bug5741: backward compatibility for replication protocol, protocol versioning for new protocol

java/com.sap.sse.replication.interfaces/src/com/sap/sse/replication/Replicable.java

@@ -72,6 +72,8 @@ import com.sap.sse.util.ThreadLocalTransporter;
  * {@code REPLICATE_ON_START} variable has its default value defined.</li>
  * </ul>
  * 
+ * The {@link #getId() ID} must be different from {@link ReplicationReceiver#VERSION_INDICATOR}.<p>
+ * 
  * @param <S>
  *            the type of state to which the operations are applied; usually this will be set to the implementing
  *            subclass

java/com.sap.sse.replication.interfaces/src/com/sap/sse/replication/ReplicationReceiver.java

@@ -3,6 +3,12 @@ package com.sap.sse.replication;
 import java.util.Map;
 
 public interface ReplicationReceiver {
+    /**
+     * A string that is sent for new replication protocol versions instead of the stringified {@link Replicable} ID.
+     * That replicable ID is usually a fully-qualified class name. It must not be equal to this version indicator string
+     * which has the value {@code "***"}.
+     */
+    static String VERSION_INDICATOR = "***";
 
     /**
      * If the replicator is suspended, messages received are queued.

java/com.sap.sse.replication.interfaces/src/com/sap/sse/replication/interfaces/impl/AbstractReplicableWithObjectInputStream.java

@@ -15,6 +15,7 @@ import com.sap.sse.replication.OperationsToMasterSender;
 import com.sap.sse.replication.OperationsToMasterSendingQueue;
 import com.sap.sse.replication.ReplicableWithObjectInputStream;
 import com.sap.sse.replication.ReplicationMasterDescriptor;
+import com.sap.sse.replication.ReplicationReceiver;
 import com.sap.sse.replication.ReplicationService;
 import com.sap.sse.util.ClearStateTestSupport;
 import com.sap.sse.util.ObjectInputStreamResolvingAgainstCache;
@@ -92,7 +93,9 @@ public abstract class AbstractReplicableWithObjectInputStream<S, O extends Opera
 
     @Override
     public Serializable getId() {
-        return getClass().getName();
+        final String result = getClass().getName();
+        assert !result.equals(ReplicationReceiver.VERSION_INDICATOR);
+        return result;
     }
 
     @Override