From 281872b0ad951afba57d5ca0582c8c4c882bb769 Mon Sep 17 00:00:00 2001
From: Alex Gleason <alex@alexgleason.me>
Date: Tue, 21 Jan 2025 18:34:34 -0600
Subject: [PATCH] Add notActivityPub middleware to stop AP requests on /users/*

---
 src/app.ts                                 |  4 ++--
 src/middleware/notActivitypubMiddleware.ts | 18 ++++++++++++++++++
 src/utils/api.ts                           | 19 -------------------
 3 files changed, 20 insertions(+), 21 deletions(-)
 create mode 100644 src/middleware/notActivitypubMiddleware.ts

diff --git a/src/app.ts b/src/app.ts
index 32061184..b18ba281 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -133,6 +133,7 @@ import { DittoTranslator } from '@/interfaces/DittoTranslator.ts';
 import { auth98Middleware, requireProof, requireRole } from '@/middleware/auth98Middleware.ts';
 import { cspMiddleware } from '@/middleware/cspMiddleware.ts';
 import { metricsMiddleware } from '@/middleware/metricsMiddleware.ts';
+import { notActivitypubMiddleware } from '@/middleware/notActivitypubMiddleware.ts';
 import { paginationMiddleware } from '@/middleware/paginationMiddleware.ts';
 import { rateLimitMiddleware } from '@/middleware/rateLimitMiddleware.ts';
 import { requireSigner } from '@/middleware/requireSigner.ts';
@@ -179,7 +180,6 @@ app.use('*', rateLimitMiddleware(300, Time.minutes(5)));
 
 app.use('/api/*', metricsMiddleware, paginationMiddleware, logger(debug));
 app.use('/.well-known/*', metricsMiddleware, logger(debug));
-app.use('/users/*', metricsMiddleware, logger(debug));
 app.use('/nodeinfo/*', metricsMiddleware, logger(debug));
 app.use('/oauth/*', metricsMiddleware, logger(debug));
 
@@ -400,7 +400,7 @@ app.use('/oauth/*', notImplementedController);
 app.get('/:acct{@.*}', frontendController);
 app.get('/:acct{@.*}/*', frontendController);
 app.get('/:bech32{^[\x21-\x7E]{1,83}1[023456789acdefghjklmnpqrstuvwxyz]{6,}$}', frontendController);
-app.get('/users/*', frontendController);
+app.get('/users/*', notActivitypubMiddleware, frontendController);
 app.get('/tags/*', frontendController);
 app.get('/statuses/*', frontendController);
 app.get('/notice/*', frontendController);
diff --git a/src/middleware/notActivitypubMiddleware.ts b/src/middleware/notActivitypubMiddleware.ts
new file mode 100644
index 00000000..b25e6f61
--- /dev/null
+++ b/src/middleware/notActivitypubMiddleware.ts
@@ -0,0 +1,18 @@
+import { MiddlewareHandler } from '@hono/hono';
+
+const ACTIVITYPUB_TYPES = [
+  'application/activity+json',
+  'application/ld+json; profile="https://www.w3.org/ns/activitystreams"',
+];
+
+/** Return 4xx errors on common (unsupported) ActivityPub routes to prevent AP traffic. */
+export const notActivitypubMiddleware: MiddlewareHandler = async (c, next) => {
+  const accept = c.req.header('accept');
+  const types = accept?.split(',')?.map((type) => type.trim()) ?? [];
+
+  if (types.every((type) => ACTIVITYPUB_TYPES.includes(type))) {
+    return c.text('ActivityPub is not supported', 406);
+  }
+
+  await next();
+};
diff --git a/src/utils/api.ts b/src/utils/api.ts
index 37cbbbf9..9e7125c6 100644
--- a/src/utils/api.ts
+++ b/src/utils/api.ts
@@ -261,24 +261,6 @@ function paginatedList(
   return c.json(results, 200, headers);
 }
 
-/** JSON-LD context. */
-type LDContext = (string | Record<string, string | Record<string, string>>)[];
-
-/** Add a basic JSON-LD context to ActivityStreams object, if it doesn't already exist. */
-function maybeAddContext<T>(object: T): T & { '@context': LDContext } {
-  return {
-    '@context': ['https://www.w3.org/ns/activitystreams'],
-    ...object,
-  };
-}
-
-/** Like hono's `c.json()` except returns JSON-LD. */
-function activityJson<T, P extends string>(c: Context<any, P>, object: T) {
-  const response = c.json(maybeAddContext(object));
-  response.headers.set('content-type', 'application/activity+json; charset=UTF-8');
-  return response;
-}
-
 /** Rewrite the URL of the request object to use the local domain. */
 function localRequest(c: Context): Request {
   return Object.create(c.req.raw, {
@@ -300,7 +282,6 @@ function assertAuthenticated(c: AppContext, author: NostrEvent): void {
 }
 
 export {
-  activityJson,
   assertAuthenticated,
   createAdminEvent,
   createEvent,