[Bug]: Unclear error message during virtual file download while server failure

[allexzander]

⚠️ Before submitting, please verify the following: ⚠️

• This is a bug, not a question or a configuration issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server and Desktop Client are up to date. See Server Maintenance and Release Schedule and Desktop Releases for supported versions.
• I agree to follow Nextcloud's Code of Conduct

Bug description

The error message provided (see screenshot) is not enough for the user to understand there is a server issue. This results in server errors being treated as desktop client VFS issues.

Steps to reproduce

1. Start local server and upload a big file (500MB at least) via WebUI
2. Connect the desktop client to that account using VFS on Windows and start the download (double-click the file in Explorer)
3. Stop the local server
4. Observe the error dialog without necessary information about server failure

Expected behavior

User must be aware this is a server problem, so, additional dialog is required + error in the activity list (optional)

Which files are affected by this bug

all

Operating system

Windows

Which version of the operating system you are running.

All Windows

Package

Other

Nextcloud Server version

all

Nextcloud Desktop Client version

all

Is this bug present after an update or on a fresh install?

Fresh desktop client install

Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

Are you using an external user-backend?

• Default internal user-backend
• LDAP/ Active Directory
• SSO - SAML
• Other

Nextcloud Server logs

No response

Additional info

No response

[allexzander]

implemented in #6140