def UnpackFromBytes(self, bytes):
if len(bytes) < 16:
raise ValueError, "Not enough bytes"
header = bytes[:12]
payload = bytes[12:-4]
trailer = bytes[-4:]
crcd_bytes = bytes[:-2]
prefix, message_id, message_len = struct.unpack('<8sHH', header)
if len(payload) != message_len:
raise ValueError, "Payload size does not match tag"
# TODO(mikey): assert checked_crc == 0
checked_crc = crc16.crc16_ccitt(crcd_bytes)
self.UnpackFromPayload(payload)
def ToBytes(self):
payload = cStringIO.StringIO()
for field_name, field in self._fields.iteritems():
field_bytes = field.ToBytes(self._values[field_name])
payload.write(struct.pack('<BB', field.tagnum, len(field_bytes)))
payload.write(field_bytes)
payload_str = payload.getvalue()
payload.close()
out = cStringIO.StringIO()
out.write(GBSP_PREFIX)
out.write(struct.pack('<HH', self.MESSAGE_ID, len(payload_str)))
out.write(payload_str)
crc = crc16.crc16_ccitt(out.getvalue())
out.write(struct.pack('<H', crc))
out.write('\r\n')
return out.getvalue()
def testCrc(self):
data = '\x01\x02\x03\x04'
crc = crc16.crc16_ccitt(data)
data += struct.pack('<H', crc)
self.assertEqual(crc16.crc16_ccitt(data), 0)
