fix(backend): fallback if `sinceId` is older than the oldest in cache when using FTT (#14061)

* fix(backend): fallback if `sinceId` is older than the oldest in cache when using FTT

* Update CHANGELOG.md

* chore: fix description of test

2 files changed, 39 insertions, 8 deletions

diff --git a/packages/backend/src/core/FanoutTimelineEndpointService.ts b/packages/backend/src/core/FanoutTimelineEndpointService.ts
index d5058f37c2..b05af99c5e 100644
--- a/packages/backend/src/core/FanoutTimelineEndpointService.ts
+++ b/packages/backend/src/core/FanoutTimelineEndpointService.ts
@@ -55,9 +55,6 @@ export class FanoutTimelineEndpointService {
 
 	@bindThis
 	private async getMiNotes(ps: TimelineOptions): Promise<MiNote[]> {
-		let noteIds: string[];
-		let shouldFallbackToDb = false;
-
 		// 呼び出し元と以下の処理をシンプルにするためにdbFallbackを置き換える
 		if (!ps.useDbFallback) ps.dbFallback = () => Promise.resolve([]);
 
@@ -67,12 +64,11 @@ export class FanoutTimelineEndpointService {
 		const redisResult = await this.fanoutTimelineService.getMulti(ps.redisTimelines, ps.untilId, ps.sinceId);
 
 		// TODO: いい感じにgetMulti内でソート済だからuniqするときにredisResultが全てソート済なのを利用して再ソートを避けたい
-		const redisResultIds = Array.from(new Set(redisResult.flat(1)));
-
-		redisResultIds.sort(idCompare);
-		noteIds = redisResultIds.slice(0, ps.limit);
+		const redisResultIds = Array.from(new Set(redisResult.flat(1))).sort(idCompare);
 
-		shouldFallbackToDb = shouldFallbackToDb || (noteIds.length === 0);
+		let noteIds = redisResultIds.slice(0, ps.limit);
+		const oldestNoteId = ascending ? redisResultIds[0] : redisResultIds[redisResultIds.length - 1];
+		const shouldFallbackToDb = noteIds.length === 0 || ps.sinceId != null && ps.sinceId < oldestNoteId;
 
 		if (!shouldFallbackToDb) {
 			let filter = ps.noteFilter ?? (_note => true);
diff --git a/packages/backend/test/e2e/timelines.ts b/packages/backend/test/e2e/timelines.ts
index 5487292afc..f6cc2bac28 100644
--- a/packages/backend/test/e2e/timelines.ts
+++ b/packages/backend/test/e2e/timelines.ts
@@ -7,6 +7,8 @@
 // pnpm jest -- e2e/timelines.ts
 
 import * as assert from 'assert';
+import { Redis } from 'ioredis';
+import { loadConfig } from '@/config.js';
 import { api, post, randomString, sendEnvUpdateRequest, signup, sleep, uploadUrl } from '../utils.js';
 
 function genHost() {
@@ -17,7 +19,13 @@ function waitForPushToTl() {
 	return sleep(500);
 }
 
+let redisForTimelines: Redis;
+
 describe('Timelines', () => {
+	beforeAll(() => {
+		redisForTimelines = new Redis(loadConfig().redisForTimelines);
+	});
+
 	describe('Home TL', () => {
 		test.concurrent('自分の visibility: followers なノートが含まれる', async () => {
 			const [alice] = await Promise.all([signup()]);
@@ -1272,6 +1280,33 @@ describe('Timelines', () => {
 
 			assert.strictEqual(res.body.some((note: any) => note.id === bobNote.id), false);
 		});
+
+		/** @see https://github.com/misskey-dev/misskey/issues/14000 */
+		test.concurrent('FTT: sinceId にキャッシュより古いノートを指定しても、sinceId による絞り込みが正しく動作する', async () => {
+			const alice = await signup();
+			const noteSince = await post(alice, { text: 'Note where id will be `sinceId`.' });
+			const note1 = await post(alice, { text: '1' });
+			const note2 = await post(alice, { text: '2' });
+			await redisForTimelines.del('list:userTimeline:' + alice.id);
+			const note3 = await post(alice, { text: '3' });
+
+			const res = await api('users/notes', { userId: alice.id, sinceId: noteSince.id });
+			assert.deepStrictEqual(res.body, [note1, note2, note3]);
+		});
+
+		test.concurrent('FTT: sinceId にキャッシュより古いノートを指定しても、sinceId と untilId による絞り込みが正しく動作する', async () => {
+			const alice = await signup();
+			const noteSince = await post(alice, { text: 'Note where id will be `sinceId`.' });
+			const note1 = await post(alice, { text: '1' });
+			const note2 = await post(alice, { text: '2' });
+			await redisForTimelines.del('list:userTimeline:' + alice.id);
+			const note3 = await post(alice, { text: '3' });
+			const noteUntil = await post(alice, { text: 'Note where id will be `untilId`.' });
+			await post(alice, { text: '4' });
+
+			const res = await api('users/notes', { userId: alice.id, sinceId: noteSince.id, untilId: noteUntil.id });
+			assert.deepStrictEqual(res.body, [note3, note2, note1]);
+		});
 	});
 
 	// TODO: リノートミュート済みユーザーのテスト