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IP-Filtering/IP-Filtering.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <RootNamespace>IP_Filtering</RootNamespace>
+  </PropertyGroup>
+
+</Project>

IP-Filtering/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace IP_Filtering
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine(IsInStringContext("192.168.0.1")); //Should return true
+            Console.WriteLine(IsInStringContext("192.168.0.2")); //Should return true
+            Console.WriteLine(IsInStringContext("192.168.0.3")); //Should return false
+            Console.WriteLine(IsInStringContext("192.168.1.133")); //Should return true (in range)
+            Console.WriteLine(IsInStringContext("192.168.4.54")); //Should return true (in range)
+            Console.WriteLine(IsInStringContext("192.168.4.53")); //Should return false (not in range)
+            Console.WriteLine(IsInStringContext("192.168.2.34")); //Should return true (in CIDR range)
+            Console.WriteLine(IsInStringContext("192.168.3.34")); //Should return false (not in CIDR range)
+            Console.WriteLine(IsInStringContext("192.168.3.212")); //Should return true (in CIDR range) !!
+        }
+
+        private static readonly List<string> StringDataContext = new List<string>{
+            "192.168.0.1", "192.168.0.2", "192.168.1.0 - 192.168.1.255", "192.168.2.0/24", "192.168.3.128/25", "192.168.4.54 - 192.168.4.62"
+        };
+
+        public static bool IsInStringContext(string ip)
+        {
+            //Check if it's explicitly in the data context
+            if (StringDataContext.Exists(d => d == ip))
+                return true;
+
+            var givenIPOctets = ip.Split('.');
+
+            //Next, check if it's in range
+            //For this, I am going to assume IP ranges can only be a range of the last octet
+            foreach (string address in StringDataContext.Where(sdc => sdc.Contains('-')))
+            {
+                string[] addresses = address.Replace(" ", "").Split('-');
+                string[] firstAddressOctets = addresses[0].Split('.');
+                string[] secondAddressOctets = addresses[1].Split('.');
+
+                //Make sure first three octets are the same
+                if (givenIPOctets[0] != firstAddressOctets[0] ||
+                    givenIPOctets[1] != firstAddressOctets[1] ||
+                    givenIPOctets[2] != firstAddressOctets[2])
+                {
+                    continue;
+                }
+
+                int ipAddressLastOctet = int.Parse(givenIPOctets[3]);
+                int firstAddressLastOctet = int.Parse(firstAddressOctets[3]);
+                int secondAddressLastOctet = int.Parse(secondAddressOctets[3]);
+
+                if (ipAddressLastOctet >= firstAddressLastOctet && ipAddressLastOctet <= secondAddressLastOctet)
+                    return true;
+            }
+
+            //Lastly, check if it's in CIDR range.
+            //Again, I'm going to assume IP ranges can only be part of the last octet.
+            foreach (string address in StringDataContext.Where(sdc => sdc.Contains('/')))
+            {
+                string[] ipAddress = address.Split('/');
+                string[] octets = ipAddress[0].Split('.');
+
+                if (givenIPOctets[0] != octets[0] ||
+                    givenIPOctets[1] != octets[1] ||
+                    givenIPOctets[2] != octets[2])
+                {
+                    continue;
+                }
+
+                int maxOctet = (int)Math.Pow(2, 32 - int.Parse(ipAddress[1])) + int.Parse(octets[3]);
+                if (int.Parse(givenIPOctets[3]) >= int.Parse(octets[3]) && int.Parse(givenIPOctets[3]) <= maxOctet)
+                    return true;
+            }
+            return false;
+        }
+    }
+}