Add emoji policy to remove emojis matching certain urls

https://git.pleroma.social/pleroma/pleroma/-/issues/2775

lib/pleroma/web/activity_pub/emoji_policy.ex

@@ -0,0 +1,158 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2023 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.EmojiPolicy do
+  require Pleroma.Constants
+
+  @moduledoc "Reject or force-unlisted emojis with certain URLs or names"
+
+  @behaviour Pleroma.Web.ActivityPub.MRF.Policy
+
+  defp config_remove_url do
+    Pleroma.Config.get([:mrf_emoji, :remove_url], [])
+  end
+
+  @impl Pleroma.Web.ActivityPub.MRF.Policy
+  def filter(%{"type" => type, "object" => %{} = object} = message)
+      when type in ["Create", "Update"] do
+    with object <- process_remove(object, :url, config_remove_url()) do
+      {:ok, Map.put(message, "object", object)}
+    end
+  end
+
+  @impl Pleroma.Web.ActivityPub.MRF.Policy
+  def filter(%{"type" => type} = object) when type in Pleroma.Constants.actor_types() do
+    with object <- process_remove(object, :url, config_remove_url()) do
+      {:ok, object}
+    end
+  end
+
+  @impl Pleroma.Web.ActivityPub.MRF.Policy
+  def filter(message) do
+    {:ok, message}
+  end
+
+  defp match_string?(string, pattern) when is_binary(pattern) do
+    string == pattern
+  end
+
+  defp match_string?(string, %Regex{} = pattern) do
+    String.match?(string, pattern)
+  end
+
+  defp match_any?(string, patterns) do
+    Enum.any?(patterns, &match_string?(string, &1))
+  end
+
+  defp process_remove(object, :url, patterns) do
+    processed_tag =
+      Enum.filter(
+        object["tag"],
+        fn
+          %{"type" => "Emoji", "icon" => %{"url" => url}} when is_binary(url) ->
+            not match_any?(url, patterns)
+
+          _ ->
+            true
+        end
+      )
+
+    processed_emoji =
+      if object["emoji"] do
+        object["emoji"]
+        |> Enum.reduce(%{}, fn {name, url}, acc ->
+          if not match_any?(url, patterns) do
+            Map.put(acc, name, url)
+          else
+            acc
+          end
+        end)
+      else
+        nil
+      end
+
+    if processed_emoji do
+      object
+      |> Map.put("tag", processed_tag)
+      |> Map.put("emoji", processed_emoji)
+    else
+      object
+      |> Map.put("tag", processed_tag)
+    end
+  end
+
+  @impl Pleroma.Web.ActivityPub.MRF.Policy
+  def describe do
+    # This horror is needed to convert regex sigils to strings
+    mrf_emoji =
+      Pleroma.Config.get(:mrf_emoji, [])
+      |> Enum.map(fn {key, value} ->
+        {key,
+         Enum.map(value, fn
+           pattern ->
+             if not is_binary(pattern) do
+               inspect(pattern)
+             else
+               pattern
+             end
+         end)}
+      end)
+      |> Enum.into(%{})
+
+    {:ok, %{mrf_emoji: mrf_emoji}}
+  end
+
+  @impl Pleroma.Web.ActivityPub.MRF.Policy
+  def config_description do
+    %{
+      key: :mrf_emoji,
+      related_policy: "Pleroma.Web.ActivityPub.MRF.EmojiPolicy",
+      label: "MRF Emoji",
+      description:
+        "Reject or force-unlisted emojis whose URLs or names match a keyword or [Regex](https://hexdocs.pm/elixir/Regex.html).",
+      children: [
+        %{
+          key: :remove_url,
+          type: {:list, :string},
+          description: """
+            A list of patterns which result in emoji whose URL matches being removed from the message. This will apply to both statuses and user profiles.
+
+            Each pattern can be a string or [Regex](https://hexdocs.pm/elixir/Regex.html) in the format of `~r/PATTERN/`.
+          """,
+          suggestions: ["foo", ~r/foo/iu]
+        },
+        %{
+          key: :remove_shortcode,
+          type: {:list, :string},
+          description: """
+            A list of patterns which result in emoji whose shortcode matches being removed from the message. This will apply to both statuses and user profiles.
+
+            Each pattern can be a string or [Regex](https://hexdocs.pm/elixir/Regex.html) in the format of `~r/PATTERN/`.
+          """,
+          suggestions: ["foo", ~r/foo/iu]
+        },
+        %{
+          key: :federated_timeline_removal_url,
+          type: {:list, :string},
+          description: """
+            A list of patterns which result in message with emojis whose URLs match being removed from federated timelines (a.k.a unlisted). This will apply only to statuses.
+
+            Each pattern can be a string or [Regex](https://hexdocs.pm/elixir/Regex.html) in the format of `~r/PATTERN/`.
+          """,
+          suggestions: ["foo", ~r/foo/iu]
+        },
+        %{
+          key: :federated_timeline_removal_shortcode,
+          type: {:list, :string},
+          description: """
+            A list of patterns which result in message with emojis whose shortcodes match being removed from federated timelines (a.k.a unlisted). This will apply only to statuses.
+
+            Each pattern can be a string or [Regex](https://hexdocs.pm/elixir/Regex.html) in the format of `~r/PATTERN/`.
+          """,
+          suggestions: ["foo", ~r/foo/iu]
+        }
+      ]
+    }
+  end
+end