def send_ack(self, seq_num, client_addr):
# Prepare Acknowledgement
packet = struct.pack('IH', seq_num, self.header)
# Calculate checksum
checksum = Checksum.calculate(packet)
# Add Checksum to the packet
packet = ctypes.create_string_buffer(8)
struct.pack_into('IHH', packet, 0, seq_num, checksum, self.header)
# Corrupt packet based on the probability
if random.random() <= self.packet_corrupt_probability:
packet[random.randint(0, len(packet) - 1)] = 0
# Send ACK
time.sleep(1)
self.server_socket.sendto(packet, client_addr)
self.logger.info('Sequence Number %d - Acknowledgement Sent', seq_num)
def get_next_packet(self, seq_num):
if self.num_packets == 0:
return None
self.num_packets -= 1
# Create packet
data = ''.join(
random.choice(string.ascii_uppercase + string.digits)
for _ in range(self.mss - 8)).encode('ascii')
length = len(data)
# Create packet
packet = struct.pack('IH' + str(length) + 's', seq_num, self.header,
data)
# Calculate checksum
checksum = Checksum.calculate(packet)
# Add Checksum to the packet
packet = ctypes.create_string_buffer(self.mss)
struct.pack_into('IHH' + str(length) + 's', packet, 0, seq_num,
checksum, self.header, data)
return packet
