crc_server.py

# First of all import the socket library
import socket
def xor(a, b):

	# initialize result
	result = []

	# Traverse all bits, if bits are
	# same, then XOR is 0, else 1
	for i in range(1, len(b)):
		if a[i] == b[i]:
			result.append('0')
		else:
			result.append('1')

	return ''.join(result)


# Performs Modulo-2 division
def mod2div(divident, divisor):

	# Number of bits to be XORed at a time.
	pick = len(divisor)

	# Slicing the divident to appropriate
	# length for particular step
	tmp = divident[0 : pick]

	while pick < len(divident):

		if tmp[0] == '1':

			# replace the divident by the result
			# of XOR and pull 1 bit down
			tmp = xor(divisor, tmp) + divident[pick]

		else: # If leftmost bit is '0'
			# If the leftmost bit of the dividend (or the
			# part used in each step) is 0, the step cannot
			# use the regular divisor; we need to use an
			# all-0s divisor.
			tmp = xor('0'*pick, tmp) + divident[pick]

		# increment pick to move further
		pick += 1

	# For the last n bits, we have to carry it out
	# normally as increased value of pick will cause
	# Index Out of Bounds.
	if tmp[0] == '1':
		tmp = xor(divisor, tmp)
	else:
		tmp = xor('0'*pick, tmp)

	checkword = tmp
	return checkword

# Function used at the receiver side to decode
# data received by sender
def decodeData(data, key):

	l_key = len(key)

	# Appends n-1 zeroes at end of data
	appended_data = data + '0'*(l_key-1)
	remainder = mod2div(appended_data, key)

	return remainder

# Creating Socket
s = socket.socket()
print ("Socket successfully created")

# reserve a port on your computer in our
# case it is 12345 but it can be anything
port = 12345

s.bind(('', port))
print ("socket binded to %s" % (port))
# put the socket into listening mode
s.listen(5)
print ("socket is listening")


while True:
	# Establish connection with client.
	c, addr = s.accept()
	print('Got connection from', addr)
	
	# Get data from client
	data = c.recv(1024).decode()

	print(data)

	if not data:
		break

	key = "1001"

	ans = decodeData(data, key)
	print("Remainder after decoding is->"+ans)
	
	# If remainder is all zeros then no error occured
	temp = "0" * (len(key) - 1)
	if ans == temp:
		c.sendall(bytes("THANK you Data ->"+data + " Received No error FOUND", 'utf-8'))
	else:
		c.sendall("Error in data")

	c.close()