change consumer to read metadata in blob header for version number

Author: workeatsleep

hollow/src/main/java/com/netflix/hollow/api/client/HollowDataHolder.java

@@ -33,8 +33,12 @@
 import com.netflix.hollow.tools.history.HollowHistoricalStateDataAccess;
 import java.io.IOException;
 import java.lang.ref.WeakReference;
+import java.util.Optional;
+import java.util.OptionalLong;
 import java.util.logging.Logger;
 
+import static com.netflix.hollow.core.HollowStateEngine.HEADER_TAG_PRODUCER_TO_VERSION;
+
 /**
  * A class comprising much of the internal state of a {@link HollowConsumer}.  Not intended for external consumption.
  */
@@ -177,7 +181,21 @@ private void applyStateEngineTransition(HollowBlobInput in, OptionalBlobPartInpu
             reader.applyDelta(in, optionalPartIn);
         }
 
-        setVersion(transition.getToVersion());
+        long expectedToVersion = transition.getToVersion();
+        Long actualToVersion = null;
+        String actualToVersionStr = stateEngine.getHeaderTag(HEADER_TAG_PRODUCER_TO_VERSION);
+        if (actualToVersionStr != null) {
+            actualToVersion = Long.valueOf(actualToVersionStr);
+        }
+
+        if (actualToVersion != null) {
+            if (actualToVersion.longValue() != expectedToVersion) {
+                LOG.warning("toVersion in blob didn't match toVersion seen in metadata; actualToVersion=" + actualToVersion + ", expectedToVersion=" + expectedToVersion);
+            }
+            setVersion(actualToVersion.longValue());
+        } else {
+            setVersion(transition.getToVersion());
+        }
 
         for(HollowConsumer.RefreshListener refreshListener : refreshListeners)
             refreshListener.blobLoaded(transition);

hollow/src/test/java/com/netflix/hollow/api/client/HollowClientUpdaterTest.java

@@ -18,6 +18,7 @@
 
 import static com.netflix.hollow.core.HollowConstants.VERSION_LATEST;
 import static com.netflix.hollow.core.HollowConstants.VERSION_NONE;
+import static com.netflix.hollow.core.HollowStateEngine.HEADER_TAG_PRODUCER_TO_VERSION;
 import static com.netflix.hollow.core.HollowStateEngine.HEADER_TAG_SCHEMA_HASH;
 import static java.util.Collections.emptyList;
 import static org.junit.Assert.assertEquals;
@@ -46,6 +47,7 @@
 import com.netflix.hollow.test.consumer.TestHollowConsumer;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.Optional;
@@ -55,6 +57,8 @@
 import java.util.logging.LogManager;
 import java.util.logging.LogRecord;
 import java.util.logging.Logger;
+
+import org.junit.Assert;
 import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
@@ -98,6 +102,26 @@ public void testUpdateTo_noVersions() throws Throwable {
         assertTrue("Should still have no types", readStateEngine.getAllTypes().isEmpty());
     }
 
+    @Test
+    public void testUpdateTo_updateToLatestButBlobOnDifferentVersion() throws Throwable {
+        long updateToVersion = 1234;
+        long blobToVersion = 1235; //this needs to be different from updateToVersion
+        HollowWriteStateEngine writeStateEngine = new HollowWriteStateEngine();
+        writeStateEngine.addHeaderTag(HEADER_TAG_PRODUCER_TO_VERSION, String.valueOf(blobToVersion));
+        ByteArrayOutputStream os = new ByteArrayOutputStream();
+        new HollowBlobWriter(writeStateEngine).writeSnapshot(os);
+        ByteArrayInputStream is = new ByteArrayInputStream(os.toByteArray());
+        HollowConsumer.Blob blob = mock(HollowConsumer.Blob.class);
+        when(blob.isSnapshot())
+                .thenReturn(true);
+        when(blob.getInputStream())
+                .thenReturn(is);
+        when(retriever.retrieveSnapshotBlob(anyLong()))
+                .thenReturn(blob);
+        subject.updateTo(updateToVersion);
+        Assert.assertEquals(subject.getCurrentVersionId(), blobToVersion);
+    }
+
     @Rule
     public ExpectedException expectedException = ExpectedException.none();