def calculate_crc(self):
"""calculate_crc() -> CRC value
Returns the frame's calculated CRC, based on the information present in
the header. This is the value that _should_ be in the bytestream, not the
one that is. Use header._crc16 to get this.
"""
# TODO: Check for empty side info?
# First two bytes of the header are skipped
buf = self.bytes(include_crc = False)
return crc16(memoryview(buf)[2:])
def bytes(self, include_crc = True):
"""bytes(include_crc = True) -> bytearray
Returns a representation of the header in packed binary format.
If include_crc is False, the CRC will be omitted regardless of
the header.crc flag.
"""
buf = bytearray(self._FORMAT.length)
bitpack_into(self._FORMAT, buf, 0, *[self.__dict__[k] for k in self._FIELDS])
pos = len(buf)
buf.extend(self._side_info)
if include_crc and self.crc:
crc = crc16(memoryview(buf)[2:])
buf[pos:pos] = 2 # Inserts two bytes at pos
struct.pack_into('>H', buf, pos, crc)
return buf
