Elasticsearch: Fix URL creation and allowlist for `/_mapping` requests (#80970)

* Elasticsearch: Fix URL creation for mapping requests

* remove leading slash by default

* add comment for es route

* hardcode `_mapping`

* update doc

pkg/tsdb/elasticsearch/elasticsearch.go

@@ -188,9 +188,10 @@ func (s *Service) CallResource(ctx context.Context, req *backend.CallResourceReq
 	logger := eslog.FromContext(ctx)
 	// allowed paths for resource calls:
 	// - empty string for fetching db version
-	// - ?/_mapping for fetching index mapping
+	// - /_mapping for fetching index mapping, e.g. requests going to `index/_mapping`
 	// - _msearch for executing getTerms queries
-	if req.Path != "" && !strings.HasSuffix(req.Path, "/_mapping") && req.Path != "_msearch" {
+	// - _mapping for fetching "root" index mappings
+	if req.Path != "" && !strings.HasSuffix(req.Path, "/_mapping") && req.Path != "_msearch" && req.Path != "_mapping" {
 		logger.Error("Invalid resource path", "path", req.Path)
 		return fmt.Errorf("invalid resource URL: %s", req.Path)
 	}

public/app/plugins/datasource/elasticsearch/datasource.test.ts

@@ -151,6 +151,15 @@ describe('ElasticDatasource', () => {
       const lastCall = fetchMock.mock.calls[fetchMock.mock.calls.length - 1];
       expect(lastCall[0].url).toBe(`${ELASTICSEARCH_MOCK_URL}/test-${today}/_mapping`);
     });
+
+    it('should call `/_mapping` with an empty index', async () => {
+      const { ds, fetchMock } = getTestContext({ jsonData: { index: '' } });
+
+      await ds.testDatasource();
+
+      const lastCall = fetchMock.mock.calls[fetchMock.mock.calls.length - 1];
+      expect(lastCall[0].url).toBe(`${ELASTICSEARCH_MOCK_URL}/_mapping`);
+    });
   });
 
   describe('When issuing metric query with interval pattern', () => {

public/app/plugins/datasource/elasticsearch/datasource.ts

@@ -195,17 +195,24 @@ export class ElasticDatasource
    *
    * When multiple indices span the provided time range, the request is sent starting from the newest index,
    * and then going backwards until an index is found.
-   *
-   * @param url the url to query the index on, for example `/_mapping`.
    */
-
-  private requestAllIndices(url: string, range = getDefaultTimeRange()) {
+  private requestAllIndices(range = getDefaultTimeRange()) {
     let indexList = this.indexPattern.getIndexList(range.from, range.to);
     if (!Array.isArray(indexList)) {
       indexList = [this.indexPattern.getIndexForToday()];
     }
 
-    const indexUrlList = indexList.map((index) => index + url);
+    const url = '_mapping';
+
+    const indexUrlList = indexList.map((index) => {
+      // make sure `index` does not end with a slash
+      index = index.replace(/\/$/, '');
+      if (index === '') {
+        return url;
+      }
+
+      return `${index}/${url}`;
+    });
 
     const maxTraversals = 7; // do not go beyond one week (for a daily pattern)
     const listLen = indexUrlList.length;
@@ -708,7 +715,7 @@ export class ElasticDatasource
       nested: 'nested',
       histogram: 'number',
     };
-    return this.requestAllIndices('/_mapping', range).pipe(
+    return this.requestAllIndices(range).pipe(
       map((result) => {
         const shouldAddField = (obj: any, key: string) => {
           if (this.isMetadataField(key)) {

public/app/plugins/datasource/elasticsearch/mocks.ts

@@ -39,9 +39,9 @@ export function createElasticDatasource(settings: Partial<DataSourceInstanceSett
     jsonData: {
       timeField: '',
       timeInterval: '',
+      index: '[test-]YYYY.MM.DD',
       ...jsonData,
     },
-    database: '[test-]YYYY.MM.DD',
     ...rest,
   };