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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.Policy
  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           |> Kernel.put_in(["object", "to"], to)
  53           |> Kernel.put_in(["object", "cc"], cc)
  54
  55         {:ok, message}
  56       else
  57         _e ->
  58           {:reject, "[ObjectAgePolicy] Unhandled error"}
  59       end
  60     else
  61       {:ok, message}
  62     end
  63   end
  64
  65   defp check_strip_followers(message, actions) do
  66     if :strip_followers in actions do
  67       with %User{} = user <- User.get_cached_by_ap_id(message["actor"]) do
  68         to = List.delete(message["to"] || [], user.follower_address)
  69         cc = List.delete(message["cc"] || [], user.follower_address)
  70
  71         message =
  72           message
  73           |> Map.put("to", to)
  74           |> Map.put("cc", cc)
  75           |> Kernel.put_in(["object", "to"], to)
  76           |> Kernel.put_in(["object", "cc"], cc)
  77
  78         {:ok, message}
  79       else
  80         _e ->
  81           {:reject, "[ObjectAgePolicy] Unhandled error"}
  82       end
  83     else
  84       {:ok, message}
  85     end
  86   end
  87
  88   @impl true
  89   def filter(%{"type" => "Create", "object" => %{"published" => _}} = message) do
  90     with actions <- Config.get([:mrf_object_age, :actions]),
  91          {:reject, _} <- check_date(message),
  92          {:ok, message} <- check_reject(message, actions),
  93          {:ok, message} <- check_delist(message, actions),
  94          {:ok, message} <- check_strip_followers(message, actions) do
  95       {:ok, message}
  96     else
  97       # check_date() is allowed to short-circuit the pipeline
  98       e -> e
  99     end
 100   end
 101
 102   @impl true
 103   def filter(message), do: {:ok, message}
 104
 105   @impl true
 106   def describe do
 107     mrf_object_age =
 108       Config.get(:mrf_object_age)
 109       |> Enum.into(%{})
 110
 111     {:ok, %{mrf_object_age: mrf_object_age}}
 112   end
 113
 114   @impl true
 115   def config_description do
 116     %{
 117       key: :mrf_object_age,
 118       related_policy: "Pleroma.Web.ActivityPub.MRF.ObjectAgePolicy",
 119       label: "MRF Object Age",
 120       description:
 121         "Rejects or delists posts based on their timestamp deviance from your server's clock.",
 122       children: [
 123         %{
 124           key: :threshold,
 125           type: :integer,
 126           description: "Required age (in seconds) of a post before actions are taken.",
 127           suggestions: [172_800]
 128         },
 129         %{
 130           key: :actions,
 131           type: {:list, :atom},
 132           description:
 133             "A list of actions to apply to the post. `:delist` removes the post from public timelines; " <>
 134               "`:strip_followers` removes followers from the ActivityPub recipient list ensuring they won't be delivered to home timelines; " <>
 135               "`:reject` rejects the message entirely",
 136           suggestions: [:delist, :strip_followers, :reject]
 137         }
 138       ]
 139     }
 140   end
 141 end