Use public preview API

[jesmrec]

Currently (2.15), Android is using only thumbnails as part of the previews. (private API)
Request is api/v1/thumbnail/448/448/<path>(private thumbnail API)

It could switch to the the public preview API:
remote.php/dav/files/[user]/[file]?x=[width]&y=[height]&c=[eTag]&preview=1
(but there's no real urgency)

x and y parameters contains 120 in iOS platform (as reference)

• AC (keep legacy behaviour):

  • Thumbnails are correctly fetched, no matter if picture is downloaded or not
  • Thumbnails are requested once browsing
  • Thumbnails are shown in the uploads view.
  • Thumbnails are shown in the folder picker (copy, move options)

PR

App: #3017

[abelgardep]

I was checking the api and the current implementation, and we can switch to the public preview api in a pretty simple way.

About the public preview api, i think that Content-Length header is missing.

x and y parameters contains 120 in iOS platform (as reference)

About the thumbnails size, currently we retrieve a 448x448 which is much bigger than that reference. I have performed a quick test and for the same image:

• 120x120 -> 4Kb
• 448x448 -> 35Kb

We have better thumbnails but maybe they are not as much important. Should we decrease thumbnails size? Admins can limit their size anyway