Add IPv6 link-local address generation from EUI-48

Add a utility method to convert an EUI-48 to an IPv6 link-local
address based on RFC 4291 (EUI-64 generation) followed by RFC 4862.

Bug: 117605977
Test: atest MacAddressTest
Merged-In: I80b683e69da6beff3b37fc345fc15aa9610d09b7
Change-Id: I80b683e69da6beff3b37fc345fc15aa9610d09b7

core/java/android/net/MacAddress.java

@@ -18,6 +18,7 @@ package android.net;
 
 import android.annotation.IntDef;
 import android.annotation.NonNull;
+import android.annotation.Nullable;
 import android.annotation.UnsupportedAppUsage;
 import android.os.Parcel;
 import android.os.Parcelable;
@@ -27,6 +28,8 @@ import com.android.internal.util.Preconditions;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.net.Inet6Address;
+import java.net.UnknownHostException;
 import java.security.SecureRandom;
 import java.util.Arrays;
 import java.util.Random;
@@ -393,4 +396,34 @@ public final class MacAddress implements Parcelable {
         }
         return out;
     }
+
+    /**
+     * Create a link-local Inet6Address from the MAC address. The EUI-48 MAC address is converted
+     * to an EUI-64 MAC address per RFC 4291. The resulting EUI-64 is used to construct a link-local
+     * IPv6 address per RFC 4862.
+     *
+     * @return A link-local Inet6Address constructed from the MAC address.
+     * @hide
+     */
+    public @Nullable Inet6Address getLinkLocalIpv6FromEui48Mac() {
+        byte[] macEui48Bytes = toByteArray();
+        byte[] addr = new byte[16];
+
+        addr[0] = (byte) 0xfe;
+        addr[1] = (byte) 0x80;
+        addr[8] = (byte) (macEui48Bytes[0] ^ (byte) 0x02); // flip the link-local bit
+        addr[9] = macEui48Bytes[1];
+        addr[10] = macEui48Bytes[2];
+        addr[11] = (byte) 0xff;
+        addr[12] = (byte) 0xfe;
+        addr[13] = macEui48Bytes[3];
+        addr[14] = macEui48Bytes[4];
+        addr[15] = macEui48Bytes[5];
+
+        try {
+            return Inet6Address.getByAddress(null, addr, 0);
+        } catch (UnknownHostException e) {
+            return null;
+        }
+    }
 }

tests/net/java/android/net/MacAddressTest.java

@@ -16,6 +16,7 @@
 
 package android.net;
 
+import static org.junit.Assert.assertArrayEquals;
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertFalse;
@@ -24,12 +25,13 @@ import static org.junit.Assert.fail;
 import android.support.test.filters.SmallTest;
 import android.support.test.runner.AndroidJUnit4;
 
-import java.util.Arrays;
-import java.util.Random;
-
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import java.net.Inet6Address;
+import java.util.Arrays;
+import java.util.Random;
+
 @SmallTest
 @RunWith(AndroidJUnit4.class)
 public class MacAddressTest {
@@ -252,6 +254,19 @@ public class MacAddressTest {
         }
     }
 
+    /**
+     * Tests that link-local address generation from MAC is valid.
+     */
+    @Test
+    public void testLinkLocalFromMacGeneration() {
+        MacAddress mac = MacAddress.fromString("52:74:f2:b1:a8:7f");
+        byte[] inet6ll = {(byte) 0xfe, (byte) 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50, 0x74,
+            (byte) 0xf2, (byte) 0xff, (byte) 0xfe, (byte) 0xb1, (byte) 0xa8, 0x7f};
+        Inet6Address llv6 = mac.getLinkLocalIpv6FromEui48Mac();
+        assertTrue(llv6.isLinkLocalAddress());
+        assertArrayEquals(inet6ll, llv6.getAddress());
+    }
+
     static byte[] toByteArray(int... in) {
         byte[] out = new byte[in.length];
         for (int i = 0; i < in.length; i++) {