Add activity expiration worker

This is a worker that runs every minute and deletes expired activities.
It's based heavily on the scheduled activities worker.

lib/pleroma/activity_expiration_worker.ex

@@ -0,0 +1,62 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.ActivityExpirationWorker do
+  alias Pleroma.Activity
+  alias Pleroma.ActivityExpiration
+  alias Pleroma.Config
+  alias Pleroma.Repo
+  alias Pleroma.User
+  alias Pleroma.Web.CommonAPI
+  require Logger
+  use GenServer
+  import Ecto.Query
+
+  @schedule_interval :timer.minutes(1)
+
+  def start_link do
+    GenServer.start_link(__MODULE__, nil)
+  end
+
+  @impl true
+  def init(_) do
+    if Config.get([ActivityExpiration, :enabled]) do
+      schedule_next()
+      {:ok, nil}
+    else
+      :ignore
+    end
+  end
+
+  def perform(:execute, expiration_id) do
+    try do
+      expiration =
+        ActivityExpiration
+        |> where([e], e.id == ^expiration_id)
+        |> Repo.one!()
+
+      activity = Activity.get_by_id_with_object(expiration.activity_id)
+      user = User.get_by_ap_id(activity.object.data["actor"])
+      CommonAPI.delete(activity.id, user)
+    rescue
+      error ->
+        Logger.error("#{__MODULE__} Couldn't delete expired activity: #{inspect(error)}")
+    end
+  end
+
+  @impl true
+  def handle_info(:perform, state) do
+    ActivityExpiration.due_expirations(@schedule_interval)
+    |> Enum.each(fn expiration ->
+      PleromaJobQueue.enqueue(:activity_expiration, __MODULE__, [:execute, expiration.id])
+    end)
+
+    schedule_next()
+    {:noreply, state}
+  end
+
+  defp schedule_next do
+    Process.send_after(self(), :perform, @schedule_interval)
+  end
+end

lib/pleroma/application.ex

@@ -115,6 +115,10 @@ defmodule Pleroma.Application do
         %{
           id: Pleroma.ScheduledActivityWorker,
           start: {Pleroma.ScheduledActivityWorker, :start_link, []}
+        },
+        %{
+          id: Pleroma.ActivityExpirationWorker,
+          start: {Pleroma.ActivityExpirationWorker, :start_link, []}
         }
       ] ++
         hackney_pool_children() ++