def __init__(self, packetString=None, header=None, data=None, checkCRC=True):
if (packetString != None):
# Sanity check
packetStringLength = len(packetString)
if (packetStringLength < 4):
raise InvalidPacketFormatError( \
'Impossible packet, must have a packet of at least 4 bytes but got {0}' \
.format(packetStringLength))
# The string can either be bytes or an actual string
# Force it to a string if that is the case.
if (type(packetString) == str):
packetString = packetString.encode('iso-8859-1')
# Extract the header information
self.headerLength = 4
headerString = packetString[:self.headerLength]
ctrlByte, packetLength, crc, command \
= struct.unpack(Formatting.CommandData.Header, headerString)
# Extract the value from the subsystem byte
subSystem = ctrlByte & BitMask.SubSystem
# Check if the response byte is an acknowledge
packetTypeCode = ctrlByte & BitMask.PacketType
packetType = packetTypeCode >> BitPosition.PacketType
# See if the packet is a response or a command packet
if (packetType == PacketType.Command):
raise InvalidPacketFormatError('Cannot create a response packet with the string of a command packet.')
self.header = NebHeader(subSystem, packetType, command, crc, packetLength)
# Extract the data substring
dataString = packetString[self.headerLength:self.headerLength + packetLength]
# Perform CRC of data bytes
if (checkCRC):
calculatedCRC = nebUtilities.genNebCRC8(bytearray(packetString))
if calculatedCRC != self.header.crc:
raise CRCError(calculatedCRC, self.header.crc)
if packetType == PacketType.Ack:
self.data = AckData()
else:
# Build the data object based on the subsystem and command.
self.data = ResponsePacketDataConstructors[subSystem][self.header.command](dataString)
elif (header != None and data != None):
self.header = header
self.data = data
def createResponsePacket(self, subSystem, commands, data, dataString):
crc = nebUtilities.crc8(bytearray(dataString))
header = NebHeader(subSystem, False, commands, crc, len(dataString))
responsePacket = NebResponsePacket(packetString=None, header=header, data=data, checkCRC=False)
responsePacket.header.crc = nebUtilities.genNebCRC8(bytearray(responsePacket.stringEncode()))
return responsePacket