Recover Android BLE connection after Pi restart

android/app/src/main/java/cloud/molberg/picar/BleClient.kt

@@ -12,6 +12,7 @@ import android.os.ParcelUuid
 import android.os.Handler
 import android.os.Looper
 import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.TimeoutCancellationException
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.withTimeout
 import org.json.JSONObject
@@ -36,19 +37,35 @@ class BleClient(private val context: Context) {
     private val writes = ArrayDeque<ByteArray>()
     private var writeInProgress = false
     private val handler = Handler(Looper.getMainLooper())
+    private val reconnect: Runnable = Runnable { connect() }
+    private val restartScan: Runnable = Runnable {
+        if (!stopped && state.value == ConnectionState.SCANNING) {
+            bluetoothManager.adapter?.bluetoothLeScanner?.stopScan(scanCallback)
+            scheduleReconnect(1_000)
+        }
+    }
     private var stopped = true
 
     fun connect() {
         stopped = false
-        val adapter = bluetoothManager.adapter ?: return
+        handler.removeCallbacks(reconnect)
+        handler.removeCallbacks(restartScan)
+        val adapter = bluetoothManager.adapter ?: run {
+            state.value = ConnectionState.DISCONNECTED
+            scheduleReconnect()
+            return
+        }
+        adapter.bluetoothLeScanner?.stopScan(scanCallback)
         state.value = ConnectionState.SCANNING
         val filter = ScanFilter.Builder().setServiceUuid(ParcelUuid(SERVICE_UUID)).build()
         adapter.bluetoothLeScanner?.startScan(listOf(filter), ScanSettings.Builder().setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY).build(), scanCallback)
+        handler.postDelayed(restartScan, 15_000)
     }
 
     fun disconnect() {
         stopped = true
-        handler.removeCallbacksAndMessages(null)
+        handler.removeCallbacks(reconnect)
+        handler.removeCallbacks(restartScan)
         bluetoothManager.adapter?.bluetoothLeScanner?.stopScan(scanCallback)
         gatt?.close(); gatt = null; rx = null
         resetWrites()
@@ -64,21 +81,30 @@ class BleClient(private val context: Context) {
         enqueue((message.toString() + "\n").toByteArray())
         return try {
             withTimeout(20_000) { deferred.await() }
+        } catch (error: TimeoutCancellationException) {
+            handler.post { gatt?.disconnect() }
+            throw error
         } finally {
             pending.remove(id)
         }
     }
 
-    private val scanCallback = object : ScanCallback() {
+    private val scanCallback: ScanCallback = object : ScanCallback() {
         override fun onScanResult(callbackType: Int, result: ScanResult) {
+            handler.removeCallbacks(restartScan)
             bluetoothManager.adapter.bluetoothLeScanner?.stopScan(this)
             state.value = ConnectionState.CONNECTING
+            gatt?.close()
             gatt = result.device.connectGatt(context, false, gattCallback, BluetoothDevice.TRANSPORT_LE)
         }
-        override fun onScanFailed(errorCode: Int) { state.value = ConnectionState.DISCONNECTED }
+        override fun onScanFailed(errorCode: Int) {
+            handler.removeCallbacks(restartScan)
+            state.value = ConnectionState.DISCONNECTED
+            scheduleReconnect()
+        }
     }
 
-    private val gattCallback = object : BluetoothGattCallback() {
+    private val gattCallback: BluetoothGattCallback = object : BluetoothGattCallback() {
         override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int, newState: Int) {
             if (status == BluetoothGatt.GATT_SUCCESS && newState == BluetoothProfile.STATE_CONNECTED) {
                 this@BleClient.gatt = gatt
@@ -88,8 +114,10 @@ class BleClient(private val context: Context) {
                 if (!gatt.requestMtu(247)) gatt.discoverServices()
             }
             else {
-                rx = null; gatt.close(); resetWrites(); state.value = ConnectionState.DISCONNECTED
-                if (!stopped) handler.postDelayed({ connect() }, 3_000)
+                rx = null; gatt.close()
+                if (this@BleClient.gatt === gatt) this@BleClient.gatt = null
+                resetWrites(); state.value = ConnectionState.DISCONNECTED
+                scheduleReconnect()
             }
         }
 
@@ -195,4 +223,10 @@ class BleClient(private val context: Context) {
         writes.clear()
         writeInProgress = false
     }
+
+    private fun scheduleReconnect(delayMillis: Long = 3_000) {
+        if (stopped) return
+        handler.removeCallbacks(reconnect)
+        handler.postDelayed(reconnect, delayMillis)
+    }
 }

systemd/pi-car-companion-bluetooth.service

@@ -7,7 +7,7 @@ Wants=pi-car-companion.service
 [Service]
 Type=simple
 ExecStart=/usr/local/libexec/pi-car-companion-bluetooth
-ExecStartPost=-/usr/bin/timeout 10 /usr/bin/btmgmt add-adv -c -u 6c7a0001-7c6d-4f74-9bb0-c5a4e5efc001 1
+ExecStartPost=/usr/bin/timeout 5 /usr/bin/script -qec '/usr/bin/btmgmt add-adv -c -u 6c7a0001-7c6d-4f74-9bb0-c5a4e5efc001 1' /dev/null
 Restart=on-failure
 RestartSec=5s
 NoNewPrivileges=true