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rdt_2_1.py
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import Network
import argparse
from time import sleep
import hashlib
class Packet:
## the number of bytes used to store packet length
seq_num_S_length = 10
length_S_length = 10
## length of md5 checksum in hex
checksum_length = 32
def __init__(self, seq_num, msg_S):
self.seq_num = seq_num
self.msg_S = msg_S
@classmethod
def from_byte_S(self, byte_S):
if Packet.corrupt(byte_S):
raise RuntimeError('Cannot initialize Packet: byte_S is corrupt')
pass
#extract the fields
seq_num = int(byte_S[Packet.length_S_length : Packet.length_S_length+Packet.seq_num_S_length])
msg_S = byte_S[Packet.length_S_length+Packet.seq_num_S_length+Packet.checksum_length :]
return self(seq_num, msg_S)
def get_byte_S(self):
#convert sequence number of a byte field of seq_num_S_length bytes
seq_num_S = str(self.seq_num).zfill(self.seq_num_S_length)
#convert length to a byte field of length_S_length bytes
length_S = str(self.length_S_length + len(seq_num_S) + self.checksum_length + len(self.msg_S)).zfill(self.length_S_length)
#compute the checksum
checksum = hashlib.md5((length_S+seq_num_S+self.msg_S).encode('utf-8'))
checksum_S = checksum.hexdigest()
#compile into a string
return length_S + seq_num_S + checksum_S + self.msg_S
@staticmethod
def corrupt(byte_S):
#extract the fields
length_S = byte_S[0:Packet.length_S_length]
seq_num_S = byte_S[Packet.length_S_length : Packet.seq_num_S_length+Packet.seq_num_S_length]
checksum_S = byte_S[Packet.seq_num_S_length+Packet.seq_num_S_length : Packet.seq_num_S_length+Packet.length_S_length+Packet.checksum_length]
msg_S = byte_S[Packet.seq_num_S_length+Packet.seq_num_S_length+Packet.checksum_length :]
#compute the checksum locally
checksum = hashlib.md5(str(length_S+seq_num_S+msg_S).encode('utf-8'))
computed_checksum_S = checksum.hexdigest()
#and check if the same
return checksum_S != computed_checksum_S
class RDT:
## latest sequence number used in a packet
seq_num = 1
## buffer of bytes read from network
byte_buffer = ''
lastPacketSent = None
#NAKLastPacketSent = False
def __init__(self, role_S, server_S, port):
self.network = Network.NetworkLayer(role_S, server_S, port)
def disconnect(self):
self.network.disconnect()
def rdt_1_0_send(self, msg_S):
p = Packet(self.seq_num, msg_S)
self.seq_num += 1
self.network.udt_send(p.get_byte_S())
def rdt_1_0_receive(self):
ret_S = None
byte_S = self.network.udt_receive()
self.byte_buffer += byte_S
#keep extracting packets - if reordered, could get more than one
while True:
#check if we have received enough bytes
if(len(self.byte_buffer) < Packet.length_S_length):
return ret_S #not enough bytes to read packet length
#extract length of packet
length = int(self.byte_buffer[:Packet.length_S_length])
if len(self.byte_buffer) < length:
return ret_S #not enough bytes to read the whole packet
#create packet from buffer content and add to return string
p = Packet.from_byte_S(self.byte_buffer[0:length])
ret_S = p.msg_S if (ret_S is None) else ret_S + p.msg_S
#remove the packet bytes from the buffer
self.byte_buffer = self.byte_buffer[length:]
#if this was the last packet, will return on the next iteration
def rdt_2_1_send(self, msg_S):
sendPacket = Packet(self.seq_num, msg_S)
if msg_S != "NAK":
self.lastPacketSent = sendPacket
#NAKLastPacketSent = False
if msg_S == "ACK":
if self.seq_num == 0:
self.seq_num = 1
self.network.udt_send(sendPacket.get_byte_S())
def rdt_2_1_receive(self):
ret_S = None
byte_S = self.network.udt_receive()
self.byte_buffer += byte_S
#keep extracting packets - if reordered, could get more than one
looping = True
while looping:
#check if we have received enough bytes
if(len(self.byte_buffer) < Packet.length_S_length):
return ret_S #not enough bytes to read packet length
#extract length of packet
length = int(self.byte_buffer[:Packet.length_S_length])
if len(self.byte_buffer) < length:
return ret_S #not enough bytes to read the whole packet
#create packet from buffer content and add to return string
if Packet.corrupt(self.byte_buffer[0:length]):
self.byte_buffer = self.byte_buffer[length:]
self.rdt_2_1_send("NAK")
#NAKLastPacketSent = True
looping = False
else:
p = Packet.from_byte_S(self.byte_buffer[0:length])
if p.msg_S == "NAK":
#if NAKLastPacketSent:
# self.rdt_2_1_send("NAK")
#else:
if self.lastPacketSent is None:
self.rdt_2_1_send("NAK")
else:
self.rdt_2_1_send(self.lastPacketSent.msg_S)
looping = False
elif p.msg_S == "ACK":
if self.seq_num == 0:
self.seq_num = 1
self.lastPacketSent = None
#NAKLastPacketSent = False
looping = False
else:
self.lastPacketSent = None
#NAKLastPacketSent = False
if p.seq_num == self.seq_num:
ret_S = p.msg_S if (ret_S is None) else ret_S + p.msg_S
#remove the packet bytes from the buffer
#if this was the last packet, will return on the next iteration
else:
pass
#if self.seq_num == 0:
# self.seq_num = 1
self.rdt_2_1_send("ACK")
self.byte_buffer = self.byte_buffer[length:]
def rdt_3_0_send(self, msg_S):
# This is what we will define
pass
def rdt_3_0_receive(self):
# This is what we will define
pass
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='RDT implementation.')
parser.add_argument('role', help='Role is either client or server.', choices=['client', 'server'])
parser.add_argument('server', help='Server.')
parser.add_argument('port', help='Port.', type=int)
args = parser.parse_args()
rdt = RDT(args.role, args.server, args.port)
if args.role == 'client':
#rdt.rdt_1_0_send('MSG_FROM_CLIENT')
rdt.rdt_2_1_send('MSG_FROM_CLIENT')
sleep(2)
#print(rdt.rdt_1_0_receive())
print(rdt.rdt_2_1_receive())
rdt.disconnect()
else:
sleep(1)
#print(rdt.rdt_1_0_receive())
print(rdt.rdt_2_1_receive())
#rdt.rdt_1_0_send('MSG_FROM_SERVER')
rdt.rdt_2_1_send('MSG_FROM_SERVER')
rdt.disconnect()