Match temporary IPv6 flags using canonical address bytes

tools/chatgui-android/app/src/main/java/com/utun/chat/data/InterfaceAddressFlags.kt

@@ -0,0 +1,13 @@
+package com.utun.chat.data
+
+/** /proc/net/if_inet6 использует 32 hex-цифры без сжатия нулей; IFA_F_TEMPORARY=0x20.
+ * Сопоставляется пара «интерфейс + 16 байтов адреса», прочие адреса/интерфейсы не меняют результат. */
+internal fun temporaryIpv6Address(ifName: String, address: ByteArray, rows: Sequence<String>): Boolean {
+    require(address.size == 16) { "IPv6 address must contain 16 bytes" }
+    val hex = address.joinToString("") { (it.toInt() and 255).toString(16).padStart(2, '0') }
+    return rows.any { line ->
+        val fields = line.trim().split(Regex("\\s+"), limit = 6)
+        fields.size == 6 && fields[0].equals(hex, ignoreCase = true) && fields[5] == ifName &&
+            fields[4].toIntOrNull(16)?.let { it and 0x20 != 0 } == true
+    }
+}

tools/chatgui-android/app/src/test/java/com/utun/chat/data/InterfaceAddressFlagsTest.kt

@@ -0,0 +1,23 @@
+package com.utun.chat.data
+
+import java.net.InetAddress
+import org.junit.Assert.*
+import org.junit.Test
+
+class InterfaceAddressFlagsTest {
+    @Test fun compressedIpv6MustMatchKernelBytesRatherThanPaddingConcatenatedGroups() {
+        val address = InetAddress.getByName("2001:db8::1234").address
+        assertTrue(temporaryIpv6Address("wlan0", address, sequenceOf("20010db8000000000000000000001234 02 40 00 20 wlan0")))
+    }
+    @Test fun anotherInterfaceCannotMarkTheCurrentAddressTemporary() {
+        val address = InetAddress.getByName("2001:db8::1234").address
+        val rows = listOf("20010db8000000000000000000001234 02 40 00 20 mobile0",
+            "20010db8000000000000000000001234 03 40 00 80 wlan0")
+        assertFalse(temporaryIpv6Address("wlan0", address, rows.asSequence()))
+    }
+    @Test fun stableAddressDoesNotInheritFlagsFromAnotherAddressOnTheSameInterface() {
+        val rows = listOf("20010db8000000000000000000001234 02 40 00 20 wlan0",
+            "20010DB8000000000000000000005678 02 40 00 80 wlan0")
+        assertFalse(temporaryIpv6Address("wlan0", InetAddress.getByName("2001:db8::5678").address, rows.asSequence()))
+    }
+}