Added IPAddressLocalityChecker + test for checking if an IP address i…

…s local or not.

gui-app/build.gradle.kts

@@ -30,6 +30,8 @@ plugins {
 dependencies {
     implementation(libs.kotlinx.serialization.json)
     implementation(libs.miglayout.swing)
+
+    testImplementation(testLibs.kotest.junit5)
 }
 
 java {

gui-app/src/main/kotlin/dev/robocode/tankroyale/gui/util/IPAddressLocalityChecker.kt

@@ -0,0 +1,34 @@
+package dev.robocode.tankroyale.gui.util
+
+import java.net.InetAddress
+import java.net.Inet4Address
+import java.net.Inet6Address
+
+fun isLocalAddress(ipAddress: String): Boolean {
+    return try {
+        val addr = InetAddress.getByName(ipAddress)
+        when (addr) {
+            is Inet4Address -> isLocalIPv4(addr)
+            is Inet6Address -> isLocalIPv6(addr)
+            else -> false
+        }
+    } catch (e: Exception) {
+        println("Error: ${e.message}")
+        false
+    }
+}
+
+private fun isLocalIPv4(addr: Inet4Address): Boolean {
+    return addr.isLoopbackAddress ||
+            addr.isLinkLocalAddress ||
+            addr.isSiteLocalAddress ||
+            addr.hostAddress.startsWith("169.254.") // IPv4 link-local
+}
+
+private fun isLocalIPv6(addr: Inet6Address): Boolean {
+    return addr.isLoopbackAddress ||
+            addr.isLinkLocalAddress ||
+            addr.isSiteLocalAddress ||
+            addr.hostAddress.lowercase().startsWith("fc") || // ULA
+            addr.hostAddress.lowercase().startsWith("fd")    // ULA
+}

gui-app/src/test/kotlin/dev/robocode/tankroyale/gui/util/IPAddressLocalityCheckerTest.kt

@@ -0,0 +1,48 @@
+package dev.robocode.tankroyale.gui.util
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class IPAddressLocalityCheckerTest : StringSpec({
+    "isLocalAddress should return true for local addresses" {
+        val localAddresses = listOf(
+            "127.0.0.1",
+            "10.0.0.1",
+            "192.168.1.1",
+            "172.16.0.1",
+            "::1",
+            "fe80::1234:5678:9abc",
+            "fc00::1",
+            "fd00::1",
+            "fe80:0:0:0:d4da:d362:c269:663f%ethernet_32769",
+        )
+        localAddresses.forEach {
+            isLocalAddress(it) shouldBe true
+        }
+    }
+
+    "isLocalAddress should return false for non-local valid addresses" {
+        val nonLocalAddresses = listOf(
+            "8.8.8.8",
+            "2001:db8::1",
+        )
+        nonLocalAddresses.forEach {
+            isLocalAddress(it) shouldBe false
+        }
+    }
+
+    "isLocalAddress should return false for invalid addresses" {
+        val nonLocalAddresses = listOf(
+            "1",
+            "1.2",
+            "1.2.3",
+            "1.2.3:1",
+            "1:2:3:4:5:6:7:8",
+            "::",
+            "::2",
+        )
+        nonLocalAddresses.forEach {
+            isLocalAddress(it) shouldBe false
+        }
+    }
+})