feat: negotiating MTU size

app/src/main/java/com/example/sensortestingapp/MainActivity.kt

@@ -36,6 +36,12 @@ private const val ENABLE_BLUETOOTH_REQUEST_CODE = 1
 
 private const val RUNTIME_PERMISSION_REQUEST_CODE = 2
 
+// Top level declaration
+private const val GATT_MAX_MTU_SIZE = 517
+
+// Top level declaration
+private const val GATT_REQUESTED_MTU_SIZE = GATT_MAX_MTU_SIZE
+
 fun Context.hasPermission(permissionType: String): Boolean {
     return ContextCompat.checkSelfPermission(this, permissionType) ==
             PackageManager.PERMISSION_GRANTED
@@ -97,6 +103,8 @@ class MainActivity : AppCompatActivity() {
 
     private val kirbyScanResults = ArrayList<ScanResult>();
 
+    private var mtuSizeInBytes = 23
+
     private val gattCallback = object : BluetoothGattCallback() {
         override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
             val deviceAddress = gatt.device.address
@@ -104,12 +112,21 @@ class MainActivity : AppCompatActivity() {
 
             if (status == BluetoothGatt.GATT_SUCCESS) {
                 if (newState == BluetoothProfile.STATE_CONNECTED) {
+
                     Log.i(
                         "BluetoothGattCallback",
                         "Successfully connected to $deviceAddress (${deviceName})"
                     )
-                    val serviceDiscoveryStarted = gatt.discoverServices()
+
-                    if (!serviceDiscoveryStarted) {
+                    if (!gatt.requestMtu(GATT_REQUESTED_MTU_SIZE)) {
+                        Log.e(
+                            "BluetoothGattCallback",
+                            "Requesting MTU size failed"
+                        )
+                    }
+
+
+                    if (!gatt.discoverServices()) {
                         Log.e(
                             "BluetoothGattCallback",
                             "Service discovery did not start"
@@ -141,6 +158,21 @@ class MainActivity : AppCompatActivity() {
                 printGattTable()
             }
         }
+
+        override fun onMtuChanged(gatt: BluetoothGatt?, mtu: Int, status: Int) {
+            if (status == BluetoothGatt.GATT_SUCCESS) {
+                Log.i(
+                    "BluetoothGattCallback",
+                    "mtuSizeInBytes set to ${mtu}"
+                )
+                mtuSizeInBytes = mtu
+            } else {
+                Log.w(
+                    "BluetoothGattCallback",
+                    "Unsuccessful MTU change. Leaving mtuSizeInBytes unchanged ${mtuSizeInBytes}"
+                )
+            }
+        }
     }
 
     private val scanResultAdapter: ScanResultAdapter by lazy {