Fix issue with single value for metaFields advanced setting (#155811)

## Summary

Resolves #94356.

Fixes an issue with the _fields_for_wildcard API when the value for
`metaFields` advanced setting is set to a single value (e.g. `_source`).

### Checklist

- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

### Release note

Fixes an issue where having a single value for the advanced setting
`metaFields` would prevent refreshing a data view.

src/plugins/data_views/server/routes/fields_for.test.ts

@@ -0,0 +1,52 @@
+/*
+ * 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.
+ */
+
+import { parseMetaFields } from './fields_for';
+
+describe('_fields_for_wildcard', () => {
+ describe('parseMetaFields', () => {
+ it('should throw if receiving a string of comma-separated values', () => {
+ const value = '_source,_id';
+ expect(() => parseMetaFields(value)).toThrowErrorMatchingInlineSnapshot(
+ `"metaFields should be an array of field names, a JSON-stringified array of field names, or a single field name"`
+ );
+ });
+
+ it('should parse a stringified list of values', () => {
+ const value = JSON.stringify(['_source', '_id']);
+ const fields = parseMetaFields(value);
+ expect(fields).toMatchInlineSnapshot(`
+ Array [
+ "_source",
+ "_id",
+ ]
+ `);
+ });
+
+ it('should wrap a single value in an array', () => {
+ const value = '_source';
+ const fields = parseMetaFields(value);
+ expect(fields).toMatchInlineSnapshot(`
+ Array [
+ "_source",
+ ]
+ `);
+ });
+
+ it('should return the array if already an array', () => {
+ const value = ['_source', '_id'];
+ const fields = parseMetaFields(value);
+ expect(fields).toMatchInlineSnapshot(`
+ Array [
+ "_source",
+ "_id",
+ ]
+ `);
+ });
+ });
+});

src/plugins/data_views/server/routes/fields_for.ts

@@ -17,22 +17,32 @@ import {
 import { IndexPatternsFetcher } from '../fetcher';
 import type { DataViewsServerPluginStart, DataViewsServerPluginStartDependencies } from '../types';
 
-const parseMetaFields = (metaFields: string | string[]) => {
- let parsedFields: string[] = [];
- if (typeof metaFields === 'string') {
- parsedFields = JSON.parse(metaFields);
- } else {
- parsedFields = metaFields;
+/**
+ * Accepts one of the following:
+ * 1. An array of field names
+ * 2. A JSON-stringified array of field names
+ * 3. A single field name (not comma-separated)
+ * @returns an array of field names
+ * @param metaFields
+ */
+export const parseMetaFields = (metaFields: string | string[]): string[] => {
+ if (Array.isArray(metaFields)) return metaFields;
+ try {
+ return JSON.parse(metaFields);
+ } catch (e) {
+ if (!metaFields.includes(',')) return [metaFields];
+ throw new Error(
+ 'metaFields should be an array of field names, a JSON-stringified array of field names, or a single field name'
+ );
  }
- return parsedFields;
 };
 
 const path = '/api/index_patterns/_fields_for_wildcard';
 
 type IBody = { index_filter?: estypes.QueryDslQueryContainer } | undefined;
 interface IQuery {
  pattern: string;
- meta_fields: string[];
+ meta_fields: string | string[];
  type?: string;
  rollup_index?: string;
  allow_no_index?: boolean;

test/api_integration/apis/data_views/fields_for_wildcard_route/params.js

@@ -49,6 +49,15 @@ export default function ({ getService }) {
  })
  .expect(200));
 
+ it('accepts single meta_fields query param', () =>
+ supertest
+ .get('/api/index_patterns/_fields_for_wildcard')
+ .query({
+ pattern: '*',
+ meta_fields: ['_id'],
+ })
+ .expect(200));
+
  it('rejects a comma-separated list of meta_fields', () =>
  supertest
  .get('/api/index_patterns/_fields_for_wildcard')