Implement storage

[georgehrke]

• Allow users to hand over a storage object (whether it's SessionStorage, LocalStorage or something completely different)
• Save all objects / properties to Storage

[georgehrke]

This will also help with mitigating internet connectivity issues.
Changes will be written to the storage object. CDAV-Library will remember that the changes have not been synced to the server yet and will sync them whenever the internet connection is back.

[skjnldsv]

I'm not sure this should be the role of this lib?
I mean, how does our apps should understand that there are changes pending and not every data is updated?

[georgehrke]

Yes, I get your point. I'm not 100% sure whether this should be the job of the Calendar / Contacts app or this library.

My idea was to introduce a method hasUnsynchedChanges() and introducing a sync method, that should periodically be called by the application using cdav-library.

One of the biggest issues, at least in the calendar app, is the waiting time of at least 5 seconds to load all calendars when you open the calendar app. I would just like to cache all vobjects / vcards, like your desktop and mobile cal- / carddav clients do, to use that data and then once the initial view is rendered, query the server for updates.

[skjnldsv]

I feel like this is not the job of the lib, but can't really figure out why. ^^
If we successfully implement this feature without the app knowing about it (I mean like no differences at all) then I feel like this is a great idea. If we have to implement specific stuff in the app to manage this feature then we should probably do that in our app instead?

[georgehrke]

I feel like this is not the job of the lib, but can't really figure out why. ^^
[...]
If we have to implement specific stuff in the app to manage this feature then we should probably do that in our app instead?

I have this feeling too a little.
But if we implement it in the app, we will have almost 3 identical implementations and lots of duplicate code.

Let's just discuss this feature at Nextcloud conference! :)

[georgehrke]

Taking into account @MorrisJobke's feedback from today, I propose the following:

• allow developers to hand over storage object to cdav library
• all the API calls are the same, whether you hand over a storage object or not
• when you don't handover a storage object:
  • every findAll() / find() request will send new requests to the server
  • sync() will simple resolve to true without doing anything
• when you handover a storage object:
  • send collection-sync on every sync() request to slowly build up storage
  • if you send any findAll() / find() / findInTime() / etc. requests and the initial sync has not been finalised, it will first send a request only for the paths & etags, to check if the contacts / calendar objects are already available locally
  • if not, it will send a multi get and add them to the cache.
  • when everything was cached, findAll()/etc. will automatically resolve from storage object and sync will check for changed sync-tokens.

Does this make sense to everyone?