core: make ManagedChannel honor Service config LB

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

@@ -31,7 +31,6 @@ import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.NameResolver;
 import io.grpc.NameResolverProvider;
-import io.grpc.PickFirstBalancerFactory;
 import io.opencensus.trace.Tracing;
 import java.net.SocketAddress;
 import java.net.URI;
@@ -85,9 +84,6 @@ public abstract class AbstractManagedChannelImplBuilder
   private static final NameResolver.Factory DEFAULT_NAME_RESOLVER_FACTORY =
       NameResolverProvider.asFactory();
 
-  private static final LoadBalancer.Factory DEFAULT_LOAD_BALANCER_FACTORY =
-      PickFirstBalancerFactory.getInstance();
-
   private static final DecompressorRegistry DEFAULT_DECOMPRESSOR_REGISTRY =
       DecompressorRegistry.getDefaultInstance();
 
@@ -117,7 +113,7 @@ public abstract class AbstractManagedChannelImplBuilder
   String authorityOverride;
 
 
-  LoadBalancer.Factory loadBalancerFactory = DEFAULT_LOAD_BALANCER_FACTORY;
+  @Nullable LoadBalancer.Factory loadBalancerFactory;
 
   boolean fullStreamDecompression;
 
@@ -236,11 +232,7 @@ public abstract class AbstractManagedChannelImplBuilder
     Preconditions.checkState(directServerAddress == null,
         "directServerAddress is set (%s), which forbids the use of LoadBalancer.Factory",
         directServerAddress);
-    if (loadBalancerFactory != null) {
-      this.loadBalancerFactory = loadBalancerFactory;
-    } else {
-      this.loadBalancerFactory = DEFAULT_LOAD_BALANCER_FACTORY;
-    }
+    this.loadBalancerFactory = loadBalancerFactory;
     return thisT();
   }
 

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

@@ -0,0 +1,192 @@
+/*
+ * Copyright 2018, gRPC Authors All rights reserved.
+ *
+ * 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.internal;
+
+import com.google.common.annotations.VisibleForTesting;
+import io.grpc.Attributes;
+import io.grpc.ConnectivityState;
+import io.grpc.ConnectivityStateInfo;
+import io.grpc.EquivalentAddressGroup;
+import io.grpc.LoadBalancer;
+import io.grpc.LoadBalancer.Helper;
+import io.grpc.LoadBalancer.PickResult;
+import io.grpc.LoadBalancer.PickSubchannelArgs;
+import io.grpc.LoadBalancer.SubchannelPicker;
+import io.grpc.PickFirstBalancerFactory;
+import io.grpc.Status;
+import java.lang.reflect.Method;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.logging.Logger;
+import javax.annotation.Nullable;
+
+final class AutoConfiguredLoadBalancerFactory extends LoadBalancer.Factory {
+  private static final Logger logger =
+      Logger.getLogger(AutoConfiguredLoadBalancerFactory.class.getName());
+
+  @VisibleForTesting
+  static final String ROUND_ROUND_LOAD_BALANCER_FACTORY_NAME =
+      "io.grpc.util.RoundRobinLoadBalancerFactory";
+  @VisibleForTesting
+  static final String GRPCLB_LOAD_BALANCER_FACTORY_NAME =
+      "io.grpc.grpclb.GrpclbLoadBalancerFactory";
+
+  AutoConfiguredLoadBalancerFactory() {}
+
+  @Override
+  public LoadBalancer newLoadBalancer(Helper helper) {
+    return new AutoConfiguredLoadBalancer(helper);
+  }
+
+  private static final class EmptySubchannelPicker extends SubchannelPicker {
+
+    @Override
+    public PickResult pickSubchannel(PickSubchannelArgs args) {
+      return PickResult.withNoResult();
+    }
+  }
+
+  @VisibleForTesting
+  static final class AutoConfiguredLoadBalancer extends LoadBalancer {
+    private final Helper helper;
+    private LoadBalancer delegate;
+    private LoadBalancer.Factory delegateFactory;
+
+    AutoConfiguredLoadBalancer(Helper helper) {
+      this.helper = helper;
+      setDelegateFactory(PickFirstBalancerFactory.getInstance());
+      setDelegate(getDelegateFactory().newLoadBalancer(helper));
+    }
+
+    //  Must be run inside ChannelExecutor.
+    @Override
+    public void handleResolvedAddressGroups(
+        List<EquivalentAddressGroup> servers, Attributes attributes) {
+      if (attributes.keys().contains(GrpcAttributes.NAME_RESOLVER_SERVICE_CONFIG)) {
+        Factory newlbf = decideLoadBalancerFactory(
+            servers, attributes.get(GrpcAttributes.NAME_RESOLVER_SERVICE_CONFIG));
+        if (newlbf != null && newlbf != delegateFactory) {
+          helper.updateBalancingState(ConnectivityState.CONNECTING, new EmptySubchannelPicker());
+          getDelegate().shutdown();
+          setDelegateFactory(newlbf);
+          setDelegate(getDelegateFactory().newLoadBalancer(helper));
+        }
+      }
+      getDelegate().handleResolvedAddressGroups(servers, attributes);
+    }
+
+    @Override
+    public void handleNameResolutionError(Status error) {
+      getDelegate().handleNameResolutionError(error);
+    }
+
+    @Override
+    public void handleSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
+      getDelegate().handleSubchannelState(subchannel, stateInfo);
+    }
+
+    @Override
+    public void shutdown() {
+      getDelegate().shutdown();
+      setDelegate(null);
+    }
+
+    @VisibleForTesting
+    LoadBalancer getDelegate() {
+      return delegate;
+    }
+
+    @VisibleForTesting
+    void setDelegate(LoadBalancer delegate) {
+      this.delegate = delegate;
+    }
+
+    @VisibleForTesting
+    LoadBalancer.Factory getDelegateFactory() {
+      return delegateFactory;
+    }
+
+    @VisibleForTesting
+    void setDelegateFactory(LoadBalancer.Factory delegateFactory) {
+      this.delegateFactory = delegateFactory;
+    }
+
+    /**
+     * Picks a load balancer based on given criteria.  In order of preference:
+     *
+     * <ol>
+     *   <li>User provided lb on the channel.  This is a degenerate case and not handled here.</li>
+     *   <li>gRPCLB if on the class path and any gRPC LB balancer addresses are present</li>
+     *   <li>RoundRobin if on the class path and picked by the service config</li>
+     *   <li>PickFirst if the service config choice does not specify</li>
+     * </ol>
+     *
+     * @param servers The list of servers reported
+     * @param config the service config object
+     * @return the new load balancer factory, or null if the existing lb should be used.
+     */
+    @Nullable
+    @VisibleForTesting
+    static LoadBalancer.Factory decideLoadBalancerFactory(
+        List<EquivalentAddressGroup> servers, Map<String, Object> config) {
+
+      // Check for balancer addresses
+      boolean haveBalancerAddress = false;
+      for (EquivalentAddressGroup s : servers) {
+        if (s.getAttributes().get(GrpcAttributes.ATTR_LB_ADDR_AUTHORITY) != null) {
+          haveBalancerAddress = true;
+          break;
+        }
+      }
+
+      if (haveBalancerAddress) {
+        try {
+          Class<?> lbFactoryClass = Class.forName(GRPCLB_LOAD_BALANCER_FACTORY_NAME);
+          Method getInstance = lbFactoryClass.getMethod("getInstance");
+          return (LoadBalancer.Factory) getInstance.invoke(null);
+        } catch (RuntimeException e) {
+          throw e;
+        } catch (Exception e) {
+          throw new RuntimeException("Can't get GRPCLB, but balancer addresses were present", e);
+        }
+      }
+
+      String serviceConfigChoiceBalancingPolicy =
+          ServiceConfigUtil.getLoadBalancingPolicy(config);
+
+      // Check for an explicitly present lb choice
+      if (serviceConfigChoiceBalancingPolicy != null) {
+        if (serviceConfigChoiceBalancingPolicy.toUpperCase(Locale.ROOT).equals("ROUND_ROBIN")) {
+          try {
+            Class<?> lbFactoryClass = Class.forName(ROUND_ROUND_LOAD_BALANCER_FACTORY_NAME);
+            Method getInstance = lbFactoryClass.getMethod("getInstance");
+            return (LoadBalancer.Factory) getInstance.invoke(null);
+          } catch (RuntimeException e) {
+            throw e;
+          } catch (Exception e) {
+            throw new RuntimeException("Can't get Round Robin LB", e);
+          }
+        }
+        throw new IllegalArgumentException(
+            "Unknown service config policy: " + serviceConfigChoiceBalancingPolicy);
+      }
+
+      return PickFirstBalancerFactory.getInstance();
+    }
+  }
+}

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

@@ -211,11 +211,9 @@ final class DnsNameResolver extends NameResolver {
             } catch (RuntimeException e) {
               logger.log(Level.WARNING, "Can't parse service Configs", e);
             }
-
-            // TODO(carl-mastrangelo): pass this as an object.
-            attrs.set(
-                GrpcAttributes.NAME_RESOLVER_ATTR_DNS_TXT,
-                Collections.unmodifiableList(new ArrayList<String>(resolvedInetAddrs.txtRecords)));
+            if (serviceConfig != null) {
+              attrs.set(GrpcAttributes.NAME_RESOLVER_SERVICE_CONFIG, serviceConfig);
+            }
           } else {
             logger.log(Level.FINE, "No TXT records found for {0}", new Object[]{host});
           }

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

@@ -17,17 +17,17 @@
 package io.grpc.internal;
 
 import io.grpc.Attributes;
-import java.util.List;
+import java.util.Map;
 
 /**
  * Special attributes that are only useful to gRPC.
  */
 public final class GrpcAttributes {
   /**
-   * Attribute key TXT DNS records.
+   * Attribute key for service config.
    */
-  public static final Attributes.Key<List<String>> NAME_RESOLVER_ATTR_DNS_TXT =
-      Attributes.Key.of("dns-txt");
+  public static final Attributes.Key<Map<String, Object>> NAME_RESOLVER_SERVICE_CONFIG =
+      Attributes.Key.of("service-config");
 
   /**
    * The naming authority of a gRPC LB server address.  It is an address-group-level attribute,

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

@@ -552,8 +552,11 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
     this.nameResolverFactory = builder.getNameResolverFactory();
     this.nameResolverParams = checkNotNull(builder.getNameResolverParams(), "nameResolverParams");
     this.nameResolver = getNameResolver(target, nameResolverFactory, nameResolverParams);
-    this.loadBalancerFactory =
-        checkNotNull(builder.loadBalancerFactory, "loadBalancerFactory");
+    if (builder.loadBalancerFactory == null) {
+      this.loadBalancerFactory = new AutoConfiguredLoadBalancerFactory();
+    } else {
+      this.loadBalancerFactory = builder.loadBalancerFactory;
+    }
     this.executorPool = checkNotNull(builder.executorPool, "executorPool");
     this.oobExecutorPool = checkNotNull(oobExecutorPool, "oobExecutorPool");
     this.executor = checkNotNull(executorPool.getObject(), "executor");
@@ -1144,11 +1147,9 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
   }
 
   private class NameResolverListenerImpl implements NameResolver.Listener {
-    final LoadBalancer balancer;
-    final LoadBalancer.Helper helper;
+    final LbHelperImpl helper;
 
     NameResolverListenerImpl(LbHelperImpl helperImpl) {
-      this.balancer = helperImpl.lb;
       this.helper = helperImpl;
     }
 
@@ -1185,7 +1186,7 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
                 re);
           }
 
-          balancer.handleResolvedAddressGroups(servers, config);
+          helper.lb.handleResolvedAddressGroups(servers, config);
         }
       }
 
@@ -1206,7 +1207,7 @@ final class ManagedChannelImpl extends ManagedChannel implements Instrumented<Ch
                   if (NameResolverListenerImpl.this.helper != ManagedChannelImpl.this.lbHelper) {
                     return;
                   }
-                  balancer.handleNameResolutionError(error);
+                  helper.lb.handleNameResolutionError(error);
                   if (nameResolverRefreshFuture != null) {
                     // The name resolver may invoke onError multiple times, but we only want to
                     // schedule one backoff attempt

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

@@ -50,6 +50,15 @@ final class ServiceConfigUtil {
 
   private ServiceConfigUtil() {}
 
+  @Nullable
+  static String getLoadBalancingPolicy(Map<String, Object> serviceConfig) {
+    String key = "loadBalancingPolicy";
+    if (serviceConfig.containsKey(key)) {
+      return getString(serviceConfig, key);
+    }
+    return null;
+  }
+
   /**
    * Determines if a given Service Config choice applies, and if so, returns it.
    *
@@ -179,6 +188,20 @@ final class ServiceConfigUtil {
         String.format("value %s for key %s in %s is not Double", value, key, obj));
   }
 
+  /**
+   * Gets a string from an object for the given key.
+   */
+  @SuppressWarnings("unchecked")
+  private static String getString(Map<String, Object> obj, String key) {
+    assert obj.containsKey(key);
+    Object value = checkNotNull(obj.get(key), "no such key %s", key);
+    if (value instanceof String) {
+      return (String) value;
+    }
+    throw new ClassCastException(
+        String.format("value %s for key %s in %s is not String", value, key, obj));
+  }
+
   /**
    * Gets a string from an object for the given index.
    */

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

@@ -117,7 +117,7 @@ public class AbstractManagedChannelImplBuilderTest {
 
   @Test
   public void loadBalancerFactory_default() {
-    assertNotNull(builder.loadBalancerFactory);
+    assertNull(builder.loadBalancerFactory);
   }
 
   @Test

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

@@ -0,0 +1,189 @@
+/*
+ * Copyright 2018, gRPC Authors All rights reserved.
+ *
+ * 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.internal;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import io.grpc.Attributes;
+import io.grpc.ConnectivityState;
+import io.grpc.ConnectivityStateInfo;
+import io.grpc.EquivalentAddressGroup;
+import io.grpc.LoadBalancer;
+import io.grpc.LoadBalancer.Helper;
+import io.grpc.LoadBalancer.Subchannel;
+import io.grpc.LoadBalancer.SubchannelPicker;
+import io.grpc.ManagedChannel;
+import io.grpc.NameResolver.Factory;
+import io.grpc.PickFirstBalancerFactory;
+import io.grpc.Status;
+import io.grpc.internal.AutoConfiguredLoadBalancerFactory.AutoConfiguredLoadBalancer;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+import javax.annotation.Nonnull;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Unit tests for {@link AutoConfiguredLoadBalancerFactory}.
+ */
+// TODO(carl-mastrangelo): Add tests for selection logic.
+@RunWith(JUnit4.class)
+public class AutoConfiguredLoadBalancerFactoryTest {
+  private final AutoConfiguredLoadBalancerFactory lbf = new AutoConfiguredLoadBalancerFactory();
+
+  @Test
+  public void newLoadBalancer_isAuto() {
+    LoadBalancer lb = lbf.newLoadBalancer(new TestHelper());
+
+    assertThat(lb).isInstanceOf(AutoConfiguredLoadBalancer.class);
+  }
+
+  @Test
+  public void defaultIsPickFirst() {
+    AutoConfiguredLoadBalancer lb =
+        (AutoConfiguredLoadBalancer) lbf.newLoadBalancer(new TestHelper());
+
+    assertThat(lb.getDelegateFactory()).isInstanceOf(PickFirstBalancerFactory.class);
+    assertThat(lb.getDelegate().getClass().getName()).contains("PickFirst");
+  }
+
+  @Test
+  public void forwardsCalls() {
+    AutoConfiguredLoadBalancer lb =
+        (AutoConfiguredLoadBalancer) lbf.newLoadBalancer(new TestHelper());
+
+    final AtomicInteger calls = new AtomicInteger();
+    TestLoadBalancer testlb = new TestLoadBalancer() {
+
+      @Override
+      public void handleNameResolutionError(Status error) {
+        calls.getAndSet(1);
+      }
+
+      @Override
+      public void handleSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
+        calls.getAndSet(2);
+      }
+
+      @Override
+      public void shutdown() {
+        calls.getAndSet(3);
+      }
+    };
+
+    lb.setDelegate(testlb);
+
+    lb.handleNameResolutionError(Status.RESOURCE_EXHAUSTED);
+    assertThat(calls.getAndSet(0)).isEqualTo(1);
+
+    lb.handleSubchannelState(null, null);
+    assertThat(calls.getAndSet(0)).isEqualTo(2);
+
+    lb.shutdown();
+    assertThat(calls.getAndSet(0)).isEqualTo(3);
+  }
+
+  public static class ForwardingLoadBalancer extends LoadBalancer {
+    private final LoadBalancer delegate;
+
+    public ForwardingLoadBalancer(LoadBalancer delegate) {
+      this.delegate = delegate;
+    }
+
+    protected LoadBalancer delegate() {
+      return delegate;
+    }
+
+    @Override
+    public void handleResolvedAddressGroups(
+        List<EquivalentAddressGroup> servers, Attributes attributes) {
+      delegate().handleResolvedAddressGroups(servers, attributes);
+    }
+
+    @Override
+    public void handleNameResolutionError(Status error) {
+      delegate().handleNameResolutionError(error);
+    }
+
+    @Override
+    public void handleSubchannelState(Subchannel subchannel, ConnectivityStateInfo stateInfo) {
+      delegate().handleSubchannelState(subchannel, stateInfo);
+    }
+
+    @Override
+    public void shutdown() {
+      delegate().shutdown();
+    }
+  }
+
+  public static class ForwardingLoadBalancerHelper extends Helper {
+
+    private final Helper delegate;
+
+    public ForwardingLoadBalancerHelper(Helper delegate) {
+      this.delegate = delegate;
+    }
+
+    protected Helper delegate() {
+      return delegate;
+    }
+
+    @Override
+    public Subchannel createSubchannel(EquivalentAddressGroup addrs, Attributes attrs) {
+      return delegate().createSubchannel(addrs, attrs);
+    }
+
+    @Override
+    public ManagedChannel createOobChannel(EquivalentAddressGroup eag, String authority) {
+      return delegate().createOobChannel(eag, authority);
+    }
+
+    @Override
+    public void updateBalancingState(
+        @Nonnull ConnectivityState newState, @Nonnull SubchannelPicker newPicker) {
+      delegate().updateBalancingState(newState, newPicker);
+    }
+
+    @Override
+    public void runSerialized(Runnable task) {
+      delegate().runSerialized(task);
+    }
+
+    @Override
+    public Factory getNameResolverFactory() {
+      return delegate().getNameResolverFactory();
+    }
+
+    @Override
+    public String getAuthority() {
+      return delegate().getAuthority();
+    }
+  }
+
+  private static class TestLoadBalancer extends ForwardingLoadBalancer {
+    TestLoadBalancer() {
+      super(null);
+    }
+  }
+
+  private static class TestHelper extends ForwardingLoadBalancerHelper {
+    TestHelper() {
+      super(null);
+    }
+  }
+}