Better pagination for ActivityPub outbox (#7356)

app/controllers/activitypub/outboxes_controller.rb

@@ -1,14 +1,14 @@
 # frozen_string_literal: true
 
 class ActivityPub::OutboxesController < Api::BaseController
+  LIMIT = 20
+
   include SignatureVerification
 
   before_action :set_account
+  before_action :set_statuses
 
   def show
-    @statuses = @account.statuses.permitted_for(@account, signed_request_account).paginate_by_max_id(20, params[:max_id], params[:since_id])
-    @statuses = cache_collection(@statuses, Status)
-
     render json: outbox_presenter, serializer: ActivityPub::OutboxSerializer, adapter: ActivityPub::Adapter, content_type: 'application/activity+json'
   end
 
@@ -19,11 +19,47 @@ class ActivityPub::OutboxesController < Api::BaseController
   end
 
   def outbox_presenter
-    ActivityPub::CollectionPresenter.new(
-      id: account_outbox_url(@account),
-      type: :ordered,
-      size: @account.statuses_count,
-      items: @statuses
-    )
+    if page_requested?
+      ActivityPub::CollectionPresenter.new(
+        id: account_outbox_url(@account, page_params),
+        type: :ordered,
+        part_of: account_outbox_url(@account),
+        prev: prev_page,
+        next: next_page,
+        items: @statuses
+      )
+    else
+      ActivityPub::CollectionPresenter.new(
+        id: account_outbox_url(@account),
+        type: :ordered,
+        size: @account.statuses_count,
+        first: account_outbox_url(@account, page: true),
+        last: account_outbox_url(@account, page: true, min_id: 0)
+      )
+    end
+  end
+
+  def next_page
+    account_outbox_url(@account, page: true, max_id: @statuses.last.id) if @statuses.size == LIMIT
+  end
+
+  def prev_page
+    account_outbox_url(@account, page: true, min_id: @statuses.first.id) unless @statuses.empty?
+  end
+
+  def set_statuses
+    return unless page_requested?
+
+    @statuses = @account.statuses.permitted_for(@account, signed_request_account)
+    @statuses = params[:min_id].present? ? @statuses.paginate_by_min_id(LIMIT, params[:min_id]).reverse : @statuses.paginate_by_max_id(LIMIT, params[:max_id])
+    @statuses = cache_collection(@statuses, Status)
+  end
+
+  def page_requested?
+    params[:page] == 'true'
+  end
+
+  def page_params
+    { page: true, max_id: params[:max_id], min_id: params[:min_id] }.compact
   end
 end