config values with arrays are merged or overwritten, but if they are just merged then there is no problem with adding these. Maybe you can check how that works and based on that we enable them by default or not.

[wrenix]

Found defaults: https://docs.nextcloud.com/server/latest/admin_manual/configuration_server/config_sample_php_parameters.html#enabledpreviewproviders

I will change it

[wrenix]

changed in f910cc6

[provokateurin]

It would be nice to add a test that generating the preview works (similar to how we test S3 in the job).

[wrenix]

Yes, it would be nice - i do not know when a preview generation is triggered (i believe in viewing)

[provokateurin]

You can request a preview via https://github.com/nextcloud/server/blob/b5ac989ecd4e6f380af4699cb8c0aae872284459/core/openapi.json#L8178