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- class packet:
- MAX_DATA_LENGTH = 500
- SEQ_NUM_MODULO = 32
- # type is 0=ACK, 1=data, 2=EOT
- # seq_num is the sequence number (mod 32)
- # data is the string which is the data (empty if no data)
- def __init__(self, type, seq_num, data):
- if len(data) > self.MAX_DATA_LENGTH:
- raise Exception("Data too large (max 500 char): ", len(data))
- self.type = type
- self.seq_num = seq_num % self.SEQ_NUM_MODULO
- self.data = data
- def get_udp_data(self):
- array = bytearray()
- array.extend(self.type.to_bytes(length=4, byteorder="big"))
- array.extend(self.seq_num.to_bytes(length=4, byteorder="big"))
- array.extend(len(self.data).to_bytes(length=4, byteorder="big"))
- array.extend(self.data.encode())
- return array
- @staticmethod
- def create_ack(seq_num):
- return packet(0, seq_num, "")
- @staticmethod
- def create_packet(seq_num, data):
- return packet(1, seq_num, data)
- @staticmethod
- def create_eot(seq_num):
- return packet(2, seq_num, "")
- @staticmethod
- def parse_udp_data(UDPdata):
- type = int.from_bytes(UDPdata[0:4], byteorder="big")
- seq_num = int.from_bytes(UDPdata[4:8], byteorder="big")
- length = int.from_bytes(UDPdata[8:12], byteorder="big")
- if type == 0:
- return packet.create_ack(seq_num)
- elif type == 2:
- return packet.create_eot(seq_num)
- else:
- UDPdata = UDPdata[12:12 + length].decode()
- return packet(type, seq_num, UDPdata)
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