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import struct
from umodbus.client.tcp import _create_request_adu, _create_mbap_header
def test_create_request_adu():
""" Validate MBAP header of ADU and check if ADU contains correct PDU. """
pdu = b'\x01'
slave_id = 1
adu = _create_request_adu(slave_id, pdu)
# 9 is length MBAP (7 bytes) with length of PDU (1 byte)
assert len(adu) == 8
assert adu[7:] == pdu
validate_mbap_fields(adu[:7], slave_id, pdu)
def test_create_mbap_header():
""" Validate fields of MBAP header. """
pdu = b'\x01x02'
slave_id = 1
mbap = _create_mbap_header(slave_id, pdu)
validate_mbap_fields(mbap, slave_id, pdu)
def validate_mbap_fields(mbap, slave_id, pdu):
""" Check if fields in MBAP header contain expected values. """
transaction_id = struct.unpack('>H', mbap[:2])[0]
protocol_id = struct.unpack('>H', mbap[2:4])[0]
length = struct.unpack('>H', mbap[4:6])[0]
unit_id = struct.unpack('>B', mbap[6:])[0]
assert len(mbap) == 7
assert 0 <= transaction_id <= 65536
assert protocol_id == 0
assert length == len(pdu) + 1
assert unit_id == slave_id
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