2 files changed, 36 insertions, 1 deletions
diff --git a/lib/pleroma/following_relationship.ex b/lib/pleroma/following_relationship.ex
index c2020d30a..83b366dd4 100644
--- a/lib/pleroma/following_relationship.ex
+++ b/lib/pleroma/following_relationship.ex
@@ -95,7 +95,11 @@ defmodule Pleroma.FollowingRelationship do
     |> where([r], r.state == ^:follow_accept)
   end
 
-  def followers_ap_ids(%User{} = user, from_ap_ids \\ nil) do
+  def followers_ap_ids(user, from_ap_ids \\ nil)
+
+  def followers_ap_ids(_, []), do: []
+
+  def followers_ap_ids(%User{} = user, from_ap_ids) do
     query =
       user
       |> followers_query()
diff --git a/lib/pleroma/web/activity_pub/mrf/simple_policy.ex b/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
index b77b8c7b4..bb193475a 100644
--- a/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
+++ b/lib/pleroma/web/activity_pub/mrf/simple_policy.ex
@@ -7,6 +7,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.SimplePolicy do
   @behaviour Pleroma.Web.ActivityPub.MRF
 
   alias Pleroma.Config
+  alias Pleroma.FollowingRelationship
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.MRF
 
@@ -108,6 +109,35 @@ defmodule Pleroma.Web.ActivityPub.MRF.SimplePolicy do
     {:ok, object}
   end
 
+  defp intersection(list1, list2) do
+    list1 -- list1 -- list2
+  end
+
+  defp check_followers_only(%{host: actor_host} = _actor_info, object) do
+    followers_only =
+      Config.get([:mrf_simple, :followers_only])
+      |> MRF.subdomains_regex()
+
+    object =
+      with true <- MRF.subdomain_match?(followers_only, actor_host),
+           user <- User.get_cached_by_ap_id(object["actor"]) do
+        # Don't use Map.get/3 intentionally, these must not be nil
+        fixed_to = object["to"] || []
+        fixed_cc = object["cc"] || []
+
+        to = FollowingRelationship.followers_ap_ids(user, fixed_to)
+        cc = FollowingRelationship.followers_ap_ids(user, fixed_cc)
+
+        object
+        |> Map.put("to", intersection([user.follower_address | to], fixed_to))
+        |> Map.put("cc", intersection([user.follower_address | cc], fixed_cc))
+      else
+        _ -> object
+      end
+
+    {:ok, object}
+  end
+
   defp check_report_removal(%{host: actor_host} = _actor_info, %{"type" => "Flag"} = object) do
     report_removal =
       Config.get([:mrf_simple, :report_removal])
@@ -174,6 +204,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.SimplePolicy do
          {:ok, object} <- check_media_removal(actor_info, object),
          {:ok, object} <- check_media_nsfw(actor_info, object),
          {:ok, object} <- check_ftl_removal(actor_info, object),
+         {:ok, object} <- check_followers_only(actor_info, object),
          {:ok, object} <- check_report_removal(actor_info, object) do
       {:ok, object}
     else