1 files changed, 18 insertions, 5 deletions
diff --git a/src/lib/activitypub.ts b/src/lib/activitypub.ts
index 0a3db7b..11f0770 100644
--- a/src/lib/activitypub.ts
+++ b/src/lib/activitypub.ts
@@ -1,9 +1,22 @@
-import { Request } from "express";
+import { Request, Response } from "express";
 
+// From https://www.w3.org/TR/activitypub/#client-to-server-interactions:
+// "Servers MAY interpret a Content-Type or Accept header of application/activity+json
+// as equivalent to application/ld+json; profile="https://www.w3.org/ns/activitystreams"
+// for client-to-server interactions.
+// For best compatibility, we always send application/ld+json; profile="https://www.w3.org/ns/activitystreams"
+// and accept both application/ld+json; profile="https://www.w3.org/ns/activitystreams" and application/activity+json.
+export const activityPubContentType =
+    'application/ld+json; profile="https://www.w3.org/ns/activitystreams"';
+export const alternateActivityPubContentType = "application/activity+json";
+
+// Cf. https://www.w3.org/TR/activitypub/#retrieving-objects
 export const acceptsActivityPub = (req: Request) => {
-    return (
-        req.headers.accept &&
-        (req.headers.accept.includes("application/activity+json") ||
-            req.headers.accept.includes("application/ld+json"))
+    const validAcceptHeaders = [
+        activityPubContentType,
+        alternateActivityPubContentType,
+    ];
+    return validAcceptHeaders.some(
+        (header) => req.headers.accept?.includes(header),
     );
 };