Detect stale USB connections on resume

app/src/main/java/pl/lebihan/authnkey/CredentialProviderActivity.kt

@@ -328,7 +328,7 @@ class CredentialProviderActivity : AppCompatActivity() {
             registerReceiver(usbAttachReceiver, usbAttachFilter)
         }
 
-        if (currentTransport == null) {
+        if (currentTransport?.isConnected != true || currentTransport is UsbTransport) {
             checkForUsbDevice()
         }
     }
@@ -374,6 +374,19 @@ class CredentialProviderActivity : AppCompatActivity() {
     }
 
     private fun checkForUsbDevice() {
+        // Verify the existing USB connection is still usable
+        val transport = currentTransport
+        if (transport is UsbTransport) {
+            try {
+                transport.reclaimConnection()
+                return // still good
+            } catch (e: AuthnkeyError.NotConnected) {
+                transport.close()
+                currentTransport = null
+                pinProtocol = null
+            }
+        }
+
         val devices = usbManager.deviceList.values.filter { UsbTransport.isFidoDevice(it) }
         if (devices.isNotEmpty()) {
             val device = devices.first()

app/src/main/java/pl/lebihan/authnkey/FidoTransport.kt

@@ -15,6 +15,14 @@ interface FidoTransport {
     val transportType: TransportType
     val isConnected: Boolean
 
+    /**
+     * Verify that the transport connection is still active and usable.
+     * Throws [AuthnkeyError.NotConnected] if the connection has been lost
+     * (e.g. another app claimed the USB interface, or an NFC tag moved out of range).
+     */
+    @Throws(AuthnkeyError.NotConnected::class)
+    fun reclaimConnection()
+
     @Throws(Exception::class)
     suspend fun sendCtapCommand(command: ByteArray): ByteArray
 

app/src/main/java/pl/lebihan/authnkey/MainActivity.kt

@@ -208,7 +208,9 @@ class MainActivity : AppCompatActivity() {
         }
 
         // Auto-connect to already-plugged USB FIDO devices
-        checkForUsbDevice()
+        if (currentTransport?.isConnected != true || currentTransport is UsbTransport) {
+            checkForUsbDevice()
+        }
 
         // Check if started by USB device attachment
         if (intent.action == UsbManager.ACTION_USB_DEVICE_ATTACHED) {
@@ -318,9 +320,19 @@ class MainActivity : AppCompatActivity() {
      * Only connects if there's exactly one device and we're not already connected.
      */
     private fun checkForUsbDevice() {
-        // Skip if already connected
-        if (currentTransport?.isConnected == true) {
-            return
+        // Verify the existing USB connection is still usable
+        val transport = currentTransport
+        if (transport is UsbTransport) {
+            try {
+                transport.reclaimConnection()
+                return // still good
+            } catch (e: AuthnkeyError.NotConnected) {
+                transport.close()
+                currentTransport = null
+                pinProtocol = null
+                credentialManagement = null
+                updateConnectionStatus()
+            }
         }
 
         val devices = usbManager.deviceList.values

app/src/main/java/pl/lebihan/authnkey/NfcTransport.kt

@@ -19,6 +19,12 @@ class NfcTransport(private val isoDep: IsoDep) : FidoTransport {
             false
         }
 
+    override fun reclaimConnection() {
+        if (!isConnected) {
+            throw AuthnkeyError.NotConnected()
+        }
+    }
+
     init {
         if (!isoDep.isConnected) {
             isoDep.connect()

app/src/main/java/pl/lebihan/authnkey/UsbTransport.kt

@@ -56,6 +56,12 @@ class UsbTransport(
         }
     }
 
+    override fun reclaimConnection() {
+        if (!_isConnected || !connection.claimInterface(hidInterface, false)) {
+            throw AuthnkeyError.NotConnected()
+        }
+    }
+
     override suspend fun sendCtapCommand(command: ByteArray): ByteArray = withContext(Dispatchers.IO) {
         // CTAPHID_CBOR command
         sendRaw(channelId, CMD_CBOR, command)