#19793

Committed 23 Apr 2025 04:18PM UTC coverage: 88.641% (+0.003%) from 88.638%

Build # #19793

Build Type

push

github

Committed by

web-flow

Commit Message

xds: XdsDepManager should ignore updates after shutdown

This prevents a NPE and subsequent channel panic when trying to build a
config (because there are no watchers, so waitingOnResource==false)
without any listener and route.
```
java.lang.NullPointerException: Cannot invoke "io.grpc.xds.XdsDependencyManager$RdsUpdateSupplier.getRdsUpdate()" because "routeSource" is null
    at io.grpc.xds.XdsDependencyManager.buildUpdate(XdsDependencyManager.java:295)
    at io.grpc.xds.XdsDependencyManager.maybePublishConfig(XdsDependencyManager.java:266)
    at io.grpc.xds.XdsDependencyManager$EdsWatcher.onChanged(XdsDependencyManager.java:899)
    at io.grpc.xds.XdsDependencyManager$EdsWatcher.onChanged(XdsDependencyManager.java:888)
    at io.grpc.xds.client.XdsClientImpl$ResourceSubscriber.notifyWatcher(XdsClientImpl.java:929)
    at io.grpc.xds.client.XdsClientImpl$ResourceSubscriber.lambda$onData$0(XdsClientImpl.java:837)
    at io.grpc.SynchronizationContext.drain(SynchronizationContext.java:96)
```

I think this fully-fixes the problem today, but not tomorrow.
subscribeToCluster() is racy as well, but not yet used.

This was noticed when idleTimeout was firing, with some other code
calling getState(true) to wake the channel back up. That may have made
this panic more visible than it would be otherwise, but that has not
been investigated.

b/412474567

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91.77

/../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 io.grpc.xds.client.XdsClient.ResourceUpdate;
import static io.grpc.xds.client.XdsLogger.XdsLogLevel.DEBUG;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.collect.Sets;
import io.grpc.InternalLogId;
import io.grpc.NameResolver;
import io.grpc.Status;
import io.grpc.StatusOr;
import io.grpc.SynchronizationContext;
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.XdsClient;
import io.grpc.xds.client.XdsClient.ResourceWatcher;
import io.grpc.xds.client.XdsLogger;
import io.grpc.xds.client.XdsResourceType;
import java.io.Closeable;
import java.io.IOException;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ScheduledExecutorService;
import java.util.stream.Collectors;
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 {
  public static final XdsClusterResource CLUSTER_RESOURCE = XdsClusterResource.getInstance();
  public static final XdsEndpointResource ENDPOINT_RESOURCE = XdsEndpointResource.getInstance();
  private static final int MAX_CLUSTER_RECURSION_DEPTH = 16; // Matches C++
  private final XdsClient xdsClient;
  private final XdsConfigWatcher xdsConfigWatcher;
  private final SynchronizationContext syncContext;
  private final String dataPlaneAuthority;

  private final InternalLogId logId;
  private final XdsLogger logger;
  private StatusOr<XdsConfig> lastUpdate = null;
  private final Map<XdsResourceType<?>, TypeWatchers<?>> resourceWatchers = new HashMap<>();

  XdsDependencyManager(XdsClient xdsClient, XdsConfigWatcher xdsConfigWatcher,
                       SynchronizationContext syncContext, String dataPlaneAuthority,
                       String listenerName, NameResolver.Args nameResolverArgs,
                       ScheduledExecutorService scheduler) {
    logId = InternalLogId.allocate("xds-dependency-manager", listenerName);
    logger = XdsLogger.withLogId(logId);
    this.xdsClient = checkNotNull(xdsClient, "xdsClient");
    this.xdsConfigWatcher = checkNotNull(xdsConfigWatcher, "xdsConfigWatcher");
    this.syncContext = checkNotNull(syncContext, "syncContext");
    this.dataPlaneAuthority = checkNotNull(dataPlaneAuthority, "dataPlaneAuthority");
    checkNotNull(nameResolverArgs, "nameResolverArgs");
    checkNotNull(scheduler, "scheduler");

    // start the ball rolling
    syncContext.execute(() -> addWatcher(new LdsWatcher(listenerName)));
  }

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

  @Override
  public Closeable subscribeToCluster(String clusterName) {

    checkNotNull(clusterName, "clusterName");
    ClusterSubscription subscription = new ClusterSubscription(clusterName);

    syncContext.execute(() -> {
      addClusterWatcher(clusterName, subscription, 1);
      maybePublishConfig();
    });

    return subscription;
  }

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

    @SuppressWarnings("unchecked")
    TypeWatchers<T> typeWatchers = (TypeWatchers<T>)resourceWatchers.get(type);
    if (typeWatchers == null) {
      typeWatchers = new TypeWatchers<>(type);
      resourceWatchers.put(type, typeWatchers);
    }

    typeWatchers.add(resourceName, watcher);
    xdsClient.watchXdsResource(type, resourceName, watcher, syncContext);
  }

  private void cancelCdsWatcher(CdsWatcher watcher, Object parentContext) {
    if (watcher == null) {
      return;
    }
    watcher.parentContexts.remove(parentContext);
    if (watcher.parentContexts.isEmpty()) {
      cancelWatcher(watcher);
    }
  }

  private void cancelEdsWatcher(EdsWatcher watcher, CdsWatcher parentContext) {
    if (watcher == null) {
      return;
    }
    watcher.parentContexts.remove(parentContext);
    if (watcher.parentContexts.isEmpty()) {
      cancelWatcher(watcher);
    }
  }

  private <T extends ResourceUpdate> void cancelWatcher(XdsWatcherBase<T> watcher) {
    syncContext.throwIfNotInThisSynchronizationContext();

    if (watcher == null) {
      return;
    }

    if (watcher instanceof CdsWatcher || watcher instanceof EdsWatcher) {
      throwIfParentContextsNotEmpty(watcher);
    }

    watcher.cancelled = true;
    XdsResourceType<T> type = watcher.type;
    String resourceName = watcher.resourceName;

    @SuppressWarnings("unchecked")
    TypeWatchers<T> typeWatchers = (TypeWatchers<T>)resourceWatchers.get(type);
    if (typeWatchers == null) {
      logger.log(DEBUG, "Trying to cancel watcher {0}, but type not watched", watcher);
      return;
    }

    typeWatchers.watchers.remove(resourceName);
    xdsClient.cancelXdsResourceWatch(type, resourceName, watcher);

  }

  private static void throwIfParentContextsNotEmpty(XdsWatcherBase<?> watcher) {
    if (watcher instanceof CdsWatcher) {
      CdsWatcher cdsWatcher = (CdsWatcher) watcher;
      if (!cdsWatcher.parentContexts.isEmpty()) {
        String msg = String.format("CdsWatcher %s has parent contexts %s",
            cdsWatcher.resourceName(), cdsWatcher.parentContexts.keySet());
        throw new IllegalStateException(msg);
      }
    } else if (watcher instanceof EdsWatcher) {
      EdsWatcher edsWatcher = (EdsWatcher) watcher;
      if (!edsWatcher.parentContexts.isEmpty()) {
        String msg = String.format("CdsWatcher %s has parent contexts %s",
            edsWatcher.resourceName(), edsWatcher.parentContexts);
        throw new IllegalStateException(msg);
      }
    }
  }

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

  private <T extends ResourceUpdate> void shutdownWatchersForType(TypeWatchers<T> watchers) {
    for (Map.Entry<String, XdsWatcherBase<T>> watcherEntry : watchers.watchers.entrySet()) {
      xdsClient.cancelXdsResourceWatch(watchers.resourceType, watcherEntry.getKey(),
          watcherEntry.getValue());
      watcherEntry.getValue().cancelled = true;
    }
  }

  private void releaseSubscription(ClusterSubscription subscription) {
    checkNotNull(subscription, "subscription");
    String clusterName = subscription.getClusterName();
    syncContext.execute(() -> {
      XdsWatcherBase<?> cdsWatcher =
          resourceWatchers.get(CLUSTER_RESOURCE).watchers.get(clusterName);
      if (cdsWatcher == null) {
        return; // already released while waiting for the syncContext
      }
      cancelClusterWatcherTree((CdsWatcher) cdsWatcher, subscription);
      maybePublishConfig();
    });
  }

  private void cancelClusterWatcherTree(CdsWatcher root, Object parentContext) {
    checkNotNull(root, "root");

    cancelCdsWatcher(root, parentContext);

    if (!root.hasDataValue() || !root.parentContexts.isEmpty()) {
      return;
    }

    XdsClusterResource.CdsUpdate cdsUpdate = root.getData().getValue();
    switch (cdsUpdate.clusterType()) {
      case EDS:
        String edsServiceName = root.getEdsServiceName();
        EdsWatcher edsWatcher =
            (EdsWatcher) resourceWatchers.get(ENDPOINT_RESOURCE).watchers.get(edsServiceName);
        cancelEdsWatcher(edsWatcher, root);
        break;
      case AGGREGATE:
        for (String cluster : cdsUpdate.prioritizedClusterNames()) {
          CdsWatcher clusterWatcher =
              (CdsWatcher) resourceWatchers.get(CLUSTER_RESOURCE).watchers.get(cluster);
          if (clusterWatcher != null) {
            cancelClusterWatcherTree(clusterWatcher, root);
          }
        }
        break;
      case LOGICAL_DNS:
        // no eds needed, so everything happens in cancelCdsWatcher()
        break;
      default:
        throw new AssertionError("Unknown cluster type: " + cdsUpdate.clusterType());
    }
  }

  /**
   * 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();
    boolean waitingOnResource = resourceWatchers.values().stream()
        .flatMap(typeWatchers -> typeWatchers.watchers.values().stream())
        .anyMatch(XdsWatcherBase::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() {
    XdsConfig.XdsConfigBuilder builder = new XdsConfig.XdsConfigBuilder();

    // Iterate watchers and build the XdsConfig

    // Will only be 1 listener and 1 route resource
    RdsUpdateSupplier routeSource = null;
    for (XdsWatcherBase<XdsListenerResource.LdsUpdate> ldsWatcher :
        getWatchers(XdsListenerResource.getInstance()).values()) {
      if (!ldsWatcher.getData().hasValue()) {
        return StatusOr.fromStatus(ldsWatcher.getData().getStatus());
      }
      XdsListenerResource.LdsUpdate ldsUpdate = ldsWatcher.getData().getValue();
      builder.setListener(ldsUpdate);
      routeSource = ((LdsWatcher) ldsWatcher).getRouteSource();
    }

    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, XdsWatcherBase<XdsEndpointResource.EdsUpdate>> edsWatchers =
        getWatchers(ENDPOINT_RESOURCE);
    Map<String, XdsWatcherBase<XdsClusterResource.CdsUpdate>> cdsWatchers =
        getWatchers(CLUSTER_RESOURCE);

    // Only care about aggregates from LDS/RDS or subscriptions and the leaf clusters
    List<String> topLevelClusters =
        cdsWatchers.values().stream()
            .filter(XdsDependencyManager::isTopLevelCluster)
            .map(XdsWatcherBase<?>::resourceName)
            .distinct()
            .collect(Collectors.toList());

    // Flatten multi-level aggregates into lists of leaf clusters
    Set<String> leafNames =
        addTopLevelClustersToBuilder(builder, edsWatchers, cdsWatchers, topLevelClusters);

    addLeavesToBuilder(builder, edsWatchers, leafNames);

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

  private <T extends ResourceUpdate> Map<String, XdsWatcherBase<T>> getWatchers(
      XdsResourceType<T> resourceType) {
    TypeWatchers<?> typeWatchers = resourceWatchers.get(resourceType);
    if (typeWatchers == null) {
      return Collections.emptyMap();
    }
    assert typeWatchers.resourceType == resourceType;
    @SuppressWarnings("unchecked")
    TypeWatchers<T> tTypeWatchers = (TypeWatchers<T>) typeWatchers;
    return tTypeWatchers.watchers;
  }

  private void addLeavesToBuilder(
      XdsConfig.XdsConfigBuilder builder,
      Map<String, XdsWatcherBase<XdsEndpointResource.EdsUpdate>> edsWatchers,
      Set<String> leafNames) {
    for (String clusterName : leafNames) {
      CdsWatcher cdsWatcher = getCluster(clusterName);
      StatusOr<XdsClusterResource.CdsUpdate> cdsUpdateOr = cdsWatcher.getData();

      if (!cdsUpdateOr.hasValue()) {
        builder.addCluster(clusterName, StatusOr.fromStatus(cdsUpdateOr.getStatus()));
        continue;
      }

      XdsClusterResource.CdsUpdate cdsUpdate = cdsUpdateOr.getValue();
      if (cdsUpdate.clusterType() == ClusterType.EDS) {
        XdsWatcherBase<XdsEndpointResource.EdsUpdate> edsWatcher =
            edsWatchers.get(cdsWatcher.getEdsServiceName());
        EndpointConfig child;
        if (edsWatcher != null) {
          child = new EndpointConfig(edsWatcher.getData());
        } else {
          child = new EndpointConfig(StatusOr.fromStatus(Status.INTERNAL.withDescription(
              "EDS resource not found for cluster " + clusterName)));
        }
        builder.addCluster(clusterName, StatusOr.fromValue(
            new XdsConfig.XdsClusterConfig(clusterName, cdsUpdate, child)));
      } else if (cdsUpdate.clusterType() == ClusterType.LOGICAL_DNS) {
        builder.addCluster(clusterName, StatusOr.fromStatus(
            Status.INTERNAL.withDescription("Logical DNS in dependency manager unsupported")));
      }
    }
  }

  // Adds the top-level clusters to the builder and returns the leaf cluster names
  private Set<String> addTopLevelClustersToBuilder(
      XdsConfig.XdsConfigBuilder builder,
      Map<String, XdsWatcherBase<XdsEndpointResource.EdsUpdate>> edsWatchers,
      Map<String, XdsWatcherBase<XdsClusterResource.CdsUpdate>> cdsWatchers,
      List<String> topLevelClusters) {

    Set<String> leafClusterNames = new HashSet<>();
    for (String clusterName : topLevelClusters) {
      CdsWatcher cdsWatcher = (CdsWatcher) cdsWatchers.get(clusterName);
      StatusOr<XdsClusterResource.CdsUpdate> cdsWatcherDataOr = cdsWatcher.getData();
      if (!cdsWatcher.hasDataValue()) {
        builder.addCluster(clusterName, StatusOr.fromStatus(cdsWatcherDataOr.getStatus()));
        continue;
      }

      XdsClusterResource.CdsUpdate cdsUpdate = cdsWatcherDataOr.getValue();
      XdsConfig.XdsClusterConfig.ClusterChild child;
      switch (cdsUpdate.clusterType()) {
        case AGGREGATE:
          Set<String> leafNames = new HashSet<>();
          addLeafNames(leafNames, cdsUpdate);
          child = new AggregateConfig(leafNames);
          leafClusterNames.addAll(leafNames);
          break;
        case EDS:
          XdsWatcherBase<XdsEndpointResource.EdsUpdate> edsWatcher =
              edsWatchers.get(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:
          // TODO get the resolved endpoint configuration
          child = new EndpointConfig(StatusOr.fromStatus(
              Status.INTERNAL.withDescription("Logical DNS in dependency manager unsupported")));
          break;
        default:
          throw new IllegalStateException("Unexpected value: " + cdsUpdate.clusterType());
      }
      builder.addCluster(clusterName, StatusOr.fromValue(
          new XdsConfig.XdsClusterConfig(clusterName, cdsUpdate, child)));
    }

    return leafClusterNames;
  }

  private void addLeafNames(Set<String> leafNames, XdsClusterResource.CdsUpdate cdsUpdate) {
    for (String cluster : cdsUpdate.prioritizedClusterNames()) {
      if (leafNames.contains(cluster)) {
        continue;
      }
      StatusOr<XdsClusterResource.CdsUpdate> data = getCluster(cluster).getData();
      if (data == null || !data.hasValue() || data.getValue() == null) {
        leafNames.add(cluster);
        continue;
      }
      if (data.getValue().clusterType() == ClusterType.AGGREGATE) {
        addLeafNames(leafNames, data.getValue());
      } else {
        leafNames.add(cluster);
      }
    }
  }

  private static boolean isTopLevelCluster(
      XdsWatcherBase<XdsClusterResource.CdsUpdate> cdsWatcher) {
    return ((CdsWatcher)cdsWatcher).parentContexts.values().stream()
        .anyMatch(depth -> depth == 1);
  }

  @Override
  public String toString() {
    return logId.toString();
  }

  // Returns true if the watcher was added, false if it already exists
  private boolean addEdsWatcher(String edsServiceName, CdsWatcher parentContext) {
    TypeWatchers<?> typeWatchers = resourceWatchers.get(XdsEndpointResource.getInstance());
    if (typeWatchers == null || !typeWatchers.watchers.containsKey(edsServiceName)) {
      addWatcher(new EdsWatcher(edsServiceName, parentContext));
      return true;
    }

    EdsWatcher watcher = (EdsWatcher) typeWatchers.watchers.get(edsServiceName);
    watcher.addParentContext(parentContext); // Is a set, so don't need to check for existence
    return false;
  }

  private void addClusterWatcher(String clusterName, Object parentContext, int depth) {
    TypeWatchers<?> clusterWatchers = resourceWatchers.get(CLUSTER_RESOURCE);
    if (clusterWatchers != null) {
      CdsWatcher watcher = (CdsWatcher) clusterWatchers.watchers.get(clusterName);
      if (watcher != null) {
        watcher.parentContexts.put(parentContext, depth);
        return;
      }
    }

    addWatcher(new CdsWatcher(clusterName, parentContext, depth));
  }

  private void updateRoutes(List<VirtualHost> virtualHosts, Object newParentContext,
                            List<VirtualHost> oldVirtualHosts, boolean sameParentContext) {
    VirtualHost oldVirtualHost =
        RoutingUtils.findVirtualHostForHostName(oldVirtualHosts, dataPlaneAuthority);
    VirtualHost virtualHost =
        RoutingUtils.findVirtualHostForHostName(virtualHosts, dataPlaneAuthority);

    Set<String> newClusters = getClusterNamesFromVirtualHost(virtualHost);
    Set<String> oldClusters = getClusterNamesFromVirtualHost(oldVirtualHost);

    if (sameParentContext) {
      // Calculate diffs.
      Set<String> addedClusters = Sets.difference(newClusters, oldClusters);
      Set<String> deletedClusters = Sets.difference(oldClusters, newClusters);

      deletedClusters.forEach(watcher ->
          cancelClusterWatcherTree(getCluster(watcher), newParentContext));
      addedClusters.forEach((cluster) -> addClusterWatcher(cluster, newParentContext, 1));
    } else {
      newClusters.forEach((cluster) -> addClusterWatcher(cluster, newParentContext, 1));
    }
  }

  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 CdsWatcher getCluster(String clusterName) {
    return (CdsWatcher) resourceWatchers.get(CLUSTER_RESOURCE).watchers.get(clusterName);
  }

  private static class TypeWatchers<T extends ResourceUpdate> {
    // Key is resource name
    final Map<String, XdsWatcherBase<T>> watchers = new HashMap<>();
    final XdsResourceType<T> resourceType;

    TypeWatchers(XdsResourceType<T> resourceType) {
      this.resourceType = resourceType;
    }

    public void add(String resourceName, XdsWatcherBase<T> watcher) {
      watchers.put(resourceName, watcher);
    }
  }

  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 class ClusterSubscription implements Closeable {
    String clusterName;

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

    public String getClusterName() {
      return clusterName;
    }

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

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

    @Nullable
    private StatusOr<T> data;


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

    @Override
    public void onError(Status error) {
      checkNotNull(error, "error");
      if (cancelled) {
        return;
      }
      // Don't update configuration on error, if we've already received configuration
      if (!hasDataValue()) {
        setDataAsStatus(Status.UNAVAILABLE.withDescription(
            String.format("Error retrieving %s: %s: %s",
              toContextString(), error.getCode(), error.getDescription())));
        maybePublishConfig();
      }
    }

    @Override
    public void onResourceDoesNotExist(String resourceName) {
      if (cancelled) {
        return;
      }

      checkArgument(this.resourceName.equals(resourceName), "Resource name does not match");
      setDataAsStatus(Status.UNAVAILABLE.withDescription(
          toContextString() + " does not exist" + nodeInfo()));
      maybePublishConfig();
    }

    boolean missingResult() {
      return data == null;
    }

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

    boolean hasDataValue() {
      return data != null && data.hasValue();
    }

    String resourceName() {
      return resourceName;
    }

    protected void setData(T data) {
      checkNotNull(data, "data");
      this.data = StatusOr.fromValue(data);
    }

    protected void setDataAsStatus(Status status) {
      checkNotNull(status, "status");
      this.data = StatusOr.fromStatus(status);
    }

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

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

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

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

    @Override
    public void onChanged(XdsListenerResource.LdsUpdate update) {
      checkNotNull(update, "update");
      if (cancelled) {
        return;
      }

      HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
      List<VirtualHost> virtualHosts;
      String rdsName;
      if (httpConnectionManager == null) {
        // TCP listener. Unsupported config
        virtualHosts = Collections.emptyList(); // Not null, to not delegate to RDS
        rdsName = null;
      } else {
        virtualHosts = httpConnectionManager.virtualHosts();
        rdsName = httpConnectionManager.rdsName();
      }
      StatusOr<RdsUpdate> activeRdsUpdate = getRouteSource().getRdsUpdate();
      List<VirtualHost> activeVirtualHosts = activeRdsUpdate.hasValue()
          ? activeRdsUpdate.getValue().virtualHosts
          : Collections.emptyList();

      boolean changedRdsName = !Objects.equals(rdsName, this.rdsName);
      if (changedRdsName) {
        cleanUpRdsWatcher();
      }

      if (virtualHosts != null) {
        // No RDS watcher since we are getting RDS updates via LDS
        updateRoutes(virtualHosts, this, activeVirtualHosts, this.rdsName == null);
        this.rdsName = null;
      } else if (changedRdsName) {
        this.rdsName = rdsName;
        addWatcher(new RdsWatcher(rdsName));
        logger.log(XdsLogger.XdsLogLevel.INFO, "Start watching RDS resource {0}", rdsName);
      }

      setData(update);
      maybePublishConfig();
    }

    @Override
    public void onResourceDoesNotExist(String resourceName) {
      if (cancelled) {
        return;
      }

      checkArgument(resourceName().equals(resourceName), "Resource name does not match");
      setDataAsStatus(Status.UNAVAILABLE.withDescription(
          toContextString() + " does not exist" + nodeInfo()));
      cleanUpRdsWatcher();
      rdsName = null;
      maybePublishConfig();
    }

    private void cleanUpRdsWatcher() {
      RdsWatcher oldRdsWatcher = getRdsWatcher();
      if (oldRdsWatcher != null) {
        cancelWatcher(oldRdsWatcher);
        logger.log(XdsLogger.XdsLogLevel.DEBUG, "Stop watching RDS resource {0}", rdsName);

        // Cleanup clusters (as appropriate) that had the old rds watcher as a parent
        if (!oldRdsWatcher.hasDataValue() || resourceWatchers.get(CLUSTER_RESOURCE) == null) {
          return;
        }
        for (XdsWatcherBase<?> watcher :
            resourceWatchers.get(CLUSTER_RESOURCE).watchers.values()) {
          cancelCdsWatcher((CdsWatcher) watcher, oldRdsWatcher);
        }
      }
    }

    private RdsWatcher getRdsWatcher() {
      if (rdsName == null) {
        return null;
      }
      TypeWatchers<?> watchers = resourceWatchers.get(XdsRouteConfigureResource.getInstance());
      if (watchers == null) {
        return null;
      }
      return (RdsWatcher) watchers.watchers.get(rdsName);
    }

    public RdsUpdateSupplier getRouteSource() {
      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();
      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 onChanged(RdsUpdate update) {
      checkNotNull(update, "update");
      if (cancelled) {
        return;
      }
      List<VirtualHost> oldVirtualHosts = hasDataValue()
          ? getData().getValue().virtualHosts
          : Collections.emptyList();
      setData(update);
      updateRoutes(update.virtualHosts, this, oldVirtualHosts, true);
      maybePublishConfig();
    }

    @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> {
    Map<Object, Integer> parentContexts = new HashMap<>();

    CdsWatcher(String resourceName, Object parentContext, int depth) {
      super(CLUSTER_RESOURCE, checkNotNull(resourceName, "resourceName"));
      this.parentContexts.put(checkNotNull(parentContext, "parentContext"), depth);
    }

    @Override
    public void onChanged(XdsClusterResource.CdsUpdate update) {
      checkNotNull(update, "update");
      if (cancelled) {
        return;
      }
      switch (update.clusterType()) {
        case EDS:
          setData(update);
          if (!addEdsWatcher(getEdsServiceName(), this))  {
            maybePublishConfig();
          }
          break;
        case LOGICAL_DNS:
          setData(update);
          maybePublishConfig();
          // no eds needed
          break;
        case AGGREGATE:
          Object parentContext = this;
          int depth = parentContexts.values().stream().max(Integer::compare).orElse(0) + 1;
          if (depth > MAX_CLUSTER_RECURSION_DEPTH) {
            logger.log(XdsLogger.XdsLogLevel.WARNING,
                "Cluster recursion depth limit exceeded for cluster {0}", resourceName());
            Status error = Status.UNAVAILABLE.withDescription(
                "aggregate cluster graph exceeds max depth at " + resourceName() + nodeInfo());
            setDataAsStatus(error);
          }
          if (hasDataValue()) {
            Set<String> oldNames = getData().getValue().clusterType() == ClusterType.AGGREGATE
                ? new HashSet<>(getData().getValue().prioritizedClusterNames())
                : Collections.emptySet();
            Set<String> newNames = new HashSet<>(update.prioritizedClusterNames());

            Set<String> deletedClusters = Sets.difference(oldNames, newNames);
            deletedClusters.forEach((cluster)
                -> cancelClusterWatcherTree(getCluster(cluster), parentContext));

            if (depth <= MAX_CLUSTER_RECURSION_DEPTH) {
              setData(update);
              Set<String> addedClusters = Sets.difference(newNames, oldNames);
              addedClusters.forEach((cluster) -> addClusterWatcher(cluster, parentContext, depth));

              if (addedClusters.isEmpty()) {
                maybePublishConfig();
              }
            } else { // data was set to error status above
              maybePublishConfig();
            }

          } else if (depth <= MAX_CLUSTER_RECURSION_DEPTH) {
            setData(update);
            update.prioritizedClusterNames()
                .forEach(name -> addClusterWatcher(name, parentContext, depth));
            maybePublishConfig();
          }
          break;
        default:
          Status error = Status.UNAVAILABLE.withDescription(
              "aggregate cluster graph exceeds max depth at " + resourceName() + nodeInfo());
          setDataAsStatus(error);
          maybePublishConfig();
      }
    }

    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 final Set<CdsWatcher> parentContexts = new HashSet<>();

    private EdsWatcher(String resourceName, CdsWatcher parentContext) {
      super(ENDPOINT_RESOURCE, checkNotNull(resourceName, "resourceName"));
      parentContexts.add(checkNotNull(parentContext, "parentContext"));
    }

    @Override
    public void onChanged(XdsEndpointResource.EdsUpdate update) {
      if (cancelled) {
        return;
      }
      setData(checkNotNull(update, "update"));
      maybePublishConfig();
    }

    void addParentContext(CdsWatcher parentContext) {
      parentContexts.add(checkNotNull(parentContext, "parentContext"));
    }
  }
}

grpc / grpc-java / #19793

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