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RTU: Calculate length from response #880

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Merged
janiversen merged 1 commit into from
May 25, 2022
Merged

RTU: Calculate length from response #880

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18 changes: 13 additions & 5 deletions pymodbus/framer/rtu_framer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -153,11 +153,9 @@ def populateHeader(self, data=None): # pylint: disable=invalid-name
`self._buffer` is not yet long enough.
"""
data = data if data is not None else self._buffer
self._header["uid"] = int(data[0])
func_code = int(data[1])
pdu_class = self.decoder.lookupPduClass(func_code)
size = pdu_class.calculateRtuFrameSize(data)
self._header["len"] = size
self._header['uid'] = int(data[0])
size = self.get_expected_response_length(data)
self._header['len'] = size

if len(data) < size:
# crc yet not available
Expand Down Expand Up @@ -330,5 +328,15 @@ def getRawFrame(self): # pylint: disable=invalid-name
_logger.debug(txt)
return self._buffer

def get_expected_response_length(self, data):
"""Get the expected response length.

:param data: Message data read so far
:raises IndexError: If not enough data to read byte count
:return: Total frame size
"""
func_code = int(data[1])
pdu_class = self.decoder.lookupPduClass(func_code)
return pdu_class.calculateRtuFrameSize(data)

# __END__
10 changes: 8 additions & 2 deletions pymodbus/transaction.py
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Original file line number Diff line number Diff line change
Expand Up @@ -343,7 +343,7 @@ def _recv(self, expected_response_length, full): # NOSONAR
if isinstance(self.client.framer, ModbusSocketFramer):
min_size = 8
elif isinstance(self.client.framer, ModbusRtuFramer):
min_size = 2
min_size = 4
elif isinstance(self.client.framer, ModbusAsciiFramer):
min_size = 5
elif isinstance(self.client.framer, ModbusBinaryFramer):
Expand All @@ -362,7 +362,7 @@ def _recv(self, expected_response_length, full): # NOSONAR
if isinstance(self.client.framer, ModbusSocketFramer):
func_code = int(read_min[-1])
elif isinstance(self.client.framer, ModbusRtuFramer):
func_code = int(read_min[-1])
func_code = int(read_min[1])
elif isinstance(self.client.framer, ModbusAsciiFramer):
func_code = int(read_min[3:5], 16)
elif isinstance(self.client.framer, ModbusBinaryFramer):
Expand All @@ -378,6 +378,12 @@ def _recv(self, expected_response_length, full): # NOSONAR
)
length = struct.unpack(">H", read_min[4:6])[0] - 1
expected_response_length = h_size + length
elif expected_response_length is None and isinstance(self.client.framer, ModbusRtuFramer):
try:
expected_response_length = self.client.framer.get_expected_response_length(read_min)
except IndexError:
# Could not determine response length with available bytes
pass
if expected_response_length is not None:
expected_response_length -= min_size
total = expected_response_length + min_size
Expand Down