[DRAFT] Introduce PluginMetadataClient

Reference RFC:

opensearch-project#13274

server/src/main/java/org/opensearch/common/settings/AbstractScopedSettings.java

@@ -790,6 +790,21 @@ public <T> T get(Setting<T> setting) {
         return setting.get(this.lastSettingsApplied, settings);
     }
 
+    /**
+     * Creates a snapshot of the scoped settings as a Settings instance.
+     * <p>
+     * Note: Updates to scoped settings are not reflected in the result Settings instance. This API is meant to
+     * represent a point in time.
+     * </p>
+     * @return The current settings
+     */
+    public Settings toSettings() {
+        return Settings.builder()
+            .put(settings)
+            .put(lastSettingsApplied)
+            .build();
+    }
+
     /**
      * Updates a target settings builder with new, updated or deleted settings from a given settings builder.
      * <p>

server/src/main/java/org/opensearch/node/Node.java

@@ -203,11 +203,14 @@
 import org.opensearch.plugins.PluginsService;
 import org.opensearch.plugins.RepositoryPlugin;
 import org.opensearch.plugins.ScriptPlugin;
+import org.opensearch.plugins.SdkAwarePlugin;
 import org.opensearch.plugins.SearchPipelinePlugin;
 import org.opensearch.plugins.SearchPlugin;
 import org.opensearch.plugins.SecureSettingsFactory;
 import org.opensearch.plugins.SystemIndexPlugin;
 import org.opensearch.plugins.TelemetryPlugin;
+import org.opensearch.plugins.sdk.DefaultPluginMetadataClient;
+import org.opensearch.plugins.sdk.PluginMetadataClient;
 import org.opensearch.ratelimitting.admissioncontrol.AdmissionControlService;
 import org.opensearch.ratelimitting.admissioncontrol.transport.AdmissionControlTransportInterceptor;
 import org.opensearch.repositories.RepositoriesModule;
@@ -890,6 +893,22 @@ protected Node(
 
             final ViewService viewService = new ViewService(clusterService, client, null);
 
+            DefaultPluginMetadataClient defaultPluginMetadataClient = new DefaultPluginMetadataClient(
+                clusterService,
+                clusterModule.getIndexNameExpressionResolver(),
+                settingsModule.getIndexScopedSettings()
+            );
+
+            SdkAwarePlugin.Dependencies sdkDependencies = new SdkAwarePlugin.Dependencies() {
+                @Override
+                public PluginMetadataClient getPluginMetadataClient() {
+                    return defaultPluginMetadataClient;
+                }
+            };
+
+            pluginsService.filterPlugins(SdkAwarePlugin.class)
+                .forEach(plugin -> plugin.setupSdkPlugin(sdkDependencies));
+
             Collection<Object> pluginComponents = pluginsService.filterPlugins(Plugin.class)
                 .stream()
                 .flatMap(
@@ -1329,6 +1348,7 @@ protected Node(
                 b.bind(PersistedStateRegistry.class).toInstance(persistedStateRegistry);
                 b.bind(SegmentReplicationStatsTracker.class).toInstance(segmentReplicationStatsTracker);
                 b.bind(SearchRequestOperationsCompositeListenerFactory.class).toInstance(searchRequestOperationsCompositeListenerFactory);
+                b.bind(PluginMetadataClient.class).toInstance(defaultPluginMetadataClient);
             });
             injector = modules.createInjector();
 

server/src/main/java/org/opensearch/plugins/SdkAwarePlugin.java

@@ -0,0 +1,27 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugins;
+
+import org.opensearch.plugins.sdk.PluginMetadataClient;
+
+/**
+ * SdkAwarePlugin is an additional extension point for {@link Plugin}'s for receiving
+ * OpenSearch abstractions.
+ */
+public interface SdkAwarePlugin {
+
+    void setupSdkPlugin(Dependencies dependencies);
+
+    /**
+     * Dependencies is a simple container class holding plugin sdk dependencies.
+     */
+    public static interface Dependencies {
+        PluginMetadataClient getPluginMetadataClient();
+    }
+}

server/src/main/java/org/opensearch/plugins/sdk/DefaultPluginMetadataClient.java

@@ -0,0 +1,149 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugins.sdk;
+
+import org.opensearch.cluster.ClusterState;
+import org.opensearch.cluster.metadata.IndexMetadata;
+import org.opensearch.cluster.metadata.IndexNameExpressionResolver;
+import org.opensearch.cluster.metadata.MappingMetadata;
+import org.opensearch.cluster.metadata.Metadata;
+import org.opensearch.cluster.service.ClusterService;
+import org.opensearch.common.CheckedSupplier;
+import org.opensearch.common.annotation.ExperimentalApi;
+import org.opensearch.common.settings.ClusterSettings;
+import org.opensearch.common.settings.IndexScopedSettings;
+import org.opensearch.common.settings.Settings;
+import org.opensearch.core.index.Index;
+import org.opensearch.plugins.sdk.actions.ConcreteIndicesRequest;
+import org.opensearch.plugins.sdk.actions.ConcreteIndicesResponse;
+import org.opensearch.plugins.sdk.actions.GetIndexMappingMetadataRequest;
+import org.opensearch.plugins.sdk.actions.GetIndexMappingMetadataResponse;
+import org.opensearch.plugins.sdk.actions.GetIndexSettingsRequest;
+import org.opensearch.plugins.sdk.actions.GetIndexSettingsResponse;
+import org.opensearch.plugins.sdk.actions.GetSystemSettingsRequest;
+import org.opensearch.plugins.sdk.actions.GetSystemSettingsResponse;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.CompletionStage;
+
+/**
+ * DefaultPluginMetadataClient is the de-facto implementation of the
+ * PluginMetadataClient.
+ *
+ * @see PluginMetadataClient
+ */
+@ExperimentalApi
+public class DefaultPluginMetadataClient implements PluginMetadataClient {
+
+    private final ClusterService clusterService;
+    private final IndexNameExpressionResolver indexNameExpressionResolver;
+    private final IndexScopedSettings indexScopedSettings;
+
+    public DefaultPluginMetadataClient(ClusterService clusterService,
+                                       IndexNameExpressionResolver indexNameExpressionResolver,
+                                       IndexScopedSettings indexScopedSettings) {
+
+        this.clusterService = clusterService;
+        this.indexNameExpressionResolver = indexNameExpressionResolver;
+        this.indexScopedSettings = indexScopedSettings;
+    }
+
+    @Override
+    public CompletionStage<ConcreteIndicesResponse> concreteIndices(
+        ConcreteIndicesRequest request
+    ) {
+        return synchronously(() -> {
+            ClusterState state = clusterService.state();
+
+            Index[] result = indexNameExpressionResolver.concreteIndices(
+                state,
+                request.indicesOptions(),
+                request.indexExpressions());
+
+            return ConcreteIndicesResponse.builder()
+                .indices(result)
+                .build();
+        });
+    }
+
+    @Override
+    public CompletionStage<GetSystemSettingsResponse> getSystemSettings(
+        GetSystemSettingsRequest request
+    ) {
+        return synchronously(() -> {
+            ClusterSettings clusterSettings = clusterService.getClusterSettings();
+            Settings settings = clusterSettings.toSettings();
+            Set<String> settingKeys = Set.of(request.settings());
+            settings = settings.filter(settingKeys::contains);
+            return GetSystemSettingsResponse.builder()
+                .settings(settings)
+                .build();
+        });
+    }
+
+    @Override
+    public CompletionStage<GetIndexMappingMetadataResponse> getIndexMappingMetadata(
+        GetIndexMappingMetadataRequest request
+    ) {
+        return synchronously(() -> {
+            ClusterState state = clusterService.state();
+            Metadata metadata = state.metadata();
+            Map<Index, MappingMetadata> result = new HashMap<>();
+            for (Index index : request.indices()) {
+                MappingMetadata mappingMetadata = metadata.getIndexSafe(index).mapping();
+                result.put(index, mappingMetadata);
+            }
+            return GetIndexMappingMetadataResponse.builder()
+                .mappingMetadata(result)
+                .build();
+        });
+    }
+
+    @Override
+    public CompletionStage<GetIndexSettingsResponse> getIndexSettings(
+        GetIndexSettingsRequest request
+    ) {
+        return synchronously(() -> {
+            ClusterState state = clusterService.state();
+            Settings currentDefaultIndexScopedSettings = indexScopedSettings.toSettings();
+            Set<String> settingsKeys = Set.of(request.settings());
+            Map<Index, Settings> result = new HashMap<>();
+
+            for (Index index : request.indices()) {
+                IndexMetadata indexMetadata = state.metadata().getIndexSafe(index);
+
+                Settings indexSettings = indexMetadata.getSettings();
+
+                Settings resultSettings = Settings.builder()
+                    .put(currentDefaultIndexScopedSettings)
+                    .put(indexSettings)
+                    .build()
+                    .filter(settingsKeys::contains);
+
+                result.put(index, resultSettings);
+            }
+
+            return GetIndexSettingsResponse.builder()
+                .settings(result)
+                .build();
+        });
+    }
+
+    private static <T> CompletionStage<T> synchronously(CheckedSupplier<T, Exception> supplier) {
+        try {
+            T result = supplier.get();
+            return CompletableFuture.completedStage(result);
+        } catch (Exception e) {
+            return CompletableFuture.failedStage(e);
+        }
+    }
+}

server/src/main/java/org/opensearch/plugins/sdk/PluginMetadataClient.java

@@ -0,0 +1,79 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugins.sdk;
+
+import org.opensearch.action.support.IndicesOptions;
+import org.opensearch.cluster.ClusterState;
+import org.opensearch.common.annotation.ExperimentalApi;
+import org.opensearch.common.settings.Setting;
+import org.opensearch.plugins.sdk.actions.ConcreteIndicesRequest;
+import org.opensearch.plugins.sdk.actions.ConcreteIndicesResponse;
+import org.opensearch.plugins.sdk.actions.GetIndexMappingMetadataRequest;
+import org.opensearch.plugins.sdk.actions.GetIndexMappingMetadataResponse;
+import org.opensearch.plugins.sdk.actions.GetIndexSettingsRequest;
+import org.opensearch.plugins.sdk.actions.GetIndexSettingsResponse;
+import org.opensearch.plugins.sdk.actions.GetSystemSettingsRequest;
+import org.opensearch.plugins.sdk.actions.GetSystemSettingsResponse;
+
+import java.util.concurrent.CompletionStage;
+
+/**
+ * PluginMetadataClient provides an abstract interface for plugins to access OpenSearch core cluster metadata.
+ */
+@ExperimentalApi
+public interface PluginMetadataClient {
+
+    /**
+     * Resolves the concrete indices for a given set of index name expressions.
+     *
+     * This is an abstraction over IndexNameExpressionResolver.
+     *
+     * @see org.opensearch.cluster.metadata.IndexNameExpressionResolver#concreteIndexNames(ClusterState, IndicesOptions, String...)
+     *
+     * @param request The index names to resolve and associated resolution options
+     * @return The resolved concrete index names
+     */
+    CompletionStage<ConcreteIndicesResponse> concreteIndices(ConcreteIndicesRequest request);
+
+    /**
+     * Gets the system settings for a particular set of setting.
+     *
+     * This is an abstraction over ClusterSetting access.
+     *
+     * @see org.opensearch.common.settings.ClusterSettings#get(Setting)
+     *
+     * @param request The settings to retrieve.
+     * @return The system settings.
+     */
+    CompletionStage<GetSystemSettingsResponse> getSystemSettings(GetSystemSettingsRequest request);
+
+    /**
+     * Gets the mapping metadata of the provided indices.
+     *
+     * This is an abstraction over ClusterState Metadata access.
+     *
+     * @see org.opensearch.cluster.metadata.Metadata#indices()
+     *
+     * @param request The indices to retrieve mapping metadata for.
+     * @return The mapping metadata for the requested indices.
+     */
+    CompletionStage<GetIndexMappingMetadataResponse> getIndexMappingMetadata(GetIndexMappingMetadataRequest request);
+
+    /**
+     * Gets the index settings for a particular set of indices.
+     *
+     * This is an abstraction over ClusterState Metadata access.
+     *
+     * @see org.opensearch.cluster.metadata.IndexMetadata#getSettings()
+     *
+     * @param request The indices to retrieve mapping metadata for.
+     * @return The mapping metadata for the requested indices.
+     */
+    CompletionStage<GetIndexSettingsResponse> getIndexSettings(GetIndexSettingsRequest request);
+}