fix: make sure to propagate the response when throttling is enabled (#1908)

Change-Id: I690c522aebea03a966155d930bff26042d1bb1f1

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Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://togithub.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: igorbernstein2

google-cloud-bigtable/src/main/java/com/google/cloud/bigtable/data/v2/stub/RateLimitingServerStreamingCallable.java

@@ -127,6 +127,7 @@ protected void onResponseImpl(MutateRowsResponse response) {
               Duration.ofSeconds(com.google.protobuf.util.Durations.toSeconds(info.getPeriod())));
         }
       }
+      outerObserver.onResponse(response);
     }
 
     @Override

google-cloud-bigtable/src/test/java/com/google/cloud/bigtable/data/v2/stub/RateLimitingCallableTest.java

@@ -27,9 +27,13 @@
 import com.google.api.gax.rpc.StreamController;
 import com.google.bigtable.v2.MutateRowsRequest;
 import com.google.bigtable.v2.MutateRowsResponse;
+import com.google.bigtable.v2.Mutation;
 import com.google.bigtable.v2.RateLimitInfo;
 import com.google.cloud.bigtable.gaxx.testing.FakeStatusCode;
+import com.google.protobuf.ByteString;
 import com.google.protobuf.Duration;
+import com.google.rpc.Code;
+import com.google.rpc.Status;
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -138,6 +142,46 @@ public void testErrorInfoLowerQPS() throws Exception {
     assertThat(newQps).isWithin(0.1).of(oldQps * RateLimitingServerStreamingCallable.MIN_FACTOR);
   }
 
+  @Test
+  public void testResponseIsPropagated() {
+    MutateRowsResponse expectedResponse =
+        MutateRowsResponse.newBuilder()
+            .addEntries(
+                MutateRowsResponse.Entry.newBuilder()
+                    .setIndex(0)
+                    .setStatus(Status.newBuilder().setCode(Code.PERMISSION_DENIED_VALUE)))
+            .build();
+    innerCallable =
+        new MockCallable() {
+          @Override
+          public void call(
+              MutateRowsRequest mutateRowsRequest,
+              ResponseObserver<MutateRowsResponse> responseObserver,
+              ApiCallContext apiCallContext) {
+            responseObserver.onResponse(expectedResponse);
+            responseObserver.onComplete();
+          }
+        };
+
+    callableToTest = new RateLimitingServerStreamingCallable(innerCallable);
+
+    ResponseObserver<MutateRowsResponse> mockObserver = Mockito.mock(ResponseObserver.class);
+
+    MutateRowsRequest req =
+        MutateRowsRequest.newBuilder()
+            .addEntries(
+                MutateRowsRequest.Entry.newBuilder()
+                    .setRowKey(ByteString.copyFromUtf8("k1"))
+                    .addMutations(
+                        Mutation.newBuilder()
+                            .setDeleteFromRow(Mutation.DeleteFromRow.getDefaultInstance())))
+            .build();
+
+    callableToTest.call(req, mockObserver, context);
+
+    Mockito.verify(mockObserver, Mockito.times(1)).onResponse(Mockito.eq(expectedResponse));
+  }
+
   private static class MockResponseObserver implements ResponseObserver<MutateRowsResponse> {
 
     private ResponseObserver<MutateRowsResponse> observer;