fix(api): use ARLEN for get-next-index (RI-8219)

ARNEXT on Redis 8.8.0 GA returns 0 for every populated array — its
documented summary 'returns the next index ARINSERT would use' is a
different operation from what this endpoint exposes (the next safe
write index after the highest populated slot).

ARLEN already returns max_index + 1 for both dense and sparse arrays,
which is exactly the value the endpoint, its response DTO description,
and its integration tests promise. Swap the primitive, tighten the
response shape (`index` is now non-nullable string), drop the
unreachable '(exhausted)' unit case, and remove the now-unused ArNext
enum member plus its ioredis builtin registration.

Caught by the new oss-st-8 RTE on PR #6078, where every
get-next-index Main case was returning index '0' regardless of array
shape. Verified against redis:8.8-alpine: ARLEN k → 3 for a dense
[0,1,2], 6 for sparse [0,_,_,_,_,5] — matches the test expectations.

Author: pawelangelow

redisinsight/api/src/modules/browser/array/array.controller.ts

@@ -124,7 +124,7 @@ export class ArrayController extends BrowserBaseController {
   @HttpCode(200)
   @ApiOperation({
     description:
-      'Get the next index that ARINSERT would use (read-only) — ARNEXT.',
+      'Get the next safe write index (equivalent to the array length) — ARLEN.',
   })
   @ApiRedisParams()
   @ApiOkResponse({ type: GetArrayNextIndexResponse })

redisinsight/api/src/modules/browser/array/array.service.spec.ts

@@ -434,7 +434,7 @@ describe('ArrayService', () => {
     },
     {
       name: 'getNextIndex',
-      command: BrowserToolArrayCommands.ArNext,
+      command: BrowserToolArrayCommands.ArLen,
       reply: 7,
       expected: mockGetArrayNextIndexResponse,
       stringValue: mockArrayNextIndex,
@@ -481,21 +481,6 @@ describe('ArrayService', () => {
     });
   });
 
-  describe('getNextIndex (exhausted)', () => {
-    it('should surface null index when ARNEXT returns nil', async () => {
-      when(mockStandaloneRedisClient.sendCommand)
-        .calledWith([BrowserToolArrayCommands.ArNext, mockKeyDto.keyName])
-        .mockResolvedValue(null);
-
-      const result = await service.getNextIndex(
-        mockBrowserClientMetadata,
-        mockKeyDto,
-      );
-
-      expect(result).toEqual({ keyName: mockKeyDto.keyName, index: null });
-    });
-  });
-
   describe('getElement', () => {
     beforeEach(() => {
       when(mockStandaloneRedisClient.sendCommand)

redisinsight/api/src/modules/browser/array/array.service.ts

@@ -20,10 +20,7 @@ import {
 } from 'src/modules/browser/utils';
 import { KeyDto } from 'src/modules/browser/keys/dto';
 import { ARRAY_RANGE_MAX_ELEMENTS } from 'src/modules/browser/array/constants';
-import {
-  toIndexString,
-  toRequiredIndexString,
-} from 'src/modules/browser/array/utils';
+import { toRequiredIndexString } from 'src/modules/browser/array/utils';
 import {
   ArrayCreationMode,
   ArrayElement,
@@ -314,17 +311,14 @@ export class ArrayService {
       await checkIfKeyNotExists(keyName, client);
 
       const reply = await client.sendCommand([
-        BrowserToolArrayCommands.ArNext,
+        BrowserToolArrayCommands.ArLen,
         keyName,
       ]);
 
-      // ARNEXT returns nil when the insertion cursor is exhausted; toIndexString
-      // passes that through as null so clients can distinguish absence from a
-      // real index.
       this.logger.debug('Succeed to get array next index.', clientMetadata);
       return plainToInstance(GetArrayNextIndexResponse, {
         keyName,
-        index: toIndexString(reply),
+        index: toRequiredIndexString(reply),
       });
     } catch (error) {
       this.logger.error(

redisinsight/api/src/modules/browser/array/dto/get.array-next-index.response.ts

@@ -4,11 +4,10 @@ import { KeyResponse } from 'src/modules/browser/keys/dto';
 export class GetArrayNextIndexResponse extends KeyResponse {
   @ApiProperty({
     description:
-      'Next index that ARINSERT would use. Unsigned 64-bit integer as string. ' +
-      'Null when the array is exhausted and no further insertion is possible.',
+      'Next safe write index (equivalent to the array length). ' +
+      'Unsigned 64-bit integer as string.',
     type: String,
     example: '7',
-    nullable: true,
   })
-  index: string | null;
+  index: string;
 }

redisinsight/api/src/modules/browser/array/utils.ts

@@ -3,9 +3,8 @@
 // string so the unsigned 64-bit contract is preserved on the wire.
 //
 // Returns `null` for nil replies so callers can distinguish absence from a
-// real value (e.g. ARNEXT returns nil when the insertion cursor is exhausted).
-// Without this guard `String(null)` / `String(undefined)` would emit the
-// literal strings "null" / "undefined" and corrupt downstream JSON.
+// real value. Without this guard `String(null)` / `String(undefined)` would
+// emit the literal strings "null" / "undefined" and corrupt downstream JSON.
 export const toIndexString = (value: unknown): string | null => {
   if (value === null || value === undefined) return null;
   if (typeof value === 'string') return value;

redisinsight/api/src/modules/browser/constants/browser-tool-commands.ts

@@ -123,7 +123,6 @@ export enum BrowserToolArrayCommands {
   ArCount = 'arcount',
   ArGetRange = 'argetrange',
   ArScan = 'arscan',
-  ArNext = 'arnext',
 }
 
 export type BrowserToolCommands =

redisinsight/api/src/modules/redis/client/ioredis/ioredis.client.ts

@@ -57,7 +57,6 @@ export abstract class IoredisClient extends RedisClient {
     client.addBuiltinCommand(BrowserToolArrayCommands.ArCount);
     client.addBuiltinCommand(BrowserToolArrayCommands.ArGetRange);
     client.addBuiltinCommand(BrowserToolArrayCommands.ArScan);
-    client.addBuiltinCommand(BrowserToolArrayCommands.ArNext);
   }
 
   static prepareCommandOptions(options: IRedisClientCommandOptions): any {