core: implement Helper#createResolvingOobChannel (#6923)

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

@@ -360,7 +360,7 @@ public abstract class LoadBalancer {
   @Deprecated
   public void handleSubchannelState(
       Subchannel subchannel, ConnectivityStateInfo stateInfo) {
-    // Do nothing.  If the implemetation doesn't implement this, it will get subchannel states from
+    // Do nothing.  If the implementation doesn't implement this, it will get subchannel states from
     // the new API.  We don't throw because there may be forwarding LoadBalancers still plumb this.
   }
 
@@ -507,7 +507,7 @@ public abstract class LoadBalancer {
      * A decision to proceed the RPC on a Subchannel.
      *
      * <p>The Subchannel should either be an original Subchannel returned by {@link
-     * Helper#createSubchannel Helper.createSubchannel()}, or a wrapper of it preferrably based on
+     * Helper#createSubchannel Helper.createSubchannel()}, or a wrapper of it preferably based on
      * {@code ForwardingSubchannel}.  At the very least its {@link Subchannel#getInternalSubchannel
      * getInternalSubchannel()} must return the same object as the one returned by the original.
      * Otherwise the Channel cannot use it for the RPC.
@@ -1024,7 +1024,7 @@ public abstract class LoadBalancer {
 
     /**
      * Updates the addresses used for connections in the {@code Channel} that was created by {@link
-     * #createOobChannel(EquivalentAddressGroup, String)}. This is supperior to {@link
+     * #createOobChannel(EquivalentAddressGroup, String)}. This is superior to {@link
      * #createOobChannel(EquivalentAddressGroup, String)} when the old and new addresses overlap,
      * since the channel can continue using an existing connection.
      *
@@ -1048,8 +1048,6 @@ public abstract class LoadBalancer {
      * <p>The LoadBalancer is responsible for closing unused OOB channels, and closing all OOB
      * channels within {@link #shutdown}.
      *
-     * <P>NOT IMPLEMENTED: this method is currently a stub and not yet implemented by gRPC.
-     *
      * @since 1.20.0
      */
     public ManagedChannel createResolvingOobChannel(String target) {

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

@@ -1259,6 +1259,49 @@ final class ManagedChannelImpl extends ManagedChannel implements
       return oobChannel;
     }
 
+    @Override
+    public ManagedChannel createResolvingOobChannel(String target) {
+      final class ResolvingOobChannelBuilder
+          extends AbstractManagedChannelImplBuilder<ResolvingOobChannelBuilder> {
+        int defaultPort = -1;
+
+        ResolvingOobChannelBuilder(String target) {
+          super(target);
+        }
+
+        @Override
+        public int getDefaultPort() {
+          return defaultPort;
+        }
+
+        @Override
+        protected ClientTransportFactory buildTransportFactory() {
+          throw new UnsupportedOperationException();
+        }
+      }
+
+      checkState(!terminated, "Channel is terminated");
+
+      ResolvingOobChannelBuilder builder = new ResolvingOobChannelBuilder(target);
+      builder.offloadExecutorPool = offloadExecutorHolder.pool;
+      builder.overrideAuthority(getAuthority());
+      builder.nameResolverFactory(nameResolverFactory);
+      builder.executorPool = executorPool;
+      builder.maxTraceEvents = maxTraceEvents;
+      builder.proxyDetector = nameResolverArgs.getProxyDetector();
+      builder.defaultPort = nameResolverArgs.getDefaultPort();
+      builder.userAgent = userAgent;
+      return
+          new ManagedChannelImpl(
+              builder,
+              transportFactory,
+              backoffPolicyProvider,
+              balancerRpcExecutorPool,
+              stopwatchSupplier,
+              Collections.<ClientInterceptor>emptyList(),
+              timeProvider);
+    }
+
     @Override
     public void updateOobChannelAddresses(ManagedChannel channel, EquivalentAddressGroup eag) {
       checkArgument(channel instanceof OobChannel,

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

@@ -18,6 +18,7 @@ package io.grpc.internal;
 
 import static com.google.common.base.Preconditions.checkState;
 import static com.google.common.truth.Truth.assertThat;
+import static com.google.common.truth.Truth.assertWithMessage;
 import static io.grpc.ConnectivityState.CONNECTING;
 import static io.grpc.ConnectivityState.IDLE;
 import static io.grpc.ConnectivityState.READY;
@@ -3948,6 +3949,28 @@ public class ManagedChannelImplTest {
     }
   }
 
+  @Test
+  public void createResolvingOobChannel() throws Exception {
+    String oobTarget = "fake://second.example.com";
+    URI oobUri = new URI(oobTarget);
+    channelBuilder
+        .nameResolverFactory(new FakeNameResolverFactory.Builder(expectedUri, oobUri).build());
+    createChannel();
+
+    ManagedChannel resolvedOobChannel = null;
+    try {
+      resolvedOobChannel = helper.createResolvingOobChannel(oobTarget);
+
+      assertWithMessage("resolving oob channel should have same authority")
+          .that(resolvedOobChannel.authority())
+          .isEqualTo(channel.authority());
+    } finally {
+      if (resolvedOobChannel != null) {
+        resolvedOobChannel.shutdownNow();
+      }
+    }
+  }
+
   private static final class ChannelBuilder
       extends AbstractManagedChannelImplBuilder<ChannelBuilder> {
 
@@ -3979,7 +4002,7 @@ public class ManagedChannelImplTest {
   }
 
   private static final class FakeNameResolverFactory extends NameResolver.Factory {
-    final URI expectedUri;
+    final List<URI> expectedUris;
     final List<EquivalentAddressGroup> servers;
     final boolean resolvedAtStart;
     final Status error;
@@ -3987,11 +4010,11 @@ public class ManagedChannelImplTest {
     final AtomicReference<ConfigOrError> nextConfigOrError = new AtomicReference<>();
 
     FakeNameResolverFactory(
-        URI expectedUri,
+        List<URI> expectedUris,
         List<EquivalentAddressGroup> servers,
         boolean resolvedAtStart,
         Status error) {
-      this.expectedUri = expectedUri;
+      this.expectedUris = expectedUris;
       this.servers = servers;
       this.resolvedAtStart = resolvedAtStart;
       this.error = error;
@@ -3999,12 +4022,12 @@ public class ManagedChannelImplTest {
 
     @Override
     public NameResolver newNameResolver(final URI targetUri, NameResolver.Args args) {
-      if (!expectedUri.equals(targetUri)) {
+      if (!expectedUris.contains(targetUri)) {
         return null;
       }
       assertEquals(DEFAULT_PORT, args.getDefaultPort());
       FakeNameResolverFactory.FakeNameResolver resolver =
-          new FakeNameResolverFactory.FakeNameResolver(error);
+          new FakeNameResolverFactory.FakeNameResolver(targetUri, error);
       resolvers.add(resolver);
       return resolver;
     }
@@ -4021,17 +4044,19 @@ public class ManagedChannelImplTest {
     }
 
     final class FakeNameResolver extends NameResolver {
+      final URI targetUri;
       Listener2 listener;
       boolean shutdown;
       int refreshCalled;
       Status error;
 
-      FakeNameResolver(Status error) {
+      FakeNameResolver(URI targetUri, Status error) {
+        this.targetUri = targetUri;
         this.error = error;
       }
 
       @Override public String getServiceAuthority() {
-        return expectedUri.getAuthority();
+        return targetUri.getAuthority();
       }
 
       @Override public void start(Listener2 listener) {
@@ -4072,13 +4097,13 @@ public class ManagedChannelImplTest {
     }
 
     static final class Builder {
-      final URI expectedUri;
+      List<URI> expectedUris;
       List<EquivalentAddressGroup> servers = ImmutableList.of();
       boolean resolvedAtStart = true;
       Status error = null;
 
-      Builder(URI expectedUri) {
+      Builder(URI... expectedUris) {
-        this.expectedUri = expectedUri;
+        this.expectedUris = Collections.unmodifiableList(Arrays.asList(expectedUris));
       }
 
       FakeNameResolverFactory.Builder setServers(List<EquivalentAddressGroup> servers) {
@@ -4097,7 +4122,7 @@ public class ManagedChannelImplTest {
       }
 
       FakeNameResolverFactory build() {
-        return new FakeNameResolverFactory(expectedUri, servers, resolvedAtStart, error);
+        return new FakeNameResolverFactory(expectedUris, servers, resolvedAtStart, error);
       }
     }
   }