Use multiple network interfaces in an app

Question

I wrote an app that is triggering a Sony qx smartphone attachable camera over wifi. However I need to transfer the images off the phone over another local network in real time. Since the wifi card is being used for qx connection I need to be able to use ethernet over usb for transferring images off the phone. Http requests will be used to trigger the camera and send the images off the phone.

Is it possible in one android app on a phone with two network interfaces setup to specify for certain http requests to use one network interface and for others to use another network interface ? Does this need to be done through routing tables, not java?

The phone I'm using is a rooted nexus 6p.

Update:

Currently, I was able to get an Ethernet adapter working with the device (Nexus 6P). The device is connected to a local network over Ethernet. When the Wi-Fi interface is off, I can ping all devices on the local network the device is connected to over Ethernet. However, I am unable to access the web servers (Not using DNS) of any of the devices on that network (which I know they are running), i.e. Http via a browser app. The nexus 6p is connected to the network over Ethernet via a Ubiquiti Station. This seems to be a routing issue.

I can tether(usb interface) and use Wi-Fi in one app, so that leads me to believe it is possible to use Ethernet and Wi-Fi.

Update2:

After more testing, it seems to be that it is a permissions issue. Since when I ping the network the device is connected to over Ethernet without first running su in the terminal the network doesn't exist. However, when I run su then ping, I can ping the network. Thus it seems my app needs to get superuser permission before accessing Ethernet. I've granted it superuser access, but nothing has changed. I read that simply running su isn't enough from one of the comments in this post. This is because su just spawns a root shell that dies. This also explains why I couldn't access any of the web servers on this network via a browser app. Is it possible to grant my app access to the Ethernet interface when making HTTP calls like give HttpURLConnection root access, if that makes any sense (running su doesn't work)? There seems to definitely be a solution since HttpURLConnection can make calls over the USB tethering interface (Nexus 6P calls it rndis0) fine.

Update 3:

I found online here , that I can make my app a System app (thought this might grant the app eth0 access). I just moved my app to /system/app and then rebooted. However, this didn't seem to give the app anymore privileges (thus not solving the problem) , or there is something else required to make the app system than just copying it to /system/app.

Update 4:

So I was able to get Ethernet working on every app without root permissions! It seemed to be that it only works over DHCP and does not like static connections, which I was using. It works with Wi-Fi enabled, however, I cannot contact any of the devices on the Wi-Fi network when Ethernet is enabled. Is there a way around this? Does it have to do with setting two default gateways?

Answer 1

Since you were programming in Nexus 6P, you can try to use the new API added in ConnectivityManager to select the ethernet as your preferred network connection for your process.

Since I can't build the similar environment like yours, I am not sure if it works. It's just a suggested solution, totally not tested and verified.

ConnectivityManager connectivityManager = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
Network etherNetwork = null;
for (Network network : connectivityManager.getAllNetworks()) {
    NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
    if (networkInfo.getType() == ConnectivityManager.TYPE_ETHERNET) {
        etherNetwork = network;
    }
}
Network boundNetwork = connectivityManager.getBoundNetworkForProcess();
if (boundNetwork != null) {
    NetworkInfo boundNetworkInfo = connectivityManager.getNetworkInfo(boundNetwork);
    if (boundNetworkInfo.getType() != ConnectivityManager.TYPE_ETHERNET) {
        if (etherNetwork != null) {
            connectivityManager.bindProcessToNetwork(etherNetwork);
        }
    }
}

Answer 2

Just to give a little more explanation on how this finally got solved.

Utilizing @alijandro's answer I was able to switch back and forth between Ethernet and Wi-Fi in one app. For some reason for the Ethernet to work it required the network gateway to supply DHCP address, not static. Then since the bindProcessToNetwork, used in @alijandro's answer is per-process, I decided to split communications with the QX camera into a Service that runs in a separate Process. The main Application (another process) would post images over Ethernet to a local network. I was successfully able to contact the devices on the local network via HTTP over Ethernet while simultaneously triggering the QX over Wi-Fi. Currently, I used Messenger to communicate using IPC to tell the QX triggering Service what methods to call.