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RTU: Raise exception for unexpected slave or function code in response #117

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RTU: Raise exception for unexpected slave or function code in response #117

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5cb3d52
Raise exception for unexpected slave or function code in response.
acolomb Mar 10, 2021
e28591e
Fix typos in parse_response_adu() docstring.
acolomb Mar 10, 2021
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9 changes: 7 additions & 2 deletions umodbus/client/serial/rtu.py
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@
WriteSingleRegister, WriteMultipleCoils,
WriteMultipleRegisters)
from umodbus.utils import recv_exactly
from umodbus.exceptions import ModbusFrameError


def _create_request_adu(slave_id, req_pdu):
Expand Down Expand Up @@ -173,9 +174,9 @@ def write_multiple_registers(slave_id, starting_address, values):

def parse_response_adu(resp_adu, req_adu=None):
""" Parse response ADU and return response data. Some functions require
request ADU to fully understand request ADU.
request ADU to fully understand response ADU.

:param resp_adu: Resonse ADU.
:param resp_adu: Response ADU.
:param req_adu: Request ADU, default None.
:return: Response data.
"""
Expand Down Expand Up @@ -217,6 +218,10 @@ def send_message(adu, serial_port):
response_error_adu = recv_exactly(serial_port.read, exception_adu_size)
raise_for_exception_adu(response_error_adu)

if response_error_adu[0:2] != adu[0:2]:
# Mismatch in response's slave address or function code
raise ModbusFrameError(response_error_adu)

expected_response_size = \
expected_response_pdu_size_from_request_pdu(adu[1:-2]) + 3
response_remainder = recv_exactly(
Expand Down
6 changes: 6 additions & 0 deletions umodbus/exceptions.py
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Expand Up @@ -3,6 +3,12 @@ class ModbusError(Exception):
pass


class ModbusFrameError(ModbusError):
"""Reply from an unexpected slave, or an error in the received frame."""

pass


class IllegalFunctionError(ModbusError):
""" The function code received in the request is not an allowable action for
the server.
Expand Down