Add RemoteReportPolicy to reject reports without enough information

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

@@ -0,0 +1,80 @@
+defmodule Pleroma.Web.ActivityPub.MRF.RemoteReportPolicy do
+  @moduledoc "Drop remote reports if they don't contain enough information."
+  @behaviour Pleroma.Web.ActivityPub.MRF.Policy
+
+  alias Pleroma.Config
+
+  @impl true
+  def filter(%{"type" => "Flag"} = object) do
+    with {_, false} <- {:local, local?(object)},
+         {:ok, _} <- maybe_reject_anonymous(object),
+         {:ok, _} <- maybe_reject_empty_message(object) do
+      {:ok, object}
+    else
+      {:local, true} -> {:ok, object}
+      {:reject, message} -> {:reject, message}
+      error -> {:reject, error}
+    end
+  end
+
+  def filter(object), do: {:ok, object}
+
+  defp maybe_reject_anonymous(%{"actor" => actor} = object) do
+    with true <- Config.get([:mrf_remote_report, :reject_anonymous]),
+         %URI{path: "/actor"} <- URI.parse(actor) do
+      {:reject, "[RemoteReportPolicy] Anonymous: #{actor}"}
+    else
+      _ -> {:ok, object}
+    end
+  end
+
+  defp maybe_reject_empty_message(%{"content" => content} = object)
+       when is_binary(content) and content != "" do
+    {:ok, object}
+  end
+
+  defp maybe_reject_empty_message(object) do
+    if Config.get([:mrf_remote_report, :reject_empty_message]) do
+      {:reject, ["RemoteReportPolicy] No content"]}
+    else
+      {:ok, object}
+    end
+  end
+
+  defp local?(%{"actor" => actor}) do
+    String.starts_with?(actor, Pleroma.Web.Endpoint.url())
+  end
+
+  @impl true
+  def describe do
+    mrf_remote_report =
+      Config.get(:mrf_remote_report)
+      |> Enum.into(%{})
+
+    {:ok, %{mrf_remote_report: mrf_remote_report}}
+  end
+
+  @impl true
+  def config_description do
+    %{
+      key: :mrf_remote_report,
+      related_policy: "Pleroma.Web.ActivityPub.MRF.RemoteReportPolicy",
+      label: "MRF Remote Report",
+      description: "Drop remote reports if they don't contain enough information.",
+      children: [
+        %{
+          key: :reject_anonymous,
+          type: :boolean,
+          description: "Reject anonymous remote reports?",
+          suggestions: [true]
+        },
+        %{
+          key: :reject_empty_message,
+          type: :boolean,
+          description: "Reject remote reports with no message?",
+          suggestions: [true]
+        }
+      ]
+    }
+  end
+end