Add hidden user folder

[icewind1991]

this can be used by apps to have apps that are within the users home folder but are hidden from the normal ui bits.

Currently, the "hidden" part is achieved in the dav plugin excluding it from listing and file search excluding results inside it.

I had originally hoped to have the "hidden" logic be more low level instead of having to implement it separately in each api by my attempts for that didn't work out as they would defeat the purpose of the folder in the first place (having it accessible trough normal endpoints by path and fileid)

[icewind1991]

added a function get generate the folder name and added a dot prefix

[skjnldsv]

A bit of tests would be awesome 🙈

[PVince81]

• BUG: create a folder "test" in the web UI then rename it to the hidden folder => this should not be possible
• BUG: rename hidden folder to another name => this should not be possible
• BUG: Webdav DELETE on hidden folder did not fail, and I can even recreate it manually
• I assume that a PROPFIND on the hidden folder should not be blocked ? it's not currently

there might be more

yeah, would be good to add maybe integration tests for this to confirm that all file operations are denied there or at least that the folder is protected in some way

[PVince81]

• BUG: I shouldn't be able to share the hidden folder with someone else (per API)
• BUG: while the folder is invisible in the web UI, if I try to create it, it will suddenly reappear with "could not create because it exists already" and suddenly I see it and can access it

[PVince81]

• don't create activity entries for any entries inside the hidden folder ? for example if apps are creating custom folders and files there

[icewind1991]

nextcloud/activity#698 for the activity path

I assume that a PROPFIND on the hidden folder should not be blocked ? it's not currently

This is intentional yes

while the folder is invisible in the web UI, if I try to create it, it will suddenly reappear with "could not create because it exists already" and suddenly I see it and can access it

I think this is ok, due to the "random" name it's very unlikely that a user hits this by accident, and being able to browse the hidden folder on purpose is fine since it's not a security feature.

[artonge]

From reading the code:

• What if the user creates a folder with the same name as the hidden folder but in a subfolder.

/
/.hidden_azeudhazud    <-- real hidden folder
/sub_folder
/sub_folder/.hidden_azeudhazud    <-- user creates this folder that should maybe not be hidden.

If I get this right, the created folder will be considered as hidden by FileSystem::isPathHidden.

Is this intended behaviour?

It makes sense if userA share his root folder with userB

/    <-- userB's root folder
/.hidden_azeudhazud    <-- userB's hidden folder
/usera_shared_root_folder    <-- what the name says
/usera_shared_root_folder/.hidden_azeudhazud    <-- userA's hidden folder that should be hidden