Improve diagnosibility of unhandled message types.

Author: anthony-tuininga

src/oracledb/errors.py

@@ -412,7 +412,8 @@ def _raise_from_string(exc_type: Exception, message: str) -> None:
     ERR_MESSAGE_HAS_NO_PAYLOAD:
             'message has no payload',
     ERR_MESSAGE_TYPE_UNKNOWN:
-            'internal error: unknown protocol message type {message_type}',
+            'internal error: unknown protocol message type {message_type} '
+            'at position {position}',
     ERR_MISSING_BIND_VALUE:
             'a bind variable replacement value for placeholder ":{name}" was '
             'not provided',

src/oracledb/impl/thin/messages.pyx

@@ -177,7 +177,8 @@ cdef class Message:
             self._process_server_side_piggyback(buf)
         else:
             errors._raise_err(errors.ERR_MESSAGE_TYPE_UNKNOWN,
-                              message_type=message_type)
+                              message_type=message_type,
+                              position=buf._pos - 1)
 
     cdef int _process_return_parameters(self, ReadBuffer buf) except -1:
         raise NotImplementedError()