Improved remote thread fetching (#10106)

* Fetch up to 5 replies when discovering a new remote status

This is used for resolving threads downwards. The originating
server must add a “replies” attributes with such replies for it to
be useful.

* Add some tests for ActivityPub::FetchRepliesWorker

* Add specs for ActivityPub::FetchRepliesService

* Serialize up to 5 public self-replies for ActivityPub notes

* Add specs for ActivityPub::NoteSerializer

* Move exponential backoff logic to a worker concern

* Fetch first page of paginated collections when fetching thread replies

* Add specs for paginated collections in replies

* Move Note replies serialization to a first CollectionPage

The collection isn't actually paginable yet as it has no id nor
a `next` field. This may come in another PR.

* Use pluck(:uri) instead of map(&:uri) to improve performances

* Fix fetching replies when they are in a CollectionPage

1 files changed, 3 insertions, 2 deletions

diff --git a/app/serializers/activitypub/collection_serializer.rb b/app/serializers/activitypub/collection_serializer.rb
index e8960131b..b03609957 100644
--- a/app/serializers/activitypub/collection_serializer.rb
+++ b/app/serializers/activitypub/collection_serializer.rb
@@ -7,7 +7,8 @@ class ActivityPub::CollectionSerializer < ActiveModel::Serializer
     super
   end
 
-  attributes :id, :type
+  attribute :id, if: -> { object.id.present? }
+  attribute :type
   attribute :total_items, if: -> { object.size.present? }
   attribute :next, if: -> { object.next.present? }
   attribute :prev, if: -> { object.prev.present? }
@@ -37,6 +38,6 @@ class ActivityPub::CollectionSerializer < ActiveModel::Serializer
   end
 
   def page?
-    object.part_of.present?
+    object.part_of.present? || object.page.present?
   end
 end