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"""
Module for Serialization and Deserialization of KNX Session Responses.
The SESSION_RESPONSE shall be sent by the KNXnet/IP secure server to the secure
client's control endpoint in response to a received secure session request frame.
"""
from __future__ import annotations
from typing import Final
from xknx.exceptions import CouldNotParseKNXIP
from .body import KNXIPBody
from .knxip_enum import KNXIPServiceType
class SessionResponse(KNXIPBody):
"""Representation of a KNX Session Response."""
SERVICE_TYPE = KNXIPServiceType.SESSION_RESPONSE
# 2 octets secure session identifier
# 32 octets for the servers ECDH public value
# 16 octets for the message authentication code
LENGTH: Final = 50
def __init__(
self,
secure_session_id: int = 0,
ecdh_server_public_key: bytes = bytes(32),
message_authentication_code: bytes = bytes(16),
) -> None:
"""Initialize SessionResponse object."""
self.ecdh_server_public_key = ecdh_server_public_key
# secure session identifier 0 shall in general be reserved for
# multicast data and shall not be used for unicast connections
self.secure_session_id = secure_session_id
self.message_authentication_code = message_authentication_code
def calculated_length(self) -> int:
"""Get length of KNX/IP body."""
return SessionResponse.LENGTH
def from_knx(self, raw: bytes) -> int:
"""Parse/deserialize from KNX/IP raw data."""
if len(raw) != SessionResponse.LENGTH:
raise CouldNotParseKNXIP("SessionResponse has wrong length")
self.secure_session_id = int.from_bytes(raw[:2], "big")
self.ecdh_server_public_key = raw[2:34]
self.message_authentication_code = raw[34:]
return SessionResponse.LENGTH
def to_knx(self) -> bytes:
"""Serialize to KNX/IP raw data."""
return (
self.secure_session_id.to_bytes(2, "big")
+ self.ecdh_server_public_key
+ self.message_authentication_code
)
def __repr__(self) -> str:
"""Return object as readable string."""
return (
f"<SessionResponse "
f'secure_session_id="{self.secure_session_id}" '
f'ecdh_server_public_key="{self.ecdh_server_public_key.hex()}" '
f'message_authentication_code="{self.message_authentication_code.hex()}" />'
)
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