Files become zero size when sync dropped due to network issues

[EukalyptusX]

### Expected behaviour
After the connection to the server dropped while syncing, the files which were not downloaded correctly should be deleted and re-downloaded.

### Actual behaviour
Files, which were downloaded incompletely, become corrupt and stay empty (zero bytes). Although it says later "successful", when the sync finished.

### Steps to reproduce

1. Sync tons of pictures.
2. Drop the connection while syncing. (It needs to be a timeout!)
3. Reconnect.
4. Force sync.
5. After finished sync ("successful sync"): See files with sizes of zero bytes on the client. (On Linux: "find . -size 0 -print")

### Client configuration
Client version: 2.5.2git
Operating system: Fedora x64 Workstation
OS language: German
Qt version used by client package (Linux only, see also Settings dialog): Qt 5.12.1
Client package (From Nextcloud or distro) (Linux only): Distro (Official Repo)

Installation path of client: /usr/bin/nextcloud

### Server configuration
Nextcloud version: 15.0.8

[EukalyptusX]

Ok, I think it's related to this: Issue-7995

I just didn't saw that earlier and thought it happened due to the network issue.

[enoch85]

This is serious and should be looked at.

Just noticed the same issue for like 400 files (mostly pictures) that dates back so long that I don't have a recent backup. :(

[ferdiga]

desktop sync tries unsuccessfully to download (sync) the file and reports "file_downloaded" in oc_activities for every try.
NC 19.0.4
the image file was taken on a Samsung Galaxy S10+ , a found the file size to be 0 Bytes, nevertheless it was somehow synced to the cloud and causes problems there.
probably an Android client issue too.

[enoch85]

Still an issue.

[enoch85]

Just curious, any update on this issue? Planned soon, or just approved (could happen in years).

Thanks!

[joshtrichards]

Duplicate of nextcloud/server#7995