sr_receiver.py

import socket
import pickle
import hashlib
import sys
import random


def sr_receiver(receiver_host_name, receiver_listening_port):

    #  IPv6 is the future and the future is now
    receiver_socket = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM)
    receiver_socket.bind((receiver_host_name, receiver_listening_port))
    print("Listening on:", receiver_host_name, str(receiver_listening_port))
    expected_seq_num = 1
    random.seed()
    while True:
        roulette_seed = random.random()
        if roulette_seed < 0.1:
            print("The receiver is dropping packets")
        else:
            #  get the raw packet and src ip and port of packet
            received_raw_packet, client_info = receiver_socket.recvfrom(4096)
            received_packet = pickle.loads(received_raw_packet)
            received_seq_number, received_checksum, payload, mss, seq_bits = received_packet
            computed_checksum = hashlib.sha256()
            computed_checksum.update(pickle.dumps(received_seq_number))
            computed_checksum.update(payload)
            computed_checksum.update(pickle.dumps(mss))
            computed_checksum.update(pickle.dumps(seq_bits))
            #  Check if the packet is corrupt
            if received_checksum == computed_checksum.digest():
                if received_seq_number == expected_seq_num:
                    print("Received Segment", received_seq_number)
                    expected_seq_num = received_seq_number
                    # successfully received mss bytes so expect next mss bytes
                    ack_checksum = hashlib.sha256()
                    ack_checksum.update(pickle.dumps(expected_seq_num))
                    ack_packet = (expected_seq_num, ack_checksum.digest())
                    receiver_socket.sendto(pickle.dumps(ack_packet), client_info)
                    print("ACK Sent:", expected_seq_num)
            else:
                #  received corrupted packet
                print("Received Corrupted segment:", received_seq_number)
                #  send ACK with previous sequence number
                ack_checksum = hashlib.sha256()
                ack_checksum.update(pickle.dumps(expected_seq_num))
                ack_packet = (expected_seq_num, ack_checksum.digest())
                receiver_socket.sendto(pickle.dumps(ack_packet), client_info)
                print("ACK Sent:", expected_seq_num)


if __name__ == '__main__':
    receiver_host = "localhost"
    listening_port = int(sys.argv[1])
    sr_receiver(receiver_host, listening_port)