Add caching for payload serialization during fan-out (#19642)

app/lib/inline_renderer.rb

@@ -11,6 +11,7 @@ class InlineRenderer
     case @template
     when :status
       serializer = REST::StatusSerializer
+      preload_associations_for_status
     when :notification
       serializer = REST::NotificationSerializer
     when :conversation
@@ -35,6 +36,16 @@ class InlineRenderer
 
   private
 
+  def preload_associations_for_status
+    ActiveRecord::Associations::Preloader.new.preload(@object, {
+      active_mentions: :account,
+
+      reblog: {
+        active_mentions: :account,
+      },
+    })
+  end
+
   def current_user
     @current_account&.user
   end

app/lib/status_cache_hydrator.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+class StatusCacheHydrator
+  def initialize(status)
+    @status = status
+  end
+
+  def hydrate(account_id)
+    # The cache of the serialized hash is generated by the fan-out-on-write service
+    payload = Rails.cache.fetch("fan-out/#{@status.id}") { InlineRenderer.render(@status, nil, :status) }
+
+    # If we're delivering to the author who disabled the display of the application used to create the
+    # status, we need to hydrate the application, since it was not rendered for the basic payload
+    payload[:application] = ActiveModelSerializers::SerializableResource.new(@status.application, serializer: REST::StatusSerializer::ApplicationSerializer).as_json if payload[:application].nil? && @status.account_id == account_id
+
+    # We take advantage of the fact that some relationships can only occur with an original status, not
+    # the reblog that wraps it, so we can assume that some values are always false
+    if payload[:reblog]
+      payload[:favourited] = false
+      payload[:reblogged]  = false
+      payload[:muted]      = false
+      payload[:bookmarked] = false
+      payload[:pinned]     = false
+      payload[:filtered]   = CustomFilter.apply_cached_filters(CustomFilter.cached_filters_for(@status.reblog_of_id), @status.reblog).map { |filter| ActiveModelSerializers::SerializableResource.new(filter, serializer: REST::FilterResultSerializer).as_json }
+
+      # If the reblogged status is being delivered to the author who disabled the display of the application
+      # used to create the status, we need to hydrate it here too
+      payload[:reblog][:application] = ActiveModelSerializers::SerializableResource.new(@status.reblog.application, serializer: REST::StatusSerializer::ApplicationSerializer).as_json if payload[:reblog][:application].nil? && @status.reblog.account_id == account_id
+
+      payload[:reblog][:favourited] = Favourite.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:reblogged]  = Status.where(account_id: account_id, reblog_of_id: @status.reblog_of_id).exists?
+      payload[:reblog][:muted]      = ConversationMute.where(account_id: account_id, conversation_id: @status.reblog.conversation_id).exists?
+      payload[:reblog][:bookmarked] = Bookmark.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:pinned]     = StatusPin.where(account_id: account_id, status_id: @status.reblog_of_id).exists?
+      payload[:reblog][:filtered]   = payload[:filtered]
+    else
+      payload[:favourited] = Favourite.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:reblogged]  = Status.where(account_id: account_id, reblog_of_id: @status.id).exists?
+      payload[:muted]      = ConversationMute.where(account_id: account_id, conversation_id: @status.conversation_id).exists?
+      payload[:bookmarked] = Bookmark.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:pinned]     = StatusPin.where(account_id: account_id, status_id: @status.id).exists?
+      payload[:filtered]   = CustomFilter.apply_cached_filters(CustomFilter.cached_filters_for(@status.id), @status).map { |filter| ActiveModelSerializers::SerializableResource.new(filter, serializer: REST::FilterResultSerializer).as_json }
+    end
+
+    payload
+  end
+end