Refactor FileServerService: Extract file handling logic into dedicated handlers (#17090)

- Introduced FileServerDriveHandler to manage drive file requests.
- Created FileServerFileResolver for resolving file access keys and downloading files.
- Added FileServerProxyHandler to handle proxy requests and image processing.
- Moved utility functions to FileServerUtils for better organization.
- Removed redundant methods from FileServerService, improving readability and maintainability.

packages/backend/src/server/file/FileServerUtils.ts

@@ -0,0 +1,107 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import * as fs from 'node:fs';
+import { FILE_TYPE_BROWSERSAFE } from '@/const.js';
+import { contentDisposition } from '@/misc/content-disposition.js';
+import type { IImageStreamable } from '@/core/ImageProcessingService.js';
+import type { FastifyReply } from 'fastify';
+
+export type RangeStream = {
+	stream: fs.ReadStream;
+	start: number;
+	end: number;
+	chunksize: number;
+};
+
+/**
+ * Range リクエストに対応したストリームを作成する
+ */
+export function createRangeStream(rangeHeader: string, size: number, path: string): RangeStream {
+	const parts = rangeHeader.replace(/bytes=/, '').split('-');
+	const start = parseInt(parts[0], 10);
+	let end = parts[1] ? parseInt(parts[1], 10) : size - 1;
+	if (end > size) {
+		end = size - 1;
+	}
+	const chunksize = end - start + 1;
+
+	return {
+		stream: fs.createReadStream(path, { start, end }),
+		start,
+		end,
+		chunksize,
+	};
+}
+
+/**
+ * ストリームにcleanupハンドラを設定する
+ * ストリームでない場合は即座にcleanupを実行する
+ */
+export function attachStreamCleanup(data: IImageStreamable['data'], cleanup: () => void): void {
+	if ('pipe' in data && typeof data.pipe === 'function') {
+		data.on('end', cleanup);
+		data.on('close', cleanup);
+	} else {
+		cleanup();
+	}
+}
+
+/**
+ * MIME タイプがブラウザセーフかどうかに応じて Content-Type を返す
+ */
+export function getSafeContentType(mime: string): string {
+	return FILE_TYPE_BROWSERSAFE.includes(mime) ? mime : 'application/octet-stream';
+}
+
+/**
+ * Range リクエストを処理してストリームを返す
+ * Range ヘッダーがない場合は通常のストリームを返す
+ */
+export function handleRangeRequest(
+	reply: FastifyReply,
+	rangeHeader: string | undefined,
+	size: number,
+	path: string,
+): fs.ReadStream {
+	if (rangeHeader && size > 0) {
+		const { stream, start, end, chunksize } = createRangeStream(rangeHeader, size, path);
+		reply.header('Content-Range', `bytes ${start}-${end}/${size}`);
+		reply.header('Accept-Ranges', 'bytes');
+		reply.header('Content-Length', chunksize);
+		reply.code(206);
+		return stream;
+	}
+	return fs.createReadStream(path);
+}
+
+export type FileResponseOptions = {
+	mime: string;
+	filename: string;
+	size?: number;
+	cacheControl?: string;
+};
+
+/**
+ * ファイルレスポンス用の共通ヘッダーを設定する
+ */
+export function setFileResponseHeaders(
+	reply: FastifyReply,
+	options: FileResponseOptions,
+): void {
+	reply.header('Content-Type', getSafeContentType(options.mime));
+	reply.header('Cache-Control', options.cacheControl ?? 'max-age=31536000, immutable');
+	reply.header('Content-Disposition', contentDisposition('inline', options.filename));
+	if (options.size !== undefined) {
+		reply.header('Content-Length', options.size);
+	}
+}
+
+/**
+ * cleanup が必要なファイルかどうかを判定する型ガード
+ */
+export function needsCleanup<T extends { kind?: string; cleanup?: () => void }>(file: T): file is T & { cleanup: () => void } {
+	return 'cleanup' in file && typeof file.cleanup === 'function';
+}