I’m working on a Kotlin app in Android Studio that requires the user’s web browsing to be monitored. I tried to use the android VPN API for this, and wrote the two functions below. The script compiles and runs fine showing logs as such

...
2024-08-07 13:52:02.492 18270-18311 WebFilterVpnService     com.example.pbapp                    D  
Packet captured from 10.0.0.2 to 142.250.68.227
2024-08-07 13:52:02.525 18270-18311 WebFilterVpnService     com.example.pbapp                    D  
Packet captured from 10.0.0.2 to 216.239.32.116
2024-08-07 13:52:02.589 18270-18311 WebFilterVpnService     com.example.pbapp                    D  
Packet captured from 10.0.0.2 to 216.239.32.116
2024-08-07 13:52:02.589 18270-18311 WebFilterVpnService     com.example.pbapp                    D  
Packet captured from 10.0.0.2 to 172.253.63.188
2024-08-07 13:52:02.589 18270-18311 WebFilterVpnService     com.example.pbapp                    D  
Packet captured from 10.0.0.2 to 216.239.32.116
...

Though, despite it running fine, it does not allow any websites to be loaded. When opening a site after running the VPN the page will load for about a minute and then throw this error “ERR_NETWORK_CHANGED”.

function to initialize the VPN:

override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
    Log.d(TAG, "VPN Service started")

    val builder = Builder()
        .addAddress("10.0.0.2", 24)
        .addRoute("0.0.0.0", 0)
        .setSession("WebFilterVpnService")

    val configureIntent = PendingIntent.getActivity(
        this,
        0,
        Intent(this, MainActivity::class.java),
        PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE
    )
    builder.setConfigureIntent(configureIntent)

    vpnInterface = builder.establish()
    if (vpnInterface == null) {
        Log.e(TAG, "Failed to establish VPN interface")
        stopSelf()
        return START_NOT_STICKY
    }
    Log.d(TAG, "VPN interface established")

    startCapture()

    return START_STICKY
}

function to sniff packets intercepted by the VPN:

 private fun startCapture() {
    vpnInterface?.let { vpnInterface ->
        executor.execute {
            Log.d(TAG, "Starting packet capture")
            val fileInputStream = FileInputStream(vpnInterface.fileDescriptor)
            val packet = ByteBuffer.allocate(32767)

            try {
                while (true) {
                    packet.clear()
                    val length = fileInputStream.read(packet.array())
                    if (length > 0) {
                        packet.limit(length)
                        if (length >= 20) {
                            val header = ByteArray(20)
                            packet.position(0)
                            packet.get(header, 0, 20)
                            val sourceIP = "${header[12].toInt() and 0xff}.${header[13].toInt() and 0xff}.${header[14].toInt() and 0xff}.${header[15].toInt() and 0xff}"
                            val destinationIP = "${header[16].toInt() and 0xff}.${header[17].toInt() and 0xff}.${header[18].toInt() and 0xff}.${header[19].toInt() and 0xff}"
                            Log.d(TAG, "Packet captured from $sourceIP to $destinationIP")
                        }
                    }
                }
            } catch (e: Exception) {
                Log.e(TAG, "Error during packet capture", e)
            } finally {
                fileInputStream.close()
            }
        }
    } ?: run {
        Log.e(TAG, "VPN interface is null, cannot start packet capture")
    }
}

I also tried to add a DNS along with the route and address as such

.builder.addDnsServer("8.8.8.8")
.builder.addDnsServer("1.1.1.1")

But that had no effect. Dose anyone know the cause for the ERR_NETWORK_CHANGED with the vpn enabled?