trezor.wire: unexpected message should interrupt workflow silently

src/trezor/wire/__init__.py

@@ -61,12 +61,14 @@ async def call(session_id, pbuf_msg, *response_types):
 
 class FailureError(Exception):
 
-    def __init__(self, code, message):
-        super(FailureError, self).__init__(code, message)
-
     def to_protobuf(self):
         from trezor.messages.Failure import Failure
-        return Failure(code=self.args[0], message=self.args[1])
+        code, message = self.args
+        return Failure(code=code, message=message)
+
+
+class CloseWorkflow(Exception):
+    pass
 
 
 def protobuf_workflow(session_id, msg_type, data_len, callback, *args):
@@ -83,6 +85,9 @@ async def _wrap_protobuf_workflow(wf, session_id):
     try:
         result = await wf
 
+    except CloseWorkflow:
+        return
+
     except FailureError as e:
         await write(session_id, e.to_protobuf())
         raise
@@ -115,15 +120,14 @@ def _handle_response(session_id, msg_type, data_len, response_types, signal):
     if msg_type in response_types:
         return _build_protobuf(msg_type, signal.send)
     else:
-        from trezor.messages.FailureType import UnexpectedMessage
-        signal.send(FailureError(UnexpectedMessage, 'Unexpected message'))
+        signal.send(CloseWorkflow())
         return _handle_workflow(session_id, msg_type, data_len)
 
 
 def _handle_workflow(session_id, msg_type, data_len):
     if msg_type in _workflow_callbacks:
-        args = _workflow_args[msg_type]
         callback = _workflow_callbacks[msg_type]
+        args = _workflow_args[msg_type]
         return callback(session_id, msg_type, data_len, *args)
     else:
         return _handle_unexpected(session_id, msg_type, data_len)
@@ -133,12 +137,20 @@ def _handle_unexpected(session_id, msg_type, data_len):
     log.warning(
         __name__, 'session %x: skip type %d, len %d', session_id, msg_type, data_len)
 
+    # read the message in full
     try:
         while True:
             yield
     except EOFError:
         pass
 
+    # respond with an unknown message error
+    from trezor.messages.Failure import Failure
+    from trezor.messages.FailureType import UnexpectedMessage
+    failure = Failure(code=UnexpectedMessage, message='Unexpected message')
+    sessions.get_codec(session_id).encode(
+        session_id, failure.MESSAGE_WIRE_TYPE, failure.dumps(), _write_report)
+
 
 def _write_report(report):
     if __debug__: