Allow certain VPN apps to access the LAN, needed for GSF-based Cast API e.g. Spotify Cast

I am using AFWall+ with Orbot and its VPN mode. Please bear with me while I explain the non-Orbot-specific background.

My AFWall+ is set to:

- block by default
- allow access to VPN by default
- certain apps also have additional access to LAN, to access the chromecast, e.g.
- VLC
- Spotify
- GSF (Google Play Services, Google Services Framework, Google Account Manager, Google Backup Transport), these are all grouped together by AFWall+.

This works fine, both VLC and Spotify can cast to my Chromecast, yay.

Note that for Spotify, we need to additionally allow LAN access for GSF as well - Spotify directly accesses the LAN to discover the device, but its application data is sent to the chromecast via GSF, using the GSF Cast API. It is entirely possible to connect to a Chromecast without using this API, e.g. VLC does it, so I only need to allow LAN access for VLC.

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Now the issue comes when trying to combine this with Orbot. My above AFWall+ settings allow me to use Orbot in a safe way - I can use its VPN mode and its app-specific settings to only give certain apps access to the VPN, and the default AFWall+ rules block access for other apps.

In Orbot, I had been allowing VPN access to GSF (Google Play Services, Google Services Framework, Google Account Manager) because I figured that they might need to contact Google, and I didn't want things to randomly break because I was forbidding access. However *this breaks the GSF Cast API*, because Orbot seems to prevent their LAN connections from working, I guess by redirecting it to the VPN although I didn't confirm this. Then Spotify can discover the device, but gets stuck when attempting to connect to it.

If in Orbot, I disable VPN access to those 3 GSF apps, then Spotify can both discover the device and connect to it again, and life is good. However it may be the case that those 3 apps really do need to access the internet in a different context, and in that case I would like them to do it via Orbot instead of directly revealing my IP address to Google.

So what would be nice, is to allow certain VPN-enabled apps to also be able to access the LAN directly bypassing Orbot - just like AFWall+ allows you to do.