def decode(self, payload, dikt):
"""
1.) Determine length of child and slice off respective payload
2.) Slice off checksum bytes
3.) Calculate checksum from child payload
4.) decode child
5.) Return remaining payload
If the checksum is not correct an exception is raised
"""
self.logger.info("data payload %r" % payload)
child_len = self.child.length(payload)
if child_len == len(payload): # consumer case
child_len -= self.length # reduce child-length by checksum
child_payload = payload[:child_len]
chk_bytes = payload[child_len:self.length]
_payload = payload[child_len + self.length:] # remaining payload
chk_bytes, dikt = Integer.decode(self, chk_bytes, dikt)
chk_sum = self.checksum(self, child_payload)
if dikt[self.name] != chk_sum:
raise ValueError('Checksum failure for %s' % self.child.name)
else:
child_payload, dikt = self.child.decode(child_payload, dikt)
return _payload, dikt
def encode(self, dikt, payload):
_payload = self.child.encode(dikt, '')
chksum = self.checksum(_payload)
dikt[self.name] = chksum
dikt, _payload = Integer.encode(self, dikt, _payload)
return dikt, payload + _payload
def __init__(self, name, length, endian='!'):
self.child = None
Integer.__init__(self, name, False, length, endian)
