merge: Fix "fetch linked note" button for AP previews (!1037)

View MR for information: https://activitypub.software/TransFem-org/Sharkey/-/merge_requests/1037

Approved-by: dakkar <dakkar@thenautilus.net>
Approved-by: Marie <github@yuugi.dev>

2 files changed, 243 insertions, 43 deletions

diff --git a/packages/backend/src/server/FileServerService.ts b/packages/backend/src/server/FileServerService.ts
index 34ef683983..4ef5539cff 100644
--- a/packages/backend/src/server/FileServerService.ts
+++ b/packages/backend/src/server/FileServerService.ts
@@ -675,9 +675,11 @@ export class FileServerService {
 		if (info.blocked) {
 			reply.code(429);
 			reply.send({
-				message: 'Rate limit exceeded. Please try again later.',
-				code: 'RATE_LIMIT_EXCEEDED',
-				id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
+				error: {
+					message: 'Rate limit exceeded. Please try again later.',
+					code: 'RATE_LIMIT_EXCEEDED',
+					id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
+				},
 			});
 
 			return false;
diff --git a/packages/backend/src/server/web/UrlPreviewService.ts b/packages/backend/src/server/web/UrlPreviewService.ts
index 0cab657c23..203bc908a8 100644
--- a/packages/backend/src/server/web/UrlPreviewService.ts
+++ b/packages/backend/src/server/web/UrlPreviewService.ts
@@ -15,15 +15,21 @@ import type Logger from '@/logger.js';
 import { query } from '@/misc/prelude/url.js';
 import { LoggerService } from '@/core/LoggerService.js';
 import { bindThis } from '@/decorators.js';
-import { ApiError } from '@/server/api/error.js';
 import { MiMeta } from '@/models/Meta.js';
 import { RedisKVCache } from '@/misc/cache.js';
 import { UtilityService } from '@/core/UtilityService.js';
 import { ApDbResolverService } from '@/core/activitypub/ApDbResolverService.js';
-import type { NotesRepository } from '@/models/_.js';
+import type { MiAccessToken, NotesRepository } from '@/models/_.js';
 import { ApUtilityService } from '@/core/activitypub/ApUtilityService.js';
 import { ApRequestService } from '@/core/activitypub/ApRequestService.js';
 import { SystemAccountService } from '@/core/SystemAccountService.js';
+import { ApNoteService } from '@/core/activitypub/models/ApNoteService.js';
+import { AuthenticateService, AuthenticationError } from '@/server/api/AuthenticateService.js';
+import { SkRateLimiterService } from '@/server/SkRateLimiterService.js';
+import { BucketRateLimit, Keyed, sendRateLimitHeaders } from '@/misc/rate-limit-utils.js';
+import type { MiLocalUser } from '@/models/User.js';
+import { getIpHash } from '@/misc/get-ip-hash.js';
+import { isRetryableError } from '@/misc/is-retryable-error.js';
 import type { FastifyRequest, FastifyReply } from 'fastify';
 
 export type LocalSummalyResult = SummalyResult & {
@@ -31,7 +37,27 @@ export type LocalSummalyResult = SummalyResult & {
 };
 
 // Increment this to invalidate cached previews after a major change.
-const cacheFormatVersion = 2;
+const cacheFormatVersion = 3;
+
+type PreviewRoute = {
+	Querystring: {
+		url?: string
+		lang?: string,
+		fetch?: string,
+		i?: string,
+	},
+};
+
+type AuthArray = [user: MiLocalUser | null | undefined, app: MiAccessToken | null | undefined, actor: MiLocalUser | string];
+
+// Up to 50 requests, then 10 / second (at 2 / 200ms rate)
+const previewLimit: Keyed<BucketRateLimit> = {
+	key: '/url',
+	type: 'bucket',
+	size: 50,
+	dripSize: 2,
+	dripRate: 200,
+};
 
 @Injectable()
 export class UrlPreviewService {
@@ -58,6 +84,9 @@ export class UrlPreviewService {
 		private readonly apDbResolverService: ApDbResolverService,
 		private readonly apRequestService: ApRequestService,
 		private readonly systemAccountService: SystemAccountService,
+		private readonly apNoteService: ApNoteService,
+		private readonly authenticateService: AuthenticateService,
+		private readonly rateLimiterService: SkRateLimiterService,
 	) {
 		this.logger = this.loggerService.getLogger('url-preview');
 		this.previewCache = new RedisKVCache<LocalSummalyResult>(this.redisClient, 'summaly', {
@@ -85,9 +114,9 @@ export class UrlPreviewService {
 
 	@bindThis
 	public async handle(
-		request: FastifyRequest<{ Querystring: { url?: string; lang?: string; } }>,
+		request: FastifyRequest<PreviewRoute>,
 		reply: FastifyReply,
-	): Promise<object | undefined> {
+	): Promise<void> {
 		const url = request.query.url;
 		if (typeof url !== 'string' || !URL.canParse(url)) {
 			reply.code(400);
@@ -101,38 +130,39 @@ export class UrlPreviewService {
 		}
 
 		if (!this.meta.urlPreviewEnabled) {
-			reply.code(403);
-			return {
-				error: new ApiError({
+			return reply.code(403).send({
+				error: {
 					message: 'URL preview is disabled',
 					code: 'URL_PREVIEW_DISABLED',
 					id: '58b36e13-d2f5-0323-b0c6-76aa9dabefb8',
-				}),
-			};
+				},
+			});
+		}
+
+		// Check rate limit
+		const auth = await this.authenticate(request);
+		if (!await this.checkRateLimit(auth, reply)) {
+			return;
 		}
 
 		if (this.utilityService.isBlockedHost(this.meta.blockedHosts, new URL(url).host)) {
-			reply.code(403);
-			return {
-				error: new ApiError({
+			return reply.code(403).send({
+				error: {
 					message: 'URL is blocked',
 					code: 'URL_PREVIEW_BLOCKED',
 					id: '50294652-857b-4b13-9700-8e5c7a8deae8',
-				}),
-			};
+				},
+			});
 		}
 
-		const cacheKey = `${url}@${lang}@${cacheFormatVersion}`;
-		const cached = await this.previewCache.get(cacheKey);
-		if (cached !== undefined) {
-			// Cache 1 day (matching redis)
-			reply.header('Cache-Control', 'public, max-age=86400');
-
-			if (cached.activityPub) {
-				cached.haveNoteLocally = !! await this.apDbResolverService.getNoteFromApId(cached.activityPub);
-			}
+		const fetch = !!request.query.fetch;
+		if (fetch && !await this.checkFetchPermissions(auth, reply)) {
+			return;
+		}
 
-			return cached;
+		const cacheKey = `${url}@${lang}@${cacheFormatVersion}`;
+		if (await this.sendCachedPreview(cacheKey, reply, fetch)) {
+			return;
 		}
 
 		try {
@@ -144,14 +174,13 @@ export class UrlPreviewService {
 
 			// Repeat check, since redirects are allowed.
 			if (this.utilityService.isBlockedHost(this.meta.blockedHosts, new URL(summary.url).host)) {
-				reply.code(403);
-				return {
-					error: new ApiError({
+				return reply.code(403).send({
+					error: {
 						message: 'URL is blocked',
 						code: 'URL_PREVIEW_BLOCKED',
 						id: '50294652-857b-4b13-9700-8e5c7a8deae8',
-					}),
-				};
+					},
+				});
 			}
 
 			this.logger.info(`Got preview of ${url} in ${lang}: ${summary.title}`);
@@ -164,33 +193,76 @@ export class UrlPreviewService {
 				await this.inferActivityPubLink(summary);
 			}
 
-			if (summary.activityPub) {
+			if (summary.activityPub && !summary.haveNoteLocally) {
 				// Avoid duplicate checks in case inferActivityPubLink already set this.
-				summary.haveNoteLocally ||= !!await this.apDbResolverService.getNoteFromApId(summary.activityPub);
+				const exists = await this.noteExists(summary.activityPub, fetch);
+
+				// Remove the AP flag if we encounter a permanent error fetching the note.
+				if (exists === false) {
+					summary.activityPub = null;
+					summary.haveNoteLocally = undefined;
+				} else {
+					summary.haveNoteLocally = exists ?? false;
+				}
 			}
 
 			// Await this to avoid hammering redis when a bunch of URLs are fetched at once
 			await this.previewCache.set(cacheKey, summary);
 
-			// Cache 1 day (matching redis)
-			reply.header('Cache-Control', 'public, max-age=86400');
+			// Cache 1 day (matching redis), but only once we finalize the result
+			if (!summary.activityPub || summary.haveNoteLocally) {
+				reply.header('Cache-Control', 'public, max-age=86400');
+			}
 
-			return summary;
+			return reply.code(200).send(summary);
 		} catch (err) {
 			this.logger.warn(`Failed to get preview of ${url} for ${lang}: ${err}`);
 
-			reply.code(422);
 			reply.header('Cache-Control', 'max-age=3600');
-			return {
-				error: new ApiError({
+			return reply.code(422).send({
+				error: {
 					message: 'Failed to get preview',
 					code: 'URL_PREVIEW_FAILED',
 					id: '09d01cb5-53b9-4856-82e5-38a50c290a3b',
-				}),
-			};
+				},
+			});
 		}
 	}
 
+	private async sendCachedPreview(cacheKey: string, reply: FastifyReply, fetch: boolean): Promise<boolean> {
+		const summary = await this.previewCache.get(cacheKey);
+		if (summary === undefined) {
+			return false;
+		}
+
+		// Check if note has loaded since we last cached the preview
+		if (summary.activityPub && !summary.haveNoteLocally) {
+			// Avoid duplicate checks in case inferActivityPubLink already set this.
+			const exists = await this.noteExists(summary.activityPub, fetch);
+
+			// Remove the AP flag if we encounter a permanent error fetching the note.
+			if (exists === false) {
+				summary.activityPub = null;
+				summary.haveNoteLocally = undefined;
+			} else {
+				summary.haveNoteLocally = exists ?? false;
+			}
+
+			// Persist the result once we finalize the result
+			if (!summary.activityPub || summary.haveNoteLocally) {
+				await this.previewCache.set(cacheKey, summary);
+			}
+		}
+
+		// Cache 1 day (matching redis), but only once we finalize the result
+		if (!summary.activityPub || summary.haveNoteLocally) {
+			reply.header('Cache-Control', 'public, max-age=86400');
+		}
+
+		reply.code(200).send(summary);
+		return true;
+	}
+
 	private fetchSummary(url: string, meta: MiMeta, lang?: string): Promise<SummalyResult> {
 		const agent = this.config.proxy
 			? {
@@ -211,6 +283,7 @@ export class UrlPreviewService {
 	}
 
 	private fetchSummaryFromProxy(url: string, meta: MiMeta, lang?: string): Promise<SummalyResult> {
+		// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
 		const proxy = meta.urlPreviewSummaryProxyUrl!;
 		const queryStr = query({
 			followRedirects: true,
@@ -302,4 +375,129 @@ export class UrlPreviewService {
 			return;
 		}
 	}
+
+	// true = exists, false = does not exist (permanently), null = does not exist (temporarily)
+	private async noteExists(uri: string, fetch = false): Promise<boolean | null> {
+		try {
+			// Local note or cached remote note
+			if (await this.apDbResolverService.getNoteFromApId(uri)) {
+				return true;
+			}
+
+			// Un-cached remote note
+			if (!fetch) {
+				return null;
+			}
+
+			// Newly cached remote note
+			if (await this.apNoteService.resolveNote(uri)) {
+				return true;
+			}
+
+			// Non-existent or deleted note
+			return false;
+		} catch (err) {
+			// Errors, including invalid notes and network errors
+			return isRetryableError(err) ? null : false;
+		}
+	}
+
+	// Adapted from ApiCallService
+	private async authenticate(request: FastifyRequest<{ Querystring?: { i?: string | string[] }, Body?: { i?: string | string[] } }>): Promise<AuthArray> {
+		const body = request.method === 'GET' ? request.query : request.body;
+
+		// https://datatracker.ietf.org/doc/html/rfc6750.html#section-2.1 (case sensitive)
+		const token = request.headers.authorization?.startsWith('Bearer ')
+			? request.headers.authorization.slice(7)
+			: body?.['i'];
+		if (token != null && typeof token !== 'string') {
+			return [undefined, undefined, getIpHash(request.ip)];
+		}
+
+		try {
+			const auth = await this.authenticateService.authenticate(token);
+			return [auth[0], auth[1], auth[0] ?? getIpHash(request.ip)];
+		} catch (err) {
+			if (err instanceof AuthenticationError) {
+				return [undefined, undefined, getIpHash(request.ip)];
+			} else {
+				throw err;
+			}
+		}
+	}
+
+	// Adapted from ApiCallService
+	private async checkFetchPermissions(auth: AuthArray, reply: FastifyReply): Promise<boolean> {
+		const [user, app] = auth;
+
+		// Authentication
+		if (user === undefined) {
+			reply.code(401).send({
+				error: {
+					message: 'Authentication failed. Please ensure your token is correct.',
+					code: 'AUTHENTICATION_FAILED',
+					id: 'b0a7f5f8-dc2f-4171-b91f-de88ad238e14',
+				},
+			});
+			return false;
+		}
+		if (user === null) {
+			reply.code(401).send({
+				error: {
+					message: 'Credential required.',
+					code: 'CREDENTIAL_REQUIRED',
+					id: '1384574d-a912-4b81-8601-c7b1c4085df1',
+				},
+			});
+			return false;
+		}
+
+		// Authorization
+		if (user.isSuspended || user.isDeleted) {
+			reply.code(403).send({
+				error: {
+					message: 'Your account has been suspended.',
+					code: 'YOUR_ACCOUNT_SUSPENDED',
+					kind: 'permission',
+
+					id: 'a8c724b3-6e9c-4b46-b1a8-bc3ed6258370',
+				},
+			});
+			return false;
+		}
+		if (app && !app.permission.includes('read:account')) {
+			reply.code(403).send({
+				error: {
+					message: 'Your app does not have the necessary permissions to use this endpoint.',
+					code: 'PERMISSION_DENIED',
+					kind: 'permission',
+					id: '1370e5b7-d4eb-4566-bb1d-7748ee6a1838',
+				},
+			});
+			return false;
+		}
+
+		return true;
+	}
+
+	private async checkRateLimit(auth: AuthArray, reply: FastifyReply): Promise<boolean> {
+		const info = await this.rateLimiterService.limit(previewLimit, auth[2]);
+
+		// Always send headers, even if not blocked
+		sendRateLimitHeaders(reply, info);
+
+		if (info.blocked) {
+			reply.code(429).send({
+				error: {
+					message: 'Rate limit exceeded. Please try again later.',
+					code: 'RATE_LIMIT_EXCEEDED',
+					id: 'd5826d14-3982-4d2e-8011-b9e9f02499ef',
+				},
+			});
+
+			return false;
+		}
+
+		return true;
+	}
 }