api: implement admin interface API (#7928)

Adds an AdminInterface API that automatically loads available admin services (currently, only supports Channelz and CSDS).

services/src/main/java/io/grpc/services/AdminInterface.java

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+/*
+ * Copyright 2021 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.services;
+
+import io.grpc.BindableService;
+import io.grpc.ExperimentalApi;
+import io.grpc.ServerServiceDefinition;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * Admin Interface provides a class of services for exposing the overall state of gRPC
+ * activity in a given binary. It aims to be a convenient API that provides available admin
+ * services.
+ */
+@ExperimentalApi("https://github.com/grpc/grpc-java/issues/7929")
+@ThreadSafe
+public final class AdminInterface {
+  private static final int DEFAULT_CHANNELZ_MAX_PAGE_SIZE = 100;
+  private static final Logger logger = Logger.getLogger(AdminInterface.class.getName());
+
+  // Do not instantiate.
+  private AdminInterface() {}
+
+  /**
+   * Returns a list of gRPC's built-in admin services.
+   *
+   * @return list of standard admin services
+   */
+  public static List<ServerServiceDefinition> getStandardServices() {
+    List<ServerServiceDefinition> services = new ArrayList<>();
+    services.add(ChannelzService.newInstance(DEFAULT_CHANNELZ_MAX_PAGE_SIZE).bindService());
+    BindableService csds = null;
+    try {
+      Class<?> clazz = Class.forName("io.grpc.xds.CsdsService");
+      Method m = clazz.getMethod("newInstance");
+      csds = (BindableService) m.invoke(null);
+    } catch (ClassNotFoundException e) {
+      logger.log(Level.FINE, "Unable to find CSDS service", e);
+    } catch (NoSuchMethodException e) {
+      logger.log(Level.FINE, "Unable to load CSDS service", e);
+    } catch (IllegalAccessException e) {
+      logger.log(Level.FINE, "Unable to load CSDS service", e);
+    } catch (InvocationTargetException e) {
+      logger.log(Level.FINE, "Unable to load CSDS service", e);
+    }
+    if (csds != null) {
+      services.add(csds.bindService());
+    }
+    return Collections.unmodifiableList(services);
+  }
+}

services/src/test/java/io/grpc/services/AdminInterfaceChannelzTest.java

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+/*
+ * Copyright 2021 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.services;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.common.collect.Iterables;
+import io.grpc.ServerServiceDefinition;
+import io.grpc.channelz.v1.ChannelzGrpc;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public class AdminInterfaceChannelzTest {
+
+  @Test
+  public void autoChannelz() {
+    ServerServiceDefinition channelz =
+        Iterables.getOnlyElement(AdminInterface.getStandardServices());
+    assertThat(channelz.getServiceDescriptor().getName()).isEqualTo(ChannelzGrpc.SERVICE_NAME);
+  }
+}