Always_Valid aspect unsupported

[treiher]

% tools/validate_spec.py -s dhcp.rflx -m DHCP::Message -v tests/data/dhcp/message/valid
tests/data/dhcp/message/valid/DHCP_MessageType_10,11,12_and_13_4.raw: FAILED
FalseNegative
pyrflx: error: cannot set value for field Hlen
pyrflx: error: Number 0 is not a valid enum value

Traceback (most recent call last):
  File "tools/validate_spec.py", line 334, in <module>
    sys.exit(cli(sys.argv))
  File "tools/validate_spec.py", line 82, in cli
    validation_main(args)
  File "tools/validate_spec.py", line 135, in validation_main
    validation_result = validator.validate_message(msg)
  File "tools/validate_spec.py", line 200, in validate_message
    parser_result = self.__parse_message(original_message.bytes)
  File "tools/validate_spec.py", line 228, in __parse_message
    pdu_model.parse(message)
  File "/home/tr/sync/RecordFlux-specifications/venv/lib/python3.7/site-packages/rflx/pyrflx/typevalue.py", line 732, in parse
    ) = set_field_without_size(current_field_name, current_field)
  File "/home/tr/sync/RecordFlux-specifications/venv/lib/python3.7/site-packages/rflx/pyrflx/typevalue.py", line 712, in set_field_without_size
    self.set(field_name, value[current_pos_in_bitstring:])
  File "/home/tr/sync/RecordFlux-specifications/venv/lib/python3.7/site-packages/rflx/pyrflx/typevalue.py", line 820, in set
    field.typeval.parse(value)
  File "/home/tr/sync/RecordFlux-specifications/venv/lib/python3.7/site-packages/rflx/pyrflx/typevalue.py", line 447, in parse
    nested_message.parse(value, check)
  File "/home/tr/sync/RecordFlux-specifications/venv/lib/python3.7/site-packages/rflx/pyrflx/typevalue.py", line 726, in parse
    current_field = self._fields[current_field_name]
KeyError: ''

The used specification and test data can be found on the issue_2 branch of RecordFlux-specification.

[rssen]

The message occurs because dhcp-auth_0.raw sets 66 as the Code. 66 is not a defined value for the Code field but since the Always Valid aspect is defined, no error is raised while setting the value to the field and UNKOWN is set as the enum literal. PyRFLX works with the literals, not the numeric values and since no literal is defined for the numeric value (66), UNKNOWN is set.

When trying to set the next field Code, the outgoing conditions are checked and none of them can be simplified to TRUE. That is because Code is UNKNOWN and the simplified method substitutes Code in the condition with it's literal. That leads to the conditions UNKNOWN = 0 or UNKNOWN = 255 and Code /= Pad_Option and Code /= End_Option. None of them can ever be TRUE. Because no condition is TRUE an empty string is returned and triggers the exception.

[treiher]

So this means PyRFLX does not support the Always_Valid aspect. I suppose the current design (i.e. reusing setters for the parser) makes it hard to fix that. Or do you see a simple solution for this issue?

[rssen]

The main problem is that UNKNOWN is not substituted with a numeric value before calling simplified(). A solution might be to simply add UNKNOWN and the associated value to the MessageValue.type_literals or simplified_mapping (would be a better fit in type_literals) once the value is assigned. That would probably be a hack/special case in the set method of MessageValue.

[treiher]

If it's that easy, we should try it.