fix #1956 - add support for LATENCY HISTORY (#2555)

* added support for LATENCY_HISTORY command

* clean code

* Update LATENCY_HISTORY.ts

---------

Co-authored-by: Leibale Eidelman <me@leibale.com>

packages/client/lib/commands/LATENCY_HISTORY.spec.ts

@@ -0,0 +1,26 @@
+import {strict as assert} from 'assert';
+import testUtils, {GLOBAL} from '../test-utils';
+import { transformArguments } from './LATENCY_HISTORY';
+
+describe('LATENCY HISTORY', () => {
+    it('transformArguments', () => {
+        assert.deepEqual(
+            transformArguments('command'),
+            ['LATENCY', 'HISTORY', 'command']
+        );
+    });
+
+    testUtils.testWithClient('client.latencyHistory', async client => {
+        await Promise.all([
+            client.configSet('latency-monitor-threshold', '100'),
+            client.sendCommand(['DEBUG', 'SLEEP', '1'])
+        ]);
+        
+        const latencyHisRes = await client.latencyHistory('command');
+        assert.ok(Array.isArray(latencyHisRes));
+        for (const [timestamp, latency] of latencyHisRes) {
+            assert.equal(typeof timestamp, 'number');
+            assert.equal(typeof latency, 'number');
+        }
+    }, GLOBAL.SERVERS.OPEN);
+});

packages/client/lib/commands/LATENCY_HISTORY.ts

@@ -0,0 +1,27 @@
+export type EventType = (
+    'active-defrag-cycle' |
+    'aof-fsync-always' |
+    'aof-stat' |
+    'aof-rewrite-diff-write' |
+    'aof-rename' |
+    'aof-write' |
+    'aof-write-active-child' |
+    'aof-write-alone' |
+    'aof-write-pending-fsync' |
+    'command' |
+    'expire-cycle' |
+    'eviction-cycle' |
+    'eviction-del' |
+    'fast-command' |
+    'fork' |
+    'rdb-unlink-temp-file'
+);
+
+export function transformArguments(event: EventType) {
+    return ['LATENCY', 'HISTORY', event];
+}
+
+export declare function transformReply(): Array<[
+    timestamp: number,
+    latency: number,
+]>;