def _get_request_length(self, mbap):
"""Parse the mbap and returns the number of bytes to be read"""
if len(mbap) < 6:
raise ModbusInvalidRequestError("The mbap is only %d bytes long",
len(mbap))
length = struct.unpack(">HHH", mbap[:6])[2]
return length
def parse_request(self, request):
"""Extract the pdu from a modbus request"""
if len(request) > 6:
mbap, pdu = request[:7], request[7:]
self._request_mbap.unpack(mbap)
error_str = self._request_mbap.check_length(len(pdu))
if len(error_str) > 0:
raise ModbusInvalidMbapError(error_str)
return self._request_mbap.unit_id, pdu
else:
raise ModbusInvalidRequestError("Request length is only {0} bytes. ".format(len(request)))
def handle_request(self, request_pdu, broadcast=False):
"""
parse the request pdu, makes the corresponding action
and returns the response pdu
"""
logger.debug("Slave (ID: %d) is handling request" % self._id)
with self._data_lock: # thread-safe
try:
# get the function code
(self.function_code, ) = struct.unpack(">B", request_pdu[:1])
# check if the function code is valid. If not returns error response
if not self.function_code in self._fn_code_map:
raise ModbusError(defines.ILLEGAL_FUNCTION)
can_broadcast = [
defines.WRITE_MULTIPLE_COILS,
defines.WRITE_MULTIPLE_REGISTERS,
defines.WRITE_SINGLE_COIL,
defines.WRITE_SINGLE_REGISTER,
]
if broadcast and (self.function_code not in can_broadcast):
raise ModbusInvalidRequestError(
"Function %d can not be broadcasted" %
self.function_code)
# execute the corresponding function
try:
response_pdu = self._fn_code_map[self.function_code](
request_pdu)
except struct.error:
raise ModbusError(exception_code=3)
if response_pdu:
if broadcast:
# not really sure whats going on here - better log it!
logger.info("Modbus broadcast: %s" %
(utils.get_log_buffer("!!", response_pdu)))
return ""
else:
return struct.pack(">B",
self.function_code) + response_pdu
raise Exception("No response for function %d" %
self.function_code)
except ModbusError as e:
logger.error(
"Exception caught: %s. (A proper response will be sent to the peer)",
e,
)
return struct.pack(">BB", self.function_code + 128,
e.get_exception_code())
def handle_request(self, request_pdu, broadcast=False):
"""
parse the request pdu, makes the corresponding action
and returns the response pdu
"""
with self._data_lock: # thread-safe
try:
# get the function code
(self.function_code, ) = struct.unpack(">B", request_pdu[0])
# check if the function code is valid. If not returns error response
if not self.function_code in self._fn_code_map:
raise ModbusError(defines.ILLEGAL_FUNCTION)
# if read query is broadcasted raises an error
cant_be_broadcasted = (defines.READ_COILS,
defines.READ_DISCRETE_INPUTS,
defines.READ_INPUT_REGISTERS,
defines.READ_HOLDING_REGISTERS)
if broadcast and (self.function_code in cant_be_broadcasted):
raise ModbusInvalidRequestError(
"Function %d can not be broadcasted" %
self.function_code)
# execute the corresponding function
response_pdu = self._fn_code_map[self.function_code](
request_pdu)
if response_pdu:
if broadcast:
#not really sure whats going on here - better log it!
logger.info("broadcast: %s" %
(utils.get_log_buffer("!!", response_pdu)))
return ""
else:
return struct.pack(">B",
self.function_code) + response_pdu
raise Exception("No response for function %d" %
self.function_code)
except ModbusError as e:
logger.error(
'Exception caught: {0}. (A proper response will be sent to the peer)'
.format(e))
return struct.pack(">BB", self.function_code + 128,
e.get_exception_code())