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"""Parse datasets TLV encoded as specified by Thread."""
from __future__ import annotations
from dataclasses import dataclass, field
from enum import IntEnum
import struct
class TLVError(Exception):
"""TLV error."""
class MeshcopTLVType(IntEnum):
"""Types."""
CHANNEL = 0
PANID = 1
EXTPANID = 2
NETWORKNAME = 3
PSKC = 4
NETWORKKEY = 5
NETWORK_KEY_SEQUENCE = 6
MESHLOCALPREFIX = 7
STEERING_DATA = 8
BORDER_AGENT_RLOC = 9
COMMISSIONER_ID = 10
COMM_SESSION_ID = 11
SECURITYPOLICY = 12
GET = 13
ACTIVETIMESTAMP = 14
COMMISSIONER_UDP_PORT = 15
STATE = 16
JOINER_DTLS = 17
JOINER_UDP_PORT = 18
JOINER_IID = 19
JOINER_RLOC = 20
JOINER_ROUTER_KEK = 21
PROVISIONING_URL = 32
VENDOR_NAME_TLV = 33
VENDOR_MODEL_TLV = 34
VENDOR_SW_VERSION_TLV = 35
VENDOR_DATA_TLV = 36
VENDOR_STACK_VERSION_TLV = 37
UDP_ENCAPSULATION_TLV = 48
IPV6_ADDRESS_TLV = 49
PENDINGTIMESTAMP = 51
DELAYTIMER = 52
CHANNELMASK = 53
COUNT = 54
PERIOD = 55
SCAN_DURATION = 56
ENERGY_LIST = 57
# Seen in a dataset imported through iOS companion app
APPLE_TAG_UNKNOWN = 74
DISCOVERYREQUEST = 128
DISCOVERYRESPONSE = 129
JOINERADVERTISEMENT = 241
@dataclass
class MeshcopTLVItem:
"""Base class for TLV items."""
tag: int
data: bytes
def __str__(self) -> str:
"""Return a string representation."""
return self.data.hex()
@dataclass
class Channel(MeshcopTLVItem):
"""Channel."""
channel: int = field(init=False)
def __post_init__(self) -> None:
"""Decode the channel."""
self.channel = int.from_bytes(self.data, "big")
if not self.channel:
raise TLVError(f"invalid channel '{self.channel}'")
@dataclass
class NetworkName(MeshcopTLVItem):
"""Network name."""
name: str = field(init=False)
def __post_init__(self) -> None:
"""Decode the name."""
try:
self.name = self.data.decode()
except UnicodeDecodeError as err:
raise TLVError(f"invalid network name '{self.data.hex()}'") from err
def __str__(self) -> str:
return self.name
@dataclass
class Timestamp(MeshcopTLVItem):
"""Timestamp."""
authoritative: bool = field(init=False)
seconds: int = field(init=False)
ticks: int = field(init=False)
def __post_init__(self) -> None:
"""Decode the timestamp."""
# The timestamps are packed in 8 bytes:
# [seconds 48 bits][ticks 15 bits][authoritative flag 1 bit]
unpacked: int = struct.unpack("!Q", self.data)[0]
self.authoritative = bool(unpacked & 1)
self.seconds = unpacked >> 16
self.ticks = (unpacked >> 1) & 0x7FF
def _encode_item(item: MeshcopTLVItem) -> bytes:
"""Encode a dataset item to TLV format."""
data_len = len(item.data)
return struct.pack(f"!BB{data_len}s", item.tag, data_len, item.data)
def encode_tlv(items: dict[MeshcopTLVType, MeshcopTLVItem]) -> str:
"""Encode a TLV encoded dataset to a hex string.
Raises if the TLV is invalid.
"""
result = b""
for item in items.values():
result += _encode_item(item)
return result.hex()
def _parse_item(tag: MeshcopTLVType, data: bytes) -> MeshcopTLVItem:
"""Parse a TLV encoded dataset item."""
if tag == MeshcopTLVType.ACTIVETIMESTAMP:
return Timestamp(tag, data)
if tag == MeshcopTLVType.CHANNEL:
return Channel(tag, data)
if tag == MeshcopTLVType.NETWORKNAME:
return NetworkName(tag, data)
return MeshcopTLVItem(tag, data)
def parse_tlv(data: str) -> dict[MeshcopTLVType, MeshcopTLVItem]:
"""Parse a TLV encoded dataset.
Raises if the TLV is invalid.
"""
try:
data_bytes = bytes.fromhex(data)
except ValueError as err:
raise TLVError("invalid tlvs") from err
result = {}
pos = 0
while pos < len(data_bytes):
try:
tag = MeshcopTLVType(data_bytes[pos])
except ValueError as err:
raise TLVError(f"unknown type {data_bytes[pos]}") from err
pos += 1
_len = data_bytes[pos]
pos += 1
val = data_bytes[pos : pos + _len]
if len(val) < _len:
raise TLVError(f"expected {_len} bytes for {tag.name}, got {len(val)}")
pos += _len
if tag in result:
raise TLVError(f"duplicated tag {tag.name}")
result[tag] = _parse_item(tag, val)
return result
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