Address review comments

Author: pawankartik-elastic

server/src/main/java/org/elasticsearch/action/search/TransportSearchAction.java

@@ -379,12 +379,15 @@ private void executeRequest(
         final ResolvedIndices resolvedIndices;
 
         /*
-         * Irrespective of whether this is the origin project or a linked project, it's wiser to relax
-         * the index options to prevent the index resolution APIs from throwing index not found errors.
-         * Also, we do not replace the indices options on the SearchRequest because we'd be needing it
-         * downstream when validating the indices from both the origin and the linked projects.
+         * If this search request is originating from a search endpoint that is CPS compatible, and,
+         * CPS is enabled, i.e. resolvesCrossProject() returns true, we need to modify and relax the
+         * indices options. This is to:
+         *   a) Prevent the downstream code from throwing an error if an index is not found since in
+         *      CPS, an index can exist either on the origin or on different linked project(s).
+         *   b) Prevent the linked projects from re-interpreting the index expressions as CPS expressions
+         *      and rather treat them as canonical/standard ones.
          */
-        IndicesOptions resolutionIdxOpts = crossProjectModeDecider.resolvesCrossProject(original)
+        IndicesOptions resolutionIdxOpts = resolvesCrossProject
             ? indicesOptionsForCrossProjectFanout(original.indicesOptions())
             : original.indicesOptions();
 
@@ -964,8 +967,9 @@ static SearchResponseMerger createSearchResponseMerger(
     }
 
     /**
-     * Outside Cross Project Search, we're sure of projects involved and their corresponding indices. However,
-     * in CPS, it may be possible that indices can exist anywhere:
+     * Reconciliation is only done when Cross Project Search is enabled and requests originate from a CPS
+     * compatible endpoints. Outside CPS, we're sure of projects involved and their corresponding indices.
+     * However, in CPS, it may be possible that indices can exist anywhere:
      * <ul>
      *     <li>Only on the origin</li>
      *     <li>Only on the linked project(s)</li>
@@ -982,7 +986,7 @@ static SearchResponseMerger createSearchResponseMerger(
      * validation is complete.
      * @param originResolvedIdxExpressions The resolution result from origin's Security Action Filter.
      * @param shardResponses Responses pieced back from SearchShards API.
-     * @param projects Clusters object to build upon.
+     * @param projects The clusters originally in scope for the query.
      * @return A new Clusters object containing only the Search-participating projects.
      */
     static SearchResponse.Clusters reconcileProjects(
@@ -991,7 +995,7 @@ static SearchResponse.Clusters reconcileProjects(
         SearchResponse.Clusters projects
     ) {
         /*
-         * We only fire a SearchShards API for a project if it needs to be searched. This can either mean that it was
+         * We only fire a SearchShards API call for a project if it needs to be searched. This can either mean that it was
          * part of the search due to the flatworld behaviour, or that it was targeted specifically. If it returns an
          * empty response, it's because the project does not host any of our specified indices.
          */
@@ -1092,7 +1096,7 @@ Map<String, SearchShardsResponse> createFinalResponse() {
                             }
                             resolvedIndexExpressions.put(entry.getKey(), entry.getValue().getResolvedIndexExpressions());
                         }
-                        // We do not use the related index options here when validating indices' existence.
+                        // We do not use the relaxed index options here when validating indices' existence.
                         ElasticsearchException validationEx = CrossProjectIndexResolutionValidator.validate(
                             originalIdxOpts,
                             originResolvedIdxExpressions,

x-pack/plugin/async-search/src/main/java/org/elasticsearch/xpack/search/RestSubmitAsyncSearchAction.java

@@ -16,6 +16,7 @@
 import org.elasticsearch.rest.ServerlessScope;
 import org.elasticsearch.rest.action.RestCancellableNodeClient;
 import org.elasticsearch.rest.action.RestRefCountedChunkedToXContentListener;
+import org.elasticsearch.search.crossproject.CrossProjectModeDecider;
 import org.elasticsearch.usage.SearchUsageHolder;
 import org.elasticsearch.xpack.core.search.action.AsyncSearchResponse;
 import org.elasticsearch.xpack.core.search.action.SubmitAsyncSearchAction;
@@ -38,11 +39,7 @@ public final class RestSubmitAsyncSearchAction extends BaseRestHandler {
 
     private final SearchUsageHolder searchUsageHolder;
     private final Predicate<NodeFeature> clusterSupportsFeature;
-    private final Settings settings;
-
-    public RestSubmitAsyncSearchAction(SearchUsageHolder searchUsageHolder, Predicate<NodeFeature> clusterSupportsFeature) {
-        this(searchUsageHolder, clusterSupportsFeature, null);
-    }
+    private final CrossProjectModeDecider crossProjectModeDecider;
 
     public RestSubmitAsyncSearchAction(
         SearchUsageHolder searchUsageHolder,
@@ -51,7 +48,7 @@ public RestSubmitAsyncSearchAction(
     ) {
         this.searchUsageHolder = searchUsageHolder;
         this.clusterSupportsFeature = clusterSupportsFeature;
-        this.settings = settings;
+        this.crossProjectModeDecider = new CrossProjectModeDecider(settings);
     }
 
     @Override
@@ -71,7 +68,7 @@ protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient cli
         }
         SubmitAsyncSearchRequest submit = new SubmitAsyncSearchRequest();
 
-        boolean crossProjectEnabled = settings != null && settings.getAsBoolean("serverless.cross_project.enabled", false);
+        boolean crossProjectEnabled = crossProjectModeDecider.crossProjectEnabled();
         if (crossProjectEnabled) {
             // accept but drop project_routing param until fully supported
             request.param("project_routing");

x-pack/plugin/async-search/src/test/java/org/elasticsearch/xpack/search/RestSubmitAsyncSearchActionTests.java

@@ -8,6 +8,7 @@
 
 import org.apache.lucene.util.SetOnce;
 import org.elasticsearch.common.bytes.BytesArray;
+import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.rest.RestRequest;
@@ -31,7 +32,11 @@ public class RestSubmitAsyncSearchActionTests extends RestActionTestCase {
 
     @Before
     public void setUpAction() {
-        RestSubmitAsyncSearchAction action = new RestSubmitAsyncSearchAction(new UsageService().getSearchUsageHolder(), nf -> false);
+        RestSubmitAsyncSearchAction action = new RestSubmitAsyncSearchAction(
+            new UsageService().getSearchUsageHolder(),
+            nf -> false,
+            Settings.EMPTY
+        );
         controller().registerHandler(action);
     }