xds: Add logical dns cluster support to XdsDepManager

ClusterResolverLb gets the NameResolverRegistry from
LoadBalancer.Helper, so a new API was added in NameResover.Args to
propagate the same object to the name resolver tree.

RetryingNameResolver was exposed to xds. This is expected to be
temporary, as the retrying is being removed from ManagedChannelImpl and
moved into the resolvers. At that point, DnsNameResolverProvider would
wrap DnsNameResolver with a similar API to RetryingNameResolver and xds
would no longer be responsible.

Author: ejona86

api/src/main/java/io/grpc/NameResolver.java

@@ -303,6 +303,7 @@ public static final class Args {
     @Nullable private final Executor executor;
     @Nullable private final String overrideAuthority;
     @Nullable private final MetricRecorder metricRecorder;
+    @Nullable private final NameResolverRegistry nameResolverRegistry;
     @Nullable private final IdentityHashMap<Key<?>, Object> customArgs;
 
     private Args(Builder builder) {
@@ -316,6 +317,7 @@ private Args(Builder builder) {
       this.executor = builder.executor;
       this.overrideAuthority = builder.overrideAuthority;
       this.metricRecorder = builder.metricRecorder;
+      this.nameResolverRegistry = builder.nameResolverRegistry;
       this.customArgs = cloneCustomArgs(builder.customArgs);
     }
 
@@ -447,6 +449,18 @@ public MetricRecorder getMetricRecorder() {
       return metricRecorder;
     }
 
+    /**
+     * Returns the {@link NameResolverRegistry} that the Channel uses to look for {@link
+     * NameResolver}s.
+     *
+     * @since 1.74.0
+     */
+    public NameResolverRegistry getNameResolverRegistry() {
+      if (nameResolverRegistry == null) {
+        throw new IllegalStateException("NameResolverRegistry is not set in Builder");
+      }
+      return nameResolverRegistry;
+    }
 
     @Override
     public String toString() {
@@ -461,6 +475,7 @@ public String toString() {
           .add("executor", executor)
           .add("overrideAuthority", overrideAuthority)
           .add("metricRecorder", metricRecorder)
+          .add("nameResolverRegistry", nameResolverRegistry)
           .toString();
     }
 
@@ -480,6 +495,7 @@ public Builder toBuilder() {
       builder.setOffloadExecutor(executor);
       builder.setOverrideAuthority(overrideAuthority);
       builder.setMetricRecorder(metricRecorder);
+      builder.setNameResolverRegistry(nameResolverRegistry);
       builder.customArgs = cloneCustomArgs(customArgs);
       return builder;
     }
@@ -508,6 +524,7 @@ public static final class Builder {
       private Executor executor;
       private String overrideAuthority;
       private MetricRecorder metricRecorder;
+      private NameResolverRegistry nameResolverRegistry;
       private IdentityHashMap<Key<?>, Object> customArgs;
 
       Builder() {
@@ -614,6 +631,16 @@ public Builder setMetricRecorder(MetricRecorder metricRecorder) {
         return this;
       }
 
+      /**
+       * See {@link Args#getNameResolverRegistry}.  This is an optional field.
+       *
+       * @since 1.74.0
+       */
+      public Builder setNameResolverRegistry(NameResolverRegistry registry) {
+        this.nameResolverRegistry = registry;
+        return this;
+      }
+
       /**
        * Builds an {@link Args}.
        *

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

@@ -597,7 +597,8 @@ ClientStream newSubstream(
             .setChannelLogger(channelLogger)
             .setOffloadExecutor(this.offloadExecutorHolder)
             .setOverrideAuthority(this.authorityOverride)
-            .setMetricRecorder(this.metricRecorder);
+            .setMetricRecorder(this.metricRecorder)
+            .setNameResolverRegistry(builder.nameResolverRegistry);
     builder.copyAllNameResolverCustomArgsTo(nameResolverArgsBuilder);
     this.nameResolverArgs = nameResolverArgsBuilder.build();
     this.nameResolver = getNameResolver(
@@ -685,11 +686,7 @@ static NameResolver getNameResolver(
     // We wrap the name resolver in a RetryingNameResolver to give it the ability to retry failures.
     // TODO: After a transition period, all NameResolver implementations that need retry should use
     //       RetryingNameResolver directly and this step can be removed.
-    NameResolver usedNameResolver = new RetryingNameResolver(resolver,
-          new BackoffPolicyRetryScheduler(new ExponentialBackoffPolicy.Provider(),
-              nameResolverArgs.getScheduledExecutorService(),
-              nameResolverArgs.getSynchronizationContext()),
-          nameResolverArgs.getSynchronizationContext());
+    NameResolver usedNameResolver = RetryingNameResolver.wrap(resolver, nameResolverArgs);
 
     if (overrideAuthority == null) {
       return usedNameResolver;

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

@@ -27,13 +27,22 @@
  *
  * <p>The {@link NameResolver} used with this
  */
-final class RetryingNameResolver extends ForwardingNameResolver {
+public final class RetryingNameResolver extends ForwardingNameResolver {
+  public static NameResolver wrap(NameResolver retriedNameResolver, Args args) {
+    // For migration, this might become conditional
+    return new RetryingNameResolver(
+        retriedNameResolver,
+        new BackoffPolicyRetryScheduler(
+            new ExponentialBackoffPolicy.Provider(),
+            args.getScheduledExecutorService(),
+            args.getSynchronizationContext()),
+        args.getSynchronizationContext());
+  }
 
   private final NameResolver retriedNameResolver;
   private final RetryScheduler retryScheduler;
   private final SynchronizationContext syncContext;
 
-
   /**
    * Creates a new {@link RetryingNameResolver}.
    *

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

@@ -207,14 +207,7 @@ private RetryingNameResolver newResolver(
 
     // In practice the DNS name resolver provider always wraps the resolver in a
     // RetryingNameResolver which adds retry capabilities to it. We use the same setup here.
-    return new RetryingNameResolver(
-        dnsResolver,
-        new BackoffPolicyRetryScheduler(
-            new ExponentialBackoffPolicy.Provider(),
-            fakeExecutor.getScheduledExecutorService(),
-            syncContext
-        ),
-        syncContext);
+    return (RetryingNameResolver) RetryingNameResolver.wrap(dnsResolver, args);
   }
 
   @Before