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fix(server): correct COTP connection confirm framing #816

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fix(server): correct COTP connection confirm framing #816

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3 changes: 1 addition & 2 deletions snap7/server/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2705,10 +2705,9 @@ def _build_cotp_cc(self) -> bytes:
pdu_size_param = struct.pack(">BBB", self.COTP_PARAM_PDU_SIZE, 1, self.tpdu_size)
pdu_length = 6 + len(pdu_size_param)
base_pdu = struct.pack(
">BBBHHB",
">BBHHB",
pdu_length, # PDU length
self.COTP_CC, # PDU type
0x00, # Reserved / CDT
self.dst_ref, # Destination reference (client's source ref)
self.src_ref, # Source reference (our ref)
0x00, # Class/option
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11 changes: 11 additions & 0 deletions tests/test_server.py
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Original file line number Diff line number Diff line change
Expand Up @@ -316,6 +316,17 @@ def test_server_area_management(self) -> None:

@pytest.mark.server
class TestServerISOConnectionLimits:
def test_connection_confirm_has_valid_length_and_tpdu_size(self) -> None:
client_socket = MagicMock()
connection = ServerISOConnection(client_socket)
connection.dst_ref = 0x000F
connection.tpdu_size = 0x09

connection_confirm = connection._build_cotp_cc()

assert connection_confirm == bytes.fromhex("09d0000f000100c00109")
assert connection_confirm[0] == len(connection_confirm) - 1

def test_partial_frame_timeout_closes_connection(self) -> None:
client_socket = MagicMock()
client_socket.recv.side_effect = [b"\x03", TimeoutError()]
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