#20243

Committed 16 Apr 2026 05:25PM UTC coverage: 88.811% (+0.01%) from 88.8%

Build # #20243

Build Type

push

github

Committed by

ejona86

Commit Message

xds: Propagate status cause through XdsDepManager

Often there is no cause, but connect(), channel credentials, and call
credentials failures on the control plane RPC can include a useful
causal exception.

This was triggered by seeing an error like below, but it didn't include
the cause, which would have included HTTP error information from the
failure fetching the credential.
```
UNAVAILABLE: Error retrieving LDS resource xdstp://traffic-director-c2p.xds.googleapis.com/envoy.config.listener.v3.Listener/bigtable.googleapis.com: UNAUTHENTICATED: Failed computing credential metadata nodeID: C2P-798500073
```

Coverage Stats

36019 of 40557 relevant lines covered (88.81%)

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Source File
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91.09

/../xds/src/main/java/io/grpc/xds/XdsDependencyManager.java

/*
 * Copyright 2024 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package io.grpc.xds;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static io.grpc.xds.client.XdsClient.ResourceUpdate;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import io.grpc.EquivalentAddressGroup;
import io.grpc.NameResolver;
import io.grpc.NameResolverProvider;
import io.grpc.Status;
import io.grpc.StatusOr;
import io.grpc.SynchronizationContext;
import io.grpc.internal.GrpcUtil;
import io.grpc.internal.RetryingNameResolver;
import io.grpc.xds.Endpoints.LocalityLbEndpoints;
import io.grpc.xds.VirtualHost.Route.RouteAction.ClusterWeight;
import io.grpc.xds.XdsClusterResource.CdsUpdate.ClusterType;
import io.grpc.xds.XdsConfig.XdsClusterConfig.AggregateConfig;
import io.grpc.xds.XdsConfig.XdsClusterConfig.EndpointConfig;
import io.grpc.xds.XdsRouteConfigureResource.RdsUpdate;
import io.grpc.xds.client.Locality;
import io.grpc.xds.client.XdsClient;
import io.grpc.xds.client.XdsClient.ResourceWatcher;
import io.grpc.xds.client.XdsResourceType;
import java.net.SocketAddress;
import java.net.URI;
import java.net.URISyntaxException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * This class acts as a layer of indirection between the XdsClient and the NameResolver. It
 * maintains the watchers for the xds resources and when an update is received, it either requests
 * referenced resources or updates the XdsConfig and notifies the XdsConfigWatcher.  Each instance
 * applies to a single data plane authority.
 */
final class XdsDependencyManager implements XdsConfig.XdsClusterSubscriptionRegistry {
  private enum TrackedWatcherTypeEnum {
    LDS, RDS, CDS, EDS, DNS
  }

  private static final TrackedWatcherType<XdsListenerResource.LdsUpdate> LDS_TYPE =
      new TrackedWatcherType<>(TrackedWatcherTypeEnum.LDS);
  private static final TrackedWatcherType<RdsUpdate> RDS_TYPE =
      new TrackedWatcherType<>(TrackedWatcherTypeEnum.RDS);
  private static final TrackedWatcherType<XdsClusterResource.CdsUpdate> CDS_TYPE =
      new TrackedWatcherType<>(TrackedWatcherTypeEnum.CDS);
  private static final TrackedWatcherType<XdsEndpointResource.EdsUpdate> EDS_TYPE =
      new TrackedWatcherType<>(TrackedWatcherTypeEnum.EDS);
  private static final TrackedWatcherType<List<EquivalentAddressGroup>> DNS_TYPE =
      new TrackedWatcherType<>(TrackedWatcherTypeEnum.DNS);

  // DNS-resolved endpoints do not have the definition of the locality it belongs to, just hardcode
  // to an empty locality.
  private static final Locality LOGICAL_DNS_CLUSTER_LOCALITY = Locality.create("", "", "");

  private static final int MAX_CLUSTER_RECURSION_DEPTH = 16; // Specified by gRFC A37

  static boolean enableLogicalDns = true;

  private final String listenerName;
  private final XdsClient xdsClient;
  private final SynchronizationContext syncContext;
  private final String dataPlaneAuthority;
  private final NameResolver.Args nameResolverArgs;
  private XdsConfigWatcher xdsConfigWatcher;

  private StatusOr<XdsConfig> lastUpdate = null;
  private final Map<TrackedWatcherTypeEnum, TypeWatchers<?>> resourceWatchers =
      new EnumMap<>(TrackedWatcherTypeEnum.class);
  private final Set<ClusterSubscription> subscriptions = new HashSet<>();

  XdsDependencyManager(
      XdsClient xdsClient,
      SynchronizationContext syncContext,
      String dataPlaneAuthority,
      String listenerName,
      NameResolver.Args nameResolverArgs) {
    this.listenerName = checkNotNull(listenerName, "listenerName");
    this.xdsClient = checkNotNull(xdsClient, "xdsClient");
    this.syncContext = checkNotNull(syncContext, "syncContext");
    this.dataPlaneAuthority = checkNotNull(dataPlaneAuthority, "dataPlaneAuthority");
    this.nameResolverArgs = checkNotNull(nameResolverArgs, "nameResolverArgs");
  }

  public static String toContextStr(String typeName, String resourceName) {
    return typeName + " resource " + resourceName;
  }

  public void start(XdsConfigWatcher xdsConfigWatcher) {
    checkState(this.xdsConfigWatcher == null, "dep manager may not be restarted");
    this.xdsConfigWatcher = checkNotNull(xdsConfigWatcher, "xdsConfigWatcher");
    // start the ball rolling
    syncContext.execute(() -> addWatcher(LDS_TYPE, new LdsWatcher(listenerName)));
  }

  @Override
  public XdsConfig.Subscription subscribeToCluster(String clusterName) {
    checkState(this.xdsConfigWatcher != null, "dep manager must first be started");
    checkNotNull(clusterName, "clusterName");
    ClusterSubscription subscription = new ClusterSubscription(clusterName);

    syncContext.execute(() -> {
      if (getWatchers(LDS_TYPE).isEmpty()) {
        subscription.closed = true;
        return; // shutdown() called
      }
      subscriptions.add(subscription);
      addClusterWatcher(clusterName);
    });

    return subscription;
  }

  /**
   * For all logical dns clusters refresh their results.
   */
  public void requestReresolution() {
    syncContext.execute(() -> {
      for (TrackedWatcher<List<EquivalentAddressGroup>> watcher : getWatchers(DNS_TYPE).values()) {
        DnsWatcher dnsWatcher = (DnsWatcher) watcher;
        dnsWatcher.refresh();
      }
    });
  }

  private <T extends ResourceUpdate> void addWatcher(
      TrackedWatcherType<T> watcherType, XdsWatcherBase<T> watcher) {
    syncContext.throwIfNotInThisSynchronizationContext();
    XdsResourceType<T> type = watcher.type;
    String resourceName = watcher.resourceName;

    getWatchers(watcherType).put(resourceName, watcher);
    xdsClient.watchXdsResource(type, resourceName, watcher, syncContext);
  }

  public void shutdown() {
    syncContext.execute(() -> {
      for (TypeWatchers<?> watchers : resourceWatchers.values()) {
        for (TrackedWatcher<?> watcher : watchers.watchers.values()) {
          watcher.close();
        }
      }
      resourceWatchers.clear();
      subscriptions.clear();
    });
  }

  private void releaseSubscription(ClusterSubscription subscription) {
    checkNotNull(subscription, "subscription");
    syncContext.execute(() -> {
      if (subscription.closed) {
        return;
      }
      subscription.closed = true;
      if (!subscriptions.remove(subscription)) {
        return; // shutdown() called
      }
      maybePublishConfig();
    });
  }

  /**
   * Check if all resources have results, and if so, generate a new XdsConfig and send it to all
   * the watchers.
   */
  private void maybePublishConfig() {
    syncContext.throwIfNotInThisSynchronizationContext();
    if (getWatchers(LDS_TYPE).isEmpty()) {
      return; // shutdown() called
    }
    boolean waitingOnResource = resourceWatchers.values().stream()
        .flatMap(typeWatchers -> typeWatchers.watchers.values().stream())
        .anyMatch(TrackedWatcher::missingResult);
    if (waitingOnResource) {
      return;
    }

    StatusOr<XdsConfig> newUpdate = buildUpdate();
    if (Objects.equals(newUpdate, lastUpdate)) {
      return;
    }
    assert newUpdate.hasValue()
        || (newUpdate.getStatus().getCode() == Status.Code.UNAVAILABLE
            || newUpdate.getStatus().getCode() == Status.Code.INTERNAL);
    lastUpdate = newUpdate;
    xdsConfigWatcher.onUpdate(lastUpdate);
  }

  @VisibleForTesting
  StatusOr<XdsConfig> buildUpdate() {
    // Create a config and discard any watchers not accessed
    WatcherTracer tracer = new WatcherTracer(resourceWatchers);
    StatusOr<XdsConfig> config = buildUpdate(
        tracer, listenerName, dataPlaneAuthority, subscriptions);
    tracer.closeUnusedWatchers();
    return config;
  }

  private static StatusOr<XdsConfig> buildUpdate(
      WatcherTracer tracer,
      String listenerName,
      String dataPlaneAuthority,
      Set<ClusterSubscription> subscriptions) {
    XdsConfig.XdsConfigBuilder builder = new XdsConfig.XdsConfigBuilder();

    // Iterate watchers and build the XdsConfig

    TrackedWatcher<XdsListenerResource.LdsUpdate> ldsWatcher
        = tracer.getWatcher(LDS_TYPE, listenerName);
    if (ldsWatcher == null) {
      return StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
          "Bug: No listener watcher found for " + listenerName));
    }
    if (!ldsWatcher.getData().hasValue()) {
      return StatusOr.fromStatus(ldsWatcher.getData().getStatus());
    }
    XdsListenerResource.LdsUpdate ldsUpdate = ldsWatcher.getData().getValue();
    builder.setListener(ldsUpdate);

    RdsUpdateSupplier routeSource = ((LdsWatcher) ldsWatcher).getRouteSource(tracer);
    if (routeSource == null) {
      return StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
          "Bug: No route source found for listener " + dataPlaneAuthority));
    }
    StatusOr<RdsUpdate> statusOrRdsUpdate = routeSource.getRdsUpdate();
    if (!statusOrRdsUpdate.hasValue()) {
      return StatusOr.fromStatus(statusOrRdsUpdate.getStatus());
    }
    RdsUpdate rdsUpdate = statusOrRdsUpdate.getValue();
    builder.setRoute(rdsUpdate);

    VirtualHost activeVirtualHost =
        RoutingUtils.findVirtualHostForHostName(rdsUpdate.virtualHosts, dataPlaneAuthority);
    if (activeVirtualHost == null) {
      String error = "Failed to find virtual host matching hostname: " + dataPlaneAuthority;
      return StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(error));
    }
    builder.setVirtualHost(activeVirtualHost);

    Map<String, StatusOr<XdsConfig.XdsClusterConfig>> clusters = new HashMap<>();
    LinkedHashSet<String> ancestors = new LinkedHashSet<>();
    for (String cluster : getClusterNamesFromVirtualHost(activeVirtualHost)) {
      addConfigForCluster(clusters, cluster, ancestors, tracer);
    }
    for (ClusterSubscription subscription : subscriptions) {
      addConfigForCluster(clusters, subscription.getClusterName(), ancestors, tracer);
    }
    for (Map.Entry<String, StatusOr<XdsConfig.XdsClusterConfig>> me : clusters.entrySet()) {
      builder.addCluster(me.getKey(), me.getValue());
    }

    return StatusOr.fromValue(builder.build());
  }

  private <T> Map<String, TrackedWatcher<T>> getWatchers(TrackedWatcherType<T> watcherType) {
    TypeWatchers<?> typeWatchers = resourceWatchers.get(watcherType.typeEnum);
    if (typeWatchers == null) {
      typeWatchers = new TypeWatchers<T>(watcherType);
      resourceWatchers.put(watcherType.typeEnum, typeWatchers);
    }
    assert typeWatchers.watcherType == watcherType;
    @SuppressWarnings("unchecked")
    TypeWatchers<T> tTypeWatchers = (TypeWatchers<T>) typeWatchers;
    return tTypeWatchers.watchers;
  }

  private static void addConfigForCluster(
      Map<String, StatusOr<XdsConfig.XdsClusterConfig>> clusters,
      String clusterName,
      @SuppressWarnings("NonApiType") // Need order-preserving set for errors
      LinkedHashSet<String> ancestors,
      WatcherTracer tracer) {
    if (clusters.containsKey(clusterName)) {
      return;
    }
    if (ancestors.contains(clusterName)) {
      clusters.put(clusterName, StatusOr.fromStatus(
          Status.INTERNAL.withDescription(
              "Aggregate cluster cycle detected: " + ancestors)));
      return;
    }
    if (ancestors.size() > MAX_CLUSTER_RECURSION_DEPTH) {
      clusters.put(clusterName, StatusOr.fromStatus(
          Status.INTERNAL.withDescription("Recursion limit reached: " + ancestors)));
      return;
    }

    CdsWatcher cdsWatcher = (CdsWatcher) tracer.getWatcher(CDS_TYPE, clusterName);
    StatusOr<XdsClusterResource.CdsUpdate> cdsWatcherDataOr = cdsWatcher.getData();
    if (!cdsWatcherDataOr.hasValue()) {
      clusters.put(clusterName, StatusOr.fromStatus(cdsWatcherDataOr.getStatus()));
      return;
    }

    XdsClusterResource.CdsUpdate cdsUpdate = cdsWatcherDataOr.getValue();
    XdsConfig.XdsClusterConfig.ClusterChild child;
    switch (cdsUpdate.clusterType()) {
      case AGGREGATE:
        // Re-inserting a present element into a LinkedHashSet does not reorder the entries, so it
        // preserves the priority across all aggregate clusters
        LinkedHashSet<String> leafNames = new LinkedHashSet<String>();
        ancestors.add(clusterName);
        for (String childCluster : cdsUpdate.prioritizedClusterNames()) {
          addConfigForCluster(clusters, childCluster, ancestors, tracer);
          StatusOr<XdsConfig.XdsClusterConfig> config = clusters.get(childCluster);
          if (!config.hasValue()) {
            // gRFC A37 says: If any of a CDS policy's watchers reports that the resource does not
            // exist the policy should report that it is in TRANSIENT_FAILURE. If any of the
            // watchers reports a transient ADS stream error, the policy should report that it is in
            // TRANSIENT_FAILURE if it has never passed a config to its child.
            //
            // But there's currently disagreement about whether that is actually what we want, and
            // that was not originally implemented in gRPC Java. So we're keeping Java's old
            // behavior for now and only failing the "leaves" (which is a bit arbitrary for a
            // cycle).
            leafNames.add(childCluster);
            continue;
          }
          XdsConfig.XdsClusterConfig.ClusterChild children = config.getValue().getChildren();
          if (children instanceof AggregateConfig) {
            leafNames.addAll(((AggregateConfig) children).getLeafNames());
          } else {
            leafNames.add(childCluster);
          }
        }
        ancestors.remove(clusterName);

        child = new AggregateConfig(ImmutableList.copyOf(leafNames));
        break;
      case EDS:
        TrackedWatcher<XdsEndpointResource.EdsUpdate> edsWatcher =
            tracer.getWatcher(EDS_TYPE, cdsWatcher.getEdsServiceName());
        if (edsWatcher != null) {
          child = new EndpointConfig(edsWatcher.getData());
        } else {
          child = new EndpointConfig(StatusOr.fromStatus(Status.INTERNAL.withDescription(
              "EDS resource not found for cluster " + clusterName)));
        }
        break;
      case LOGICAL_DNS:
        if (enableLogicalDns) {
          TrackedWatcher<List<EquivalentAddressGroup>> dnsWatcher =
              tracer.getWatcher(DNS_TYPE, cdsUpdate.dnsHostName());
          child = new EndpointConfig(dnsToEdsUpdate(dnsWatcher.getData(), cdsUpdate.dnsHostName()));
        } else {
          child = new EndpointConfig(StatusOr.fromStatus(
              Status.INTERNAL.withDescription("Logical DNS in dependency manager unsupported")));
        }
        break;
      default:
        child = new EndpointConfig(StatusOr.fromStatus(Status.UNAVAILABLE.withDescription(
              "Unknown type in cluster " + clusterName + " " + cdsUpdate.clusterType())));
    }
    if (clusters.containsKey(clusterName)) {
      // If a cycle is detected, we'll have detected it while recursing, so now there will be a key
      // present. We don't want to overwrite it with a non-error value.
      return;
    }
    clusters.put(clusterName, StatusOr.fromValue(
        new XdsConfig.XdsClusterConfig(clusterName, cdsUpdate, child)));
  }

  private static StatusOr<XdsEndpointResource.EdsUpdate> dnsToEdsUpdate(
      StatusOr<List<EquivalentAddressGroup>> dnsData, String dnsHostName) {
    if (!dnsData.hasValue()) {
      return StatusOr.fromStatus(dnsData.getStatus());
    }

    List<SocketAddress> addresses = new ArrayList<>();
    for (EquivalentAddressGroup eag : dnsData.getValue()) {
      addresses.addAll(eag.getAddresses());
    }
    EquivalentAddressGroup eag = new EquivalentAddressGroup(addresses);
    List<Endpoints.LbEndpoint> endpoints = ImmutableList.of(
        Endpoints.LbEndpoint.create(eag, 1, true, dnsHostName, ImmutableMap.of()));
    LocalityLbEndpoints lbEndpoints =
        LocalityLbEndpoints.create(endpoints, 1, 0, ImmutableMap.of());
    return StatusOr.fromValue(new XdsEndpointResource.EdsUpdate(
        "fakeEds_logicalDns",
        Collections.singletonMap(LOGICAL_DNS_CLUSTER_LOCALITY, lbEndpoints),
        new ArrayList<>()));
  }

  private void addRdsWatcher(String resourceName) {
    if (getWatchers(RDS_TYPE).containsKey(resourceName)) {
      return;
    }

    addWatcher(RDS_TYPE, new RdsWatcher(resourceName));
  }

  private void addEdsWatcher(String edsServiceName) {
    if (getWatchers(EDS_TYPE).containsKey(edsServiceName)) {
      return;
    }

    addWatcher(EDS_TYPE, new EdsWatcher(edsServiceName));
  }

  private void addClusterWatcher(String clusterName) {
    if (getWatchers(CDS_TYPE).containsKey(clusterName)) {
      return;
    }

    addWatcher(CDS_TYPE, new CdsWatcher(clusterName));
  }

  private void addDnsWatcher(String dnsHostName) {
    syncContext.throwIfNotInThisSynchronizationContext();
    if (getWatchers(DNS_TYPE).containsKey(dnsHostName)) {
      return;
    }

    DnsWatcher watcher = new DnsWatcher(dnsHostName, nameResolverArgs);
    getWatchers(DNS_TYPE).put(dnsHostName, watcher);
    watcher.start();
  }

  private void updateRoutes(List<VirtualHost> virtualHosts) {
    VirtualHost virtualHost =
        RoutingUtils.findVirtualHostForHostName(virtualHosts, dataPlaneAuthority);
    Set<String> newClusters = getClusterNamesFromVirtualHost(virtualHost);
    newClusters.forEach((cluster) -> addClusterWatcher(cluster));
  }

  private String nodeInfo() {
    return " nodeID: " + xdsClient.getBootstrapInfo().node().getId();
  }

  private static Set<String> getClusterNamesFromVirtualHost(VirtualHost virtualHost) {
    if (virtualHost == null) {
      return Collections.emptySet();
    }

    // Get all cluster names to which requests can be routed through the virtual host.
    Set<String> clusters = new HashSet<>();
    for (VirtualHost.Route route : virtualHost.routes()) {
      VirtualHost.Route.RouteAction action = route.routeAction();
      if (action == null) {
        continue;
      }
      if (action.cluster() != null) {
        clusters.add(action.cluster());
      } else if (action.weightedClusters() != null) {
        for (ClusterWeight weighedCluster : action.weightedClusters()) {
          clusters.add(weighedCluster.name());
        }
      }
    }

    return clusters;
  }

  private static NameResolver createNameResolver(
      String dnsHostName,
      NameResolver.Args nameResolverArgs) {
    URI uri;
    try {
      uri = new URI("dns", "", "/" + dnsHostName, null);
    } catch (URISyntaxException e) {
      return new FailingNameResolver(
          Status.INTERNAL.withDescription("Bug, invalid URI creation: " + dnsHostName)
            .withCause(e));
    }

    NameResolverProvider provider =
        nameResolverArgs.getNameResolverRegistry().getProviderForScheme("dns");
    if (provider == null) {
      return new FailingNameResolver(
          Status.INTERNAL.withDescription("Could not find dns name resolver"));
    }

    NameResolver bareResolver = provider.newNameResolver(uri, nameResolverArgs);
    if (bareResolver == null) {
      return new FailingNameResolver(
          Status.INTERNAL.withDescription("DNS name resolver provider returned null: " + uri));
    }
    return RetryingNameResolver.wrap(bareResolver, nameResolverArgs);
  }

  private static class TypeWatchers<T> {
    // Key is resource name
    final Map<String, TrackedWatcher<T>> watchers = new HashMap<>();
    final TrackedWatcherType<T> watcherType;

    TypeWatchers(TrackedWatcherType<T> watcherType) {
      this.watcherType = checkNotNull(watcherType, "watcherType");
    }
  }

  public interface XdsConfigWatcher {
    /**
     * An updated XdsConfig or RPC-safe Status. The status code will be either UNAVAILABLE or
     * INTERNAL.
     */
    void onUpdate(StatusOr<XdsConfig> config);
  }

  private final class ClusterSubscription implements XdsConfig.Subscription {
    private final String clusterName;
    boolean closed; // Accessed from syncContext

    public ClusterSubscription(String clusterName) {
      this.clusterName = checkNotNull(clusterName, "clusterName");
    }

    String getClusterName() {
      return clusterName;
    }

    @Override
    public void close() {
      releaseSubscription(this);
    }
  }

  /** State for tracing garbage collector. */
  private static final class WatcherTracer {
    private final Map<TrackedWatcherTypeEnum, TypeWatchers<?>> resourceWatchers;
    private final Map<TrackedWatcherTypeEnum, TypeWatchers<?>> usedWatchers;

    public WatcherTracer(Map<TrackedWatcherTypeEnum, TypeWatchers<?>> resourceWatchers) {
      this.resourceWatchers = resourceWatchers;

      this.usedWatchers = new EnumMap<>(TrackedWatcherTypeEnum.class);
      for (Map.Entry<TrackedWatcherTypeEnum, TypeWatchers<?>> me : resourceWatchers.entrySet()) {
        usedWatchers.put(me.getKey(), newTypeWatchers(me.getValue().watcherType));
      }
    }

    private static <T> TypeWatchers<T> newTypeWatchers(TrackedWatcherType<T> type) {
      return new TypeWatchers<T>(type);
    }

    public <T> TrackedWatcher<T> getWatcher(TrackedWatcherType<T> watcherType, String name) {
      TypeWatchers<?> typeWatchers = resourceWatchers.get(watcherType.typeEnum);
      if (typeWatchers == null) {
        return null;
      }
      assert typeWatchers.watcherType == watcherType;
      @SuppressWarnings("unchecked")
      TypeWatchers<T> tTypeWatchers = (TypeWatchers<T>) typeWatchers;
      TrackedWatcher<T> watcher = tTypeWatchers.watchers.get(name);
      if (watcher == null) {
        return null;
      }
      @SuppressWarnings("unchecked")
      TypeWatchers<T> usedTypeWatchers = (TypeWatchers<T>) usedWatchers.get(watcherType.typeEnum);
      usedTypeWatchers.watchers.put(name, watcher);
      return watcher;
    }

    /** Shut down unused watchers. */
    public void closeUnusedWatchers() {
      boolean changed = false; // Help out the GC by preferring old objects
      for (TrackedWatcherTypeEnum key : resourceWatchers.keySet()) {
        TypeWatchers<?> orig = resourceWatchers.get(key);
        TypeWatchers<?> used = usedWatchers.get(key);
        for (String name : orig.watchers.keySet()) {
          if (used.watchers.containsKey(name)) {
            continue;
          }
          orig.watchers.get(name).close();
          changed = true;
        }
      }
      if (changed) {
        resourceWatchers.putAll(usedWatchers);
      }
    }
  }

  @SuppressWarnings("UnusedTypeParameter")
  private static final class TrackedWatcherType<T> {
    public final TrackedWatcherTypeEnum typeEnum;

    public TrackedWatcherType(TrackedWatcherTypeEnum typeEnum) {
      this.typeEnum = checkNotNull(typeEnum, "typeEnum");
    }
  }

  private interface TrackedWatcher<T> {
    @Nullable
    StatusOr<T> getData();

    default boolean missingResult() {
      return getData() == null;
    }

    default boolean hasDataValue() {
      StatusOr<T> data = getData();
      return data != null && data.hasValue();
    }

    void close();
  }

  private abstract class XdsWatcherBase<T extends ResourceUpdate>
      implements ResourceWatcher<T>, TrackedWatcher<T> {
    private final XdsResourceType<T> type;
    private final String resourceName;
    boolean cancelled;

    @Nullable
    private StatusOr<T> data;
    @Nullable
    @SuppressWarnings("unused")
    private Status ambientError;


    private XdsWatcherBase(XdsResourceType<T> type, String resourceName) {
      this.type = checkNotNull(type, "type");
      this.resourceName = checkNotNull(resourceName, "resourceName");
    }

    @Override
    public void onResourceChanged(StatusOr<T> update) {
      if (cancelled) {
        return;
      }
      ambientError = null;
      if (update.hasValue()) {
        data = update;
        subscribeToChildren(update.getValue());
      } else {
        Status translatedStatus = GrpcUtil.statusWithDetails(
            Status.Code.UNAVAILABLE,
            "Error retrieving " + toContextString() + nodeInfo(),
            update.getStatus());

        data = StatusOr.fromStatus(translatedStatus);
      }
      maybePublishConfig();
    }

    @Override
    public void onAmbientError(Status error) {
      if (cancelled) {
        return;
      }
      ambientError = error.withDescription(
          String.format("Ambient error for %s: %s. Details: %s%s",
              toContextString(),
              error.getCode(),
              error.getDescription() != null ? error.getDescription() : "",
              nodeInfo()));
    }

    protected abstract void subscribeToChildren(T update);

    @Override
    public void close() {
      cancelled = true;
      xdsClient.cancelXdsResourceWatch(type, resourceName, this);
    }

    @Override
    @Nullable
    public StatusOr<T> getData() {
      return data;
    }

    public String toContextString() {
      return toContextStr(type.typeName(), resourceName);
    }
  }

  private interface RdsUpdateSupplier {
    StatusOr<RdsUpdate> getRdsUpdate();
  }

  private class LdsWatcher extends XdsWatcherBase<XdsListenerResource.LdsUpdate>
      implements RdsUpdateSupplier {

    private LdsWatcher(String resourceName) {
      super(XdsListenerResource.getInstance(), resourceName);
    }

    @Override
    public void subscribeToChildren(XdsListenerResource.LdsUpdate update) {
      HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
      List<VirtualHost> virtualHosts;
      if (httpConnectionManager == null) {
        // TCP listener. Unsupported config
        virtualHosts = Collections.emptyList(); // Not null, to not delegate to RDS
      } else {
        virtualHosts = httpConnectionManager.virtualHosts();
      }
      if (virtualHosts != null) {
        updateRoutes(virtualHosts);
      }

      String rdsName = getRdsName(update);
      if (rdsName != null) {
        addRdsWatcher(rdsName);
      }
    }

    private String getRdsName(XdsListenerResource.LdsUpdate update) {
      HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
      if (httpConnectionManager == null) {
        // TCP listener. Unsupported config
        return null;
      }
      return httpConnectionManager.rdsName();
    }

    private RdsWatcher getRdsWatcher(XdsListenerResource.LdsUpdate update, WatcherTracer tracer) {
      String rdsName = getRdsName(update);
      if (rdsName == null) {
        return null;
      }
      return (RdsWatcher) tracer.getWatcher(RDS_TYPE, rdsName);
    }

    public RdsUpdateSupplier getRouteSource(WatcherTracer tracer) {
      if (!hasDataValue()) {
        return this;
      }
      HttpConnectionManager hcm = getData().getValue().httpConnectionManager();
      if (hcm == null) {
        return this;
      }
      List<VirtualHost> virtualHosts = hcm.virtualHosts();
      if (virtualHosts != null) {
        return this;
      }
      RdsWatcher rdsWatcher = getRdsWatcher(getData().getValue(), tracer);
      assert rdsWatcher != null;
      return rdsWatcher;
    }

    @Override
    public StatusOr<RdsUpdate> getRdsUpdate() {
      if (missingResult()) {
        return StatusOr.fromStatus(Status.UNAVAILABLE.withDescription("Not yet loaded"));
      }
      if (!getData().hasValue()) {
        return StatusOr.fromStatus(getData().getStatus());
      }
      HttpConnectionManager hcm = getData().getValue().httpConnectionManager();
      if (hcm == null) {
        return StatusOr.fromStatus(
            Status.UNAVAILABLE.withDescription("Not an API listener" + nodeInfo()));
      }
      List<VirtualHost> virtualHosts = hcm.virtualHosts();
      if (virtualHosts == null) {
        // Code shouldn't trigger this case, as it should be calling RdsWatcher instead. This would
        // be easily implemented with getRdsWatcher().getRdsUpdate(), but getting here is likely a
        // bug
        return StatusOr.fromStatus(Status.INTERNAL.withDescription("Routes are in RDS, not LDS"));
      }
      return StatusOr.fromValue(new RdsUpdate(virtualHosts));
    }
  }

  private class RdsWatcher extends XdsWatcherBase<RdsUpdate> implements RdsUpdateSupplier {

    public RdsWatcher(String resourceName) {
      super(XdsRouteConfigureResource.getInstance(), checkNotNull(resourceName, "resourceName"));
    }

    @Override
    public void subscribeToChildren(RdsUpdate update) {
      updateRoutes(update.virtualHosts);
    }

    @Override
    public StatusOr<RdsUpdate> getRdsUpdate() {
      if (missingResult()) {
        return StatusOr.fromStatus(Status.UNAVAILABLE.withDescription("Not yet loaded"));
      }
      return getData();
    }
  }

  private class CdsWatcher extends XdsWatcherBase<XdsClusterResource.CdsUpdate> {
    CdsWatcher(String resourceName) {
      super(XdsClusterResource.getInstance(), checkNotNull(resourceName, "resourceName"));
    }

    @Override
    public void subscribeToChildren(XdsClusterResource.CdsUpdate update) {
      switch (update.clusterType()) {
        case EDS:
          addEdsWatcher(getEdsServiceName());
          break;
        case LOGICAL_DNS:
          if (enableLogicalDns) {
            addDnsWatcher(update.dnsHostName());
          }
          break;
        case AGGREGATE:
          update.prioritizedClusterNames()
              .forEach(name -> addClusterWatcher(name));
          break;
        default:
      }
    }

    public String getEdsServiceName() {
      XdsClusterResource.CdsUpdate cdsUpdate = getData().getValue();
      assert cdsUpdate.clusterType() == ClusterType.EDS;
      String edsServiceName = cdsUpdate.edsServiceName();
      if (edsServiceName == null) {
        edsServiceName = cdsUpdate.clusterName();
      }
      return edsServiceName;
    }
  }

  private class EdsWatcher extends XdsWatcherBase<XdsEndpointResource.EdsUpdate> {
    private EdsWatcher(String resourceName) {
      super(XdsEndpointResource.getInstance(), checkNotNull(resourceName, "resourceName"));
    }

    @Override
    public void subscribeToChildren(XdsEndpointResource.EdsUpdate update) {}
  }

  private final class DnsWatcher implements TrackedWatcher<List<EquivalentAddressGroup>> {
    private final NameResolver resolver;
    @Nullable
    private StatusOr<List<EquivalentAddressGroup>> data;
    private boolean cancelled;

    public DnsWatcher(String dnsHostName, NameResolver.Args nameResolverArgs) {
      this.resolver = createNameResolver(dnsHostName, nameResolverArgs);
    }

    public void start() {
      resolver.start(new NameResolverListener());
    }

    public void refresh() {
      if (cancelled) {
        return;
      }
      resolver.refresh();
    }

    @Override
    @Nullable
    public StatusOr<List<EquivalentAddressGroup>> getData() {
      return data;
    }

    @Override
    public void close() {
      if (cancelled) {
        return;
      }
      cancelled = true;
      resolver.shutdown();
    }

    private class NameResolverListener extends NameResolver.Listener2 {
      @Override
      public void onResult(final NameResolver.ResolutionResult resolutionResult) {
        syncContext.execute(() -> onResult2(resolutionResult));
      }

      @Override
      public Status onResult2(final NameResolver.ResolutionResult resolutionResult) {
        if (cancelled) {
          return Status.OK;
        }
        data = resolutionResult.getAddressesOrError();
        maybePublishConfig();
        return resolutionResult.getAddressesOrError().getStatus();
      }

      @Override
      public void onError(final Status error) {
        syncContext.execute(new Runnable() {
          @Override
          public void run() {
            if (cancelled) {
              return;
            }
            // DnsNameResolver cannot distinguish between address-not-found and transient errors.
            // Assume it is a transient error.
            // TODO: Once the resolution note API is available, don't throw away the error if
            // hasDataValue(); pass it as the note instead
            if (!hasDataValue()) {
              data = StatusOr.fromStatus(error);
              maybePublishConfig();
            }
          }
        });
      }
    }
  }

  private static final class FailingNameResolver extends NameResolver {
    private final Status status;

    public FailingNameResolver(Status status) {
      checkNotNull(status, "status");
      checkArgument(!status.isOk(), "Status must not be OK");
      this.status = status;
    }

    @Override
    public void start(Listener2 listener) {
      listener.onError(status);
    }

    @Override
    public String getServiceAuthority() {
      return "bug-if-you-see-this-authority";
    }

    @Override
    public void shutdown() {}
  }
}

grpc / grpc-java / #20243

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