mrf simple: add accept lists

accept lists supplement reject lists by requiring that any message accepted by contained
by the accept list.

in other words, this functionality can be used to implement instances similar to
awoo.space.

CONFIGURATION.md

@@ -49,7 +49,8 @@ Restricts the visibility of posts from certain instances.
       media_removal: [],
       media_nsfw: [],
       federated_timeline_removal: [],
-      reject: []
+      reject: [],
+      accept: []
 
 * `media_removal`: posts from these instances will have attachments 
    removed
@@ -58,6 +59,7 @@ Restricts the visibility of posts from certain instances.
 * `federated_timeline_removal`: posts from these instances will be 
    marked as unlisted
 * `reject`: posts from these instances will be dropped
+* `accept`: if not empty, only posts from these instances will be accepted
 
 ### RejectNonPublic
 

config/config.exs

@@ -67,7 +67,8 @@ config :pleroma, :mrf_simple,
   media_removal: [],
   media_nsfw: [],
   federated_timeline_removal: [],
-  reject: []
+  reject: [],
+  accept: []
 
 config :pleroma, :media_proxy,
   enabled: false,

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

@@ -4,6 +4,15 @@ defmodule Pleroma.Web.ActivityPub.MRF.SimplePolicy do
 
   @mrf_policy Application.get_env(:pleroma, :mrf_simple)
 
+  @accept Keyword.get(@mrf_policy, :accept)
+  defp check_accept(actor_info, object) do
+    if length(@accept) > 0 and not actor_info.host in @accept do
+      {:reject, nil}
+    else
+      {:ok, object}
+    end
+  end
+
   @reject Keyword.get(@mrf_policy, :reject)
   defp check_reject(actor_info, object) do
     if actor_info.host in @reject do
@@ -74,7 +83,8 @@ defmodule Pleroma.Web.ActivityPub.MRF.SimplePolicy do
   def filter(object) do
     actor_info = URI.parse(object["actor"])
 
-    with {:ok, object} <- check_reject(actor_info, object),
+    with {:ok, object} <- check_accept(actor_info, object),
+         {:ok, object} <- check_reject(actor_info, object),
          {:ok, object} <- check_media_removal(actor_info, object),
          {:ok, object} <- check_media_nsfw(actor_info, object),
          {:ok, object} <- check_ftl_removal(actor_info, object) do