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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2019 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   @moduledoc "Block messages with too much mentions (configurable)"
   8
   9   @behaviour Pleroma.Web.ActivityPub.MRF
  10
  11   defp delist_message(message, threshold) when threshold > 0 do
  12     follower_collection = User.get_cached_by_ap_id(message["actor"]).follower_address
  13
  14     follower_collection? = Enum.member?(message["to"] ++ message["cc"], follower_collection)
  15
  16     message =
  17       case get_recipient_count(message) do
  18         {:public, recipients}
  19         when follower_collection? and recipients > threshold ->
  20           message
  21           |> Map.put("to", [follower_collection])
  22           |> Map.put("cc", ["https://www.w3.org/ns/activitystreams#Public"])
  23
  24         {:public, recipients} when recipients > threshold ->
  25           message
  26           |> Map.put("to", [])
  27           |> Map.put("cc", ["https://www.w3.org/ns/activitystreams#Public"])
  28
  29         _ ->
  30           message
  31       end
  32
  33     {:ok, message}
  34   end
  35
  36   defp delist_message(message, _threshold), do: {:ok, message}
  37
  38   defp reject_message(message, threshold) when threshold > 0 do
  39     with {_, recipients} <- get_recipient_count(message) do
  40       if recipients > threshold do
  41         {:reject, nil}
  42       else
  43         {:ok, message}
  44       end
  45     end
  46   end
  47
  48   defp reject_message(message, _threshold), do: {:ok, message}
  49
  50   defp get_recipient_count(message) do
  51     recipients = (message["to"] || []) ++ (message["cc"] || [])
  52     follower_collection = User.get_cached_by_ap_id(message["actor"]).follower_address
  53
  54     if Enum.member?(recipients, "https://www.w3.org/ns/activitystreams#Public") do
  55       recipients =
  56         recipients
  57         |> List.delete("https://www.w3.org/ns/activitystreams#Public")
  58         |> List.delete(follower_collection)
  59
  60       {:public, length(recipients)}
  61     else
  62       recipients =
  63         recipients
  64         |> List.delete(follower_collection)
  65
  66       {:not_public, length(recipients)}
  67     end
  68   end
  69
  70   @impl true
  71   def filter(%{"type" => "Create"} = message) do
  72     reject_threshold =
  73       Pleroma.Config.get(
  74         [:mrf_hellthread, :reject_threshold],
  75         Pleroma.Config.get([:mrf_hellthread, :threshold])
  76       )
  77
  78     delist_threshold = Pleroma.Config.get([:mrf_hellthread, :delist_threshold])
  79
  80     with {:ok, message} <- reject_message(message, reject_threshold),
  81          {:ok, message} <- delist_message(message, delist_threshold) do
  82       {:ok, message}
  83     else
  84       _e -> {:reject, nil}
  85     end
  86   end
  87
  88   @impl true
  89   def filter(message), do: {:ok, message}
  90 end