feat: cancel in-flight on-device prompts

Add TrezorClient.cancel() so the host can abort a prompt the device is showing (e.g. on-device passphrase entry) and send it back to its home screen

Author: redsh4de

trezor-flutter/lib/src/api/connection_manager.dart

@@ -14,6 +14,8 @@ abstract class ConnectionManager {
     TrezorTransformer? transformer,
   );
 
+  Future<void> sendOutOfBand(TrezorDevice device, TrezorOperation operation);
+
   Future<void> dispose();
 
   ConnectionType get connectionType;

trezor-flutter/lib/src/api/gatt_gateway.dart

@@ -25,6 +25,8 @@ abstract class GattGateway {
 
   Future<T> sendOperation<T>(TrezorOperation<T> operation, {TrezorTransformer? transformer});
 
+  Future<void> sendWriteOnly(TrezorOperation operation);
+
   Future<BleService?> getService(String serviceId);
 
   Future<BleCharacteristic?> getCharacteristic(BleService service, String characteristic);

trezor-flutter/lib/src/connect/trezor_client.dart

@@ -5,6 +5,7 @@ import 'package:flutter/foundation.dart';
 import 'package:trezor_flutter/src/connect/acquire.dart';
 import 'package:trezor_flutter/src/connect/pairing.dart';
 import 'package:trezor_flutter/src/connect/trezor_thp_call.dart';
+import 'package:trezor_flutter/src/operations/trezor/thp_encrypted_operation.dart';
 import 'package:trezor_flutter/src/operations/trezor/v1_operation.dart';
 import 'package:trezor_flutter/src/trezor/protobuf/messages-common.pb.dart';
 import 'package:trezor_flutter/src/trezor/protobuf/messages-management.pb.dart';
@@ -40,6 +41,9 @@ abstract class TrezorClient {
   /// Make a call to the Trezor Device
   Future<(int, Uint8List)> call(Uint8List message, TrezorMessageType messageType);
 
+  /// Abort an in-flight on-device prompt; the pending call fails with ActionCancelled
+  Future<void> cancel();
+
   /// Whether the device forces passphrase entry on its own screen
   bool get passphraseAlwaysOnDevice;
 }
@@ -79,6 +83,9 @@ class TrezorClientV1 extends TrezorClient {
     }
   }
 
+  @override
+  Future<void> cancel() => connection.disconnect();
+
   @override
   Future<void> createChannel({TrezorPassphrase? passphrase}) async {
     if (passphrase != null) _sessionIntent.store(passphrase);
@@ -115,8 +122,7 @@ class TrezorClientV1 extends TrezorClient {
     _features = features;
 
     return TrezorSessionInfo(
-      enteredOnDevice:
-          passphrase is TrezorPassphraseOnDevice || features.passphraseAlwaysOnDevice,
+      enteredOnDevice: passphrase is TrezorPassphraseOnDevice || features.passphraseAlwaysOnDevice,
       resumed: listEquals(features.sessionId, resumeSessionId),
       sessionId: features.sessionId,
     );
@@ -159,6 +165,19 @@ class TrezorClientV2 extends TrezorClient {
     }
   }
 
+  @override
+  Future<void> cancel() {
+    if (!state.cancelablePromise) return connection.disconnect();
+
+    return connection.sendOutOfBand(
+      TrezorThpEncryptedOperation(
+        state,
+        data: Cancel().writeToBuffer(),
+        messageType: TrezorMessageType.cancel,
+      ),
+    );
+  }
+
   @override
   Future<void> createChannel({TrezorPassphrase? passphrase}) async {
     await getThpChannel(

trezor-flutter/lib/src/connect/trezor_thp_call.dart

@@ -30,8 +30,12 @@ Future<(TrezorMessageType, Uint8List)> thpCall(
 
   if (response.messageType == TrezorMessageType.buttonRequest) {
     state.cancelablePromise = true;
-
-    return thpCall(connection, state, ButtonAck().writeToBuffer(), TrezorMessageType.buttonAck);
+    try {
+      return await thpCall(
+          connection, state, ButtonAck().writeToBuffer(), TrezorMessageType.buttonAck);
+    } finally {
+      state.cancelablePromise = false;
+    }
   }
 
   return (response.messageType, response.payload);

trezor-flutter/lib/src/trezor/protobuf/utils.dart

@@ -10,6 +10,7 @@ enum TrezorMessageType {
   success(2),
   failure(3),
   features(17),
+  cancel(20),
   getFeatures(55),
 
   buttonRequest(26), // device is waiting for user confirmation

trezor-flutter/lib/src/trezor/trezor_ble_manager.dart

@@ -159,6 +159,21 @@ class TrezorBleConnectionManager extends ConnectionManager {
     );
   }
 
+  @override
+  Future<void> sendOutOfBand(TrezorDevice device, TrezorOperation operation) async {
+    if (_disposed) throw TrezorManagerDisposedException(ConnectionType.ble);
+
+    final d = _connectedDevices[device.id];
+    if (d == null) {
+      throw DeviceNotConnectedException(
+        requestedOperation: 'ble_manager: sendOutOfBand',
+        connectionType: ConnectionType.ble,
+      );
+    }
+
+    return d.gateway.sendWriteOnly(operation);
+  }
+
   @override
   Future<AvailabilityState> get status {
     if (_disposed) throw TrezorManagerDisposedException(ConnectionType.ble);

trezor-flutter/lib/src/trezor/trezor_gatt_gateway.dart

@@ -218,6 +218,19 @@ class TrezorGattGateway extends GattGateway {
       _pendingOperations.addFirst(_Request(operation, transformer, completer));
     }
 
+    await _writePayloads(operation);
+
+    if (operation is TrezorThpAckOperation) {
+      completer.complete();
+    }
+
+    return completer.future;
+  }
+
+  @override
+  Future<void> sendWriteOnly(TrezorOperation operation) => _writePayloads(operation);
+
+  Future<void> _writePayloads(TrezorOperation operation) async {
     final writer = ByteDataWriter();
     final output = await operation.write(writer);
     final payloads = _packer.pack(output, 244);
@@ -230,13 +243,7 @@ class TrezorGattGateway extends GattGateway {
         withoutResponse: false,
         timeout: _bleWriteTimeout,
       );
-
-      if (operation is TrezorThpAckOperation) {
-        completer.complete();
-      }
     }
-
-    return completer.future;
   }
 
   @override

trezor-flutter/lib/src/trezor/trezor_usb_manager.dart

@@ -88,6 +88,19 @@ class TrezorUsbManager extends ConnectionManager {
     }
   }
 
+  @override
+  Future<void> sendOutOfBand(TrezorDevice device, TrezorOperation operation) async {
+    if (_disposed) throw TrezorManagerDisposedException(connectionType);
+
+    try {
+      final writer = ByteDataWriter();
+      final payload = await operation.write(writer);
+      await _usbTransport.transferOut(payload);
+    } on PlatformException catch (ex) {
+      throw TrezorExceptionUtils.fromPlatformException(ex, connectionType);
+    }
+  }
+
   @override // TODO this may need to be implemented
   Stream<BleConnectionState> get deviceStateChanges {
     if (_disposed) throw TrezorManagerDisposedException(connectionType);

trezor-flutter/lib/src/trezor_connection.dart

@@ -51,6 +51,12 @@ class TrezorConnection {
     );
   }
 
+  Future<void> sendOutOfBand(TrezorOperation operation) {
+    if (_isDisconnected) return Future.value();
+
+    return _connectionManager.sendOutOfBand(device, operation);
+  }
+
   Future<T> _sendOperationImpl<T>(
     TrezorDevice device,
     TrezorOperation<T> operation,