Add MRF MentionPolicy for dropping posts which mention specific actors

CHANGELOG.md

@@ -24,6 +24,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Added
 - MRF: Support for priming the mediaproxy cache (`Pleroma.Web.ActivityPub.MRF.MediaProxyWarmingPolicy`)
 - MRF: Support for excluding specific domains from Transparency.
+- MRF: Support for filtering posts based on who they mention (`Pleroma.Web.ActivityPub.MRF.MentionPolicy`)
 - Configuration: `federation_incoming_replies_max_depth` option
 - Mastodon API: Support for the [`tagged` filter](https://github.com/tootsuite/mastodon/pull/9755) in [`GET /api/v1/accounts/:id/statuses`](https://docs.joinmastodon.org/api/rest/accounts/#get-api-v1-accounts-id-statuses)
 - Mastodon API, streaming: Add support for passing the token in the `Sec-WebSocket-Protocol` header

docs/config.md

@@ -101,6 +101,7 @@ config :pleroma, Pleroma.Emails.Mailer,
   * `Pleroma.Web.ActivityPub.MRF.EnsureRePrepended`: Rewrites posts to ensure that replies to posts with subjects do not have an identical subject and instead begin with re:.
   * `Pleroma.Web.ActivityPub.MRF.AntiLinkSpamPolicy`: Rejects posts from likely spambots by rejecting posts from new users that contain links.
   * `Pleroma.Web.ActivityPub.MRF.MediaProxyWarmingPolicy`: Crawls attachments using their MediaProxy URLs so that the MediaProxy cache is primed.
+  * `Pleroma.Web.ActivityPub.MRF.MentionPolicy`: Drops posts mentioning configurable users. (see `:mrf_mention` section)
 * `public`: Makes the client API in authentificated mode-only except for user-profiles. Useful for disabling the Local Timeline and The Whole Known Network.
 * `quarantined_instances`: List of ActivityPub instances where private(DMs, followers-only) activities will not be send.
 * `managed_config`: Whenether the config for pleroma-fe is configured in this config or in ``static/config.json``
@@ -271,6 +272,9 @@ config :pleroma, :mrf_subchain,
 * `federated_timeline_removal`: A list of patterns which result in message being removed from federated timelines (a.k.a unlisted), each pattern can be a string or a [regular expression](https://hexdocs.pm/elixir/Regex.html)
 * `replace`: A list of tuples containing `{pattern, replacement}`, `pattern` can be a string or a [regular expression](https://hexdocs.pm/elixir/Regex.html)
 
+## :mrf_mention
+* `actors`: A list of actors, for which to drop any posts mentioning.
+
 ## :media_proxy
 * `enabled`: Enables proxying of remote media to the instance’s proxy
 * `base_url`: The base URL to access a user-uploaded file. Useful when you want to proxy the media files via another host/CDN fronts.

lib/pleroma/web/activity_pub/mrf/mention_policy.ex

@@ -0,0 +1,24 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.MentionPolicy do
+  @moduledoc "Block messages which mention a user"
+
+  @behaviour Pleroma.Web.ActivityPub.MRF
+
+  @impl true
+  def filter(%{"type" => "Create"} = message) do
+    reject_actors = Pleroma.Config.get([:mrf_mention, :actors], [])
+    recipients = (message["to"] || []) ++ (message["cc"] || [])
+
+    if Enum.any?(recipients, fn recipient -> Enum.member?(reject_actors, recipient) end) do
+      {:reject, nil}
+    else
+      {:ok, message}
+    end
+  end
+
+  @impl true
+  def filter(message), do: {:ok, message}
+end

test/web/activity_pub/mrf/mention_policy_test.exs

@@ -0,0 +1,92 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.MRF.MentionPolicyTest do
+  use Pleroma.DataCase
+
+  alias Pleroma.Web.ActivityPub.MRF.MentionPolicy
+
+  test "pass filter if allow list is empty" do
+    Pleroma.Config.delete([:mrf_mention])
+
+    message = %{
+      "type" => "Create",
+      "to" => ["https://example.com/ok"],
+      "cc" => ["https://example.com/blocked"]
+    }
+
+    assert MentionPolicy.filter(message) == {:ok, message}
+  end
+
+  describe "allow" do
+    test "empty" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create"
+      }
+
+      assert MentionPolicy.filter(message) == {:ok, message}
+    end
+
+    test "to" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create",
+        "to" => ["https://example.com/ok"]
+      }
+
+      assert MentionPolicy.filter(message) == {:ok, message}
+    end
+
+    test "cc" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create",
+        "cc" => ["https://example.com/ok"]
+      }
+
+      assert MentionPolicy.filter(message) == {:ok, message}
+    end
+
+    test "both" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create",
+        "to" => ["https://example.com/ok"],
+        "cc" => ["https://example.com/ok2"]
+      }
+
+      assert MentionPolicy.filter(message) == {:ok, message}
+    end
+  end
+
+  describe "deny" do
+    test "to" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create",
+        "to" => ["https://example.com/blocked"]
+      }
+
+      assert MentionPolicy.filter(message) == {:reject, nil}
+    end
+
+    test "cc" do
+      Pleroma.Config.put([:mrf_mention], %{actors: ["https://example.com/blocked"]})
+
+      message = %{
+        "type" => "Create",
+        "to" => ["https://example.com/ok"],
+        "cc" => ["https://example.com/blocked"]
+      }
+
+      assert MentionPolicy.filter(message) == {:reject, nil}
+    end
+  end
+end