Plumb target to load balancer

gRFC A78 has WRR and pick-first include a `grpc.target` label, defined
in A66:

> `grpc.target` : Canonicalized target URI used when creating gRPC
> Channel, e.g. "dns:///pubsub.googleapis.com:443",
> "xds:///helloworld-gke:8000". Canonicalized target URI is the form
> with the scheme included if the user didn't mention the scheme
> (`scheme://[authority]/path`). For channels such as inprocess channels
> where a target URI is not available, implementations can synthesize a
> target URI.

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

@@ -1185,6 +1185,13 @@ public abstract class LoadBalancer {
      */
     public abstract String getAuthority();
 
+    /**
+     * Returns the target string of the channel, guaranteed to include its scheme.
+     */
+    public String getChannelTarget() {
+      throw new UnsupportedOperationException();
+    }
+
     /**
      * Returns the ChannelCredentials used to construct the channel, without bearer tokens.
      *

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

@@ -166,6 +166,8 @@ final class ManagedChannelImpl extends ManagedChannel implements
   @Nullable
   private final String authorityOverride;
   private final NameResolverRegistry nameResolverRegistry;
+  private final URI targetUri;
+  private final NameResolverProvider nameResolverProvider;
   private final NameResolver.Args nameResolverArgs;
   private final AutoConfiguredLoadBalancerFactory loadBalancerFactory;
   private final ClientTransportFactory originalTransportFactory;
@@ -383,8 +385,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
       nameResolverStarted = false;
       if (channelIsActive) {
         nameResolver = getNameResolver(
-            target, authorityOverride, nameResolverRegistry, nameResolverArgs,
-            transportFactory.getSupportedSocketAddressTypes());
+            targetUri, authorityOverride, nameResolverProvider, nameResolverArgs);
       } else {
         nameResolver = null;
       }
@@ -621,6 +622,10 @@ final class ManagedChannelImpl extends ManagedChannel implements
     this.retryEnabled = builder.retryEnabled;
     this.loadBalancerFactory = new AutoConfiguredLoadBalancerFactory(builder.defaultLbPolicy);
     this.nameResolverRegistry = builder.nameResolverRegistry;
+    ResolvedNameResolver resolvedResolver = getNameResolverProvider(
+        target, nameResolverRegistry, transportFactory.getSupportedSocketAddressTypes());
+    this.targetUri = resolvedResolver.targetUri;
+    this.nameResolverProvider = resolvedResolver.provider;
     ScParser serviceConfigParser =
         new ScParser(
             retryEnabled,
@@ -640,8 +645,7 @@ final class ManagedChannelImpl extends ManagedChannel implements
             .setOverrideAuthority(this.authorityOverride)
             .build();
     this.nameResolver = getNameResolver(
-        target, authorityOverride, nameResolverRegistry, nameResolverArgs,
-        transportFactory.getSupportedSocketAddressTypes());
+        targetUri, authorityOverride, nameResolverProvider, nameResolverArgs);
     this.balancerRpcExecutorPool = checkNotNull(balancerRpcExecutorPool, "balancerRpcExecutorPool");
     this.balancerRpcExecutorHolder = new ExecutorHolder(balancerRpcExecutorPool);
     this.delayedTransport = new DelayedClientTransport(this.executor, this.syncContext);
@@ -713,8 +717,20 @@ final class ManagedChannelImpl extends ManagedChannel implements
     }
   }
 
-  private static NameResolver getNameResolver(
-      String target, NameResolverRegistry nameResolverRegistry, NameResolver.Args nameResolverArgs,
+  @VisibleForTesting
+  static class ResolvedNameResolver {
+    public final URI targetUri;
+    public final NameResolverProvider provider;
+
+    public ResolvedNameResolver(URI targetUri, NameResolverProvider provider) {
+      this.targetUri = checkNotNull(targetUri, "targetUri");
+      this.provider = checkNotNull(provider, "provider");
+    }
+  }
+
+  @VisibleForTesting
+  static ResolvedNameResolver getNameResolverProvider(
+      String target, NameResolverRegistry nameResolverRegistry,
       Collection<Class<? extends SocketAddress>> channelTransportSocketAddressTypes) {
     // Finding a NameResolver. Try using the target string as the URI. If that fails, try prepending
     // "dns:///".
@@ -761,23 +777,17 @@ final class ManagedChannelImpl extends ManagedChannel implements
       }
     }
 
-    NameResolver resolver = provider.newNameResolver(targetUri, nameResolverArgs);
-    if (resolver != null) {
-      return resolver;
-    }
-
-    throw new IllegalArgumentException(String.format(
-        "cannot create a NameResolver for %s%s",
-        target, uriSyntaxErrors.length() > 0 ? " (" + uriSyntaxErrors + ")" : ""));
+    return new ResolvedNameResolver(targetUri, provider);
   }
 
   @VisibleForTesting
   static NameResolver getNameResolver(
-      String target, @Nullable final String overrideAuthority,
-      NameResolverRegistry nameResolverRegistry, NameResolver.Args nameResolverArgs,
-      Collection<Class<? extends SocketAddress>> channelTransportSocketAddressTypes) {
-    NameResolver resolver = getNameResolver(target, nameResolverRegistry, nameResolverArgs,
-        channelTransportSocketAddressTypes);
+      URI targetUri, @Nullable final String overrideAuthority,
+      NameResolverProvider provider, NameResolver.Args nameResolverArgs) {
+    NameResolver resolver = provider.newNameResolver(targetUri, nameResolverArgs);
+    if (resolver == null) {
+      throw new IllegalArgumentException("cannot create a NameResolver for " + targetUri);
+    }
 
     // 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
@@ -1703,6 +1713,11 @@ final class ManagedChannelImpl extends ManagedChannel implements
       return ManagedChannelImpl.this.authority();
     }
 
+    @Override
+    public String getChannelTarget() {
+      return targetUri.toString();
+    }
+
     @Override
     public SynchronizationContext getSynchronizationContext() {
       return syncContext;

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

@@ -17,21 +17,12 @@
 package io.grpc.internal;
 
 import static com.google.common.truth.Truth.assertThat;
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.fail;
-import static org.mockito.Mockito.mock;
 
-import io.grpc.ChannelLogger;
 import io.grpc.NameResolver;
-import io.grpc.NameResolver.Args;
-import io.grpc.NameResolver.ServiceConfigParser;
 import io.grpc.NameResolverProvider;
 import io.grpc.NameResolverRegistry;
-import io.grpc.ProxyDetector;
-import io.grpc.SynchronizationContext;
 import io.grpc.inprocess.InProcessSocketAddress;
-import java.lang.Thread.UncaughtExceptionHandler;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.util.Collections;
@@ -39,18 +30,9 @@ import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
 
-/** Unit tests for ManagedChannelImpl#getNameResolver(). */
+/** Unit tests for ManagedChannelImpl#getNameResolverProvider(). */
 @RunWith(JUnit4.class)
 public class ManagedChannelImplGetNameResolverTest {
-  private static final NameResolver.Args NAMERESOLVER_ARGS = NameResolver.Args.newBuilder()
-      .setDefaultPort(447)
-      .setProxyDetector(mock(ProxyDetector.class))
-      .setSynchronizationContext(new SynchronizationContext(mock(UncaughtExceptionHandler.class)))
-      .setServiceConfigParser(mock(ServiceConfigParser.class))
-      .setChannelLogger(mock(ChannelLogger.class))
-      .setScheduledExecutorService(new FakeClock().getScheduledExecutorService())
-      .build();
-
   @Test
   public void invalidUriTarget() {
     testInvalidTarget("defaultscheme:///[invalid]");
@@ -68,18 +50,6 @@ public class ManagedChannelImplGetNameResolverTest {
         new URI("defaultscheme", "", "/foo.googleapis.com:8080", null));
   }
 
-  @Test
-  public void validAuthorityTarget_overrideAuthority() throws Exception {
-    String target = "foo.googleapis.com:8080";
-    String overrideAuthority = "override.authority";
-    URI expectedUri = new URI("defaultscheme", "", "/foo.googleapis.com:8080", null);
-    NameResolverRegistry nameResolverRegistry = getTestRegistry(expectedUri.getScheme());
-    NameResolver nameResolver = ManagedChannelImpl.getNameResolver(
-        target, overrideAuthority, nameResolverRegistry, NAMERESOLVER_ARGS,
-        Collections.singleton(InetSocketAddress.class));
-    assertThat(nameResolver.getServiceAuthority()).isEqualTo(overrideAuthority);
-  }
-
   @Test
   public void validUriTarget() throws Exception {
     testValidTarget("scheme:///foo.googleapis.com:8080", "scheme:///foo.googleapis.com:8080",
@@ -121,47 +91,12 @@ public class ManagedChannelImplGetNameResolverTest {
         new URI("defaultscheme", "", "//target", null));
   }
 
-  @Test
-  public void validTargetNoResolver() {
-    NameResolverRegistry nameResolverRegistry = new NameResolverRegistry();
-    NameResolverProvider nameResolverProvider = new NameResolverProvider() {
-      @Override
-      protected boolean isAvailable() {
-        return true;
-      }
-
-      @Override
-      protected int priority() {
-        return 5;
-      }
-
-      @Override
-      public NameResolver newNameResolver(URI targetUri, Args args) {
-        return null;
-      }
-
-      @Override
-      public String getDefaultScheme() {
-        return "defaultscheme";
-      }
-    };
-    nameResolverRegistry.register(nameResolverProvider);
-    try {
-      ManagedChannelImpl.getNameResolver(
-          "foo.googleapis.com:8080", null, nameResolverRegistry, NAMERESOLVER_ARGS,
-          Collections.singleton(InetSocketAddress.class));
-      fail("Should fail");
-    } catch (IllegalArgumentException e) {
-      // expected
-    }
-  }
-
   @Test
   public void validTargetNoProvider() {
     NameResolverRegistry nameResolverRegistry = new NameResolverRegistry();
     try {
-      ManagedChannelImpl.getNameResolver(
-          "foo.googleapis.com:8080", null, nameResolverRegistry, NAMERESOLVER_ARGS,
+      ManagedChannelImpl.getNameResolverProvider(
+          "foo.googleapis.com:8080", nameResolverRegistry,
           Collections.singleton(InetSocketAddress.class));
       fail("Should fail");
     } catch (IllegalArgumentException e) {
@@ -173,8 +108,8 @@ public class ManagedChannelImplGetNameResolverTest {
   public void validTargetProviderAddrTypesNotSupported() {
     NameResolverRegistry nameResolverRegistry = getTestRegistry("testscheme");
     try {
-      ManagedChannelImpl.getNameResolver(
-          "testscheme:///foo.googleapis.com:8080", null, nameResolverRegistry, NAMERESOLVER_ARGS,
+      ManagedChannelImpl.getNameResolverProvider(
+          "testscheme:///foo.googleapis.com:8080", nameResolverRegistry,
           Collections.singleton(InProcessSocketAddress.class));
       fail("Should fail");
     } catch (IllegalArgumentException e) {
@@ -184,26 +119,23 @@ public class ManagedChannelImplGetNameResolverTest {
     }
   }
 
-
   private void testValidTarget(String target, String expectedUriString, URI expectedUri) {
     NameResolverRegistry nameResolverRegistry = getTestRegistry(expectedUri.getScheme());
-    FakeNameResolver nameResolver
-        = (FakeNameResolver) ((RetryingNameResolver) ManagedChannelImpl.getNameResolver(
-        target, null, nameResolverRegistry, NAMERESOLVER_ARGS,
-        Collections.singleton(InetSocketAddress.class))).getRetriedNameResolver();
-    assertNotNull(nameResolver);
-    assertEquals(expectedUri, nameResolver.uri);
-    assertEquals(expectedUriString, nameResolver.uri.toString());
+    ManagedChannelImpl.ResolvedNameResolver resolved = ManagedChannelImpl.getNameResolverProvider(
+        target, nameResolverRegistry, Collections.singleton(InetSocketAddress.class));
+    assertThat(resolved.provider).isInstanceOf(FakeNameResolverProvider.class);
+    assertThat(resolved.targetUri).isEqualTo(expectedUri);
+    assertThat(resolved.targetUri.toString()).isEqualTo(expectedUriString);
   }
 
   private void testInvalidTarget(String target) {
     NameResolverRegistry nameResolverRegistry = getTestRegistry("dns");
 
     try {
-      FakeNameResolver nameResolver = (FakeNameResolver) ManagedChannelImpl.getNameResolver(
-          target, null, nameResolverRegistry, NAMERESOLVER_ARGS,
-          Collections.singleton(InetSocketAddress.class));
-      fail("Should have failed, but got resolver with " + nameResolver.uri);
+      ManagedChannelImpl.ResolvedNameResolver resolved = ManagedChannelImpl.getNameResolverProvider(
+          target, nameResolverRegistry, Collections.singleton(InetSocketAddress.class));
+      FakeNameResolverProvider nameResolverProvider = (FakeNameResolverProvider) resolved.provider;
+      fail("Should have failed, but got resolver provider " + nameResolverProvider);
     } catch (IllegalArgumentException e) {
       // expected
     }

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

@@ -104,6 +104,7 @@ import io.grpc.MethodDescriptor.MethodType;
 import io.grpc.NameResolver;
 import io.grpc.NameResolver.ConfigOrError;
 import io.grpc.NameResolver.ResolutionResult;
+import io.grpc.NameResolverProvider;
 import io.grpc.NameResolverRegistry;
 import io.grpc.ProxiedSocketAddress;
 import io.grpc.ProxyDetector;
@@ -112,6 +113,7 @@ import io.grpc.ServerMethodDefinition;
 import io.grpc.Status;
 import io.grpc.Status.Code;
 import io.grpc.StringMarshaller;
+import io.grpc.SynchronizationContext;
 import io.grpc.internal.ClientTransportFactory.ClientTransportOptions;
 import io.grpc.internal.ClientTransportFactory.SwapChannelCredentialsResult;
 import io.grpc.internal.InternalSubchannel.TransportLogger;
@@ -188,6 +190,15 @@ public class ManagedChannelImplTest {
           .setUserAgent(USER_AGENT);
   private static final String TARGET = "fake://" + SERVICE_NAME;
   private static final String MOCK_POLICY_NAME = "mock_lb";
+  private static final NameResolver.Args NAMERESOLVER_ARGS = NameResolver.Args.newBuilder()
+      .setDefaultPort(447)
+      .setProxyDetector(mock(ProxyDetector.class))
+      .setSynchronizationContext(
+          new SynchronizationContext(mock(Thread.UncaughtExceptionHandler.class)))
+      .setServiceConfigParser(mock(NameResolver.ServiceConfigParser.class))
+      .setScheduledExecutorService(new FakeClock().getScheduledExecutorService())
+      .build();
+
   private URI expectedUri;
   private final SocketAddress socketAddress =
       new SocketAddress() {
@@ -4306,6 +4317,80 @@ public class ManagedChannelImplTest {
     assertEquals(1, terminationCallbackCalled.get());
   }
 
+  @Test
+  public void validAuthorityTarget_overrideAuthority() throws Exception {
+    String overrideAuthority = "override.authority";
+    String serviceAuthority = "fakeauthority";
+    NameResolverProvider nameResolverProvider = new NameResolverProvider() {
+      @Override protected boolean isAvailable() {
+        return true;
+      }
+
+      @Override protected int priority() {
+        return 5;
+      }
+
+      @Override public NameResolver newNameResolver(URI targetUri, NameResolver.Args args) {
+        return new NameResolver() {
+          @Override public String getServiceAuthority() {
+            return serviceAuthority;
+          }
+
+          @Override public void start(final Listener2 listener) {}
+
+          @Override public void shutdown() {}
+        };
+      }
+
+      @Override public String getDefaultScheme() {
+        return "defaultscheme";
+      }
+    };
+
+    URI targetUri = new URI("defaultscheme", "", "/foo.googleapis.com:8080", null);
+    NameResolver nameResolver = ManagedChannelImpl.getNameResolver(
+        targetUri, null, nameResolverProvider, NAMERESOLVER_ARGS);
+    assertThat(nameResolver.getServiceAuthority()).isEqualTo(serviceAuthority);
+
+    nameResolver = ManagedChannelImpl.getNameResolver(
+        targetUri, overrideAuthority, nameResolverProvider, NAMERESOLVER_ARGS);
+    assertThat(nameResolver.getServiceAuthority()).isEqualTo(overrideAuthority);
+  }
+
+  @Test
+  public void validTargetNoResolver_throws() {
+    NameResolverProvider nameResolverProvider = new NameResolverProvider() {
+      @Override
+      protected boolean isAvailable() {
+        return true;
+      }
+
+      @Override
+      protected int priority() {
+        return 5;
+      }
+
+      @Override
+      public NameResolver newNameResolver(URI targetUri, NameResolver.Args args) {
+        return null;
+      }
+
+      @Override
+      public String getDefaultScheme() {
+        return "defaultscheme";
+      }
+    };
+    try {
+      ManagedChannelImpl.getNameResolver(
+          URI.create("defaultscheme:///foo.gogoleapis.com:8080"),
+          null, nameResolverProvider, NAMERESOLVER_ARGS);
+      fail("Should fail");
+    } catch (IllegalArgumentException e) {
+      // expected
+    }
+  }
+
+
   private static final class FakeBackoffPolicyProvider implements BackoffPolicy.Provider {
     @Override
     public BackoffPolicy get() {

util/src/main/java/io/grpc/util/ForwardingLoadBalancerHelper.java

@@ -106,6 +106,11 @@ public abstract class ForwardingLoadBalancerHelper extends LoadBalancer.Helper {
     return delegate().getAuthority();
   }
 
+  @Override
+  public String getChannelTarget() {
+    return delegate().getChannelTarget();
+  }
+
   @Override
   public ChannelCredentials getChannelCredentials() {
     return delegate().getChannelCredentials();