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fix(android): retry CAN subscribe dropped by GATT-busy race #200

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dkneeland wants to merge 1 commit into from
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fix(android): retry CAN subscribe dropped by GATT-busy race #200

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48 changes: 38 additions & 10 deletions ...lot-android/app/src/main/java/com/softwiredtech/dashpilot/datasource/DashKitDataSource.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,8 @@ import android.bluetooth.BluetoothGatt
import android.bluetooth.BluetoothGattCharacteristic
import android.bluetooth.BluetoothGattDescriptor
import android.os.Build
import android.os.Handler
import android.os.Looper
import android.util.Log
import com.softwiredtech.dashpilot.datamodel.dash.CarState
import kotlinx.coroutines.flow.Flow
Expand All @@ -29,8 +31,17 @@ class DashKitDataSource(
private val CCCD_UUID = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb")
// The firmware now applies CAN acceptance filtering in hardware (per-bus
// MCP251xFD filters), so the app no longer pushes a BLE filter list.

// The app subscribes to two characteristics back-to-back when services
// become ready (this one and the Tesla status char). Android's GATT
// client allows only one operation in flight, so the second write can be
// refused while the first is still pending. Retry a few times.
private const val MAX_SUBSCRIBE_ATTEMPTS = 3
private const val SUBSCRIBE_RETRY_DELAY_MS = 250L
}

private val handler = Handler(Looper.getMainLooper())

private val _incoming = MutableSharedFlow<CarState>(replay = 1)
@OptIn(FlowPreview::class)
override val incomingMessages: Flow<CarState> = _incoming.sample(40)
Expand Down Expand Up @@ -58,18 +69,35 @@ class DashKitDataSource(
return
}
gatt.setCharacteristicNotification(characteristic, true)
subscribeCan(gatt, characteristic, 0)
}

private fun subscribeCan(gatt: BluetoothGatt, characteristic: BluetoothGattCharacteristic, attempt: Int) {
val descriptor = characteristic.getDescriptor(CCCD_UUID)
if (descriptor != null) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
gatt.writeDescriptor(descriptor, BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE)
} else {
@Suppress("DEPRECATION")
descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
@Suppress("DEPRECATION")
gatt.writeDescriptor(descriptor)
}
if (descriptor == null) {
Log.e(TAG, "CAN CCCD (0x2902) not discovered")
return
}
// API 33+ writeDescriptor() returns Int (0 = queued); older returns Boolean.
val queued = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
gatt.writeDescriptor(descriptor, BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE) ==
BluetoothGatt.GATT_SUCCESS
} else {
@Suppress("DEPRECATION")
descriptor.value = BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE
@Suppress("DEPRECATION")
gatt.writeDescriptor(descriptor)
}
if (!queued && attempt < MAX_SUBSCRIBE_ATTEMPTS) {
// Android allows one GATT op in flight, so this write can be refused
// while the app-channel status subscribe is pending; retry after it
// completes. Only fires when the subscription would otherwise drop.
Log.d(TAG, "CAN CCCD write not queued (attempt=$attempt); retrying")
handler.postDelayed(
{ subscribeCan(gatt, characteristic, attempt + 1) },
SUBSCRIBE_RETRY_DELAY_MS
)
}
Log.d(TAG, "Subscribed to CAN notifications")
}

override fun onCharacteristicChanged(
Expand Down
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