Propagate Bluetooth error message out to UI

mobile/src/main/java/be/mygod/vpnhotspot/manage/BluetoothTethering.kt

@@ -84,14 +84,17 @@ class BluetoothTethering(context: Context, val stateListener: (Int) -> Unit) :
     }
 
     private var pan: BluetoothProfile? = null
+    var activeFailureCause: Throwable? = null
     /**
      * Based on: https://android.googlesource.com/platform/packages/apps/Settings/+/78d5efd/src/com/android/settings/TetherSettings.java
      */
     val active: Boolean? get() {
+        activeFailureCause = null
         val pan = pan ?: return null
         return BluetoothAdapter.getDefaultAdapter()?.state == BluetoothAdapter.STATE_ON && try {
             isTetheringOn.invoke(pan) as Boolean
         } catch (e: InvocationTargetException) {
+            activeFailureCause = e
             if (e.cause is SecurityException && BuildCompat.isAtLeastR()) Timber.d(e) else Timber.w(e)
             return null
         }

mobile/src/main/java/be/mygod/vpnhotspot/manage/TetherManager.kt

@@ -109,9 +109,11 @@ sealed class TetherManager(protected val parent: TetheringFragment) : Manager(),
             return e.readableMessage
         })
     }
+    protected open fun makeErrorMessage(errored: List<String>): CharSequence = errored
+            .filter { TetherType.ofInterface(it) == tetherType }
+            .joinToString("\n") { "$it: ${getErrorMessage(it)}" }
     fun updateErrorMessage(errored: List<String>) {
-        data.text = errored.filter { TetherType.ofInterface(it) == tetherType }
-                .joinToString("\n") { "$it: ${getErrorMessage(it)}" }
+        data.text = makeErrorMessage(errored)
         data.notifyChange()
     }
 
@@ -149,6 +151,9 @@ sealed class TetherManager(protected val parent: TetheringFragment) : Manager(),
         override val isStarted get() = tethering.active == true
 
         override fun onException() = ManageBar.start(parent.context ?: app)
+        override fun makeErrorMessage(errored: List<String>) = listOfNotNull(
+                if (tethering.active == null) tethering.activeFailureCause?.readableMessage else null,
+                super.makeErrorMessage(errored).let { if (it.isEmpty()) null else it }).joinToString("\n")
 
         override fun start() = BluetoothTethering.start(this)
         override fun stop() {