Error: java.io.IOException: read failed, socket might closed or timeout, read ret: -1 when connecting to BLE module (Kotlin)

Question

I am trying to connect to an RN4870 BLE module using my Kotlin app, but keep getting an error when trying to connect a socket. I am able to pair my phone and the BLE module, and verify in kotlin they they are bonded correctly, but when I try to run these two lines.

btSocket = RN4780Device.createInsecureRfcommSocketToServiceRecord(RN4870_UUID)
btSocket.connect()

I always get this error: java.io.IOException: read failed, socket might closed or timeout, read ret: -1

Note: I am able to send and receive data using another app (SmartData iOS app) so I know the Bluetooth FW is working correctly.

After doing a lot of research, I can only assume that there is an issue with my UUID. I'm not sure if I should use the generic one I am now, or somehow get a UUID that is being used by the RN4870 module.

Main Activity:

class MainActivity : AppCompatActivity() {

    lateinit var btAdapter: BluetoothAdapter
    lateinit var RN4780Device: BluetoothDevice
    lateinit var btSocket: BluetoothSocket
    lateinit var btService: MyBluetoothService

    @SuppressLint("MissingPermission")
    @RequiresApi(Build.VERSION_CODES.S)
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Initialize bluetooth adapter
        val btManager = getSystemService(Context.BLUETOOTH_SERVICE) as BluetoothManager
        btAdapter = btManager.adapter

        // Start home activity if connected to Bluetooth module
        btn_cont.setOnClickListener {

            if (checkPaired()) {
                // Connect client socket
                try {
                    btSocket = RN4780Device.createInsecureRfcommSocketToServiceRecord(RN4870_UUID)
                    btSocket.connect()
                } catch (e: IOException) {
                    e.printStackTrace()
                }

            }
        }
    }


    @SuppressLint("MissingPermission")
    private fun checkPaired() : Boolean {
        // Find RN4780 device and check bond state
        val device: BluetoothDevice = btAdapter.getRemoteDevice(RN4780_ADDRESS)
        if (device.bondState != BluetoothDevice.BOND_BONDED) {
            Toast.makeText(this, "RN4870 BLE Module is not Connected", Toast.LENGTH_LONG).show()
            return false
        }
        RN4780Device = device
        return true
    }

}

Constants

object Constants {
    var RN4780_ADDRESS = "04:91:62:A1:7D:0D"
    var RN4870_UUID = UUID.fromString("49535343-8841-43F4-A8D4-ECBE34729BB3")
}

Full StackTrace

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.geoboard, PID: 1294
    java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:958)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:958) 
     Caused by: java.io.IOException: read failed, socket might closed or timeout, read ret: -1
        at android.bluetooth.BluetoothSocket.readAll(BluetoothSocket.java:758)
        at android.bluetooth.BluetoothSocket.readInt(BluetoothSocket.java:772)
        at android.bluetooth.BluetoothSocket.connect(BluetoothSocket.java:404)
        at com.example.geoboard.MainActivity.onCreate$lambda-0(MainActivity.kt:54)
        at com.example.geoboard.MainActivity.$r8$lambda$z_JWuogCboqpr2BmqKXIU9Cwb9g(Unknown Source:0)
        at com.example.geoboard.MainActivity$$ExternalSyntheticLambda2.onClick(Unknown Source:2)
        at android.view.View.performClick(View.java:7471)
        at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1194)
        at android.view.View.performClickInternal(View.java:7448)
        at android.view.View.access$3600(View.java:813)
        at android.view.View$PerformClick.run(View.java:28408)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:250)
        at android.app.ActivityThread.main(ActivityThread.java:7755)
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:958)

I have been looking at different stack overflow posts for hours and was unable to find a solution. Thanks for any help!

Answer 1

Turns out that you can't connect to Low Energy Bluetooth with a socket. Instead, see https://developer.android.com/guide/topics/connectivity/bluetooth/connect-gatt-server