[CSV] Include custom field label in CSV reports (#181565)

- Closes https://github.com/elastic/kibana/issues/100374

## Summary

This PR adds `field.customLabel` to CSV reports (column names) if
available.

Before:
<img width="800" alt="Screenshot 2024-04-24 at 15 16 45"
src="870c9146-dd3a-4cc6-a12f-f67fbd7196f5">

After:
<img width="800" alt="Screenshot 2024-04-24 at 15 17 04"
src="7f870899-71a2-42e7-ade4-d92acca9b96a">


### Checklist

- [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

---------

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

packages/kbn-generate-csv/src/__snapshots__/generate_csv.test.ts.snap

@@ -271,8 +271,8 @@ exports[`CsvGenerator fields from job.searchSource.getFields() (7.12 generated)
 `;
 
 exports[`CsvGenerator formats a search result to CSV content 1`] = `
-"date,ip,message
-\\"2020-12-31T00:14:28.000Z\\",\\"110.135.176.89\\",\\"This is a great message!\\"
+"date,ip,message,\\"bytes_custom_label (bytes)\\"
+\\"2020-12-31T00:14:28.000Z\\",\\"110.135.176.89\\",\\"This is a great message!\\",100
 "
 `;
 

packages/kbn-generate-csv/src/generate_csv.test.ts

@@ -20,6 +20,8 @@ import {
   savedObjectsClientMock,
   uiSettingsServiceMock,
 } from '@kbn/core/server/mocks';
+import { createStubDataView } from '@kbn/data-views-plugin/common/data_views/data_view.stub';
+import { stubLogstashFieldSpecMap } from '@kbn/data-views-plugin/common/field.stub';
 import { ISearchClient, ISearchStartSearchSource } from '@kbn/data-plugin/common';
 import { searchSourceInstanceMock } from '@kbn/data-plugin/common/search/search_source/mocks';
 import type { IScopedSearchClient } from '@kbn/data-plugin/server';
@@ -132,20 +134,31 @@ describe('CsvGenerator', () => {
 
     mockConfig = getMockConfig();
 
+    const dataView = createStubDataView({
+      spec: {
+        id: 'test',
+        title: 'logstash-*',
+        fields: {
+          ...stubLogstashFieldSpecMap,
+          bytes: {
+            ...stubLogstashFieldSpecMap.bytes,
+            customLabel: 'bytes_custom_label',
+          },
+        },
+      },
+      opts: {
+        metaFields: ['_id', '_index', '_type', '_score'],
+      },
+    });
+
+    dataView.getFormatterForField = jest.fn();
+
     searchSourceMock.getField = jest.fn((key: string) => {
       switch (key) {
         case 'pit':
           return { id: mockCursorId };
         case 'index':
-          return {
-            fields: {
-              getByName: jest.fn(() => []),
-              getByType: jest.fn(() => []),
-            },
-            metaFields: ['_id', '_index', '_type', '_score'],
-            getFormatterForField: jest.fn(),
-            getIndexPattern: () => 'logstash-*',
-          };
+          return dataView;
       }
     });
 
@@ -184,13 +197,14 @@ describe('CsvGenerator', () => {
               date: `["2020-12-31T00:14:28.000Z"]`,
               ip: `["110.135.176.89"]`,
               message: `["This is a great message!"]`,
+              bytes: `[100]`,
             },
           } as unknown as estypes.SearchHit,
         ]),
       })
     );
     const generateCsv = new CsvGenerator(
-      createMockJob({ columns: ['date', 'ip', 'message'] }),
+      createMockJob({ columns: ['date', 'ip', 'message', 'bytes'] }),
       mockConfig,
       mockTaskInstanceFields,
       {

packages/kbn-generate-csv/src/generate_csv.ts

@@ -11,7 +11,7 @@ import type { Writable } from 'stream';
 
 import { errors as esErrors, estypes } from '@elastic/elasticsearch';
 import type { IScopedClusterClient, IUiSettingsClient, Logger } from '@kbn/core/server';
-import type { ISearchClient, ISearchStartSearchSource } from '@kbn/data-plugin/common';
+import type { DataView, ISearchClient, ISearchStartSearchSource } from '@kbn/data-plugin/common';
 import { cellHasFormulas, tabifyDocs } from '@kbn/data-plugin/common';
 import type { Datatable } from '@kbn/expressions-plugin/server';
 import type {
@@ -146,11 +146,21 @@ export class CsvGenerator {
   private generateHeader(
     columns: Set<string>,
     builder: MaxSizeStringBuilder,
-    settings: CsvExportSettings
+    settings: CsvExportSettings,
+    dataView: DataView
   ) {
     this.logger.debug(`Building CSV header row`);
     const header =
-      Array.from(columns).map(this.escapeValues(settings)).join(settings.separator) + '\n';
+      Array.from(columns)
+        .map((column) => {
+          const field = dataView?.fields.getByName(column);
+          if (field && field.customLabel && field.customLabel !== column) {
+            return `${field.customLabel} (${column})`;
+          }
+          return column;
+        })
+        .map(this.escapeValues(settings))
+        .join(settings.separator) + '\n';
 
     if (!builder.tryAppend(header)) {
       return {
@@ -364,7 +374,7 @@ export class CsvGenerator {
 
         if (first) {
           first = false;
-          this.generateHeader(columns, builder, settings);
+          this.generateHeader(columns, builder, settings, index);
         }
 
         if (table.rows.length < 1) {

packages/kbn-generate-csv/tsconfig.json

@@ -29,5 +29,6 @@
     "@kbn/es-query",
     "@kbn/es-types",
     "@kbn/esql-utils",
+    "@kbn/data-views-plugin",
   ]
 }