Expose share owner id and display name via files webdav

[PVince81]

• Required by the Webdav files UI: we need the share owner to be able to display it in the UI. It was formerly available in the "ajax/list.php" response.
• This PR brings this value to the files' Webdav response, when requested explicitly.
• Whether a folder is an incoming share is already available in the "S" permission (oc:permissions)
• This does not cause a performance penalty because the share info has already been resolved at the time the mount point was created. So we're basically reading information that is already available.

To test:

1. Create two users "root" and "user1"
2. Login as "user1"
3. Share a folder "test" with "root"
4. Save the following into "propfind.txt"

<?xml version="1.0"?>
<a:propfind xmlns:a="DAV:" xmlns:oc="http://owncloud.org/ns">
        <a:prop><oc:permissions/></a:prop>
        <a:prop><oc:owner-id/></a:prop>
        <a:prop><oc:owner-display-name/></a:prop>
</a:propfind>

1. curl -X PROPFIND -H "Content-Type: text/xml" --data-binary "@propfind.txt" http://root:admin@localhost/owncloud/remote.php/webdav/test | xmllint --format -

This PR will output two additional properties, when requested as above:

<d:response>
    <d:href>/owncloud/remote.php/webdav/test/</d:href>
    <d:propstat>
      <d:prop>
        <oc:owner-id>user1</oc:share-owner-id>
        <oc:owner-display-name>User One</oc:share-owner-display-name>
        <oc:permissions>SRDNVCK</oc:permissions>
      </d:prop>
      <d:status>HTTP/1.1 200 OK</d:status>
    </d:propstat>
  </d:response>

Edit: now renamed to "owner-id" and "owner-display-name"

Open questions:

• Should we rename "share owner" to simply "owner" ? If yes:
  • In ownCloud's terms, the owner of a file is always either the current user or the sharer.
  • Note that is we rename it to "owner" we'll need to return the current user.
  • It is still possible to detect if this is a shared mount by checking the "S" permission.
  • We'd then remove SharesPlugin and move the attribute to FilesPlugin, as it is more generic
• @icewind1991 do you think we should cache the getOwner() for better performance ? The code path looks like it goes up to the SharedStorage which has the share cached
• TODO: add unit tests once everything is clarified

Let's discuss @DeepDiver1975 @icewind1991 @schiesbn @rullzer @nickvergessen

[PVince81]

I realized that this PR already returns the current user "root" when doing a PROPFIND on a non-shared item. If we really want this only for shares, then the property would need to be adjusted.

I think I'm more in favor of having a more generic "owner-id" and "owner-display-name" attribute.
Thinking further, I wonder how this would fit in with principals in the future. But we need a short term solution.

[PVince81]

• TODO: make sure to return 403 if someone tries to PROPPATCH these new properties

[icewind1991]

I agree with moving to owner-id

[icewind1991]

@icewind1991 do you think we should cache the getOwner() for better performance ? The code path looks like it goes up to the SharedStorage which has the share cached

Might be good to add getOwner to the FileInfo which could then be used to cache it

[PVince81]

@icewind1991 I added getOwner to the FileInfo interface and also Node API, please check my implementation: f563648

And I renamed the properties to "owner-id" and "owner-display-name".

Please review

[PVince81]

Regarding getOwner on the interface: I checked that the Common storage, SharedStorage and all the external storages have that method implemented. External storages all directly or indirectly extend Common.

[icewind1991]

@icewind1991 I added getOwner to the FileInfo interface and also Node API, please check my implementation: f563648

Since we also want the display name it makes more sense imo to return a user object.

See #20224

[rullzer]

@PVince81 rebase now that #20224 is in.

[PVince81]

I'll fix it to use the "new" API, as we're now getting a user object.

[PVince81]

I have updated the API usage and the unit tests to reflect the fact that getOwner() now returns user objects.

Please review @icewind1991 @rullzer @DeepDiver1975 @blizzz @schiesbn

[icewind1991]

👍 looks good

[PVince81]

CC @dragotin @guruz @rperezb in case desktop and mobile clients are interested in this property too.
Note that the original reason I added it is because the web UI will need it when using Webdav.

[DeepDiver1975]

👍