MRF: add ObjectAgePolicy which deals with old posts being imported

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

@@ -0,0 +1,103 @@
+# 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.ObjectAgePolicy do
+  alias Pleroma.Config
+  alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.MRF
+
+  require Logger
+  require Pleroma.Constants
+
+  @moduledoc "Filter activities depending on their age"
+  @behaviour MRF
+
+  defp check_date(%{"published" => published} = message) do
+    with %DateTime{} = now <- DateTime.utc_now(),
+         {:ok, %DateTime{} = then, _} <- DateTime.from_iso8601(published),
+         max_ttl <- Config.get([:mrf_object_age, :threshold]),
+         {:ttl, false} <- {:ttl, DateTime.diff(now, then) > max_ttl} do
+      {:ok, message}
+    else
+      {:ttl, true} ->
+        {:reject, nil}
+
+      e ->
+        {:error, e}
+    end
+  end
+
+  defp check_reject(message, actions) do
+    if :reject in actions do
+      {:reject, nil}
+    else
+      {:ok, message}
+    end
+  end
+
+  defp check_delist(message, actions) do
+    if :delist in actions do
+      with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
+        to = List.delete(message["to"], Pleroma.Constants.as_public()) ++ [user.follower_address]
+        cc = List.delete(message["cc"], user.follower_address) ++ [Pleroma.Constants.as_public()]
+
+        message =
+          message
+          |> Map.put("to", to)
+          |> Map.put("cc", cc)
+
+        {:ok, message}
+      else
+        # Unhandleable error: somebody is messing around, just drop the message.
+        e ->
+          Logger.error("ERROR: #{inspect(e)}")
+          {:reject, nil}
+      end
+    else
+      {:ok, message}
+    end
+  end
+
+  defp check_strip_followers(message, actions) do
+    if :strip_followers in actions do
+      with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
+        to = List.delete(message["to"], user.follower_address)
+        cc = List.delete(message["cc"], user.follower_address)
+
+        message =
+          message
+          |> Map.put("to", to)
+          |> Map.put("cc", cc)
+
+        {:ok, message}
+      else
+        # Unhandleable error: somebody is messing around, just drop the message.
+        _e ->
+          {:reject, nil}
+      end
+    else
+      {:ok, message}
+    end
+  end
+
+  @impl true
+  def filter(%{"type" => "Create", "published" => _} = message) do
+    with actions <- Config.get([:mrf_object_age, :actions]),
+         {:reject, _} <- check_date(message),
+         {:ok, message} <- check_reject(message, actions),
+         {:ok, message} <- check_delist(message, actions),
+         {:ok, message} <- check_strip_followers(message, actions) do
+      {:ok, message}
+    else
+      # check_date() is allowed to short-circuit the pipeline
+      e -> e
+    end
+  end
+
+  @impl true
+  def filter(message), do: {:ok, message}
+
+  @impl true
+  def describe, do: {:ok, %{}}
+end