Add support for direct message assertions

app/serializers/activitypub/note_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class ActivityPub::NoteSerializer < ActivityPub::Serializer
-  context_extensions :atom_uri, :conversation, :sensitive, :voters_count
+  context_extensions :atom_uri, :conversation, :sensitive, :voters_count, :direct_message
 
   attributes :id, :type, :summary,
              :in_reply_to, :published, :url,
@@ -12,6 +12,8 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
   attribute :content
   attribute :content_map, if: :language?
 
+  attribute :direct_message, if: :non_public?
+
   has_many :media_attachments, key: :attachment
   has_many :virtual_tags, key: :tag
 
@@ -42,6 +44,14 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     object.sensitive || (!instance_options[:allow_local_only] && Setting.outgoing_spoilers.present?)
   end
 
+  def direct_message
+    object.direct_visibility?
+  end
+
+  def non_public?
+    !object.distributable?
+  end
+
   def content
     Formatter.instance.format(object)
   end