IP in CIDR Block

ip_in_cidr.py

'''
Given an IP and a CIDR block, write a utility function to determine whether an input IP belongs to the CIDR block or not. Solution from a recent interview:

# Write a function to return back a boolean (true or false) given inputs of the following:
# 1. Candidate IP - 10.25.22.233
# 2. Mask size - 22 
# 3. Subnet IP - 10.25.11.111
'''

def convert_to_int(ip):
    octets = ip.split('.')
    return (int(octets[0]) << 24) + (int(octets[1]) << 16) + (int(octets[2]) << 8) + int(octets[3])


def ip_in_cidr(candidate_ip, mask_size, subnet_ip):
    try:
        # split both those string into octets
        # t = list(map(int, candidate_ip.split(".")))
        # s = list(map(int, subnet_ip.split(".")))
        
        # This is the bit operator I forgot how to use, so I looked that up
        subnet_mask = (1 << 32) - (1 << (32 - mask_size))

        # Convert both dot notations the decimal representation of their binary form
        subnet_ip_int = convert_to_int(subnet_ip)
        candidate_ip_int = convert_to_int(candidate_ip)

        # The bitwise & comparison will remove the last 10 bits for the mask and then 
        # compare if everything up to that point is equivalent
        return (candidate_ip_int & subnet_mask) == (subnet_ip_int & subnet_mask)
    except ValueError:
        return False


print(ip_in_cidr("10.25.22.233", 22, "10.25.11.111"))
    
'''
Validating in binary notation
Mask   11111111 11111111 11111100 00000000
Subnet 00001010 00011001 00001011 01101111
Input  00001010 00011001 00010110 11101001
                            ^fail
'''