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diff --git a/lib/pleroma/web/activity_pub/mrf/activity_expiration_policy.ex b/lib/pleroma/web/activity_pub/mrf/activity_expiration_policy.ex
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+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.ActivityExpirationPolicy do
+  @moduledoc "Adds expiration to all local Create activities"
+  @behaviour Pleroma.Web.ActivityPub.MRF
+
+  @impl true
+  def filter(activity) do
+    activity =
+      if note?(activity) and local?(activity) do
+        maybe_add_expiration(activity)
+      else
+        activity
+      end
+
+    {:ok, activity}
+  end
+
+  @impl true
+  def describe, do: {:ok, %{}}
+
+  defp local?(%{"actor" => actor}) do
+    String.starts_with?(actor, Pleroma.Web.Endpoint.url())
+  end
+
+  defp note?(activity) do
+    match?(%{"type" => "Create", "object" => %{"type" => "Note"}}, activity)
+  end
+
+  defp maybe_add_expiration(activity) do
+    days = Pleroma.Config.get([:mrf_activity_expiration, :days], 365)
+    expires_at = NaiveDateTime.utc_now() |> Timex.shift(days: days)
+
+    with %{"expires_at" => existing_expires_at} <- activity,
+         :lt <- NaiveDateTime.compare(existing_expires_at, expires_at) do
+      activity
+    else
+      _ -> Map.put(activity, "expires_at", expires_at)
+    end
+  end
+end