core: add default implementation of managed channel builder

benchmarks/src/jmh/java/io/grpc/benchmarks/TransportBenchmark.java

@@ -20,6 +20,7 @@ import static io.grpc.benchmarks.Utils.pickUnusedPort;
 
 import com.google.protobuf.ByteString;
 import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
 import io.grpc.Server;
 import io.grpc.Status;
 import io.grpc.StatusRuntimeException;
@@ -30,7 +31,6 @@ import io.grpc.benchmarks.proto.Messages.SimpleResponse;
 import io.grpc.benchmarks.qps.AsyncServer;
 import io.grpc.inprocess.InProcessChannelBuilder;
 import io.grpc.inprocess.InProcessServerBuilder;
-import io.grpc.internal.AbstractManagedChannelImplBuilder;
 import io.grpc.internal.AbstractServerImplBuilder;
 import io.grpc.netty.NegotiationType;
 import io.grpc.netty.NettyChannelBuilder;
@@ -81,7 +81,7 @@ public class TransportBenchmark {
   @Setup
   public void setUp() throws Exception {
     AbstractServerImplBuilder<?> serverBuilder;
-    AbstractManagedChannelImplBuilder<?> channelBuilder;
+    ManagedChannelBuilder<?> channelBuilder;
     switch (transport) {
       case INPROCESS:
       {

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

@@ -51,7 +51,7 @@ import java.util.logging.Logger;
 import javax.annotation.Nullable;
 
 /**
- * The base class for channel builders.
+ * Abstract base class for channel builders.
  *
  * @param <T> The concrete type of this builder.
  */

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

@@ -0,0 +1,198 @@
+/*
+ * Copyright 2020 The gRPC Authors
+ *
+ * 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.base.Preconditions;
+import io.grpc.ManagedChannelBuilder;
+import java.net.SocketAddress;
+import java.util.concurrent.Executor;
+import javax.annotation.Nullable;
+
+/**
+ * Default managed channel builder, for usage in Transport implementations.
+ */
+public final class ManagedChannelImplBuilder
+    extends AbstractManagedChannelImplBuilder<ManagedChannelImplBuilder> {
+
+  private boolean authorityCheckerDisabled;
+  @Deprecated
+  @Nullable
+  private OverrideAuthorityChecker authorityChecker;
+
+  /**
+   * An interface for Transport implementors to provide the {@link ClientTransportFactory}
+   * appropriate for the channel.
+   */
+  public interface ClientTransportFactoryBuilder {
+    ClientTransportFactory buildClientTransportFactory();
+  }
+
+  /**
+   * An interface for Transport implementors to provide a default port to {@link
+   * io.grpc.NameResolver} for use in cases where the target string doesn't include a port. The
+   * default implementation returns {@link GrpcUtil#DEFAULT_PORT_SSL}.
+   */
+  public interface ChannelBuilderDefaultPortProvider {
+    int getDefaultPort();
+  }
+
+  /**
+   * Default implementation of {@link ChannelBuilderDefaultPortProvider} that returns a fixed port.
+   */
+  public static final class FixedPortProvider implements ChannelBuilderDefaultPortProvider {
+    private final int port;
+
+    public FixedPortProvider(int port) {
+      this.port = port;
+    }
+
+    @Override
+    public int getDefaultPort() {
+      return port;
+    }
+  }
+
+  private final class ManagedChannelDefaultPortProvider implements
+      ChannelBuilderDefaultPortProvider {
+    @Override
+    public int getDefaultPort() {
+      return ManagedChannelImplBuilder.super.getDefaultPort();
+    }
+  }
+
+  private final ClientTransportFactoryBuilder clientTransportFactoryBuilder;
+  private final ChannelBuilderDefaultPortProvider channelBuilderDefaultPortProvider;
+
+  /**
+   * Creates a new managed channel builder with a target string, which can be either a valid {@link
+   * io.grpc.NameResolver}-compliant URI, or an authority string. Transport implementors must
+   * provide client transport factory builder, and may set custom channel default port provider.
+   */
+  public ManagedChannelImplBuilder(String target,
+      ClientTransportFactoryBuilder clientTransportFactoryBuilder,
+      @Nullable ChannelBuilderDefaultPortProvider channelBuilderDefaultPortProvider) {
+    super(target);
+    this.clientTransportFactoryBuilder = Preconditions
+        .checkNotNull(clientTransportFactoryBuilder, "clientTransportFactoryBuilder");
+
+    if (channelBuilderDefaultPortProvider != null) {
+      this.channelBuilderDefaultPortProvider = channelBuilderDefaultPortProvider;
+    } else {
+      this.channelBuilderDefaultPortProvider = new ManagedChannelDefaultPortProvider();
+    }
+  }
+
+  /**
+   * Creates a new managed channel builder with the given server address, authority string of the
+   * channel. Transport implementors must provide client transport factory builder, and may set
+   * custom channel default port provider.
+   */
+  public ManagedChannelImplBuilder(SocketAddress directServerAddress, String authority,
+      ClientTransportFactoryBuilder clientTransportFactoryBuilder,
+      @Nullable ChannelBuilderDefaultPortProvider channelBuilderDefaultPortProvider) {
+    super(directServerAddress, authority);
+    this.clientTransportFactoryBuilder = Preconditions
+        .checkNotNull(clientTransportFactoryBuilder, "clientTransportFactoryBuilder");
+
+    if (channelBuilderDefaultPortProvider != null) {
+      this.channelBuilderDefaultPortProvider = channelBuilderDefaultPortProvider;
+    } else {
+      this.channelBuilderDefaultPortProvider = new ManagedChannelDefaultPortProvider();
+    }
+  }
+
+  @Override
+  protected ClientTransportFactory buildTransportFactory() {
+    return clientTransportFactoryBuilder.buildClientTransportFactory();
+  }
+
+  @Override
+  protected int getDefaultPort() {
+    return channelBuilderDefaultPortProvider.getDefaultPort();
+  }
+
+  /** Disable the check whether the authority is valid. */
+  public ManagedChannelImplBuilder disableCheckAuthority() {
+    authorityCheckerDisabled = true;
+    return this;
+  }
+
+  /** Enable previously disabled authority check. */
+  public ManagedChannelImplBuilder enableCheckAuthority() {
+    authorityCheckerDisabled = false;
+    return this;
+  }
+
+  @Deprecated
+  public interface OverrideAuthorityChecker {
+    String checkAuthority(String authority);
+  }
+
+  @Deprecated
+  public void overrideAuthorityChecker(@Nullable OverrideAuthorityChecker authorityChecker) {
+    this.authorityChecker = authorityChecker;
+  }
+
+  @Override
+  protected String checkAuthority(String authority) {
+    if (authorityCheckerDisabled) {
+      return authority;
+    }
+    if (authorityChecker != null) {
+      return authorityChecker.checkAuthority(authority);
+    }
+    return super.checkAuthority(authority);
+  }
+
+  @Override
+  public void setStatsEnabled(boolean value) {
+    super.setStatsEnabled(value);
+  }
+
+  @Override
+  public void setStatsRecordStartedRpcs(boolean value) {
+    super.setStatsRecordStartedRpcs(value);
+  }
+
+  @Override
+  public void setStatsRecordFinishedRpcs(boolean value) {
+    super.setStatsRecordFinishedRpcs(value);
+  }
+
+  @Override
+  public void setStatsRecordRealTimeMetrics(boolean value) {
+    super.setStatsRecordRealTimeMetrics(value);
+  }
+
+  @Override
+  public void setTracingEnabled(boolean value) {
+    super.setTracingEnabled(value);
+  }
+
+  @Override
+  public ObjectPool<? extends Executor> getOffloadExecutorPool() {
+    return super.getOffloadExecutorPool();
+  }
+
+  public static ManagedChannelBuilder<?> forAddress(String name, int port) {
+    throw new UnsupportedOperationException("ClientTransportFactoryBuilder is required");
+  }
+
+  public static ManagedChannelBuilder<?> forTarget(String target) {
+    throw new UnsupportedOperationException("ClientTransportFactoryBuilder is required");
+  }
+}

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

@@ -0,0 +1,162 @@
+/*
+ * Copyright 2020 The gRPC Authors
+ *
+ * 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 org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import io.grpc.internal.ManagedChannelImplBuilder.ChannelBuilderDefaultPortProvider;
+import io.grpc.internal.ManagedChannelImplBuilder.ClientTransportFactoryBuilder;
+import io.grpc.internal.ManagedChannelImplBuilder.FixedPortProvider;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnit;
+import org.mockito.junit.MockitoRule;
+
+/** Unit tests for {@link ManagedChannelImplBuilder}. */
+@RunWith(JUnit4.class)
+public class ManagedChannelImplBuilderTest {
+  private static final int DUMMY_PORT = 42;
+  private static final String DUMMY_TARGET = "fake-target";
+  private static final String DUMMY_AUTHORITY_VALID = "valid:1234";
+  private static final String DUMMY_AUTHORITY_INVALID = "[ : : 1]";
+
+  @Rule public final MockitoRule mocks = MockitoJUnit.rule();
+  @Rule public final ExpectedException thrown = ExpectedException.none();
+
+  @Mock private ClientTransportFactoryBuilder mockClientTransportFactoryBuilder;
+  @Mock private ChannelBuilderDefaultPortProvider mockChannelBuilderDefaultPortProvider;
+  private ManagedChannelImplBuilder builder;
+
+  @Before
+  public void setUp() throws Exception {
+    builder = new ManagedChannelImplBuilder(
+        DUMMY_TARGET,
+        mockClientTransportFactoryBuilder,
+        mockChannelBuilderDefaultPortProvider);
+  }
+
+  /** Ensure buildTransportFactory() delegates to the custom implementation. */
+  @Test
+  public void buildTransportFactory() {
+    final ClientTransportFactory clientTransportFactory = mock(ClientTransportFactory.class);
+    when(mockClientTransportFactoryBuilder.buildClientTransportFactory())
+        .thenReturn(clientTransportFactory);
+    assertEquals(clientTransportFactory, builder.buildTransportFactory());
+    verify(mockClientTransportFactoryBuilder).buildClientTransportFactory();
+  }
+
+  /** Ensure getDefaultPort() returns default port when no custom implementation provided. */
+  @Test
+  public void getDefaultPort_default() {
+    final ManagedChannelImplBuilder builderNoPortProvider = new ManagedChannelImplBuilder(
+        DUMMY_TARGET, mockClientTransportFactoryBuilder, null);
+    assertEquals(GrpcUtil.DEFAULT_PORT_SSL, builderNoPortProvider.getDefaultPort());
+  }
+
+  /** Ensure getDefaultPort() delegates to the custom implementation. */
+  @Test
+  public void getDefaultPort_custom() {
+    when(mockChannelBuilderDefaultPortProvider.getDefaultPort()).thenReturn(DUMMY_PORT);
+    assertEquals(DUMMY_PORT, builder.getDefaultPort());
+    verify(mockChannelBuilderDefaultPortProvider).getDefaultPort();
+  }
+
+  /** Test FixedPortProvider(int port). */
+  @Test
+  public void getDefaultPort_fixedPortProvider() {
+    final ManagedChannelImplBuilder builderFixedPortProvider = new ManagedChannelImplBuilder(
+        DUMMY_TARGET,
+        mockClientTransportFactoryBuilder,
+        new FixedPortProvider(DUMMY_PORT));
+    assertEquals(DUMMY_PORT, builderFixedPortProvider.getDefaultPort());
+  }
+
+  @Test
+  public void checkAuthority_validAuthorityAllowed() {
+    assertEquals(DUMMY_AUTHORITY_VALID, builder.checkAuthority(DUMMY_AUTHORITY_VALID));
+  }
+
+  @Test
+  public void checkAuthority_invalidAuthorityFailed() {
+    thrown.expect(IllegalArgumentException.class);
+    thrown.expectMessage("Invalid authority");
+
+    builder.checkAuthority(DUMMY_AUTHORITY_INVALID);
+  }
+
+  @Test
+  public void disableCheckAuthority_validAuthorityAllowed() {
+    builder.disableCheckAuthority();
+    assertEquals(DUMMY_AUTHORITY_VALID, builder.checkAuthority(DUMMY_AUTHORITY_VALID));
+  }
+
+  @Test
+  public void disableCheckAuthority_invalidAuthorityAllowed() {
+    builder.disableCheckAuthority();
+    assertEquals(DUMMY_AUTHORITY_INVALID, builder.checkAuthority(DUMMY_AUTHORITY_INVALID));
+  }
+
+  @Test
+  public void enableCheckAuthority_validAuthorityAllowed() {
+    builder.disableCheckAuthority().enableCheckAuthority();
+    assertEquals(DUMMY_AUTHORITY_VALID, builder.checkAuthority(DUMMY_AUTHORITY_VALID));
+  }
+
+  @Test
+  public void disableCheckAuthority_invalidAuthorityFailed() {
+    thrown.expect(IllegalArgumentException.class);
+    thrown.expectMessage("Invalid authority");
+
+    builder.disableCheckAuthority().enableCheckAuthority();
+    builder.checkAuthority(DUMMY_AUTHORITY_INVALID);
+  }
+
+  /** Ensure authority check can disabled with custom authority check implementation. */
+  @Test
+  @SuppressWarnings("deprecation")
+  public void overrideAuthorityChecker_default() {
+    builder.overrideAuthorityChecker(
+        new io.grpc.internal.ManagedChannelImplBuilder.OverrideAuthorityChecker() {
+          @Override public String checkAuthority(String authority) {
+            return authority;
+          }
+        });
+    assertEquals(DUMMY_AUTHORITY_INVALID, builder.checkAuthority(DUMMY_AUTHORITY_INVALID));
+  }
+
+  /** Ensure custom authority is ignored after disableCheckAuthority(). */
+  @Test
+  @SuppressWarnings("deprecation")
+  public void overrideAuthorityChecker_ignored() {
+    builder.overrideAuthorityChecker(
+        new io.grpc.internal.ManagedChannelImplBuilder.OverrideAuthorityChecker() {
+          @Override public String checkAuthority(String authority) {
+            throw new IllegalArgumentException();
+          }
+        });
+    builder.disableCheckAuthority();
+    assertEquals(DUMMY_AUTHORITY_INVALID, builder.checkAuthority(DUMMY_AUTHORITY_INVALID));
+  }
+}

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

@@ -62,6 +62,7 @@ import io.grpc.NameResolver.ResolutionResult;
 import io.grpc.Status;
 import io.grpc.StringMarshaller;
 import io.grpc.internal.FakeClock.ScheduledTask;
+import io.grpc.internal.ManagedChannelImplBuilder.ClientTransportFactoryBuilder;
 import io.grpc.internal.TestUtils.MockClientTransportInfo;
 import java.net.SocketAddress;
 import java.net.URI;
@@ -159,21 +160,15 @@ public class ManagedChannelImplIdlenessTest {
     when(mockTransportFactory.getScheduledExecutorService())
         .thenReturn(timer.getScheduledExecutorService());
 
-    class Builder extends AbstractManagedChannelImplBuilder<Builder> {
-      Builder(String target) {
-        super(target);
-      }
-
-      @Override protected ClientTransportFactory buildTransportFactory() {
+    ManagedChannelImplBuilder builder = new ManagedChannelImplBuilder("fake://target",
+        new ClientTransportFactoryBuilder() {
+          @Override public ClientTransportFactory buildClientTransportFactory() {
             throw new UnsupportedOperationException();
           }
+        },
+        null);
 
-      @Override public Builder usePlaintext() {
-        throw new UnsupportedOperationException();
-      }
-    }
-
-    Builder builder = new Builder("fake://target")
+    builder
         .nameResolverFactory(mockNameResolverFactory)
         .defaultLoadBalancingPolicy(MOCK_POLICY_NAME)
         .idleTimeout(IDLE_TIMEOUT_SECONDS, TimeUnit.SECONDS)

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

@@ -107,6 +107,8 @@ import io.grpc.StringMarshaller;
 import io.grpc.internal.ClientTransportFactory.ClientTransportOptions;
 import io.grpc.internal.InternalSubchannel.TransportLogger;
 import io.grpc.internal.ManagedChannelImpl.ScParser;
+import io.grpc.internal.ManagedChannelImplBuilder.ClientTransportFactoryBuilder;
+import io.grpc.internal.ManagedChannelImplBuilder.FixedPortProvider;
 import io.grpc.internal.ServiceConfigUtil.PolicySelection;
 import io.grpc.internal.TestUtils.MockClientTransportInfo;
 import io.grpc.stub.ClientCalls;
@@ -269,7 +271,7 @@ public class ManagedChannelImplTest {
   private CallCredentials creds;
   @Mock
   private Executor offloadExecutor;
-  private ChannelBuilder channelBuilder;
+  private ManagedChannelImplBuilder channelBuilder;
   private boolean requestConnection = true;
   private BlockingQueue<MockClientTransportInfo> transports;
   private boolean panicExpected;
@@ -325,13 +327,19 @@ public class ManagedChannelImplTest {
     when(balancerRpcExecutorPool.getObject())
         .thenReturn(balancerRpcExecutor.getScheduledExecutorService());
 
-    channelBuilder =
-        new ChannelBuilder()
+    channelBuilder = new ManagedChannelImplBuilder(TARGET,
+        new ClientTransportFactoryBuilder() {
+          @Override
+          public ClientTransportFactory buildClientTransportFactory() {
+            throw new UnsupportedOperationException();
+          }
+        },
+        new FixedPortProvider(DEFAULT_PORT));
+    channelBuilder
         .nameResolverFactory(new FakeNameResolverFactory.Builder(expectedUri).build())
         .defaultLoadBalancingPolicy(MOCK_POLICY_NAME)
         .userAgent(USER_AGENT)
-            .idleTimeout(
-                AbstractManagedChannelImplBuilder.IDLE_MODE_MAX_TIMEOUT_DAYS, TimeUnit.DAYS)
+        .idleTimeout(ManagedChannelImplBuilder.IDLE_MODE_MAX_TIMEOUT_DAYS, TimeUnit.DAYS)
         .offloadExecutor(offloadExecutor);
     channelBuilder.executorPool = executorPool;
     channelBuilder.binlog = null;
@@ -3466,21 +3474,18 @@ public class ManagedChannelImplTest {
     }
 
     FakeNameResolverFactory2 factory = new FakeNameResolverFactory2();
-    final class CustomBuilder extends AbstractManagedChannelImplBuilder<CustomBuilder> {
-
-      CustomBuilder() {
-        super(TARGET);
-        this.executorPool = ManagedChannelImplTest.this.executorPool;
-        this.channelz = ManagedChannelImplTest.this.channelz;
-      }
 
+    ManagedChannelImplBuilder customBuilder = new ManagedChannelImplBuilder(TARGET,
+        new ClientTransportFactoryBuilder() {
           @Override
-      protected ClientTransportFactory buildTransportFactory() {
+          public ClientTransportFactory buildClientTransportFactory() {
             return mockTransportFactory;
           }
-    }
-
-    ManagedChannel mychannel = new CustomBuilder().nameResolverFactory(factory).build();
+        },
+        null);
+    customBuilder.executorPool = executorPool;
+    customBuilder.channelz = channelz;
+    ManagedChannel mychannel = customBuilder.nameResolverFactory(factory).build();
 
     ClientCall<Void, Void> call1 =
         mychannel.newCall(TestMethodDescriptors.voidMethod(), CallOptions.DEFAULT);
@@ -4025,22 +4030,6 @@ public class ManagedChannelImplTest {
     }
   }
 
-  private static final class ChannelBuilder
-      extends AbstractManagedChannelImplBuilder<ChannelBuilder> {
-
-    ChannelBuilder() {
-      super(TARGET);
-    }
-
-    @Override protected ClientTransportFactory buildTransportFactory() {
-      throw new UnsupportedOperationException();
-    }
-
-    @Override protected int getDefaultPort() {
-      return DEFAULT_PORT;
-    }
-  }
-
   private static final class FakeBackoffPolicyProvider implements BackoffPolicy.Provider {
     @Override
     public BackoffPolicy get() {

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

@@ -46,6 +46,8 @@ import io.grpc.LoadBalancerRegistry;
 import io.grpc.NameResolver;
 import io.grpc.NameResolver.ConfigOrError;
 import io.grpc.Status;
+import io.grpc.internal.ManagedChannelImplBuilder.ClientTransportFactoryBuilder;
+import io.grpc.internal.ManagedChannelImplBuilder.FixedPortProvider;
 import java.net.SocketAddress;
 import java.net.URI;
 import java.util.ArrayList;
@@ -151,7 +153,7 @@ public class ServiceConfigErrorHandlingTest {
   private ObjectPool<Executor> balancerRpcExecutorPool;
   @Mock
   private Executor blockingExecutor;
-  private ChannelBuilder channelBuilder;
+  private ManagedChannelImplBuilder channelBuilder;
 
   private void createChannel(ClientInterceptor... interceptors) {
     checkState(channel == null);
@@ -197,13 +199,20 @@ public class ServiceConfigErrorHandlingTest {
         .thenReturn(timer.getScheduledExecutorService());
     when(executorPool.getObject()).thenReturn(executor.getScheduledExecutorService());
 
-    channelBuilder =
-        new ChannelBuilder()
+    channelBuilder = new ManagedChannelImplBuilder(TARGET,
+        new ClientTransportFactoryBuilder() {
+          @Override
+          public ClientTransportFactory buildClientTransportFactory() {
+            throw new UnsupportedOperationException();
+          }
+        },
+        new FixedPortProvider(DEFAULT_PORT));
+
+    channelBuilder
         .nameResolverFactory(new FakeNameResolverFactory.Builder(expectedUri).build())
         .defaultLoadBalancingPolicy(MOCK_POLICY_NAME)
         .userAgent(USER_AGENT)
-            .idleTimeout(
-                AbstractManagedChannelImplBuilder.IDLE_MODE_MAX_TIMEOUT_DAYS, TimeUnit.DAYS)
+        .idleTimeout(ManagedChannelImplBuilder.IDLE_MODE_MAX_TIMEOUT_DAYS, TimeUnit.DAYS)
         .offloadExecutor(blockingExecutor);
     channelBuilder.executorPool = executorPool;
     channelBuilder.binlog = null;
@@ -527,22 +536,6 @@ public class ServiceConfigErrorHandlingTest {
     verify(mockLoadBalancer, never()).handleNameResolutionError(any(Status.class));
   }
 
-  private static final class ChannelBuilder
-      extends AbstractManagedChannelImplBuilder<ChannelBuilder> {
-
-    ChannelBuilder() {
-      super(TARGET);
-    }
-
-    @Override protected ClientTransportFactory buildTransportFactory() {
-      throw new UnsupportedOperationException();
-    }
-
-    @Override protected int getDefaultPort() {
-      return DEFAULT_PORT;
-    }
-  }
-
   private static final class FakeBackoffPolicyProvider implements BackoffPolicy.Provider {
     @Override
     public BackoffPolicy get() {