2 files changed, 39 insertions, 4 deletions
diff --git a/java/src/main/java/com/google/protobuf/nano/MessageNano.java b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
index 82dc6cca5..d6288c928 100644
--- a/java/src/main/java/com/google/protobuf/nano/MessageNano.java
+++ b/java/src/main/java/com/google/protobuf/nano/MessageNano.java
@@ -38,7 +38,7 @@ import java.io.IOException;
  * @author wink@google.com Wink Saville
  */
 public abstract class MessageNano {
-    protected int cachedSize = -1;
+    protected volatile int cachedSize = -1;
 
     /**
      * Get the number of bytes required to encode this message.
@@ -61,9 +61,18 @@ public abstract class MessageNano {
      * using getCachedSize().
      */
     public int getSerializedSize() {
-        // This is overridden if the generated message has serialized fields.
-        cachedSize = 0;
-        return 0;
+        int size = computeSerializedSize();
+        cachedSize = size;
+        return size;
+    }
+
+    /**
+     * Computes the number of bytes required to encode this message. This does not update the
+     * cached size.
+     */
+    protected int computeSerializedSize() {
+      // This is overridden if the generated message has serialized fields.
+      return 0;
     }
 
     /**
diff --git a/java/src/test/java/com/google/protobuf/NanoTest.java b/java/src/test/java/com/google/protobuf/NanoTest.java
index 9987caced..00e2597ed 100644
--- a/java/src/test/java/com/google/protobuf/NanoTest.java
+++ b/java/src/test/java/com/google/protobuf/NanoTest.java
@@ -105,6 +105,12 @@ public class NanoTest extends TestCase {
     assertEquals(456, newMsg.d);
     assertEquals(2, msg.nestedMsg.bb);
     assertEquals(SimpleMessageNano.BAR, msg.defaultNestedEnum);
+
+    msg.nestedMsg = null;
+    assertTrue(msgSerializedSize != msg.getSerializedSize());
+
+    msg.clear();
+    assertEquals(0, msg.getSerializedSize());
   }
 
   public void testRecursiveMessageNano() throws Exception {
@@ -143,6 +149,12 @@ public class NanoTest extends TestCase {
     assertEquals(3, newMsg.repeatedRecursiveMessageNano[0].id);
   }
 
+  public void testMessageNoFields() {
+    SingleMessageNano msg = new SingleMessageNano();
+    assertEquals(0, msg.getSerializedSize());
+    assertEquals(0, MessageNano.toByteArray(msg).length);
+  }
+
   public void testNanoRequiredInt32() throws Exception {
     TestAllTypesNano msg = new TestAllTypesNano();
     msg.id = 123;
@@ -2898,6 +2910,20 @@ public class NanoTest extends TestCase {
     assertTrue(Arrays.equals(enums, message.getExtension(RepeatedExtensions.repeatedEnum)));
   }
 
+  public void testNullExtensions() throws Exception {
+    // Check that clearing the extension on an empty message is a no-op.
+    Extensions.ExtendableMessage message = new Extensions.ExtendableMessage();
+    message.setExtension(SingularExtensions.someMessage, null);
+    assertEquals(0, MessageNano.toByteArray(message).length);
+
+    // Check that the message is empty after setting and clearing an extension.
+    AnotherMessage another = new AnotherMessage();
+    message.setExtension(SingularExtensions.someMessage, another);
+    assertTrue(MessageNano.toByteArray(message).length > 0);
+    message.setExtension(SingularExtensions.someMessage, null);
+    assertEquals(0, MessageNano.toByteArray(message).length);
+  }
+
   public void testUnknownFields() throws Exception {
     // Check that we roundtrip (serialize and deserialize) unrecognized fields.
     AnotherMessage message = new AnotherMessage();