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

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package io.grpc.internal;

import com.google.common.base.Preconditions;

import io.grpc.Attributes;
import io.grpc.ClientInterceptor;
import io.grpc.LoadBalancer;
import io.grpc.ManagedChannelBuilder;
import io.grpc.NameResolver;
import io.grpc.NameResolverRegistry;
import io.grpc.ResolvedServerInfo;
import io.grpc.SimpleLoadBalancerFactory;

import java.net.SocketAddress;
import java.net.URI;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.Executor;

import javax.annotation.Nullable;

/**
 * The base class for channel builders.
 *
 * @param <T> The concrete type of this builder.
 */
public abstract class AbstractManagedChannelImplBuilder
        <T extends AbstractManagedChannelImplBuilder<T>> extends ManagedChannelBuilder<T> {

  @Nullable
  private Executor executor;
  private final List<ClientInterceptor> interceptors = new ArrayList<ClientInterceptor>();

  private final String target;

  @Nullable
  private final SocketAddress directServerAddress;

  @Nullable
  private String userAgent;

  @Nullable
  private String authorityOverride;

  @Nullable
  private NameResolver.Factory nameResolverFactory;

  @Nullable
  private LoadBalancer.Factory loadBalancerFactory;

  protected AbstractManagedChannelImplBuilder(String target) {
    this.target = Preconditions.checkNotNull(target);
    this.directServerAddress = null;
  }

  protected AbstractManagedChannelImplBuilder(SocketAddress directServerAddress, String authority) {
    this.target = "directaddress:///" + directServerAddress;
    this.directServerAddress = directServerAddress;
    this.nameResolverFactory = new DirectAddressNameResolverFactory(directServerAddress, authority);
  }

  @Override
  public final T executor(Executor executor) {
    this.executor = executor;
    return thisT();
  }

  @Override
  public final T intercept(List<ClientInterceptor> interceptors) {
    this.interceptors.addAll(interceptors);
    return thisT();
  }

  @Override
  public final T intercept(ClientInterceptor... interceptors) {
    return intercept(Arrays.asList(interceptors));
  }

  @Override
  public final T nameResolverFactory(NameResolver.Factory resolverFactory) {
    Preconditions.checkState(directServerAddress == null,
        "directServerAddress is set (%s), which forbids the use of NameResolverFactory",
        directServerAddress);
    this.nameResolverFactory = resolverFactory;
    return thisT();
  }

  @Override
  public final T loadBalancerFactory(LoadBalancer.Factory loadBalancerFactory) {
    Preconditions.checkState(directServerAddress == null,
        "directServerAddress is set (%s), which forbids the use of LoadBalancerFactory",
        directServerAddress);
    this.loadBalancerFactory = loadBalancerFactory;
    return thisT();
  }

  private T thisT() {
    @SuppressWarnings("unchecked")
    T thisT = (T) this;
    return thisT;
  }

  @Override
  public final T userAgent(String userAgent) {
    this.userAgent = userAgent;
    return thisT();
  }

  @Override
  public final T overrideAuthority(String authority) {
    this.authorityOverride = checkAuthority(authority);
    return thisT();
  }

  /**
   * Verifies the authority is valid.  This method exists as an escape hatch for putting in an
   * authority that is valid, but would fail the default validation provided by this
   * implementation.
   */
  protected String checkAuthority(String authority) {
    return GrpcUtil.checkAuthority(authority);
  }

  @Override
  public ManagedChannelImpl build() {
    ClientTransportFactory transportFactory = new AuthorityOverridingTransportFactory(
        buildTransportFactory(), authorityOverride);
    return new ManagedChannelImpl(
        target,
        // TODO(carl-mastrangelo): Allow clients to pass this in
        new ExponentialBackoffPolicy.Provider(),
        nameResolverFactory == null ? NameResolverRegistry.getDefaultRegistry()
            : nameResolverFactory,
        getNameResolverParams(),
        loadBalancerFactory == null ? SimpleLoadBalancerFactory.getInstance()
            : loadBalancerFactory,
        transportFactory, executor, userAgent, interceptors);
  }

  /**
   * Subclasses should override this method to provide the {@link ClientTransportFactory}
   * appropriate for this channel. This method is meant for Transport implementors and should not
   * be used by normal users.
   */
  protected abstract ClientTransportFactory buildTransportFactory();

  /**
   * Subclasses can override this method to provide additional parameters to {@link
   * NameResolver.Factory#newNameResolver}. The default implementation returns {@link
   * Attributes.EMPTY}.
   */
  protected Attributes getNameResolverParams() {
    return Attributes.EMPTY;
  }

  private static class AuthorityOverridingTransportFactory implements ClientTransportFactory {
    final ClientTransportFactory factory;
    @Nullable final String authorityOverride;

    AuthorityOverridingTransportFactory(
        ClientTransportFactory factory, @Nullable String authorityOverride) {
      this.factory = factory;
      this.authorityOverride = authorityOverride;
    }

    @Override
    public ClientTransport newClientTransport(SocketAddress serverAddress, String authority) {
      return factory.newClientTransport(
          serverAddress, authorityOverride != null ? authorityOverride : authority);
    }

    @Override
    public int referenceCount() {
      return factory.referenceCount();
    }

    @Override
    public ReferenceCounted retain() {
      factory.retain();
      return this;
    }

    @Override
    public ReferenceCounted release() {
      factory.release();
      return this;
    }
  }

  private static class DirectAddressNameResolverFactory extends NameResolver.Factory {
    final SocketAddress address;
    final String authority;

    DirectAddressNameResolverFactory(SocketAddress address, String authority) {
      this.address = address;
      this.authority = authority;
    }

    @Override
    public NameResolver newNameResolver(URI notUsedUri, Attributes params) {
      return new NameResolver() {
        @Override
        public String getServiceAuthority() {
          return authority;
        }

        @Override
        public void start(final Listener listener) {
          listener.onUpdate(
              Collections.singletonList(new ResolvedServerInfo(address, Attributes.EMPTY)),
              Attributes.EMPTY);
        }

        @Override
        public void shutdown() {}
      };
    }
  }
}