iOS Photo Roll Uploads 0-Byte Files When Device is Out Of Disk Space

Expected behaviour

A warning or error displayed to the user to instruct the user that the device does not contain enough free space to hold the cache for the Photo Roll transfer.

Actual behaviour

The Nextcloud app uploads the Photo Roll, but because not enough free space exists, some or all of the photos are uploaded as 0-byte files. No errors or warnings are displayed, and no anomalous log entries are generated.

Steps to reproduce

Use an iOS device which is out of storage space and attempt to upload a large number of photos to the Nextcloud instance.

Reasoning or why should it be changed/implemented?

A user may be unaware that they require significant free disk space in order to initiate a Photo roll transfer. If a user is not warned and no error is displayed, they will perhaps believe that the issue exists with the forward proxy or the Nextcloud application. Several such errors appear to already have been filed in GitHub related to this - fixing this could help cut down the number of bugs / help requests.

iOS version

14.1

App version

3.3.1.1

Server configuration

Nextcloud as TrueNAS plugin with Nginx as an HTTPS forward proxy.

Operating system:
TrueNAS 12

Web server:
Nginx

Database:
default

PHP version:
default

Nextcloud version: (see Nextcloud admin page)
21.0.0

Start by reproducing the Photo Roll transfer on an iOS 14.1 device with insufficient storage, using app version 3.3.1.1, and trace how the transfer cache and upload errors are handled. Done means the user receives a clear warning or error before or during transfer and photos are not uploaded as 0-byte files.