Excessive CPU usage in case of firewall blocking

[bterradillos]

⚠️ 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 have searched for 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

On macOS, when I'm commuting and limiting my outbound connections to selected apps through a network filter to save data traffic, the NextCloud Client seems to enter in a high CPU usage loop if it is not allowed to have outbound traffic, thus consuming the battery for nothing.
It seems the client sees an active internet connexion and try to contact the servers repetitively. As the network filter is blocking the connections, the client can't do its requests.
This bug was present in the client as far as I can remember (using it since ~5 years).

Steps to reproduce

1. Install a network filter like TripMode or LittleSnitch

2. Prohibit connections for Nextcloud client

3. Monitor the cpu usage

Expected behavior

When connections are not allowed specifically for the client, it should be less aggressive with its requests.

Which files are affected by this bug

/Applications/Nextcloud.app/Contents/MacOS/Nextcloud

Operating system

macOS

Which version of the operating system you are running.

Sonoma 14.8.5 (23J423)

Installation method

Official Installer for macOS 13 and later

Nextcloud Server version

30.0.6

Nextcloud Desktop Client version

33.0.4

Did this occur after an update or on a clean installation?

Clean desktop client installation

Are you using the Nextcloud Server Encryption module?

Yes

Are you using an external user-backend?

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

Nextcloud Server logs

Additional info

No response

[i2h3]

I could not reproduce this with ProxyMan and a rule which blocks the Nextcloud desktop client by intercepting and blocking its request. Like with an unreachable server, the Nextcloud desktop client does not use the CPU excessively.

Tripmode and LittleSnitch require paid subscriptions for reproduction attempts which we do not have. Hence we cannot attempt the reproduction of the issue with them in particular.

We need more information (like a client debug archive) about the client's requests and how they were responded to or cancelled.

[bterradillos]

Thanks for your blazing fast answer!
I'm not sure Proxyman has the same blocking behaviour as a Network Filter implemented following macOS rules. Such a filter is meant to register itself in the system and is listed after registration in the "Filters and proxies" section of the Network system preferences.
I just tried with LuLu, an OpenSource and free network filter by security researcher Patrick Wardle and Nextcloud's client behaviour is the same when blocked: heavy CPU usage.
Tiny Shield, from the same editor as Proxyman, may perhaps allow you to see the problem, but it's also a paid software.
In attachment a log of the client when the blocking occurs. I hope it will help you analyze the problem.

blocking-log.txt

[i2h3]

@bterradillos Thanks for reminding me on LuLu. I know it and Patrick Wardle. Actually, I mistook LittleSnitch and its developer first for LuLu and Patrick Wardle but then figured they are not what I have in memory.

I could reproduce the issue with LuLu. Further investigation will follow later.