mrf: add subchain policy

config/config.exs

@@ -320,6 +320,9 @@
   federated_timeline_removal: [],
   replace: []
 
+config :pleroma, :mrf_subchain,
+  match_actor: %{}
+
 config :pleroma, :rich_media, enabled: true
 
 config :pleroma, :media_proxy,

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

@@ -0,0 +1,36 @@
+# 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.SubchainPolicy do
+  alias Pleroma.Config
+  alias Pleroma.Web.ActivityPub.MRF
+
+  require Logger
+
+  @behaviour MRF
+
+  defp lookup_subchain(actor) do
+    with matches <- Config.get([:mrf_subchain, :match_actor]),
+         {match, subchain} <- Enum.find(matches, fn {k, _v} -> String.match?(actor, k) end) do
+      {:ok, match, subchain}
+    else
+      _e -> {:error, :notfound}
+    end
+  end
+
+  @impl true
+  def filter(%{"actor" => actor} = message) do
+    with {:ok, match, subchain} <- lookup_subchain(actor) do
+      Logger.debug("[SubchainPolicy] Matched #{actor} against #{inspect(match)} with subchain #{inspect(subchain)}")
+
+      subchain
+      |> MRF.filter(message)
+    else
+      _e -> {:ok, message}
+    end
+  end
+
+  @impl true
+  def filter(message), do: {:ok, message}
+end