MRF: add vocabulary policy module

config/config.exs

@@ -336,6 +336,10 @@
 
 config :pleroma, :mrf_subchain, match_actor: %{}
 
+config :pleroma, :mrf_vocabulary,
+  accept: [],
+  reject: []
+
 config :pleroma, :rich_media,
   enabled: true,
   ignore_hosts: [],

lib/pleroma/web/activity_pub/mrf/vocabulary_policy.ex

@@ -0,0 +1,34 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.VocabularyPolicy do
+  @moduledoc "Filter messages which belong to certain activity vocabularies"
+
+  @behaviour Pleroma.Web.ActivityPub.MRF
+
+  def filter(%{"type" => "Undo", "object" => child_message} = message) do
+    with {:ok, _} <- filter(child_message) do
+      {:ok, message}
+    else
+      {:reject, nil} ->
+        {:reject, nil}
+    end
+  end
+
+  def filter(%{"type" => message_type} = message) do
+    with accepted_vocabulary <- Pleroma.Config.get([:mrf_vocabulary, :accept]),
+         rejected_vocabulary <- Pleroma.Config.get([:mrf_vocabulary, :reject]),
+         true <-
+           length(accepted_vocabulary) == 0 || Enum.member?(accepted_vocabulary, message_type),
+         false <-
+           length(rejected_vocabulary) > 0 && Enum.member?(rejected_vocabulary, message_type),
+         {:ok, _} <- filter(message["object"]) do
+      {:ok, message}
+    else
+      _ -> {:reject, nil}
+    end
+  end
+
+  def filter(message), do: {:ok, message}
+end