String+IPv4: A simplified check for IPv4 subnet equality

Author: mickeyl

Sources/CornucopiaCore/Extensions/String/String+IPv4.swift

@@ -0,0 +1,23 @@
+//
+//  Cornucopia – (C) Dr. Lauer Information Technology
+//
+import Foundation
+
+public extension String {
+
+    /// A simplified check if this and another string are in the same IPv4 subnet.
+    func CC_isInSameIPv4SubnetAs(other: String) -> Bool {
+
+        if self.hasPrefix("169.254.") && other.hasPrefix("169.254.") {
+            // Link-local uses /16
+            let part1 = self.components(separatedBy: ".")[...1].joined(separator: ".")
+            let part2 = other.components(separatedBy: ".")[...1].joined(separator: ".")
+            return part1 == part2
+        } else {
+            // Assume /24 for everything else
+            let part1 = self.components(separatedBy: ".")[...2].joined(separator: ".")
+            let part2 = other.components(separatedBy: ".")[...2].joined(separator: ".")
+            return part1 == part2
+        }
+    }
+}