If RTU response is empty, don't validate CRC but fail earlier. about umodbus HOT 10 CLOSED

If I understand you correctly the validate_crc of a response failes? Could you post a stacktrace/error?

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Hi! Thanks for responding.

I can dig up the exception, but it has to do with the fact that write_multiple_registers() is expecting a response and when it times out, it still calls validate_crc() with an empty buffer, which then gives the exception. Should I trap for that and then handle exceptions that way?

Do you still need a stack trace or is that expected behavior?

from umodbus.

I understand the case and I agree that the raising the exception in validate_crc is a bit weird. Earlier in the process an error should be raised.

def send_message(adu, serial_port):
    """ Send Modbus message over serial port and parse response. """
    serial_port.write(adu)
    response = serial_port.read(serial_port.in_waiting)

    if len(response) == 0:
        raise TimeoutError

    return parse_response_adu(response, adu)

from umodbus.

from umodbus.

If you want to fix it I'm happy to receive a pull request.

from umodbus.

from umodbus.

Good finding. I don't think that validate_crc is a proper place to do the length check. What would be
good error tho raise in this place and how should both rtu client and server handle it?

I think rtu.RTUServer.serve_once should check if length of request_adu. If length is 0 the method must not return the try to process the request and return a response, like you said, but it should raise an error. I think a TimeoutError fits best.

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Hi there,
Is this issue is still unsolved?

from umodbus.

No, it isn't yet. But the solution already thought trough in the above comments. So it's very easy to implement. I'll try to fix in somewhere this week.

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This has been fixed in the 1.0.0

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