A wireless drive keeps Gearslip in the foreground

From the moment the car's Bluetooth channel opens until the drive ends, a quiet
notification keeps Gearslip in the foreground, so Android lets it join the car's
Wi-Fi with the phone locked.

gearslip/src/main/AndroidManifest.xml

@@ -19,6 +19,8 @@
     <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
     <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE_LOCATION" />
+    <!-- Keeps a wireless start going with the phone locked; see WirelessKeepAlive. -->
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_CONNECTED_DEVICE" />
 
     <!--
         Wireless Android Auto: Bluetooth reaches the paired car's Android Auto service, which
@@ -204,6 +206,11 @@
             android:exported="false"
             android:foregroundServiceType="location" />
 
+        <service
+            android:name=".wireless.WirelessKeepAlive"
+            android:exported="false"
+            android:foregroundServiceType="connectedDevice" />
+
         <!--
           Holds the capture session that carries a media app's audio to the car. It also claims
           the microphone, so voice replies can hear the driver with the phone locked.

gearslip/src/main/java/app/seb3thehacker/gearslip/wireless/WirelessKeepAlive.kt

@@ -0,0 +1,57 @@
+package app.seb3thehacker.gearslip.wireless
+
+import android.app.Notification
+import android.app.NotificationChannel
+import android.app.NotificationManager
+import android.app.Service
+import android.content.Context
+import android.content.Intent
+import android.content.pm.ServiceInfo
+import android.os.IBinder
+import app.seb3thehacker.gearslip.GearslipLog
+
+/**
+ * Keeps Gearslip in the foreground while a wireless car is connected, from the moment its
+ * Bluetooth channel opens until the drive ends. Android treats an app in the background as
+ * unwanted and may refuse its Wi-Fi request or kill it, which is what happens to a start-up with
+ * the phone locked in a pocket. It does no work of its own; the notification is the cost.
+ */
+class WirelessKeepAlive : Service() {
+
+    override fun onBind(intent: Intent?): IBinder? = null
+
+    override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
+        val manager = getSystemService(NotificationManager::class.java)
+        manager.createNotificationChannel(
+            NotificationChannel(CHANNEL, "Wireless car connection", NotificationManager.IMPORTANCE_LOW),
+        )
+        val notification = Notification.Builder(this, CHANNEL)
+            .setSmallIcon(android.R.drawable.stat_sys_data_bluetooth)
+            .setContentTitle("Gearslip is connected to the car wirelessly")
+            .setOngoing(true)
+            .build()
+        // Refused if Android thinks Gearslip may not start one now; the start-up carries on
+        // without it, as it did before this service existed.
+        runCatching {
+            startForeground(NOTIFICATION_ID, notification, ServiceInfo.FOREGROUND_SERVICE_TYPE_CONNECTED_DEVICE)
+        }.onFailure {
+            GearslipLog.w("wireless keep-alive: could not start the foreground service - ${it.message}")
+            stopSelf()
+        }
+        return START_NOT_STICKY
+    }
+
+    companion object {
+        private const val CHANNEL = "gearslip_wireless"
+        private const val NOTIFICATION_ID = 45
+
+        fun start(context: Context) {
+            runCatching { context.startForegroundService(Intent(context, WirelessKeepAlive::class.java)) }
+                .onFailure { GearslipLog.w("wireless keep-alive: start refused - ${it.message}") }
+        }
+
+        fun stop(context: Context) {
+            runCatching { context.stopService(Intent(context, WirelessKeepAlive::class.java)) }
+        }
+    }
+}

gearslip/src/main/java/app/seb3thehacker/gearslip/wireless/WirelessLink.kt

@@ -132,6 +132,15 @@ object WirelessLink {
      */
     private fun startUp(context: Context, device: BluetoothDevice) {
         val me = Thread.currentThread()
+        try {
+            tryAndRetry(context, device, me)
+        } finally {
+            // A newer start-up has the service now; stop() already ended this one's.
+            if (worker === me) WirelessKeepAlive.stop(context)
+        }
+    }
+
+    private fun tryAndRetry(context: Context, device: BluetoothDevice, me: Thread) {
         var tries = 0
         while (true) {
             handedOver = false
@@ -165,6 +174,7 @@ object WirelessLink {
         worker?.interrupt()
         worker = null
         release(context)
+        WirelessKeepAlive.stop(context)
         // Stopped before the car's session began, so nothing else resets Home's card.
         if (starting) {
             log.i("wireless start-up stopped")
@@ -219,6 +229,8 @@ object WirelessLink {
         }
         rfcomm = socket
         log.i("Bluetooth: channel open")
+        // Before the Wi-Fi request: Android may refuse one from an app it sees as in the background.
+        WirelessKeepAlive.start(context)
         SessionStatus.connecting("Bluetooth: talking to $name")
 
         val input = DataInputStream(socket.inputStream)