util: Outlier detection tracer delegation (grpc#10459)

OutlierDetectionLoadBalancer did not delegate calls to an existing
ClientStreamTracer from the tracer it installed. This change has the OD
tracer delegate all calls to the underlying one.

core/src/main/java/io/grpc/util/OutlierDetectionLoadBalancer.java

@@ -394,47 +394,55 @@ public PickResult pickSubchannel(PickSubchannelArgs args) {
 
       Subchannel subchannel = pickResult.getSubchannel();
       if (subchannel != null) {
-        return PickResult.withSubchannel(subchannel,
-            new ResultCountingClientStreamTracerFactory(
-                subchannel.getAttributes().get(ADDRESS_TRACKER_ATTR_KEY)));
+        return PickResult.withSubchannel(subchannel, new ResultCountingClientStreamTracerFactory(
+            subchannel.getAttributes().get(ADDRESS_TRACKER_ATTR_KEY),
+            pickResult.getStreamTracerFactory()));
       }
 
       return pickResult;
     }
 
     /**
-     * Builds instances of {@link ResultCountingClientStreamTracer}.
+     * Builds instances of a {@link ClientStreamTracer} that increments the call count in the
+     * tracker for each closed stream.
      */
     class ResultCountingClientStreamTracerFactory extends ClientStreamTracer.Factory {
 
       private final AddressTracker tracker;
 
-      ResultCountingClientStreamTracerFactory(AddressTracker tracker) {
-        this.tracker = tracker;
-      }
-
-      @Override
-      public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata headers) {
-        return new ResultCountingClientStreamTracer(tracker);
-      }
-    }
+      @Nullable
+      private final ClientStreamTracer.Factory delegateFactory;
 
-    /**
-     * Counts the results (successful/unsuccessful) of a particular {@link
-     * OutlierDetectionSubchannel}s streams and increments the counter in the associated {@link
-     * AddressTracker}.
-     */
-    class ResultCountingClientStreamTracer extends ClientStreamTracer {
-
-      AddressTracker tracker;
-
-      public ResultCountingClientStreamTracer(AddressTracker tracker) {
+      ResultCountingClientStreamTracerFactory(AddressTracker tracker,
+          @Nullable ClientStreamTracer.Factory delegateFactory) {
         this.tracker = tracker;
+        this.delegateFactory = delegateFactory;
       }
 
       @Override
-      public void streamClosed(Status status) {
-        tracker.incrementCallCount(status.isOk());
+      public ClientStreamTracer newClientStreamTracer(StreamInfo info, Metadata headers) {
+        if (delegateFactory != null) {
+          ClientStreamTracer delegateTracer = delegateFactory.newClientStreamTracer(info, headers);
+          return new ForwardingClientStreamTracer() {
+            @Override
+            protected ClientStreamTracer delegate() {
+              return delegateTracer;
+            }
+
+            @Override
+            public void streamClosed(Status status) {
+              tracker.incrementCallCount(status.isOk());
+              delegate().streamClosed(status);
+            }
+          };
+        } else {
+          return new ClientStreamTracer() {
+            @Override
+            public void streamClosed(Status status) {
+              tracker.incrementCallCount(status.isOk());
+            }
+          };
+        }
       }
     }
   }

core/src/test/java/io/grpc/util/OutlierDetectionLoadBalancerTest.java

@@ -24,6 +24,7 @@
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
 import static org.mockito.Mockito.when;
 
 import com.google.common.collect.ImmutableList;
@@ -46,6 +47,7 @@
 import io.grpc.LoadBalancer.SubchannelPicker;
 import io.grpc.LoadBalancer.SubchannelStateListener;
 import io.grpc.LoadBalancerProvider;
+import io.grpc.Metadata;
 import io.grpc.Status;
 import io.grpc.SynchronizationContext;
 import io.grpc.internal.FakeClock;
@@ -96,6 +98,10 @@ public class OutlierDetectionLoadBalancerTest {
   private Helper mockHelper;
   @Mock
   private SocketAddress mockSocketAddress;
+  @Mock
+  private ClientStreamTracer.Factory mockStreamTracerFactory;
+  @Mock
+  private ClientStreamTracer mockStreamTracer;
 
   @Captor
   private ArgumentCaptor<ConnectivityState> connectivityStateCaptor;
@@ -193,6 +199,9 @@ public Void answer(InvocationOnMock invocation) throws Throwable {
           }
         });
 
+    when(mockStreamTracerFactory.newClientStreamTracer(any(),
+        any())).thenReturn(mockStreamTracer);
+
     loadBalancer = new OutlierDetectionLoadBalancer(mockHelper, fakeClock.getTimeProvider());
   }
 
@@ -355,6 +364,72 @@ public void delegatePick() throws Exception {
         readySubchannel);
   }
 
+  /**
+   * Any ClientStreamTracer.Factory set by the delegate picker should still get used.
+   */
+  @Test
+  public void delegatePickTracerFactoryPreserved() throws Exception {
+    OutlierDetectionLoadBalancerConfig config = new OutlierDetectionLoadBalancerConfig.Builder()
+        .setSuccessRateEjection(new SuccessRateEjection.Builder().build())
+        .setChildPolicy(new PolicySelection(fakeLbProvider, null)).build();
+
+    loadBalancer.acceptResolvedAddresses(buildResolvedAddress(config, servers.get(0)));
+
+    // Make one of the subchannels READY.
+    final Subchannel readySubchannel = subchannels.values().iterator().next();
+    deliverSubchannelState(readySubchannel, ConnectivityStateInfo.forNonError(READY));
+
+    verify(mockHelper, times(2)).updateBalancingState(stateCaptor.capture(),
+        pickerCaptor.capture());
+
+    // Make sure that we can pick the single READY subchannel.
+    SubchannelPicker picker = pickerCaptor.getAllValues().get(1);
+    PickResult pickResult = picker.pickSubchannel(mock(PickSubchannelArgs.class));
+
+    // Calls to a stream tracer created with the factory in the result should make it to a stream
+    // tracer the underlying LB/picker is using.
+    ClientStreamTracer clientStreamTracer = pickResult.getStreamTracerFactory()
+        .newClientStreamTracer(ClientStreamTracer.StreamInfo.newBuilder().build(), new Metadata());
+    clientStreamTracer.inboundHeaders();
+    // The underlying fake LB provider is configured with a factory that returns a mock stream
+    // tracer.
+    verify(mockStreamTracer).inboundHeaders();
+  }
+
+  /**
+   * Assure the tracer works even when the underlying LB does not have a tracer to delegate to.
+   */
+  @Test
+  public void delegatePickTracerFactoryNotSet() throws Exception {
+    // We set the mock factory to null to indicate that the delegate does not have its own tracer.
+    mockStreamTracerFactory = null;
+
+    OutlierDetectionLoadBalancerConfig config = new OutlierDetectionLoadBalancerConfig.Builder()
+        .setSuccessRateEjection(new SuccessRateEjection.Builder().build())
+        .setChildPolicy(new PolicySelection(fakeLbProvider, null)).build();
+
+    loadBalancer.acceptResolvedAddresses(buildResolvedAddress(config, servers.get(0)));
+
+    // Make one of the subchannels READY.
+    final Subchannel readySubchannel = subchannels.values().iterator().next();
+    deliverSubchannelState(readySubchannel, ConnectivityStateInfo.forNonError(READY));
+
+    verify(mockHelper, times(2)).updateBalancingState(stateCaptor.capture(),
+        pickerCaptor.capture());
+
+    // Make sure that we can pick the single READY subchannel.
+    SubchannelPicker picker = pickerCaptor.getAllValues().get(1);
+    PickResult pickResult = picker.pickSubchannel(mock(PickSubchannelArgs.class));
+
+    // With no delegate tracers factory a call to the OD tracer should still work
+    ClientStreamTracer clientStreamTracer = pickResult.getStreamTracerFactory()
+        .newClientStreamTracer(ClientStreamTracer.StreamInfo.newBuilder().build(), new Metadata());
+    clientStreamTracer.inboundHeaders();
+
+    // Sanity check to make sure the delegate tracer does not get called.
+    verifyNoInteractions(mockStreamTracer);
+  }
+
   /**
    * The success rate algorithm leaves a healthy set of addresses alone.
    */
@@ -1121,7 +1196,7 @@ void assertEjectedSubchannels(Set<SocketAddress> addresses) {
   }
 
   /** Round robin like fake load balancer. */
-  private static final class FakeLoadBalancer extends LoadBalancer {
+  private final class FakeLoadBalancer extends LoadBalancer {
     private final Helper helper;
 
     List<Subchannel> subchannelList;
@@ -1159,7 +1234,8 @@ public PickResult pickSubchannel(PickSubchannelArgs args) {
           if (lastPickIndex < 0 || lastPickIndex > subchannelList.size() - 1) {
             lastPickIndex = 0;
           }
-          return PickResult.withSubchannel(subchannelList.get(lastPickIndex++));
+          return PickResult.withSubchannel(subchannelList.get(lastPickIndex++),
+              mockStreamTracerFactory);
         }
       };
       helper.updateBalancingState(state, picker);