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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.HellthreadPolicy do
   6   alias Pleroma.User
   7
   8   require Pleroma.Constants
   9
  10   @moduledoc "Block messages with too much mentions (configurable)"
  11
  12   @behaviour Pleroma.Web.ActivityPub.MRF.Policy
  13
  14   defp delist_message(message, threshold) when threshold > 0 do
  15     follower_collection = User.get_cached_by_ap_id(message["actor"]).follower_address
  16     to = message["to"] || []
  17     cc = message["cc"] || []
  18
  19     follower_collection? = Enum.member?(to ++ cc, follower_collection)
  20
  21     message =
  22       case get_recipient_count(message) do
  23         {:public, recipients}
  24         when follower_collection? and recipients > threshold ->
  25           message
  26           |> Map.put("to", [follower_collection])
  27           |> Map.put("cc", [Pleroma.Constants.as_public()])
  28
  29         {:public, recipients} when recipients > threshold ->
  30           message
  31           |> Map.put("to", [])
  32           |> Map.put("cc", [Pleroma.Constants.as_public()])
  33
  34         _ ->
  35           message
  36       end
  37
  38     {:ok, message}
  39   end
  40
  41   defp delist_message(message, _threshold), do: {:ok, message}
  42
  43   defp reject_message(message, threshold) when threshold > 0 do
  44     with {_, recipients} <- get_recipient_count(message) do
  45       if recipients > threshold do
  46         {:reject, "[HellthreadPolicy] #{recipients} recipients is over the limit of #{threshold}"}
  47       else
  48         {:ok, message}
  49       end
  50     end
  51   end
  52
  53   defp reject_message(message, _threshold), do: {:ok, message}
  54
  55   defp get_recipient_count(message) do
  56     recipients = (message["to"] || []) ++ (message["cc"] || [])
  57     follower_collection = User.get_cached_by_ap_id(message["actor"]).follower_address
  58
  59     if Enum.member?(recipients, Pleroma.Constants.as_public()) do
  60       recipients =
  61         recipients
  62         |> List.delete(Pleroma.Constants.as_public())
  63         |> List.delete(follower_collection)
  64
  65       {:public, length(recipients)}
  66     else
  67       recipients =
  68         recipients
  69         |> List.delete(follower_collection)
  70
  71       {:not_public, length(recipients)}
  72     end
  73   end
  74
  75   @impl true
  76   def filter(%{"type" => type, "object" => %{"type" => object_type}} = message)
  77       when type in ~w{Create Update} and object_type in ~w{Note Article} do
  78     reject_threshold =
  79       Pleroma.Config.get(
  80         [:mrf_hellthread, :reject_threshold],
  81         Pleroma.Config.get([:mrf_hellthread, :threshold])
  82       )
  83
  84     delist_threshold = Pleroma.Config.get([:mrf_hellthread, :delist_threshold])
  85
  86     with {:ok, message} <- reject_message(message, reject_threshold),
  87          {:ok, message} <- delist_message(message, delist_threshold) do
  88       {:ok, message}
  89     else
  90       e -> e
  91     end
  92   end
  93
  94   @impl true
  95   def filter(message), do: {:ok, message}
  96
  97   @impl true
  98   def describe,
  99     do: {:ok, %{mrf_hellthread: Pleroma.Config.get(:mrf_hellthread) |> Enum.into(%{})}}
 100
 101   @impl true
 102   def config_description do
 103     %{
 104       key: :mrf_hellthread,
 105       related_policy: "Pleroma.Web.ActivityPub.MRF.HellthreadPolicy",
 106       label: "MRF Hellthread",
 107       description: "Block messages with excessive user mentions",
 108       children: [
 109         %{
 110           key: :delist_threshold,
 111           type: :integer,
 112           description:
 113             "Number of mentioned users after which the message gets removed from timelines and" <>
 114               "disables notifications. Set to 0 to disable.",
 115           suggestions: [10]
 116         },
 117         %{
 118           key: :reject_threshold,
 119           type: :integer,
 120           description:
 121             "Number of mentioned users after which the messaged gets rejected. Set to 0 to disable.",
 122           suggestions: [20]
 123         }
 124       ]
 125     }
 126   end
 127 end