#19678

Committed 05 Feb 2025 06:37PM UTC coverage: 88.566% (-0.03%) from 88.592%

Build # #19678

Build Type

push

github

Committed by

web-flow

Commit Message

xds: Improve XdsNR's selectConfig() variable handling

The variables from the do-while are no longer initialized to let the
compiler verify that the loop sets each. Unnecessary comparisons to null
are also removed and is more obvious as the variables are never set to
null. Added a minor optimization of computing the RPCs path once instead
of once for each route. The variable declarations were also sorted to
match their initialization order.

This does fix an unlikely bug where if the old code could successfully
matched a route but fail to retain the cluster, then when trying a
second time if the route was _not_ matched it would re-use the prior route
and thus infinite-loop failing to retain that same cluster.

It also adds a missing cast to unsigned long for a uint32 weight. The old
code would detect if the _sum_ was negative, but a weight using 32 bits
would have been negative and never selected.

Run Details

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94.98

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

/*
 * Copyright 2019 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.Bootstrapper.XDSTP_SCHEME;

import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Joiner;
import com.google.common.base.Strings;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.Sets;
import com.google.gson.Gson;
import com.google.protobuf.util.Durations;
import io.grpc.Attributes;
import io.grpc.CallOptions;
import io.grpc.Channel;
import io.grpc.ClientCall;
import io.grpc.ClientInterceptor;
import io.grpc.ClientInterceptors;
import io.grpc.ForwardingClientCall.SimpleForwardingClientCall;
import io.grpc.ForwardingClientCallListener.SimpleForwardingClientCallListener;
import io.grpc.InternalConfigSelector;
import io.grpc.InternalLogId;
import io.grpc.LoadBalancer.PickSubchannelArgs;
import io.grpc.Metadata;
import io.grpc.MethodDescriptor;
import io.grpc.MetricRecorder;
import io.grpc.NameResolver;
import io.grpc.Status;
import io.grpc.Status.Code;
import io.grpc.SynchronizationContext;
import io.grpc.internal.GrpcUtil;
import io.grpc.internal.ObjectPool;
import io.grpc.xds.ClusterSpecifierPlugin.PluginConfig;
import io.grpc.xds.Filter.ClientInterceptorBuilder;
import io.grpc.xds.Filter.FilterConfig;
import io.grpc.xds.Filter.NamedFilterConfig;
import io.grpc.xds.RouteLookupServiceClusterSpecifierPlugin.RlsPluginConfig;
import io.grpc.xds.ThreadSafeRandom.ThreadSafeRandomImpl;
import io.grpc.xds.VirtualHost.Route;
import io.grpc.xds.VirtualHost.Route.RouteAction;
import io.grpc.xds.VirtualHost.Route.RouteAction.ClusterWeight;
import io.grpc.xds.VirtualHost.Route.RouteAction.HashPolicy;
import io.grpc.xds.VirtualHost.Route.RouteAction.RetryPolicy;
import io.grpc.xds.VirtualHost.Route.RouteMatch;
import io.grpc.xds.XdsNameResolverProvider.CallCounterProvider;
import io.grpc.xds.XdsRouteConfigureResource.RdsUpdate;
import io.grpc.xds.client.Bootstrapper.AuthorityInfo;
import io.grpc.xds.client.Bootstrapper.BootstrapInfo;
import io.grpc.xds.client.XdsClient;
import io.grpc.xds.client.XdsClient.ResourceWatcher;
import io.grpc.xds.client.XdsLogger;
import io.grpc.xds.client.XdsLogger.XdsLogLevel;
import java.net.URI;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.atomic.AtomicInteger;
import javax.annotation.Nullable;

/**
 * A {@link NameResolver} for resolving gRPC target names with "xds:" scheme.
 *
 * <p>Resolving a gRPC target involves contacting the control plane management server via xDS
 * protocol to retrieve service information and produce a service config to the caller.
 *
 * @see XdsNameResolverProvider
 */
final class XdsNameResolver extends NameResolver {

  static final CallOptions.Key<String> CLUSTER_SELECTION_KEY =
      CallOptions.Key.create("io.grpc.xds.CLUSTER_SELECTION_KEY");
  static final CallOptions.Key<Long> RPC_HASH_KEY =
      CallOptions.Key.create("io.grpc.xds.RPC_HASH_KEY");
  static final CallOptions.Key<Boolean> AUTO_HOST_REWRITE_KEY =
      CallOptions.Key.create("io.grpc.xds.AUTO_HOST_REWRITE_KEY");
  @VisibleForTesting
  static boolean enableTimeout =
      Strings.isNullOrEmpty(System.getenv("GRPC_XDS_EXPERIMENTAL_ENABLE_TIMEOUT"))
          || Boolean.parseBoolean(System.getenv("GRPC_XDS_EXPERIMENTAL_ENABLE_TIMEOUT"));

  private final InternalLogId logId;
  private final XdsLogger logger;
  @Nullable
  private final String targetAuthority;
  private final String target;
  private final String serviceAuthority;
  // Encoded version of the service authority as per 
  // https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.
  private final String encodedServiceAuthority;
  private final String overrideAuthority;
  private final ServiceConfigParser serviceConfigParser;
  private final SynchronizationContext syncContext;
  private final ScheduledExecutorService scheduler;
  private final XdsClientPoolFactory xdsClientPoolFactory;
  private final ThreadSafeRandom random;
  private final FilterRegistry filterRegistry;
  private final XxHash64 hashFunc = XxHash64.INSTANCE;
  // Clusters (with reference counts) to which new/existing requests can be/are routed.
  // put()/remove() must be called in SyncContext, and get() can be called in any thread.
  private final ConcurrentMap<String, ClusterRefState> clusterRefs = new ConcurrentHashMap<>();
  private final ConfigSelector configSelector = new ConfigSelector();
  private final long randomChannelId;
  private final MetricRecorder metricRecorder;

  private volatile RoutingConfig routingConfig = RoutingConfig.EMPTY;
  private Listener2 listener;
  private ObjectPool<XdsClient> xdsClientPool;
  private XdsClient xdsClient;
  private CallCounterProvider callCounterProvider;
  private ResolveState resolveState;
  // Workaround for https://github.com/grpc/grpc-java/issues/8886 . This should be handled in
  // XdsClient instead of here.
  private boolean receivedConfig;

  XdsNameResolver(
      URI targetUri, String name, @Nullable String overrideAuthority,
      ServiceConfigParser serviceConfigParser,
      SynchronizationContext syncContext, ScheduledExecutorService scheduler,
      @Nullable Map<String, ?> bootstrapOverride,
      MetricRecorder metricRecorder) {
    this(targetUri, targetUri.getAuthority(), name, overrideAuthority, serviceConfigParser,
        syncContext, scheduler, SharedXdsClientPoolProvider.getDefaultProvider(),
        ThreadSafeRandomImpl.instance, FilterRegistry.getDefaultRegistry(), bootstrapOverride,
        metricRecorder);
  }

  @VisibleForTesting
  XdsNameResolver(
      URI targetUri, @Nullable String targetAuthority, String name,
      @Nullable String overrideAuthority, ServiceConfigParser serviceConfigParser,
      SynchronizationContext syncContext, ScheduledExecutorService scheduler,
      XdsClientPoolFactory xdsClientPoolFactory, ThreadSafeRandom random,
      FilterRegistry filterRegistry, @Nullable Map<String, ?> bootstrapOverride,
      MetricRecorder metricRecorder) {
    this.targetAuthority = targetAuthority;
    target = targetUri.toString();

    // The name might have multiple slashes so encode it before verifying.
    serviceAuthority = checkNotNull(name, "name");
    this.encodedServiceAuthority = 
      GrpcUtil.checkAuthority(GrpcUtil.AuthorityEscaper.encodeAuthority(serviceAuthority));

    this.overrideAuthority = overrideAuthority;
    this.serviceConfigParser = checkNotNull(serviceConfigParser, "serviceConfigParser");
    this.syncContext = checkNotNull(syncContext, "syncContext");
    this.scheduler = checkNotNull(scheduler, "scheduler");
    this.xdsClientPoolFactory = bootstrapOverride == null ? checkNotNull(xdsClientPoolFactory,
            "xdsClientPoolFactory") : new SharedXdsClientPoolProvider();
    this.xdsClientPoolFactory.setBootstrapOverride(bootstrapOverride);
    this.random = checkNotNull(random, "random");
    this.filterRegistry = checkNotNull(filterRegistry, "filterRegistry");
    this.metricRecorder = metricRecorder;
    randomChannelId = random.nextLong();
    logId = InternalLogId.allocate("xds-resolver", name);
    logger = XdsLogger.withLogId(logId);
    logger.log(XdsLogLevel.INFO, "Created resolver for {0}", name);
  }

  @Override
  public String getServiceAuthority() {
    return encodedServiceAuthority;
  }

  @Override
  public void start(Listener2 listener) {
    this.listener = checkNotNull(listener, "listener");
    try {
      xdsClientPool = xdsClientPoolFactory.getOrCreate(target, metricRecorder);
    } catch (Exception e) {
      listener.onError(
          Status.UNAVAILABLE.withDescription("Failed to initialize xDS").withCause(e));
      return;
    }
    xdsClient = xdsClientPool.getObject();
    BootstrapInfo bootstrapInfo = xdsClient.getBootstrapInfo();
    String listenerNameTemplate;
    if (targetAuthority == null) {
      listenerNameTemplate = bootstrapInfo.clientDefaultListenerResourceNameTemplate();
    } else {
      AuthorityInfo authorityInfo = bootstrapInfo.authorities().get(targetAuthority);
      if (authorityInfo == null) {
        listener.onError(Status.INVALID_ARGUMENT.withDescription(
            "invalid target URI: target authority not found in the bootstrap"));
        return;
      }
      listenerNameTemplate = authorityInfo.clientListenerResourceNameTemplate();
    }
    String replacement = serviceAuthority;
    if (listenerNameTemplate.startsWith(XDSTP_SCHEME)) {
      replacement = XdsClient.percentEncodePath(replacement);
    }
    String ldsResourceName = expandPercentS(listenerNameTemplate, replacement);
    if (!XdsClient.isResourceNameValid(ldsResourceName, XdsListenerResource.getInstance().typeUrl())
        ) {
      listener.onError(Status.INVALID_ARGUMENT.withDescription(
          "invalid listener resource URI for service authority: " + serviceAuthority));
      return;
    }
    ldsResourceName = XdsClient.canonifyResourceName(ldsResourceName);
    callCounterProvider = SharedCallCounterMap.getInstance();
    resolveState = new ResolveState(ldsResourceName);

    resolveState.start();
  }

  private static String expandPercentS(String template, String replacement) {
    return template.replace("%s", replacement);
  }

  @Override
  public void shutdown() {
    logger.log(XdsLogLevel.INFO, "Shutdown");
    if (resolveState != null) {
      resolveState.stop();
    }
    if (xdsClient != null) {
      xdsClient = xdsClientPool.returnObject(xdsClient);
    }
  }

  @VisibleForTesting
  static Map<String, ?> generateServiceConfigWithMethodConfig(
      @Nullable Long timeoutNano, @Nullable RetryPolicy retryPolicy) {
    if (timeoutNano == null
        && (retryPolicy == null || retryPolicy.retryableStatusCodes().isEmpty())) {
      return Collections.emptyMap();
    }
    ImmutableMap.Builder<String, Object> methodConfig = ImmutableMap.builder();
    methodConfig.put(
        "name", Collections.singletonList(Collections.emptyMap()));
    if (retryPolicy != null && !retryPolicy.retryableStatusCodes().isEmpty()) {
      ImmutableMap.Builder<String, Object> rawRetryPolicy = ImmutableMap.builder();
      rawRetryPolicy.put("maxAttempts", (double) retryPolicy.maxAttempts());
      rawRetryPolicy.put("initialBackoff", Durations.toString(retryPolicy.initialBackoff()));
      rawRetryPolicy.put("maxBackoff", Durations.toString(retryPolicy.maxBackoff()));
      rawRetryPolicy.put("backoffMultiplier", 2D);
      List<String> codes = new ArrayList<>(retryPolicy.retryableStatusCodes().size());
      for (Code code : retryPolicy.retryableStatusCodes()) {
        codes.add(code.name());
      }
      rawRetryPolicy.put(
          "retryableStatusCodes", Collections.unmodifiableList(codes));
      if (retryPolicy.perAttemptRecvTimeout() != null) {
        rawRetryPolicy.put(
            "perAttemptRecvTimeout", Durations.toString(retryPolicy.perAttemptRecvTimeout()));
      }
      methodConfig.put("retryPolicy", rawRetryPolicy.buildOrThrow());
    }
    if (timeoutNano != null) {
      String timeout = timeoutNano / 1_000_000_000.0 + "s";
      methodConfig.put("timeout", timeout);
    }
    return Collections.singletonMap(
        "methodConfig", Collections.singletonList(methodConfig.buildOrThrow()));
  }

  @VisibleForTesting
  XdsClient getXdsClient() {
    return xdsClient;
  }

  // called in syncContext
  private void updateResolutionResult() {
    syncContext.throwIfNotInThisSynchronizationContext();

    ImmutableMap.Builder<String, Object> childPolicy = new ImmutableMap.Builder<>();
    for (String name : clusterRefs.keySet()) {
      Map<String, ?> lbPolicy = clusterRefs.get(name).toLbPolicy();
      childPolicy.put(name, ImmutableMap.of("lbPolicy", ImmutableList.of(lbPolicy)));
    }
    Map<String, ?> rawServiceConfig = ImmutableMap.of(
        "loadBalancingConfig",
        ImmutableList.of(ImmutableMap.of(
            XdsLbPolicies.CLUSTER_MANAGER_POLICY_NAME,
            ImmutableMap.of("childPolicy", childPolicy.buildOrThrow()))));

    if (logger.isLoggable(XdsLogLevel.INFO)) {
      logger.log(
          XdsLogLevel.INFO, "Generated service config:\n{0}", new Gson().toJson(rawServiceConfig));
    }
    ConfigOrError parsedServiceConfig = serviceConfigParser.parseServiceConfig(rawServiceConfig);
    Attributes attrs =
        Attributes.newBuilder()
            .set(XdsAttributes.XDS_CLIENT_POOL, xdsClientPool)
            .set(XdsAttributes.CALL_COUNTER_PROVIDER, callCounterProvider)
            .set(InternalConfigSelector.KEY, configSelector)
            .build();
    ResolutionResult result =
        ResolutionResult.newBuilder()
            .setAttributes(attrs)
            .setServiceConfig(parsedServiceConfig)
            .build();
    listener.onResult(result);
    receivedConfig = true;
  }

  /**
   * Returns {@code true} iff {@code hostName} matches the domain name {@code pattern} with
   * case-insensitive.
   *
   * <p>Wildcard pattern rules:
   * <ol>
   * <li>A single asterisk (*) matches any domain.</li>
   * <li>Asterisk (*) is only permitted in the left-most or the right-most part of the pattern,
   *     but not both.</li>
   * </ol>
   */
  @VisibleForTesting
  static boolean matchHostName(String hostName, String pattern) {
    checkArgument(hostName.length() != 0 && !hostName.startsWith(".") && !hostName.endsWith("."),
        "Invalid host name");
    checkArgument(pattern.length() != 0 && !pattern.startsWith(".") && !pattern.endsWith("."),
        "Invalid pattern/domain name");

    hostName = hostName.toLowerCase(Locale.US);
    pattern = pattern.toLowerCase(Locale.US);
    // hostName and pattern are now in lower case -- domain names are case-insensitive.

    if (!pattern.contains("*")) {
      // Not a wildcard pattern -- hostName and pattern must match exactly.
      return hostName.equals(pattern);
    }
    // Wildcard pattern

    if (pattern.length() == 1) {
      return true;
    }

    int index = pattern.indexOf('*');

    // At most one asterisk (*) is allowed.
    if (pattern.indexOf('*', index + 1) != -1) {
      return false;
    }

    // Asterisk can only match prefix or suffix.
    if (index != 0 && index != pattern.length() - 1) {
      return false;
    }

    // HostName must be at least as long as the pattern because asterisk has to
    // match one or more characters.
    if (hostName.length() < pattern.length()) {
      return false;
    }

    if (index == 0 && hostName.endsWith(pattern.substring(1))) {
      // Prefix matching fails.
      return true;
    }

    // Pattern matches hostname if suffix matching succeeds.
    return index == pattern.length() - 1
        && hostName.startsWith(pattern.substring(0, pattern.length() - 1));
  }

  private final class ConfigSelector extends InternalConfigSelector {
    @Override
    public Result selectConfig(PickSubchannelArgs args) {
      RoutingConfig routingCfg;
      RouteData selectedRoute;
      String cluster;
      ClientInterceptor filters;
      Metadata headers = args.getHeaders();
      String path = "/" + args.getMethodDescriptor().getFullMethodName();
      do {
        routingCfg = routingConfig;
        selectedRoute = null;
        for (RouteData route : routingCfg.routes) {
          if (RoutingUtils.matchRoute(route.routeMatch, path, headers, random)) {
            selectedRoute = route;
            break;
          }
        }
        if (selectedRoute == null) {
          return Result.forError(
              Status.UNAVAILABLE.withDescription("Could not find xDS route matching RPC"));
        }
        if (selectedRoute.routeAction == null) {
          return Result.forError(Status.UNAVAILABLE.withDescription(
              "Could not route RPC to Route with non-forwarding action"));
        }
        RouteAction action = selectedRoute.routeAction;
        if (action.cluster() != null) {
          cluster = prefixedClusterName(action.cluster());
          filters = selectedRoute.filterChoices.get(0);
        } else if (action.weightedClusters() != null) {
          // XdsRouteConfigureResource verifies the total weight will not be 0 or exceed uint32
          long totalWeight = 0;
          for (ClusterWeight weightedCluster : action.weightedClusters()) {
            totalWeight += weightedCluster.weight();
          }
          long select = random.nextLong(totalWeight);
          long accumulator = 0;
          for (int i = 0; ; i++) {
            ClusterWeight weightedCluster = action.weightedClusters().get(i);
            accumulator += weightedCluster.weight();
            if (select < accumulator) {
              cluster = prefixedClusterName(weightedCluster.name());
              filters = selectedRoute.filterChoices.get(i);
              break;
            }
          }
        } else if (action.namedClusterSpecifierPluginConfig() != null) {
          cluster =
              prefixedClusterSpecifierPluginName(action.namedClusterSpecifierPluginConfig().name());
          filters = selectedRoute.filterChoices.get(0);
        } else {
          // updateRoutes() discards routes with unknown actions
          throw new AssertionError();
        }
      } while (!retainCluster(cluster));

      final RouteAction routeAction = selectedRoute.routeAction;
      Long timeoutNanos = null;
      if (enableTimeout) {
        timeoutNanos = routeAction.timeoutNano();
        if (timeoutNanos == null) {
          timeoutNanos = routingCfg.fallbackTimeoutNano;
        }
        if (timeoutNanos <= 0) {
          timeoutNanos = null;
        }
      }
      RetryPolicy retryPolicy = routeAction.retryPolicy();
      // TODO(chengyuanzhang): avoid service config generation and parsing for each call.
      Map<String, ?> rawServiceConfig =
          generateServiceConfigWithMethodConfig(timeoutNanos, retryPolicy);
      ConfigOrError parsedServiceConfig = serviceConfigParser.parseServiceConfig(rawServiceConfig);
      Object config = parsedServiceConfig.getConfig();
      if (config == null) {
        releaseCluster(cluster);
        return Result.forError(
            parsedServiceConfig.getError().augmentDescription(
                "Failed to parse service config (method config)"));
      }
      final String finalCluster = cluster;
      final long hash = generateHash(routeAction.hashPolicies(), headers);
      class ClusterSelectionInterceptor implements ClientInterceptor {
        @Override
        public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
            final MethodDescriptor<ReqT, RespT> method, CallOptions callOptions,
            final Channel next) {
          CallOptions callOptionsForCluster =
              callOptions.withOption(CLUSTER_SELECTION_KEY, finalCluster)
                  .withOption(RPC_HASH_KEY, hash);
          if (routeAction.autoHostRewrite()) {
            callOptionsForCluster = callOptionsForCluster.withOption(AUTO_HOST_REWRITE_KEY, true);
          }
          return new SimpleForwardingClientCall<ReqT, RespT>(
              next.newCall(method, callOptionsForCluster)) {
            @Override
            public void start(Listener<RespT> listener, Metadata headers) {
              listener = new SimpleForwardingClientCallListener<RespT>(listener) {
                boolean committed;

                @Override
                public void onHeaders(Metadata headers) {
                  committed = true;
                  releaseCluster(finalCluster);
                  delegate().onHeaders(headers);
                }

                @Override
                public void onClose(Status status, Metadata trailers) {
                  if (!committed) {
                    releaseCluster(finalCluster);
                  }
                  delegate().onClose(status, trailers);
                }
              };
              delegate().start(listener, headers);
            }
          };
        }
      }

      return
          Result.newBuilder()
              .setConfig(config)
              .setInterceptor(combineInterceptors(
                  ImmutableList.of(filters, new ClusterSelectionInterceptor())))
              .build();
    }

    private boolean retainCluster(String cluster) {
      ClusterRefState clusterRefState = clusterRefs.get(cluster);
      if (clusterRefState == null) {
        return false;
      }
      AtomicInteger refCount = clusterRefState.refCount;
      int count;
      do {
        count = refCount.get();
        if (count == 0) {
          return false;
        }
      } while (!refCount.compareAndSet(count, count + 1));
      return true;
    }

    private void releaseCluster(final String cluster) {
      int count = clusterRefs.get(cluster).refCount.decrementAndGet();
      if (count == 0) {
        syncContext.execute(new Runnable() {
          @Override
          public void run() {
            if (clusterRefs.get(cluster).refCount.get() == 0) {
              clusterRefs.remove(cluster);
              updateResolutionResult();
            }
          }
        });
      }
    }

    private long generateHash(List<HashPolicy> hashPolicies, Metadata headers) {
      Long hash = null;
      for (HashPolicy policy : hashPolicies) {
        Long newHash = null;
        if (policy.type() == HashPolicy.Type.HEADER) {
          String value = getHeaderValue(headers, policy.headerName());
          if (value != null) {
            if (policy.regEx() != null && policy.regExSubstitution() != null) {
              value = policy.regEx().matcher(value).replaceAll(policy.regExSubstitution());
            }
            newHash = hashFunc.hashAsciiString(value);
          }
        } else if (policy.type() == HashPolicy.Type.CHANNEL_ID) {
          newHash = hashFunc.hashLong(randomChannelId);
        }
        if (newHash != null ) {
          // Rotating the old value prevents duplicate hash rules from cancelling each other out
          // and preserves all of the entropy.
          long oldHash = hash != null ? ((hash << 1L) | (hash >> 63L)) : 0;
          hash = oldHash ^ newHash;
        }
        // If the policy is a terminal policy and a hash has been generated, ignore
        // the rest of the hash policies.
        if (policy.isTerminal() && hash != null) {
          break;
        }
      }
      return hash == null ? random.nextLong() : hash;
    }
  }

  static final class PassthroughClientInterceptor implements ClientInterceptor {
    @Override
    public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
        MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
      return next.newCall(method, callOptions);
    }
  }

  private static ClientInterceptor combineInterceptors(final List<ClientInterceptor> interceptors) {
    if (interceptors.size() == 0) {
      return new PassthroughClientInterceptor();
    }
    if (interceptors.size() == 1) {
      return interceptors.get(0);
    }
    return new ClientInterceptor() {
      @Override
      public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
          MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
        next = ClientInterceptors.interceptForward(next, interceptors);
        return next.newCall(method, callOptions);
      }
    };
  }

  @Nullable
  private static String getHeaderValue(Metadata headers, String headerName) {
    if (headerName.endsWith(Metadata.BINARY_HEADER_SUFFIX)) {
      return null;
    }
    if (headerName.equals("content-type")) {
      return "application/grpc";
    }
    Metadata.Key<String> key;
    try {
      key = Metadata.Key.of(headerName, Metadata.ASCII_STRING_MARSHALLER);
    } catch (IllegalArgumentException e) {
      return null;
    }
    Iterable<String> values = headers.getAll(key);
    return values == null ? null : Joiner.on(",").join(values);
  }

  private static String prefixedClusterName(String name) {
    return "cluster:" + name;
  }

  private static String prefixedClusterSpecifierPluginName(String pluginName) {
    return "cluster_specifier_plugin:" + pluginName;
  }

  private static final class FailingConfigSelector extends InternalConfigSelector {
    private final Result result;

    public FailingConfigSelector(Status error) {
      this.result = Result.forError(error);
    }

    @Override
    public Result selectConfig(PickSubchannelArgs args) {
      return result;
    }
  }

  private class ResolveState implements ResourceWatcher<XdsListenerResource.LdsUpdate> {
    private final ConfigOrError emptyServiceConfig =
        serviceConfigParser.parseServiceConfig(Collections.<String, Object>emptyMap());
    private final String ldsResourceName;
    private boolean stopped;
    @Nullable
    private Set<String> existingClusters;  // clusters to which new requests can be routed
    @Nullable
    private RouteDiscoveryState routeDiscoveryState;

    ResolveState(String ldsResourceName) {
      this.ldsResourceName = ldsResourceName;
    }

    @Override
    public void onChanged(final XdsListenerResource.LdsUpdate update) {
      if (stopped) {
        return;
      }
      logger.log(XdsLogLevel.INFO, "Receive LDS resource update: {0}", update);
      HttpConnectionManager httpConnectionManager = update.httpConnectionManager();
      List<VirtualHost> virtualHosts = httpConnectionManager.virtualHosts();
      String rdsName = httpConnectionManager.rdsName();
      cleanUpRouteDiscoveryState();
      if (virtualHosts != null) {
        updateRoutes(virtualHosts, httpConnectionManager.httpMaxStreamDurationNano(),
            httpConnectionManager.httpFilterConfigs());
      } else {
        routeDiscoveryState = new RouteDiscoveryState(
            rdsName, httpConnectionManager.httpMaxStreamDurationNano(),
            httpConnectionManager.httpFilterConfigs());
        logger.log(XdsLogLevel.INFO, "Start watching RDS resource {0}", rdsName);
        xdsClient.watchXdsResource(XdsRouteConfigureResource.getInstance(),
            rdsName, routeDiscoveryState, syncContext);
      }
    }

    @Override
    public void onError(final Status error) {
      if (stopped || receivedConfig) {
        return;
      }
      listener.onError(Status.UNAVAILABLE.withCause(error.getCause()).withDescription(
          String.format("Unable to load LDS %s. xDS server returned: %s: %s",
          ldsResourceName, error.getCode(), error.getDescription())));
    }

    @Override
    public void onResourceDoesNotExist(final String resourceName) {
      if (stopped) {
        return;
      }
      String error = "LDS resource does not exist: " + resourceName;
      logger.log(XdsLogLevel.INFO, error);
      cleanUpRouteDiscoveryState();
      cleanUpRoutes(error);
    }

    private void start() {
      logger.log(XdsLogLevel.INFO, "Start watching LDS resource {0}", ldsResourceName);
      xdsClient.watchXdsResource(XdsListenerResource.getInstance(),
          ldsResourceName, this, syncContext);
    }

    private void stop() {
      logger.log(XdsLogLevel.INFO, "Stop watching LDS resource {0}", ldsResourceName);
      stopped = true;
      cleanUpRouteDiscoveryState();
      xdsClient.cancelXdsResourceWatch(XdsListenerResource.getInstance(), ldsResourceName, this);
    }

    // called in syncContext
    private void updateRoutes(List<VirtualHost> virtualHosts, long httpMaxStreamDurationNano,
        @Nullable List<NamedFilterConfig> filterConfigs) {
      String authority = overrideAuthority != null ? overrideAuthority : encodedServiceAuthority;
      VirtualHost virtualHost = RoutingUtils.findVirtualHostForHostName(virtualHosts, authority);
      if (virtualHost == null) {
        String error = "Failed to find virtual host matching hostname: " + authority;
        logger.log(XdsLogLevel.WARNING, error);
        cleanUpRoutes(error);
        return;
      }

      List<Route> routes = virtualHost.routes();
      ImmutableList.Builder<RouteData> routesData = ImmutableList.builder();

      // Populate all clusters to which requests can be routed to through the virtual host.
      Set<String> clusters = new HashSet<>();
      // uniqueName -> clusterName
      Map<String, String> clusterNameMap = new HashMap<>();
      // uniqueName -> pluginConfig
      Map<String, RlsPluginConfig> rlsPluginConfigMap = new HashMap<>();
      for (Route route : routes) {
        RouteAction action = route.routeAction();
        String prefixedName;
        if (action == null) {
          routesData.add(new RouteData(route.routeMatch(), null, ImmutableList.of()));
        } else if (action.cluster() != null) {
          prefixedName = prefixedClusterName(action.cluster());
          clusters.add(prefixedName);
          clusterNameMap.put(prefixedName, action.cluster());
          ClientInterceptor filters = createFilters(filterConfigs, virtualHost, route, null);
          routesData.add(new RouteData(route.routeMatch(), route.routeAction(), filters));
        } else if (action.weightedClusters() != null) {
          ImmutableList.Builder<ClientInterceptor> filterList = ImmutableList.builder();
          for (ClusterWeight weightedCluster : action.weightedClusters()) {
            prefixedName = prefixedClusterName(weightedCluster.name());
            clusters.add(prefixedName);
            clusterNameMap.put(prefixedName, weightedCluster.name());
            filterList.add(createFilters(filterConfigs, virtualHost, route, weightedCluster));
          }
          routesData.add(
              new RouteData(route.routeMatch(), route.routeAction(), filterList.build()));
        } else if (action.namedClusterSpecifierPluginConfig() != null) {
          PluginConfig pluginConfig = action.namedClusterSpecifierPluginConfig().config();
          if (pluginConfig instanceof RlsPluginConfig) {
            prefixedName = prefixedClusterSpecifierPluginName(
                action.namedClusterSpecifierPluginConfig().name());
            clusters.add(prefixedName);
            rlsPluginConfigMap.put(prefixedName, (RlsPluginConfig) pluginConfig);
          }
          ClientInterceptor filters = createFilters(filterConfigs, virtualHost, route, null);
          routesData.add(new RouteData(route.routeMatch(), route.routeAction(), filters));
        } else {
          // Discard route
        }
      }

      // Updates channel's load balancing config whenever the set of selectable clusters changes.
      boolean shouldUpdateResult = existingClusters == null;
      Set<String> addedClusters =
          existingClusters == null ? clusters : Sets.difference(clusters, existingClusters);
      Set<String> deletedClusters =
          existingClusters == null
              ? Collections.emptySet() : Sets.difference(existingClusters, clusters);
      existingClusters = clusters;
      for (String cluster : addedClusters) {
        if (clusterRefs.containsKey(cluster)) {
          clusterRefs.get(cluster).refCount.incrementAndGet();
        } else {
          if (clusterNameMap.containsKey(cluster)) {
            clusterRefs.put(
                cluster,
                ClusterRefState.forCluster(new AtomicInteger(1), clusterNameMap.get(cluster)));
          }
          if (rlsPluginConfigMap.containsKey(cluster)) {
            clusterRefs.put(
                cluster,
                ClusterRefState.forRlsPlugin(
                    new AtomicInteger(1), rlsPluginConfigMap.get(cluster)));
          }
          shouldUpdateResult = true;
        }
      }
      for (String cluster : clusters) {
        RlsPluginConfig rlsPluginConfig = rlsPluginConfigMap.get(cluster);
        if (!Objects.equals(rlsPluginConfig, clusterRefs.get(cluster).rlsPluginConfig)) {
          ClusterRefState newClusterRefState =
              ClusterRefState.forRlsPlugin(clusterRefs.get(cluster).refCount, rlsPluginConfig);
          clusterRefs.put(cluster, newClusterRefState);
          shouldUpdateResult = true;
        }
      }
      // Update service config to include newly added clusters.
      if (shouldUpdateResult) {
        updateResolutionResult();
      }
      // Make newly added clusters selectable by config selector and deleted clusters no longer
      // selectable.
      routingConfig = new RoutingConfig(httpMaxStreamDurationNano, routesData.build());
      shouldUpdateResult = false;
      for (String cluster : deletedClusters) {
        int count = clusterRefs.get(cluster).refCount.decrementAndGet();
        if (count == 0) {
          clusterRefs.remove(cluster);
          shouldUpdateResult = true;
        }
      }
      if (shouldUpdateResult) {
        updateResolutionResult();
      }
    }

    private ClientInterceptor createFilters(
        @Nullable List<NamedFilterConfig> filterConfigs,
        VirtualHost virtualHost,
        Route route,
        @Nullable ClusterWeight weightedCluster) {
      if (filterConfigs == null) {
        return new PassthroughClientInterceptor();
      }
      Map<String, FilterConfig> selectedOverrideConfigs =
          new HashMap<>(virtualHost.filterConfigOverrides());
      selectedOverrideConfigs.putAll(route.filterConfigOverrides());
      if (weightedCluster != null) {
        selectedOverrideConfigs.putAll(weightedCluster.filterConfigOverrides());
      }
      ImmutableList.Builder<ClientInterceptor> filterInterceptors = ImmutableList.builder();
      for (NamedFilterConfig namedFilter : filterConfigs) {
        FilterConfig filterConfig = namedFilter.filterConfig;
        Filter filter = filterRegistry.get(filterConfig.typeUrl());
        if (filter instanceof ClientInterceptorBuilder) {
          ClientInterceptor interceptor = ((ClientInterceptorBuilder) filter)
              .buildClientInterceptor(
                  filterConfig, selectedOverrideConfigs.get(namedFilter.name),
                  scheduler);
          if (interceptor != null) {
            filterInterceptors.add(interceptor);
          }
        }
      }
      return combineInterceptors(filterInterceptors.build());
    }

    private void cleanUpRoutes(String error) {
      if (existingClusters != null) {
        for (String cluster : existingClusters) {
          int count = clusterRefs.get(cluster).refCount.decrementAndGet();
          if (count == 0) {
            clusterRefs.remove(cluster);
          }
        }
        existingClusters = null;
      }
      routingConfig = RoutingConfig.EMPTY;
      // Without addresses the default LB (normally pick_first) should become TRANSIENT_FAILURE, and
      // the config selector handles the error message itself. Once the LB API allows providing
      // failure information for addresses yet still providing a service config, the config seector
      // could be avoided.
      String errorWithNodeId =
          error + ", xDS node ID: " + xdsClient.getBootstrapInfo().node().getId();
      listener.onResult(ResolutionResult.newBuilder()
          .setAttributes(Attributes.newBuilder()
            .set(InternalConfigSelector.KEY,
              new FailingConfigSelector(Status.UNAVAILABLE.withDescription(errorWithNodeId)))
            .build())
          .setServiceConfig(emptyServiceConfig)
          .build());
      receivedConfig = true;
    }

    private void cleanUpRouteDiscoveryState() {
      if (routeDiscoveryState != null) {
        String rdsName = routeDiscoveryState.resourceName;
        logger.log(XdsLogLevel.INFO, "Stop watching RDS resource {0}", rdsName);
        xdsClient.cancelXdsResourceWatch(XdsRouteConfigureResource.getInstance(), rdsName,
            routeDiscoveryState);
        routeDiscoveryState = null;
      }
    }

    /**
     * Discovery state for RouteConfiguration resource. One instance for each Listener resource
     * update.
     */
    private class RouteDiscoveryState implements ResourceWatcher<RdsUpdate> {
      private final String resourceName;
      private final long httpMaxStreamDurationNano;
      @Nullable
      private final List<NamedFilterConfig> filterConfigs;

      private RouteDiscoveryState(String resourceName, long httpMaxStreamDurationNano,
          @Nullable List<NamedFilterConfig> filterConfigs) {
        this.resourceName = resourceName;
        this.httpMaxStreamDurationNano = httpMaxStreamDurationNano;
        this.filterConfigs = filterConfigs;
      }

      @Override
      public void onChanged(final RdsUpdate update) {
        if (RouteDiscoveryState.this != routeDiscoveryState) {
          return;
        }
        logger.log(XdsLogLevel.INFO, "Received RDS resource update: {0}", update);
        updateRoutes(update.virtualHosts, httpMaxStreamDurationNano, filterConfigs);
      }

      @Override
      public void onError(final Status error) {
        if (RouteDiscoveryState.this != routeDiscoveryState || receivedConfig) {
          return;
        }
        listener.onError(Status.UNAVAILABLE.withCause(error.getCause()).withDescription(
            String.format("Unable to load RDS %s. xDS server returned: %s: %s",
            resourceName, error.getCode(), error.getDescription())));
      }

      @Override
      public void onResourceDoesNotExist(final String resourceName) {
        if (RouteDiscoveryState.this != routeDiscoveryState) {
          return;
        }
        String error = "RDS resource does not exist: " + resourceName;
        logger.log(XdsLogLevel.INFO, error);
        cleanUpRoutes(error);
      }
    }
  }

  /**
   * VirtualHost-level configuration for request routing.
   */
  private static class RoutingConfig {
    private final long fallbackTimeoutNano;
    final ImmutableList<RouteData> routes;

    private static final RoutingConfig EMPTY = new RoutingConfig(0, ImmutableList.of());

    private RoutingConfig(long fallbackTimeoutNano, ImmutableList<RouteData> routes) {
      this.fallbackTimeoutNano = fallbackTimeoutNano;
      this.routes = checkNotNull(routes, "routes");
    }
  }

  static final class RouteData {
    final RouteMatch routeMatch;
    /** null implies non-forwarding action. */
    @Nullable
    final RouteAction routeAction;
    /**
     * Only one of these interceptors should be used per-RPC. There are only multiple values in the
     * list for weighted clusters, in which case the order of the list mirrors the weighted
     * clusters.
     */
    final ImmutableList<ClientInterceptor> filterChoices;

    RouteData(RouteMatch routeMatch, @Nullable RouteAction routeAction, ClientInterceptor filter) {
      this(routeMatch, routeAction, ImmutableList.of(filter));
    }

    RouteData(
        RouteMatch routeMatch,
        @Nullable RouteAction routeAction,
        ImmutableList<ClientInterceptor> filterChoices) {
      this.routeMatch = checkNotNull(routeMatch, "routeMatch");
      checkArgument(
          routeAction == null || !filterChoices.isEmpty(),
          "filter may be empty only for non-forwarding action");
      this.routeAction = routeAction;
      if (routeAction != null && routeAction.weightedClusters() != null) {
        checkArgument(
            routeAction.weightedClusters().size() == filterChoices.size(),
            "filter choices must match size of weighted clusters");
      }
      for (ClientInterceptor filter : filterChoices) {
        checkNotNull(filter, "entry in filterChoices is null");
      }
      this.filterChoices = checkNotNull(filterChoices, "filterChoices");
    }
  }

  private static class ClusterRefState {
    final AtomicInteger refCount;
    @Nullable
    final String traditionalCluster;
    @Nullable
    final RlsPluginConfig rlsPluginConfig;

    private ClusterRefState(
        AtomicInteger refCount, @Nullable String traditionalCluster,
        @Nullable RlsPluginConfig rlsPluginConfig) {
      this.refCount = refCount;
      checkArgument(traditionalCluster == null ^ rlsPluginConfig == null,
          "There must be exactly one non-null value in traditionalCluster and pluginConfig");
      this.traditionalCluster = traditionalCluster;
      this.rlsPluginConfig = rlsPluginConfig;
    }

    private Map<String, ?> toLbPolicy() {
      if (traditionalCluster != null) {
        return ImmutableMap.of(
            XdsLbPolicies.CDS_POLICY_NAME,
            ImmutableMap.of("cluster", traditionalCluster));
      } else {
        ImmutableMap<String, ?> rlsConfig = new ImmutableMap.Builder<String, Object>()
            .put("routeLookupConfig", rlsPluginConfig.config())
            .put(
                "childPolicy",
                ImmutableList.of(ImmutableMap.of(XdsLbPolicies.CDS_POLICY_NAME, ImmutableMap.of())))
            .put("childPolicyConfigTargetFieldName", "cluster")
            .buildOrThrow();
        return ImmutableMap.of("rls_experimental", rlsConfig);
      }
    }

    static ClusterRefState forCluster(AtomicInteger refCount, String name) {
      return new ClusterRefState(refCount, name, null);
    }

    static ClusterRefState forRlsPlugin(AtomicInteger refCount, RlsPluginConfig rlsPluginConfig) {
      return new ClusterRefState(refCount, null, rlsPluginConfig);
    }
  }
}

grpc / grpc-java / #19678

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