Make NoEmptyPolicy work with Update

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

@@ -11,6 +11,7 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoEmptyPolicy do
   @impl true
   def filter(%{"actor" => actor} = object) do
     with true <- is_local?(actor),
+         true <- is_eligible_type?(object),
          true <- is_note?(object),
          false <- has_attachment?(object),
          true <- only_mentions?(object) do
@@ -32,7 +33,6 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoEmptyPolicy do
   end
 
   defp has_attachment?(%{
-         "type" => "Create",
          "object" => %{"type" => "Note", "attachment" => attachments}
        })
        when length(attachments) > 0,
@@ -40,7 +40,13 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoEmptyPolicy do
 
   defp has_attachment?(_), do: false
 
-  defp only_mentions?(%{"type" => "Create", "object" => %{"type" => "Note", "source" => source}}) do
+  defp only_mentions?(%{"object" => %{"type" => "Note", "source" => source}}) do
+    source =
+      case source do
+        %{"content" => text} -> text
+        _ -> source
+      end
+
     non_mentions =
       source |> String.split() |> Enum.filter(&(not String.starts_with?(&1, "@"))) |> length
 
@@ -53,9 +59,12 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoEmptyPolicy do
 
   defp only_mentions?(_), do: false
 
-  defp is_note?(%{"type" => "Create", "object" => %{"type" => "Note"}}), do: true
+  defp is_note?(%{"object" => %{"type" => "Note"}}), do: true
   defp is_note?(_), do: false
 
+  defp is_eligible_type?(%{"type" => type}) when type in ["Create", "Update"], do: true
+  defp is_eligible_type?(_), do: false
+
   @impl true
   def describe, do: {:ok, %{}}
 end

test/pleroma/web/activity_pub/mrf/no_empty_policy_test.exs

@@ -151,4 +151,27 @@ defmodule Pleroma.Web.ActivityPub.MRF.NoEmptyPolicyTest do
 
     assert NoEmptyPolicy.filter(message) == {:reject, "[NoEmptyPolicy]"}
   end
+
+  test "works with Update" do
+    message = %{
+      "actor" => "http://localhost:4001/users/testuser",
+      "cc" => ["http://localhost:4001/users/testuser/followers"],
+      "object" => %{
+        "actor" => "http://localhost:4001/users/testuser",
+        "attachment" => [],
+        "cc" => ["http://localhost:4001/users/testuser/followers"],
+        "source" => "",
+        "to" => [
+          "https://www.w3.org/ns/activitystreams#Public"
+        ],
+        "type" => "Note"
+      },
+      "to" => [
+        "https://www.w3.org/ns/activitystreams#Public"
+      ],
+      "type" => "Update"
+    }
+
+    assert NoEmptyPolicy.filter(message) == {:reject, "[NoEmptyPolicy]"}
+  end
 end