I'm developing a mobile app that uses WiFi without internet connection (in order to communicate to an IOT device) and it uses cellular data as well (see TL;DR section for more).
The problem -> some devices don't automatically switch their default route to cellular (rmnet interface) while others are capable.
The workaround -> create a *"local" VPN in order to manage and re-routing network traffic via cellular interface (there are apps like Speedify that can do this by assigning priority to interfaces)
The question -> there is a simple way to accomplish this or it's pretty tricky? When I say "simple" I mean the calls of several well documented API and when I say "tricky" I mean to starting read and parse routing table with customized rules depending on every vendors?
"*local" = a VPN without web server or VPN gateway because I'm not actually interested to do the VPN's job (I seem to have understood that I need a VPN level to manage network traffic of others app but I'm pretty newbie of VPN topic)
TL;DR My goal is to remaining connected to my access point (in order to call its APIs) AND use cellular data for all others requests I.e: login via my backend, use Google Maps and so on. Handle this scenario it's quite easy because combining network objects, socketFactory and bindProcessToNetwork I'm able to do this. Troubles come for others app like YouTube, WhatsApp that stop working because as default network they are using my access point without internet (Android doesn't switch default interface to a cellular) I'm going crazy because seems that each vendor (or Android OS version?) handles "WiFi without connectivity" with cellular active in a different way. There are certain devices that all work fine (similar to iOS) but there are others that it's a nightmare. See this question for further details
Thanks for reading, I really love Android but those issues make me sadder every day more and I'm thinking to pass to the Dark Side of mobile development (iOS). You've the chance to change my mind ;)
