Re-organize all projects (#4166)

Content.Server/IP/IPAddressExt.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections;
+using System.Linq;
+using System.Net.Sockets;
+
+namespace Content.Server.IP
+{
+    public static class IPAddressExt
+    {
+        // Taken from https://stackoverflow.com/a/56461160/4678631
+        public static bool IsInSubnet(this System.Net.IPAddress address, string subnetMask)
+        {
+            var slashIdx = subnetMask.IndexOf("/", StringComparison.Ordinal);
+            if (slashIdx == -1)
+            {
+                // We only handle netmasks in format "IP/PrefixLength".
+                throw new NotSupportedException("Only SubNetMasks with a given prefix length are supported.");
+            }
+
+            // First parse the address of the netmask before the prefix length.
+            var maskAddress = System.Net.IPAddress.Parse(subnetMask.Substring(0, slashIdx));
+
+            if (maskAddress.AddressFamily != address.AddressFamily)
+            {
+                // We got something like an IPV4-Address for an IPv6-Mask. This is not valid.
+                return false;
+            }
+
+            // Now find out how long the prefix is.
+            int maskLength = int.Parse(subnetMask.Substring(slashIdx + 1));
+
+            if (maskAddress.AddressFamily == AddressFamily.InterNetwork)
+            {
+                // Convert the mask address to an unsigned integer.
+                var maskAddressBits = BitConverter.ToUInt32(maskAddress.GetAddressBytes().Reverse().ToArray(), 0);
+
+                // And convert the IpAddress to an unsigned integer.
+                var ipAddressBits = BitConverter.ToUInt32(address.GetAddressBytes().Reverse().ToArray(), 0);
+
+                // Get the mask/network address as unsigned integer.
+                uint mask = uint.MaxValue << (32 - maskLength);
+
+                // https://stackoverflow.com/a/1499284/3085985
+                // Bitwise AND mask and MaskAddress, this should be the same as mask and IpAddress
+                // as the end of the mask is 0000 which leads to both addresses to end with 0000
+                // and to start with the prefix.
+                return (maskAddressBits & mask) == (ipAddressBits & mask);
+            }
+
+            if (maskAddress.AddressFamily == AddressFamily.InterNetworkV6)
+            {
+                // Convert the mask address to a BitArray.
+                var maskAddressBits = new BitArray(maskAddress.GetAddressBytes());
+
+                // And convert the IpAddress to a BitArray.
+                var ipAddressBits = new BitArray(address.GetAddressBytes());
+
+                if (maskAddressBits.Length != ipAddressBits.Length)
+                {
+                    throw new ArgumentException("Length of IP Address and Subnet Mask do not match.");
+                }
+
+                // Compare the prefix bits.
+                for (int maskIndex = 0; maskIndex < maskLength; maskIndex++)
+                {
+                    if (ipAddressBits[maskIndex] != maskAddressBits[maskIndex])
+                    {
+                        return false;
+                    }
+                }
+
+                return true;
+            }
+
+            throw new NotSupportedException("Only InterNetworkV6 or InterNetwork address families are supported.");
+        }
+    }
+}