def parse(message: bytes, validate: bool = False, mode: int = 0) -> object:
"""
Parse UBX byte stream to UBXMessage object.
Includes option to validate incoming payload length and checksum
(the UBXMessage constructor can calculate and assign its own values anyway).
:param bytes message: binary message to parse
:param bool validate: validate message length and checksum (False (default), True)
:param int mode: message mode (0=GET (default), 1=SET, 2=POLL)
:return: UBXMessage object
:rtype: UBXMessage
:raises: UBXParseError (if data stream contains invalid data or unknown message type)
"""
if mode not in (0, 1, 2):
raise ube.UBXParseError(
f"Invalid message mode {mode} - must be 0, 1 or 2")
lenm = len(message)
hdr = message[0:2]
clsid = message[2:3]
msgid = message[3:4]
lenb = message[4:6]
if lenb == b"\x00\x00":
payload = None
leni = 0
else:
payload = message[6:lenm - 2]
leni = len(payload)
ckm = message[lenm - 2:lenm]
if payload is not None:
ckv = calc_checksum(clsid + msgid + lenb + payload)
else:
ckv = calc_checksum(clsid + msgid + lenb)
if validate:
if hdr != ubt.UBX_HDR:
raise ube.UBXParseError((f"Invalid message header {hdr}"
f" - should be {ubt.UBX_HDR}"))
if leni != UBXMessage.bytes2val(lenb, ubt.U2):
raise ube.UBXParseError(
(f"Invalid payload length {lenb}"
f" - should be {UBXMessage.val2bytes(leni, ubt.U2)}"))
if ckm != ckv:
raise ube.UBXParseError((f"Message checksum {ckm}"
f" invalid - should be {ckv}"))
try:
if payload is None:
return UBXMessage(clsid, msgid, mode)
return UBXMessage(clsid, msgid, mode, payload=payload)
except KeyError as err:
modestr = ["GET", "SET", "POLL"][mode]
raise ube.UBXParseError((
f"Unknown message type clsid {clsid}, msgid {msgid}, mode {modestr}"
)) from err
def _do_len_checksum(self):
"""
Calculate and format payload length and checksum as bytes."""
if self._payload is None:
self._length = self.val2bytes(0, ubt.U2)
self._checksum = calc_checksum(self._ubxClass + self._ubxID + self._length)
else:
self._length = self.val2bytes(len(self._payload), ubt.U2)
self._checksum = calc_checksum(
self._ubxClass + self._ubxID + self._length + self._payload
)
def parse(message: bytes, *args, **kwargs) -> object:
"""
Parse UBX byte stream to UBXMessage object.
Includes option to validate incoming payload length and checksum
(the UBXMessage constructor can calculate and assign its own values anyway).
:param bytes message: binary message to parse
:param int validate: (kwarg) validate cksum (VALCKSUM (1)=True (default), VALNONE (0)=False)
:param int msgmode: (kwarg) message mode (0=GET (default), 1=SET, 2=POLL)
:return: UBXMessage object
:rtype: UBXMessage
:raises: UBXParseError (if data stream contains invalid data or unknown message type)
"""
msgmode = kwargs.get("msgmode", ubt.GET)
validate = kwargs.get("validate", VALCKSUM)
parsebf = kwargs.get("parsebitfield", True)
decnavdat = kwargs.get("deocdenavdata", False)
# accept args for backwards compatibility if no kwargs
if len(kwargs) == 0:
if len(args) > 0:
validate = args[0]
if len(args) > 1:
msgmode = args[1]
if msgmode not in (0, 1, 2):
raise ube.UBXParseError(
f"Invalid message mode {msgmode} - must be 0, 1 or 2")
lenm = len(message)
hdr = message[0:2]
clsid = message[2:3]
msgid = message[3:4]
lenb = message[4:6]
if lenb == b"\x00\x00":
payload = None
leni = 0
else:
payload = message[6:lenm - 2]
leni = len(payload)
ckm = message[lenm - 2:lenm]
if payload is not None:
ckv = calc_checksum(clsid + msgid + lenb + payload)
else:
ckv = calc_checksum(clsid + msgid + lenb)
if validate & VALCKSUM:
if hdr != ubt.UBX_HDR:
raise ube.UBXParseError((f"Invalid message header {hdr}"
f" - should be {ubt.UBX_HDR}"))
if leni != UBXMessage.bytes2val(lenb, ubt.U2):
raise ube.UBXParseError(
(f"Invalid payload length {lenb}"
f" - should be {UBXMessage.val2bytes(leni, ubt.U2)}"))
if ckm != ckv:
raise ube.UBXParseError((f"Message checksum {ckm}"
f" invalid - should be {ckv}"))
try:
if payload is None:
return UBXMessage(clsid, msgid, msgmode)
return UBXMessage(clsid,
msgid,
msgmode,
payload=payload,
parsebitfield=parsebf,
decodenavdata=decnavdat)
except KeyError as err:
modestr = ["GET", "SET", "POLL"][msgmode]
raise ube.UBXParseError((
f"Unknown message type clsid {clsid}, msgid {msgid}, mode {modestr}"
)) from err
def testCalcChecksum(self):
res = calc_checksum(b'\x06\x01\x02\x00\xf0\x05')
self.assertEqual(res, b'\xfe\x16')
