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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 defmodule Pleroma.Web.ActivityPub.MRF.ObjectAgePolicy do
   6   alias Pleroma.Config
   7   alias Pleroma.User
   8
   9   require Pleroma.Constants
  10
  11   @moduledoc "Filter activities depending on their age"
  12   @behaviour Pleroma.Web.ActivityPub.MRF
  13
  14   defp check_date(%{"object" => %{"published" => published}} = message) do
  15     with %DateTime{} = now <- DateTime.utc_now(),
  16          {:ok, %DateTime{} = then, _} <- DateTime.from_iso8601(published),
  17          max_ttl <- Config.get([:mrf_object_age, :threshold]),
  18          {:ttl, false} <- {:ttl, DateTime.diff(now, then) > max_ttl} do
  19       {:ok, message}
  20     else
  21       {:ttl, true} ->
  22         {:reject, nil}
  23
  24       e ->
  25         {:error, e}
  26     end
  27   end
  28
  29   defp check_reject(message, actions) do
  30     if :reject in actions do
  31       {:reject, "[ObjectAgePolicy]"}
  32     else
  33       {:ok, message}
  34     end
  35   end
  36
  37   defp check_delist(message, actions) do
  38     if :delist in actions do
  39       with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
  40         to =
  41           List.delete(message["to"] || [], Pleroma.Constants.as_public()) ++
  42             [user.follower_address]
  43
  44         cc =
  45           List.delete(message["cc"] || [], user.follower_address) ++
  46             [Pleroma.Constants.as_public()]
  47
  48         message =
  49           message
  50           |> Map.put("to", to)
  51           |> Map.put("cc", cc)
  52
  53         {:ok, message}
  54       else
  55         _e ->
  56           {:reject, "[ObjectAgePolicy] Unhandled error"}
  57       end
  58     else
  59       {:ok, message}
  60     end
  61   end
  62
  63   defp check_strip_followers(message, actions) do
  64     if :strip_followers in actions do
  65       with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
  66         to = List.delete(message["to"] || [], user.follower_address)
  67         cc = List.delete(message["cc"] || [], user.follower_address)
  68
  69         message =
  70           message
  71           |> Map.put("to", to)
  72           |> Map.put("cc", cc)
  73
  74         {:ok, message}
  75       else
  76         _e ->
  77           {:reject, "[ObjectAgePolicy] Unhandled error"}
  78       end
  79     else
  80       {:ok, message}
  81     end
  82   end
  83
  84   @impl true
  85   def filter(%{"type" => "Create", "published" => _} = message) do
  86     with actions <- Config.get([:mrf_object_age, :actions]),
  87          {:reject, _} <- check_date(message),
  88          {:ok, message} <- check_reject(message, actions),
  89          {:ok, message} <- check_delist(message, actions),
  90          {:ok, message} <- check_strip_followers(message, actions) do
  91       {:ok, message}
  92     else
  93       # check_date() is allowed to short-circuit the pipeline
  94       e -> e
  95     end
  96   end
  97
  98   @impl true
  99   def filter(message), do: {:ok, message}
 100
 101   @impl true
 102   def describe do
 103     mrf_object_age =
 104       Config.get(:mrf_object_age)
 105       |> Enum.into(%{})
 106
 107     {:ok, %{mrf_object_age: mrf_object_age}}
 108   end
 109
 110   @impl true
 111   def config_description do
 112     %{
 113       key: :mrf_object_age,
 114       related_policy: "Pleroma.Web.ActivityPub.MRF.ObjectAgePolicy",
 115       label: "MRF Object Age",
 116       description:
 117         "Rejects or delists posts based on their timestamp deviance from your server's clock.",
 118       children: [
 119         %{
 120           key: :threshold,
 121           type: :integer,
 122           description: "Required age (in seconds) of a post before actions are taken.",
 123           suggestions: [172_800]
 124         },
 125         %{
 126           key: :actions,
 127           type: {:list, :atom},
 128           description:
 129             "A list of actions to apply to the post. `:delist` removes the post from public timelines; " <>
 130               "`:strip_followers` removes followers from the ActivityPub recipient list ensuring they won't be delivered to home timelines; " <>
 131               "`:reject` rejects the message entirely",
 132           suggestions: [:delist, :strip_followers, :reject]
 133         }
 134       ]
 135     }
 136   end
 137 end