Make address resolution error use the default service config (#11577)

Fixes #11040.

core/src/main/java/io/grpc/internal/ManagedChannelImpl.java

@@ -956,7 +956,15 @@ final class ManagedChannelImpl extends ManagedChannel implements
     // Must run in SynchronizationContext.
     void onConfigError() {
       if (configSelector.get() == INITIAL_PENDING_SELECTOR) {
-        updateConfigSelector(null);
+        // Apply Default Service Config if initial name resolution fails.
+        if (defaultServiceConfig != null) {
+          updateConfigSelector(defaultServiceConfig.getDefaultConfigSelector());
+          lastServiceConfig = defaultServiceConfig;
+          channelLogger.log(ChannelLogLevel.ERROR,
+              "Initial Name Resolution error, using default service config");
+        } else {
+          updateConfigSelector(null);
+        }
       }
     }
 

core/src/test/java/io/grpc/internal/ManagedChannelImplTest.java

@@ -84,6 +84,7 @@ import io.grpc.IntegerMarshaller;
 import io.grpc.InternalChannelz;
 import io.grpc.InternalChannelz.ChannelStats;
 import io.grpc.InternalChannelz.ChannelTrace;
+import io.grpc.InternalChannelz.ChannelTrace.Event.Severity;
 import io.grpc.InternalConfigSelector;
 import io.grpc.InternalInstrumented;
 import io.grpc.LoadBalancer;
@@ -123,6 +124,7 @@ import io.grpc.internal.InternalSubchannel.TransportLogger;
 import io.grpc.internal.ManagedChannelImplBuilder.ClientTransportFactoryBuilder;
 import io.grpc.internal.ManagedChannelImplBuilder.FixedPortProvider;
 import io.grpc.internal.ManagedChannelImplBuilder.UnsupportedClientTransportFactoryBuilder;
+import io.grpc.internal.ManagedChannelServiceConfig.MethodInfo;
 import io.grpc.internal.ServiceConfigUtil.PolicySelection;
 import io.grpc.internal.TestUtils.MockClientTransportInfo;
 import io.grpc.stub.ClientCalls;
@@ -1127,6 +1129,55 @@ public class ManagedChannelImplTest {
     verifyNoMoreInteractions(mockLoadBalancer);
   }
 
+  @Test
+  public void addressResolutionError_noPriorNameResolution_usesDefaultServiceConfig()
+      throws Exception {
+    Map<String, Object> rawServiceConfig =
+        parseConfig("{\"methodConfig\":[{"
+            + "\"name\":[{\"service\":\"service\"}],"
+            + "\"waitForReady\":true}]}");
+    ManagedChannelServiceConfig managedChannelServiceConfig =
+        createManagedChannelServiceConfig(rawServiceConfig, null);
+    FakeNameResolverFactory nameResolverFactory =
+        new FakeNameResolverFactory.Builder(expectedUri)
+            .setServers(Collections.singletonList(new EquivalentAddressGroup(socketAddress)))
+            .setResolvedAtStart(false)
+            .build();
+    nameResolverFactory.nextConfigOrError.set(
+        ConfigOrError.fromConfig(managedChannelServiceConfig));
+    channelBuilder.nameResolverFactory(nameResolverFactory);
+    Map<String, Object> defaultServiceConfig =
+        parseConfig("{\"methodConfig\":[{"
+            + "\"name\":[{\"service\":\"service\"}],"
+            + "\"waitForReady\":true}]}");
+    channelBuilder.defaultServiceConfig(defaultServiceConfig);
+    Status resolutionError = Status.UNAVAILABLE.withDescription("Resolution failed");
+    channelBuilder.maxTraceEvents(10);
+    createChannel();
+    FakeNameResolverFactory.FakeNameResolver resolver = nameResolverFactory.resolvers.get(0);
+
+    resolver.listener.onError(resolutionError);
+
+    InternalConfigSelector configSelector = channel.getConfigSelector();
+    ManagedChannelServiceConfig config =
+        (ManagedChannelServiceConfig) configSelector.selectConfig(null).getConfig();
+    MethodInfo methodConfig = config.getMethodConfig(method);
+    assertThat(methodConfig.waitForReady).isTrue();
+    timer.forwardNanos(1234);
+    assertThat(getStats(channel).channelTrace.events).contains(new ChannelTrace.Event.Builder()
+        .setDescription("Initial Name Resolution error, using default service config")
+        .setSeverity(Severity.CT_ERROR)
+        .setTimestampNanos(0)
+        .build());
+
+    // Check that "lastServiceConfig" variable has been set above: a config resolution with the same
+    // config simply gets ignored and not gets reassigned.
+    resolver.resolved();
+    timer.forwardNanos(1234);
+    assertThat(getStats(channel).channelTrace.events.stream().filter(
+        event -> event.description.equals("Service config changed")).count()).isEqualTo(0);
+  }
+
   @Test
   public void interceptor() throws Exception {
     final AtomicLong atomic = new AtomicLong();
@@ -4595,7 +4646,7 @@ public class ManagedChannelImplTest {
     int size = getStats(channel).channelTrace.events.size();
     assertThat(getStats(channel).channelTrace.events.get(size - 1))
         .isNotEqualTo(new ChannelTrace.Event.Builder()
-            .setDescription("Using default service config")
+            .setDescription("timer.forwardNanos(1234);")
             .setSeverity(ChannelTrace.Event.Severity.CT_INFO)
             .setTimestampNanos(timer.getTicker().read())
             .build());