[#1505] Background fetching of incoming activities' replies collections.

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -424,7 +424,13 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
           ])
       }
 
-      ActivityPub.create(params)
+      with {:ok, created_activity} <- ActivityPub.create(params) do
+        for reply_id <- replies(object) do
+          Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{"id" => reply_id})
+        end
+
+        {:ok, created_activity}
+      end
     else
       %Activity{} = activity -> {:ok, activity}
       _e -> :error
@@ -946,6 +952,13 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     Map.merge(obj, %{"replies" => replies_collection})
   end
 
+  def replies(%{"replies" => replies = %{}}) do
+    replies = with %{} <- replies["first"], do: replies["first"], else: (_ -> replies)
+    replies["items"] || []
+  end
+
+  def replies(_), do: []
+
   # Prepares the object of an outgoing create activity.
   def prepare_object(object) do
     object

lib/pleroma/workers/remote_fetcher_worker.ex

@@ -0,0 +1,20 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Workers.RemoteFetcherWorker do
+  alias Pleroma.Object.Fetcher
+
+  use Pleroma.Workers.WorkerHelper, queue: "remote_fetcher"
+
+  @impl Oban.Worker
+  def perform(
+        %{
+          "op" => "fetch_remote",
+          "id" => id
+        },
+        _job
+      ) do
+    Fetcher.fetch_object_from_id!(id)
+  end
+end