Make LinkPropertiesTest pass, and fix an NPE.

aosp/973686 added the DHCP server address to LinkProperties, but
it did not have any tests, and would throw NPE when parceling a
LinkProperties that did not have a DHCP server.

Add tests and fix the bug.

Bug: 134098566
Test: unit test now passes
Change-Id: If28f0be650963e8d9af7eb53f6940824582a2db3

core/java/android/net/LinkProperties.java

@@ -1674,7 +1674,7 @@ public final class LinkProperties implements Parcelable {
         dest.writeString(mPrivateDnsServerName);
         writeAddresses(dest, mPcscfs);
         dest.writeString(mDomains);
-        dest.writeByteArray(mDhcpServerAddress.getAddress());
+        writeAddress(dest, mDhcpServerAddress);
         dest.writeInt(mMtu);
         dest.writeString(mTcpBufferSizes);
         dest.writeInt(mRoutes.size());
@@ -1703,8 +1703,9 @@ public final class LinkProperties implements Parcelable {
         }
     }
 
-    private static void writeAddress(@NonNull Parcel dest, @NonNull InetAddress addr) {
-        dest.writeByteArray(addr.getAddress());
+    private static void writeAddress(@NonNull Parcel dest, @Nullable InetAddress addr) {
+        byte[] addressBytes = (addr == null ? null : addr.getAddress());
+        dest.writeByteArray(addressBytes);
         if (addr instanceof Inet6Address) {
             final Inet6Address v6Addr = (Inet6Address) addr;
             final boolean hasScopeId = v6Addr.getScopeId() != 0;
@@ -1713,9 +1714,11 @@ public final class LinkProperties implements Parcelable {
         }
     }
 
-    @NonNull
+    @Nullable
     private static InetAddress readAddress(@NonNull Parcel p) throws UnknownHostException {
         final byte[] addr = p.createByteArray();
+        if (addr == null) return null;
+
         if (addr.length == INET6_ADDR_LENGTH) {
             final boolean hasScopeId = p.readBoolean();
             final int scopeId = hasScopeId ? p.readInt() : 0;

tests/net/common/java/android/net/LinkPropertiesTest.java

@@ -38,6 +38,7 @@ import androidx.test.runner.AndroidJUnit4;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -65,6 +66,7 @@ public class LinkPropertiesTest {
     private static final InetAddress GATEWAY62 = address("fe80::6:22%lo");
     private static final InetAddress TESTIPV4ADDR = address("192.168.47.42");
     private static final InetAddress TESTIPV6ADDR = address("fe80::7:33%43");
+    private static final Inet4Address DHCPSERVER = (Inet4Address) address("192.0.2.1");
     private static final String NAME = "qmi0";
     private static final String DOMAINS = "google.com";
     private static final String PRIV_DNS_SERVER_NAME = "private.dns.com";
@@ -93,6 +95,7 @@ public class LinkPropertiesTest {
         assertNull(lp.getHttpProxy());
         assertNull(lp.getTcpBufferSizes());
         assertNull(lp.getNat64Prefix());
+        assertNull(lp.getDhcpServerAddress());
         assertFalse(lp.isProvisioned());
         assertFalse(lp.isIpv4Provisioned());
         assertFalse(lp.isIpv6Provisioned());
@@ -119,6 +122,7 @@ public class LinkPropertiesTest {
         lp.setMtu(MTU);
         lp.setTcpBufferSizes(TCP_BUFFER_SIZES);
         lp.setNat64Prefix(new IpPrefix("2001:db8:0:64::/96"));
+        lp.setDhcpServerAddress(DHCPSERVER);
         lp.setWakeOnLanSupported(true);
         return lp;
     }
@@ -960,11 +964,13 @@ public class LinkPropertiesTest {
 
         source.setWakeOnLanSupported(true);
 
+        source.setDhcpServerAddress((Inet4Address) GATEWAY1);
+
         final LinkProperties stacked = new LinkProperties();
         stacked.setInterfaceName("test-stacked");
         source.addStackedLink(stacked);
 
-        assertParcelSane(source, 15 /* fieldCount */);
+        assertParcelSane(source, 16 /* fieldCount */);
     }
 
     @Test
@@ -1090,6 +1096,15 @@ public class LinkPropertiesTest {
         assertFalse(lp.isPrivateDnsActive());
     }
 
+    @Test
+    public void testDhcpServerAddress() {
+        final LinkProperties lp = makeTestObject();
+        assertEquals(DHCPSERVER, lp.getDhcpServerAddress());
+
+        lp.clear();
+        assertNull(lp.getDhcpServerAddress());
+    }
+
     @Test
     public void testWakeOnLanSupported() {
         final LinkProperties lp = makeTestObject();