car audio: choose Bluetooth or USB, offer Bluetooth after a refused screen share

USB audio needs Android's screen-sharing consent every drive. A new Car audio setting on the phone and car screens picks Bluetooth instead, and the first refusal opens a dialog offering Bluetooth, asking again, or the one-time adb command.

gearslip/src/main/java/app/seb3thehacker/gearslip/GearslipActivity.kt

@@ -15,6 +15,8 @@ import android.view.Surface
 import android.view.WindowManager
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.setContent
+import androidx.compose.runtime.collectAsState
+import androidx.compose.runtime.getValue
 import androidx.activity.enableEdgeToEdge
 import androidx.activity.result.contract.ActivityResultContracts.StartActivityForResult
 import android.content.res.Configuration
@@ -85,9 +87,13 @@ class GearslipActivity : ComponentActivity(), Projection {
         } else {
             GearslipLog.w("audio: capture consent declined")
             CarAudio.denied()
+            if (!CarSettings.audioChoiceAsked) offerBluetooth.value = true
         }
     }
 
+    /** Raised once, after the first "no" to the capture dialog; see [AudioChoiceDialog]. */
+    private val offerBluetooth = kotlinx.coroutines.flow.MutableStateFlow(false)
+
     private val detachReceiver = object : BroadcastReceiver() {
         override fun onReceive(context: Context?, intent: Intent?) {
             if (intent?.action == UsbManager.ACTION_USB_ACCESSORY_DETACHED) {
@@ -128,6 +134,20 @@ class GearslipActivity : ComponentActivity(), Projection {
         setContent {
             GearslipTheme {
                 GearslipApp(onDisconnect = ::closeAccessory, onRequestCallScreening = ::requestCallScreeningRole)
+                val offer by offerBluetooth.collectAsState()
+                if (offer) {
+                    fun close() {
+                        CarSettings.markAudioChoiceAsked()
+                        offerBluetooth.value = false
+                    }
+                    app.seb3thehacker.gearslip.ui.AudioChoiceDialog(
+                        onUseBluetooth = {
+                            CarSettings.setPipeAudio(false)
+                            close()
+                        },
+                        onKeepAsking = ::close,
+                    )
+                }
             }
         }
 

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarSettings.kt

@@ -2,6 +2,7 @@ package app.seb3thehacker.gearslip.car
 
 import android.content.Context
 import app.seb3thehacker.gearslip.AppSettings
+import app.seb3thehacker.gearslip.audio.CarAudio
 import app.seb3thehacker.gearslip.car.theme.GsTheme
 import app.seb3thehacker.gearslip.car.theme.GsThemes
 import kotlinx.coroutines.flow.MutableStateFlow
@@ -27,6 +28,7 @@ object CarSettings {
     private const val KEY_OPEN = "car_open_on_connect"
     private const val KEY_NIGHT = "car_night_mode"
     private const val KEY_PIPE_AUDIO = "car_pipe_audio"
+    private const val KEY_AUDIO_CHOICE_ASKED = "car_audio_choice_asked"
     private const val KEY_LAST_NAV = "car_last_nav"
     private const val KEY_LAST_MEDIA = "car_last_media"
     private const val KEY_AUTOPLAY = "car_autoplay"
@@ -148,10 +150,20 @@ object CarSettings {
      * Whether a media app's sound is captured and sent over the car link. On by default, since
      * sound in the car is the point of the exercise; the platform allows the capture only behind a
      * consent dialog, which [app.seb3thehacker.gearslip.audio.CarAudio] raises once the car has
-     * somewhere to play it. Turned off, the app plays through the phone's normal output instead.
+     * somewhere to play it. Turned off ("Bluetooth" in the settings), the app plays through the
+     * phone's normal output instead, and Android never asks.
      */
     val pipeAudio: StateFlow<Boolean> = pipeAudioFlow
 
+    /**
+     * Whether the driver has already been offered Bluetooth after turning down the capture
+     * dialog. Offered once only: someone who chose to keep the USB route shouldn't be nagged.
+     */
+    val audioChoiceAsked: Boolean
+        get() = AppSettings.getString(app, KEY_AUDIO_CHOICE_ASKED, "false") == "true"
+
+    fun markAudioChoiceAsked() = AppSettings.putString(app, KEY_AUDIO_CHOICE_ASKED, "true")
+
     /**
      * Off by default: a driver has to opt into experimental features as a whole before any of
      * them - the voice assistant included - show up to turn on individually.
@@ -265,9 +277,15 @@ object CarSettings {
         AppSettings.putString(app, KEY_AUTOPLAY, on.toString())
     }
 
+    /**
+     * Takes effect at once: switching to Bluetooth mid-drive stops the capture, and switching
+     * back asks for it again (or waits for the car, if none is connected).
+     */
     fun setPipeAudio(on: Boolean) {
+        if (pipeAudioFlow.value == on) return
         pipeAudioFlow.value = on
         AppSettings.putString(app, KEY_PIPE_AUDIO, on.toString())
+        if (on) CarAudio.request() else CarAudio.release()
     }
 
     fun setExperimentalFeaturesEnabled(on: Boolean) {

gearslip/src/main/java/app/seb3thehacker/gearslip/car/CarSettingsScreen.kt

@@ -126,14 +126,14 @@ fun CarSettingsScreen() {
         ) { CarSettings.setAutoplay(it) }
 
         ChoiceRow(
-            "Media audio",
+            "Car audio",
-            listOf(false to "Phone audio", true to "Car audio"),
+            listOf(false to "Bluetooth", true to "USB"),
             pipeAudio,
         ) { CarSettings.setPipeAudio(it) }
         Text(
-            "Car audio sends the phone's sound to the car over USB. Android asks for permission " +
+            "USB sends the phone's sound through Gearslip. Android asks to share your screen each " +
-                "when the car connects, and a few apps block it. Phone audio plays as the phone " +
+                "drive, and a few apps block it. Bluetooth plays as the phone normally would, and " +
-                "normally would, for example over Bluetooth to the car.",
+                "Android never asks.",
             style = MaterialTheme.typography.bodySmall,
             color = MaterialTheme.colorScheme.onSurfaceVariant,
         )

gearslip/src/main/java/app/seb3thehacker/gearslip/ui/AudioChoiceDialog.kt

@@ -0,0 +1,49 @@
+package app.seb3thehacker.gearslip.ui
+
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Column
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.unit.dp
+import app.seb3thehacker.gearslip.BuildConfig
+
+/**
+ * Shown once, the first time the driver turns down Android's screen-sharing dialog: that dialog
+ * is the price of sending music over USB, and most people who refuse it would rather not see it
+ * again. Offers the two ways out: Bluetooth, or the one-time adb command.
+ */
+@Composable
+fun AudioChoiceDialog(onUseBluetooth: () -> Unit, onKeepAsking: () -> Unit) {
+    var showCommand by remember { mutableStateOf(false) }
+    AlertDialog(
+        onDismissRequest = onKeepAsking,
+        title = { Text("Play car audio over Bluetooth?") },
+        text = {
+            Column(verticalArrangement = Arrangement.spacedBy(12.dp)) {
+                Text(
+                    "Android treats music sent over USB like sharing your screen, so it asks every " +
+                        "drive. Over Bluetooth it never asks. You can change this later in Settings.",
+                )
+                if (showCommand) {
+                    Text(
+                        "Or keep USB and stop the question for good: plug the phone into a " +
+                            "computer with USB debugging on, and run this once.",
+                        style = MaterialTheme.typography.bodyMedium,
+                    )
+                    CopyableCommand("adb shell appops set ${BuildConfig.APPLICATION_ID} PROJECT_MEDIA allow")
+                } else {
+                    TextButton(onClick = { showCommand = true }) { Text("Never ask, using a computer") }
+                }
+            }
+        },
+        confirmButton = { TextButton(onClick = onUseBluetooth) { Text("Use Bluetooth") } },
+        dismissButton = { TextButton(onClick = onKeepAsking) { Text("Keep asking") } },
+    )
+}

gearslip/src/main/java/app/seb3thehacker/gearslip/ui/SettingsScreen.kt

@@ -12,6 +12,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.rememberScrollState
+import androidx.compose.foundation.selection.selectable
 import androidx.compose.foundation.selection.toggleable
 import androidx.compose.foundation.text.KeyboardOptions
 import androidx.compose.foundation.verticalScroll
@@ -33,12 +34,14 @@ import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.OutlinedTextField
+import androidx.compose.material3.RadioButton
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Switch
 import androidx.compose.material3.Text
 import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
@@ -55,6 +58,7 @@ import androidx.compose.ui.unit.dp
 import app.seb3thehacker.gearslip.AppSettings
 import app.seb3thehacker.gearslip.BuildConfig
 import app.seb3thehacker.gearslip.CertProvider
+import app.seb3thehacker.gearslip.car.CarSettings
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 import androidx.compose.runtime.LaunchedEffect
@@ -103,6 +107,7 @@ fun SettingsScreen(
             Spacer(Modifier.height(0.dp))
             AboutSection(onOpenWhatsNew, onReplayTutorial)
             ConnectionSection()
+            CarAudioSection()
             if (SHOW_RECOMMENDED_APPS) AppsSection(onOpenRecommendedApps)
             CertificateSection()
             SettingsSection("Usage notes", header = USAGE_STATS_INTRO) { UsageStatsRows() }
@@ -163,6 +168,30 @@ private fun ConnectionSection() {
     }
 }
 
+/** How music reaches the car: through Gearslip over USB, or by Bluetooth as usual. */
+@Composable
+private fun CarAudioSection() {
+    val usb by CarSettings.pipeAudio.collectAsState()
+    SettingsSection(
+        "Car audio",
+        footer = "Run the command in Help once, and USB stops asking.",
+    ) {
+        SettingsRow(
+            "USB",
+            Modifier.selectable(usb, role = Role.RadioButton) { CarSettings.setPipeAudio(true) },
+            subtitle = "Sound goes through Gearslip. Android asks to share your screen each drive",
+            trailing = { RadioButton(selected = usb, onClick = null) },
+        )
+        SettingsDivider()
+        SettingsRow(
+            "Bluetooth",
+            Modifier.selectable(!usb, role = Role.RadioButton) { CarSettings.setPipeAudio(false) },
+            subtitle = "Sound plays over the phone's Bluetooth link to the car. Android never asks",
+            trailing = { RadioButton(selected = !usb, onClick = null) },
+        )
+    }
+}
+
 @Composable
 private fun AppsSection(onOpenRecommendedApps: () -> Unit) {
     SettingsSection("Apps") {