[Response Ops] Allow _source field for ES DSL query rules (#142223)

* Allowing _source in ES query DSL

* Adding functional test

* Adding to doc

Co-authored-by: Kibana Machine <42973632+kibanamachine@users.noreply.github.com>

docs/user/alerting/rule-types/es-query.asciidoc

@@ -26,7 +26,7 @@ the *time window*.
 Size:: Specifies the number of documents to pass to the configured actions when 
 the threshold condition is met.
 {es} query:: Specifies the ES DSL query. The number of documents that 
-match this query is evaluated against the threshold condition. Only the `query`, `fields` and `runtime_mappings`
+match this query is evaluated against the threshold condition. Only the `query`, `fields`, `_source` and `runtime_mappings`
 fields are used, other DSL fields are not considered. 
 Threshold:: Defines a threshold value and a comparison operator  (`is above`, 
 `is above or equals`, `is below`, `is below or equals`, or `is between`). The 

x-pack/plugins/stack_alerts/common/build_sorted_events_query.ts

@@ -23,6 +23,7 @@ export interface BuildSortedEventsQuery extends BuildSortedEventsQueryOpts {
   timeField: string;
   fields?: string[];
   runtime_mappings?: unknown;
+  _source?: unknown;
 }
 
 export const buildSortedEventsQuery = ({
@@ -40,6 +41,7 @@ export const buildSortedEventsQuery = ({
   fields,
   // eslint-disable-next-line @typescript-eslint/naming-convention
   runtime_mappings,
+  _source,
 }: BuildSortedEventsQuery): ESSearchRequest => {
   const sortField = timeField;
   const docFields = [timeField].map((tstamp) => ({
@@ -89,6 +91,7 @@ export const buildSortedEventsQuery = ({
     },
     ...(runtime_mappings ? { runtime_mappings } : {}),
     ...(fields ? { fields } : {}),
+    ...(_source != null ? { _source } : {}),
   };
 
   if (searchAfterSortId) {

x-pack/plugins/stack_alerts/server/alert_types/es_query/lib/fetch_es_query.ts

@@ -28,7 +28,7 @@ export async function fetchEsQuery(
   const esClient = scopedClusterClient.asCurrentUser;
   const {
     // eslint-disable-next-line @typescript-eslint/naming-convention
-    parsedQuery: { query, fields, runtime_mappings },
+    parsedQuery: { query, fields, runtime_mappings, _source },
     dateStart,
     dateEnd,
   } = getSearchParams(params);
@@ -76,6 +76,7 @@ export async function fetchEsQuery(
     track_total_hits: true,
     fields,
     runtime_mappings,
+    _source,
   });
 
   logger.debug(

x-pack/test/alerting_api_integration/spaces_only/tests/alerting/builtin_alert_types/es_query/index.ts

@@ -11,5 +11,6 @@ import { FtrProviderContext } from '../../../../../common/ftr_provider_context';
 export default function alertingTests({ loadTestFile }: FtrProviderContext) {
   describe('es_query', () => {
     loadTestFile(require.resolve('./rule'));
+    loadTestFile(require.resolve('./query_dsl_only'));
   });
 }

x-pack/test/alerting_api_integration/spaces_only/tests/alerting/builtin_alert_types/es_query/query_dsl_only.ts

@@ -159,7 +159,7 @@ export default function ruleTests({ getService }: FtrProviderContext) {
             "fields": [
               {
                 "field": "@timestamp",
-                "format": "epoch_millis" 
+                "format": "epoch_millis"
               }
             ],
             "query": {
@@ -190,6 +190,73 @@ export default function ruleTests({ getService }: FtrProviderContext) {
       }
     });
 
+    it(`runs correctly: _source: false field for esQuery search type`, async () => {
+      // write documents from now to the future end date in groups
+      await createEsDocumentsInGroups(ES_GROUPS_TO_WRITE, endDate);
+      await createRule({
+        name: 'always fire',
+        esQuery: `
+          {
+            "query": {
+                "match_all": { }
+            },
+            "_source": false
+        }`.replace(`"`, `\"`),
+        size: 100,
+        thresholdComparator: '>',
+        threshold: [-1],
+      });
+
+      const docs = await waitForDocs(2);
+      for (let i = 0; i < docs.length; i++) {
+        const doc = docs[i];
+        const { name, title } = doc._source.params;
+        expect(name).to.be('always fire');
+        expect(title).to.be(`rule 'always fire' matched query`);
+
+        const hits = JSON.parse(doc._source.hits);
+        expect(hits).not.to.be.empty();
+        hits.forEach((hit: any) => {
+          expect(hit._source).to.be(undefined);
+        });
+      }
+    });
+
+    it(`runs correctly: _source field for esQuery search type`, async () => {
+      // write documents from now to the future end date in groups
+      await createEsDocumentsInGroups(ES_GROUPS_TO_WRITE, endDate);
+      await createRule({
+        name: 'always fire',
+        esQuery: `
+          {
+            "query": {
+                "match_all": { }
+            },
+            "_source": "testedValue*"
+        }`.replace(`"`, `\"`),
+        size: 100,
+        thresholdComparator: '>',
+        threshold: [-1],
+      });
+
+      const docs = await waitForDocs(2);
+      for (let i = 0; i < docs.length; i++) {
+        const doc = docs[i];
+        const { name, title } = doc._source.params;
+        expect(name).to.be('always fire');
+        expect(title).to.be(`rule 'always fire' matched query`);
+
+        const hits = JSON.parse(doc._source.hits);
+        expect(hits).not.to.be.empty();
+        hits.forEach((hit: any) => {
+          expect(hit._source).not.to.be.empty();
+          Object.keys(hit._source).forEach((key) => {
+            expect(key.startsWith('testedValue')).to.be(true);
+          });
+        });
+      }
+    });
+
     async function createRule(params: CreateRuleParams): Promise<string> {
       const action = {
         id: connectorId,