fix #538 -- don't crash on wrong setup codes for ac-message, don't use "expect(), added test

python/src/deltachat/message.py

@@ -110,7 +110,13 @@ class Message(object):
 
     def continue_key_transfer(self, setup_code):
         """ extract key and use it as primary key for this account. """
-        lib.dc_continue_key_transfer(self._dc_context, self.id, as_dc_charpointer(setup_code))
+        res = lib.dc_continue_key_transfer(
+                self._dc_context,
+                self.id,
+                as_dc_charpointer(setup_code)
+        )
+        if res == 0:
+            raise ValueError("could not decrypt")
 
     @props.with_doc
     def time_sent(self):

python/tests/test_account.py

@@ -537,6 +537,9 @@ class TestOnlineAccount:
         ev = ac2._evlogger.get_matching("DC_EVENT_INCOMING_MSG|DC_EVENT_MSGS_CHANGED")
         msg = ac2.get_message_by_id(ev[2])
         assert msg.is_setup_message()
+        # first try a bad setup code
+        with pytest.raises(ValueError):
+            msg.continue_key_transfer(str(reversed(setup_code)))
         print("*************** Incoming ASM File at: ", msg.filename)
         print("*************** Setup Code: ", setup_code)
         msg.continue_key_transfer(setup_code)