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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.plugins;

import org.elasticsearch.bootstrap.BootstrapCheck;
import org.elasticsearch.client.Client;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.metadata.IndexTemplateMetadata;
import org.elasticsearch.cluster.metadata.Metadata;
import org.elasticsearch.cluster.node.DiscoveryNodeRole;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.component.LifecycleComponent;
import org.elasticsearch.common.inject.Module;
import org.elasticsearch.common.io.stream.NamedWriteable;
import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.SettingUpgrader;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.xcontent.NamedXContentRegistry;
import org.elasticsearch.common.xcontent.XContentParser;
import org.elasticsearch.env.Environment;
import org.elasticsearch.env.NodeEnvironment;
import org.elasticsearch.index.IndexModule;
import org.elasticsearch.index.shard.IndexSettingProvider;
import org.elasticsearch.repositories.RepositoriesService;
import org.elasticsearch.script.ScriptService;
import org.elasticsearch.threadpool.ExecutorBuilder;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.watcher.ResourceWatcherService;

import java.io.Closeable;
import java.io.IOException;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.Set;
import java.util.function.Supplier;
import java.util.function.UnaryOperator;

/**
 * An extension point allowing to plug in custom functionality. This class has a number of extension points that are available to all
 * plugins, in addition you can implement any of the following interfaces to further customize Elasticsearch:
 * 
    
 * 
  • {@link ActionPlugin}
 * 
  • {@link AnalysisPlugin}
 * 
  • {@link ClusterPlugin}
 * 
  • {@link DiscoveryPlugin}
 * 
  • {@link IngestPlugin}
 * 
  • {@link MapperPlugin}
 * 
  • {@link NetworkPlugin}
 * 
  • {@link RepositoryPlugin}
 * 
  • {@link ScriptPlugin}
 * 
  • {@link SearchPlugin}
 * 
  • {@link ReloadablePlugin}
 * 

 */
public abstract class Plugin implements Closeable {

    /**
     * A feature exposed by the plugin. This should be used if a plugin exposes {@link ClusterState.Custom} or {@link Metadata.Custom}; see
     * also {@link ClusterState.FeatureAware}.
     *
     * @return a feature set represented by this plugin, or the empty optional if the plugin does not expose cluster state or metadata
     * customs
     */
    protected Optional getFeature() {
        return Optional.empty();
    }

    /**
     * Node level guice modules.
     */
    public Collection createGuiceModules() {
        return Collections.emptyList();
    }

    /**
     * Node level services that will be automatically started/stopped/closed. This classes must be constructed
     * by injection with guice.
     */
    public Collection> getGuiceServiceClasses() {
        return Collections.emptyList();
    }

    /**
     * Returns components added by this plugin.
     *
     * Any components returned that implement {@link LifecycleComponent} will have their lifecycle managed.
     * Note: To aid in the migration away from guice, all objects returned as components will be bound in guice
     * to themselves.
     *
     * @param client A client to make requests to the system
     * @param clusterService A service to allow watching and updating cluster state
     * @param threadPool A service to allow retrieving an executor to run an async action
     * @param resourceWatcherService A service to watch for changes to node local files
     * @param scriptService A service to allow running scripts on the local node
     * @param xContentRegistry the registry for extensible xContent parsing
     * @param environment the environment for path and setting configurations
     * @param nodeEnvironment the node environment used coordinate access to the data paths
     * @param namedWriteableRegistry the registry for {@link NamedWriteable} object parsing
     * @param indexNameExpressionResolver A service that resolves expression to index and alias names
     * @param repositoriesServiceSupplier A supplier for the service that manages snapshot repositories; will return null when this method
     *                                   is called, but will return the repositories service once the node is initialized.
     */
    public Collection createComponents(Client client, ClusterService clusterService, ThreadPool threadPool,
                                               ResourceWatcherService resourceWatcherService, ScriptService scriptService,
                                               NamedXContentRegistry xContentRegistry, Environment environment,
                                               NodeEnvironment nodeEnvironment, NamedWriteableRegistry namedWriteableRegistry,
                                               IndexNameExpressionResolver indexNameExpressionResolver,
                                               Supplier repositoriesServiceSupplier) {
        return Collections.emptyList();
    }

    /**
     * Additional node settings loaded by the plugin. Note that settings that are explicit in the nodes settings can't be
     * overwritten with the additional settings. These settings added if they don't exist.
     */
    public Settings additionalSettings() {
        return Settings.Builder.EMPTY_SETTINGS;
    }

    /**
     * Returns parsers for {@link NamedWriteable} this plugin will use over the transport protocol.
     * @see NamedWriteableRegistry
     */
    public List getNamedWriteables() {
        return Collections.emptyList();
    }

    /**
     * Returns parsers for named objects this plugin will parse from {@link XContentParser#namedObject(Class, String, Object)}.
     * @see NamedWriteableRegistry
     */
    public List getNamedXContent() {
        return Collections.emptyList();
    }

    /**
     * Called before a new index is created on a node. The given module can be used to register index-level
     * extensions.
     */
    public void onIndexModule(IndexModule indexModule) {}

    /**
     * Returns a list of additional {@link Setting} definitions for this plugin.
     */
    public List> getSettings() { return Collections.emptyList(); }

    /**
     * Returns a list of additional settings filter for this plugin
     */
    public List getSettingsFilter() { return Collections.emptyList(); }

    /**
     * Get the setting upgraders provided by this plugin.
     *
     * @return the settings upgraders
     */
    public List> getSettingUpgraders() {
        return Collections.emptyList();
    }

    /**
     * Provides a function to modify index template meta data on startup.
     * 

     * Plugins should return the input template map via {@link UnaryOperator#identity()} if no upgrade is required.
     * 

     * The order of the template upgrader calls is undefined and can change between runs so, it is expected that
     * plugins will modify only templates owned by them to avoid conflicts.
     * 

     * @return Never {@code null}. The same or upgraded {@code IndexTemplateMetadata} map.
     * @throws IllegalStateException if the node should not start because at least one {@code IndexTemplateMetadata}
     *                               cannot be upgraded
     */
    public UnaryOperator> getIndexTemplateMetadataUpgrader() {
        return UnaryOperator.identity();
    }

    /**
     * Provides the list of this plugin's custom thread pools, empty if
     * none.
     *
     * @param settings the current settings
     * @return executors builders for this plugin's custom thread pools
     */
    public List> getExecutorBuilders(Settings settings) {
        return Collections.emptyList();
    }

    /**
     * Returns a list of checks that are enforced when a node starts up once a node has the transport protocol bound to a non-loopback
     * interface. In this case we assume the node is running in production and all bootstrap checks must pass. This allows plugins
     * to provide a better out of the box experience by pre-configuring otherwise (in production) mandatory settings or to enforce certain
     * configurations like OS settings or 3rd party resources.
     */
    public List getBootstrapChecks() { return Collections.emptyList(); }

    public Set getRoles() {
        return Collections.emptySet();
    }

    /**
     * Close the resources opened by this plugin.
     *
     * @throws IOException if the plugin failed to close its resources
     */
    @Override
    public void close() throws IOException {

    }

    /**
     * An {@link IndexSettingProvider} allows hooking in to parts of an index
     * lifecycle to provide explicit default settings for newly created indices. Rather than changing
     * the default values for an index-level setting, these act as though the setting has been set
     * explicitly, but still allow the setting to be overridden by a template or creation request body.
     */
    public Collection getAdditionalIndexSettingProviders() {
        return Collections.emptyList();
    }
}
 















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