refactor(backend): ノートのエクスポート処理でStreams APIを使うように (#13465)

* refactor(backend): ノートのエクスポート処理でStreams APIを使うように

* fixup! refactor(backend): ノートのエクスポート処理でStreams APIを使うように

`await`忘れにより、ジョブがすぐに完了したことになり削除されてしまっていた。
それによって、`NoteStream`内での`updateProgress`メソッドの呼び出しで、`Missing key for job`のエラーが発生することがあった。

---------

Co-authored-by: syuilo <4439005+syuilo@users.noreply.github.com>

packages/backend/src/misc/FileWriterStream.ts

@@ -0,0 +1,31 @@
+import * as fs from 'node:fs/promises';
+import type { PathLike } from 'node:fs';
+
+/**
+ * `fs.createWriteStream()`相当のことを行う`WritableStream` (Web標準)
+ */
+export class FileWriterStream extends WritableStream<Uint8Array> {
+	constructor(path: PathLike) {
+		let file: fs.FileHandle | null = null;
+
+		super({
+			start: async () => {
+				file = await fs.open(path, 'a');
+			},
+			write: async (chunk, controller) => {
+				if (file === null) {
+					controller.error();
+					throw new Error();
+				}
+
+				await file.write(chunk);
+			},
+			close: async () => {
+				await file?.close();
+			},
+			abort: async () => {
+				await file?.close();
+			},
+		});
+	}
+}

packages/backend/src/misc/JsonArrayStream.ts

@@ -0,0 +1,30 @@
+import { TransformStream } from 'node:stream/web';
+
+/**
+ * ストリームに流れてきた各データについて`JSON.stringify()`した上で、それらを一つの配列にまとめる
+ */
+export class JsonArrayStream extends TransformStream<unknown, string> {
+	constructor() {
+		/** 最初の要素かどうかを変数に記録 */
+		let isFirst = true;
+
+		super({
+			start(controller) {
+				controller.enqueue('[');
+			},
+			flush(controller) {
+				controller.enqueue(']');
+			},
+			transform(chunk, controller) {
+				if (isFirst) {
+					isFirst = false;
+				} else {
+					// 妥当なJSON配列にするためには最初以外の要素の前に`,`を挿入しなければならない
+					controller.enqueue(',\n');
+				}
+
+				controller.enqueue(JSON.stringify(chunk));
+			},
+		});
+	}
+}

packages/backend/src/queue/processors/ExportNotesProcessorService.ts

@@ -3,7 +3,7 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import * as fs from 'node:fs';
+import { ReadableStream, TextEncoderStream } from 'node:stream/web';
 import { Inject, Injectable } from '@nestjs/common';
 import { MoreThan } from 'typeorm';
 import { format as dateFormat } from 'date-fns';
@@ -18,10 +18,82 @@ import { bindThis } from '@/decorators.js';
 import { DriveFileEntityService } from '@/core/entities/DriveFileEntityService.js';
 import { Packed } from '@/misc/json-schema.js';
 import { IdService } from '@/core/IdService.js';
+import { JsonArrayStream } from '@/misc/JsonArrayStream.js';
+import { FileWriterStream } from '@/misc/FileWriterStream.js';
 import { QueueLoggerService } from '../QueueLoggerService.js';
 import type * as Bull from 'bullmq';
 import type { DbJobDataWithUser } from '../types.js';
 
+class NoteStream extends ReadableStream<Record<string, unknown>> {
+	constructor(
+		job: Bull.Job,
+		notesRepository: NotesRepository,
+		pollsRepository: PollsRepository,
+		driveFileEntityService: DriveFileEntityService,
+		idService: IdService,
+		userId: string,
+	) {
+		let exportedNotesCount = 0;
+		let cursor: MiNote['id'] | null = null;
+
+		const serialize = (
+			note: MiNote,
+			poll: MiPoll | null,
+			files: Packed<'DriveFile'>[],
+		): Record<string, unknown> => {
+			return {
+				id: note.id,
+				text: note.text,
+				createdAt: idService.parse(note.id).date.toISOString(),
+				fileIds: note.fileIds,
+				files: files,
+				replyId: note.replyId,
+				renoteId: note.renoteId,
+				poll: poll,
+				cw: note.cw,
+				visibility: note.visibility,
+				visibleUserIds: note.visibleUserIds,
+				localOnly: note.localOnly,
+				reactionAcceptance: note.reactionAcceptance,
+			};
+		};
+
+		super({
+			async pull(controller): Promise<void> {
+				const notes = await notesRepository.find({
+					where: {
+						userId,
+						...(cursor !== null ? { id: MoreThan(cursor) } : {}),
+					},
+					take: 100, // 100件ずつ取得
+					order: { id: 1 },
+				});
+
+				if (notes.length === 0) {
+					job.updateProgress(100);
+					controller.close();
+				}
+
+				cursor = notes.at(-1)?.id ?? null;
+
+				for (const note of notes) {
+					const poll = note.hasPoll
+						? await pollsRepository.findOneByOrFail({ noteId: note.id }) // N+1
+						: null;
+					const files = await driveFileEntityService.packManyByIds(note.fileIds); // N+1
+					const content = serialize(note, poll, files);
+
+					controller.enqueue(content);
+					exportedNotesCount++;
+				}
+
+				const total = await notesRepository.countBy({ userId });
+				job.updateProgress(exportedNotesCount / total);
+			},
+		});
+	}
+}
+
 @Injectable()
 export class ExportNotesProcessorService {
 	private logger: Logger;
@@ -59,67 +131,19 @@ export class ExportNotesProcessorService {
 		this.logger.info(`Temp file is ${path}`);
 
 		try {
-			const stream = fs.createWriteStream(path, { flags: 'a' });
+			// メモリが足りなくならないようにストリームで処理する
+			await new NoteStream(
+				job,
+				this.notesRepository,
+				this.pollsRepository,
+				this.driveFileEntityService,
+				this.idService,
+				user.id,
+			)
+				.pipeThrough(new JsonArrayStream())
+				.pipeThrough(new TextEncoderStream())
+				.pipeTo(new FileWriterStream(path));
 
-			const write = (text: string): Promise<void> => {
-				return new Promise<void>((res, rej) => {
-					stream.write(text, err => {
-						if (err) {
-							this.logger.error(err);
-							rej(err);
-						} else {
-							res();
-						}
-					});
-				});
-			};
-
-			await write('[');
-
-			let exportedNotesCount = 0;
-			let cursor: MiNote['id'] | null = null;
-
-			while (true) {
-				const notes = await this.notesRepository.find({
-					where: {
-						userId: user.id,
-						...(cursor ? { id: MoreThan(cursor) } : {}),
-					},
-					take: 100,
-					order: {
-						id: 1,
-					},
-				}) as MiNote[];
-
-				if (notes.length === 0) {
-					job.updateProgress(100);
-					break;
-				}
-
-				cursor = notes.at(-1)?.id ?? null;
-
-				for (const note of notes) {
-					let poll: MiPoll | undefined;
-					if (note.hasPoll) {
-						poll = await this.pollsRepository.findOneByOrFail({ noteId: note.id });
-					}
-					const files = await this.driveFileEntityService.packManyByIds(note.fileIds);
-					const content = JSON.stringify(this.serialize(note, poll, files));
-					const isFirst = exportedNotesCount === 0;
-					await write(isFirst ? content : ',\n' + content);
-					exportedNotesCount++;
-				}
-
-				const total = await this.notesRepository.countBy({
-					userId: user.id,
-				});
-
-				job.updateProgress(exportedNotesCount / total);
-			}
-
-			await write(']');
-
-			stream.end();
 			this.logger.succ(`Exported to: ${path}`);
 
 			const fileName = 'notes-' + dateFormat(new Date(), 'yyyy-MM-dd-HH-mm-ss') + '.json';
@@ -130,22 +154,4 @@ export class ExportNotesProcessorService {
 			cleanup();
 		}
 	}
-
-	private serialize(note: MiNote, poll: MiPoll | null = null, files: Packed<'DriveFile'>[]): Record<string, unknown> {
-		return {
-			id: note.id,
-			text: note.text,
-			createdAt: this.idService.parse(note.id).date.toISOString(),
-			fileIds: note.fileIds,
-			files: files,
-			replyId: note.replyId,
-			renoteId: note.renoteId,
-			poll: poll,
-			cw: note.cw,
-			visibility: note.visibility,
-			visibleUserIds: note.visibleUserIds,
-			localOnly: note.localOnly,
-			reactionAcceptance: note.reactionAcceptance,
-		};
-	}
 }