Android app fails bluetooth connection with ESP when calling connect() - android-studio

Question

I'm trying to build an Android app in Android Studio using Kotlin to send some simple data between an ESP32 and a mobile over Bluetooth. I've been following along a number of tutorials but just can't seem to get the connection established, permissions and scanning for devices looks to be working correctly. When I call connect() on the socket the app hangs for a few seconds and then crashes with this error:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.btleveller, PID: 28899
java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=0, result=-1, data=Intent { (has extras) }} to activity {com.example.btleveller/com.example.btleveller.MainActivity}: java.io.IOException: read failed, socket might closed or timeout, read ret: -1
at android.app.ActivityThread.deliverResults(ActivityThread.java:5368)
at android.app.ActivityThread.handleSendResult(ActivityThread.java:5407)
etc... I can post the full output if it's helpful
My ESP is running some very basic helloworld style code using the NimBLE-Arduino code, programmed through VSCode with the PlatformIO extension. I think this side of it is all working correct as I can see the device in the "nRF Connect" app on my mobile. The scanning is done through the CompanionDeviceManager library:
I thought maybe there was a problem with the UUID I was supplying, or that I needed to make changes for BLE as opposed to regular Bluetooth but so far nothing I've found online has worked. I've also tried using "createL2capChannel()" to create the socket but got stuck on the PSM value. These are the relevant bits of code:
//private val ESP_UUID = UUID.fromString("0000dead-0000-1000-8000-00805F9B34FB")
private val ESP_UUID = UUID.fromString("0000baad-0000-1000-8000-00805F9B34FB")
...
// Look for connection, kicked off by button press
fun lookForConn(view: View) {
val deviceFilter: BluetoothDeviceFilter = BluetoothDeviceFilter.Builder()
.setNamePattern(Pattern.compile("BLE"))
.build()
// The argument provided in setSingleDevice() determines whether a single
// device name or a list of them appears.
val pairingRequest: AssociationRequest = AssociationRequest.Builder()
.addDeviceFilter(deviceFilter)
.setSingleDevice(false)
.build()
// When the app tries to pair with a Bluetooth device, show the
// corresponding dialog box to the user.
deviceManager.associate(pairingRequest,
object : CompanionDeviceManager.Callback() {
override fun onDeviceFound(chooserLauncher: IntentSender) {
startIntentSenderForResult(chooserLauncher,
SELECT_DEVICE_REQUEST_CODE, null, 0, 0, 0)
}
override fun onFailure(error: CharSequence?) {
// Handle the failure.
Log.d("DEVHandler","failed to find dev?")
}
}, null)
}
override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
when (requestCode) {
SELECT_DEVICE_REQUEST_CODE -> when(resultCode) {
Activity.RESULT_OK -> {
// The user chose to pair the app with a Bluetooth device.
val deviceToPair: BluetoothDevice? =
data?.getParcelableExtra(CompanionDeviceManager.EXTRA_DEVICE)
Log.d("DEVHandler","try to bond:" + deviceToPair?.name)
deviceToPair?.let { device ->
device.createBond()
val newConn = ConnectThread(deviceToPair).run()
}
}
}
else -> super.onActivityResult(requestCode, resultCode, data)
}
}
private inner class ConnectThread(device: BluetoothDevice) : Thread() {
private var mHaveConn = false
public fun IsConnected(): Boolean {
return mHaveConn
}
private val mmSocket: BluetoothSocket? by lazy(LazyThreadSafetyMode.NONE) {
//device.createRfcommSocketToServiceRecord(ESP_UUID)
device.createInsecureRfcommSocketToServiceRecord(ESP_UUID)
}
public override fun run() {
// Cancel discovery because it otherwise slows down the connection.
BTMan.mBTAdapter?.cancelDiscovery()
mmSocket?.let { socket ->
// Connect to the remote device through the socket. This call blocks
// until it succeeds or throws an exception.
if (socket == null)
Log.d("CONNThread", "Socket is null...")
if (socket.isConnected == true)
Log.d("CONNThread", "Socket is already connected...")
socket.connect()
Log.d("CONNThread", "Made a connection")
// The connection attempt succeeded. Perform work associated with
// the connection in a separate thread.
//manageMyConnectedSocket(socket)
mHaveConn = true
}
}
// Closes the client socket and causes the thread to finish.
fun cancel() {
try {
mmSocket?.close()
} catch (e: IOException) {
Log.e("CONNThread", "Could not close the client socket", e)
}
mHaveConn = false
}
}