Allow metadata-only uploads and downloads

[ckamm]

In some cases file metadata changes, but the file content stays the same. This situation is detected through checksums (see #4375 #4754). When that happens, we want to avoid re-uploading or downloading the full file and just update the metadata instead.

1. When the current and the stored checksum of a local file are identical, but metadata (mtime, possibly permissions in the future) changed, use a PROPSET to update the remote metadata.
2. When the remote metadata changed but the remote and local checksums are identical, update the local metadata.

[ckamm]

Depends on owncloud/core#20474

[moscicki]

I would also consider to allow syncing additional metadata (maybe OS dependent, such as labels on OSX). This maybe a separate issue though...

[ogoffart]

(I removed the milestone because it depends on a server issue which is not scheduled.)

[guruz]

CC @PVince81

[guruz]

Maybe we'd then need a server capability can-change-metadata-without-etag-change?

[PVince81]

yes, or "etag-propagation-behavior v2.0" or "metadata-behavior v2.0"
then every time we change it we increase its major version like for APIs

[moscicki]

IMO at this point individual server capability is more manegable. It is very clear and understandable what it does (maybe the exact wording could be improved, e.g. "supports-metadata-agnostic-etag"). The risk of course that there will be many of them after some time and that will have to managed. Longer term etag-propagation-behaviours-v.2.0 makes sense but it requires a fully documented and consistent behaviour associated with such a tag (part of the famous "protocol" we discussed). Otherwise the risk is that we are colocating several loosely related properties under such a tag, without clear documentation and with potential for ambiguity. And at the end it risks to be not so much different from using a server version number.

…

On Fri, Jul 6, 2018 at 9:40 AM, Vincent Petry ***@***.***> wrote: yes, or "etag-propagation-behavior v2.0" or "metadata-behavior v2.0" then every time we change it we increase its major version like for APIs — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#4755 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAl9jbZXRTIccU0tnXAGk0-zRpxCyOH6ks5uDxRSgaJpZM4IRxyZ> .

-- --- Best regards, Kuba