[#1505] Restricted max thread distance for fetching replies on incoming federation (in addition to reply-to depth restriction).

config/description.exs

@@ -659,7 +659,7 @@
         label: "Fed. incoming replies max depth",
         type: :integer,
         description:
-          "Max. depth of reply-to activities fetching on incoming federation, to prevent out-of-memory situations while" <>
+          "Max. depth of reply-to and reply activities fetching on incoming federation, to prevent out-of-memory situations while" <>
             " fetching very long threads. If set to `nil`, threads of any depth will be fetched. Lower this value if you experience out-of-memory crashes.",
         suggestions: [
           100

docs/introduction.md

@@ -41,7 +41,7 @@ On the top right you will also see a wrench icon. This opens your personal setti
 This is where the interesting stuff happens!
 Depending on the timeline you will see different statuses, but each status has a standard structure:
 
-- Profile pic, name and link to profile. An optional left-arrow if it's a reply to another status (hovering will reveal the replied-to status). Clicking on the profile pic will uncollapse the user's profile.
+- Profile pic, name and link to profile. An optional left-arrow if it's a reply to another status (hovering will reveal the reply-to status). Clicking on the profile pic will uncollapse the user's profile.
 - A `+` button on the right allows you to Expand/Collapse an entire discussion thread. It also updates in realtime!
 - An arrow icon allows you to open the status on the instance where it's originating from.
 - The text of the status, including mentions and attachements. If you click on a mention, it will automatically open the profile page of that person.

lib/pleroma/object/fetcher.ex

@@ -10,6 +10,7 @@ defmodule Pleroma.Object.Fetcher do
   alias Pleroma.Signature
   alias Pleroma.Web.ActivityPub.InternalFetchActor
   alias Pleroma.Web.ActivityPub.Transmogrifier
+  alias Pleroma.Web.Federator
 
   require Logger
   require Pleroma.Constants
@@ -59,20 +60,23 @@ def refetch_object(%Object{data: %{"id" => id}} = object) do
     end
   end
 
-  # TODO:
-  # This will create a Create activity, which we need internally at the moment.
+  # Note: will create a Create activity, which we need internally at the moment.
   def fetch_object_from_id(id, options \\ []) do
-    with {:fetch_object, nil} <- {:fetch_object, Object.get_cached_by_ap_id(id)},
-         {:fetch, {:ok, data}} <- {:fetch, fetch_and_contain_remote_object_from_id(id)},
-         {:normalize, nil} <- {:normalize, Object.normalize(data, false)},
+    with {_, nil} <- {:fetch_object, Object.get_cached_by_ap_id(id)},
+         {_, true} <- {:allowed_depth, Federator.allowed_thread_distance?(options[:depth])},
+         {_, {:ok, data}} <- {:fetch, fetch_and_contain_remote_object_from_id(id)},
+         {_, nil} <- {:normalize, Object.normalize(data, false)},
          params <- prepare_activity_params(data),
-         {:containment, :ok} <- {:containment, Containment.contain_origin(id, params)},
-         {:transmogrifier, {:ok, activity}} <-
+         {_, :ok} <- {:containment, Containment.contain_origin(id, params)},
+         {_, {:ok, activity}} <-
            {:transmogrifier, Transmogrifier.handle_incoming(params, options)},
-         {:object, _data, %Object{} = object} <-
+         {_, _data, %Object{} = object} <-
            {:object, data, Object.normalize(activity, false)} do
       {:ok, object}
     else
+      {:allowed_depth, false} ->
+        {:error, "Max thread distance exceeded."}
+
       {:containment, _} ->
         {:error, "Object containment failed."}
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -156,8 +156,9 @@ def fix_in_reply_to(%{"inReplyTo" => in_reply_to} = object, options)
       when not is_nil(in_reply_to) do
     in_reply_to_id = prepare_in_reply_to(in_reply_to)
     object = Map.put(object, "inReplyToAtomUri", in_reply_to_id)
+    depth = (options[:depth] || 0) + 1
 
-    if Federator.allowed_incoming_reply_depth?(options[:depth]) do
+    if Federator.allowed_thread_distance?(depth) do
       with {:ok, replied_object} <- get_obj_helper(in_reply_to_id, options),
            %Activity{} = _ <- Activity.get_create_by_object_ap_id(replied_object.data["id"]) do
         object
@@ -312,7 +313,7 @@ def fix_type(object, options \\ [])
 
   def fix_type(%{"inReplyTo" => reply_id, "name" => _} = object, options)
       when is_binary(reply_id) do
-    with true <- Federator.allowed_incoming_reply_depth?(options[:depth]),
+    with true <- Federator.allowed_thread_distance?(options[:depth]),
          {:ok, %{data: %{"type" => "Question"} = _} = _} <- get_obj_helper(reply_id, options) do
       Map.put(object, "type", "Answer")
     else
@@ -406,7 +407,6 @@ def handle_incoming(
 
     with nil <- Activity.get_create_by_object_ap_id(object["id"]),
          {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
-      options = Keyword.put(options, :depth, (options[:depth] || 0) + 1)
       object = fix_object(object, options)
 
       params = %{
@@ -425,8 +425,15 @@ def handle_incoming(
       }
 
       with {:ok, created_activity} <- ActivityPub.create(params) do
-        for reply_id <- replies(object) do
-          Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{"id" => reply_id})
+        reply_depth = (options[:depth] || 0) + 1
+
+        if Federator.allowed_thread_distance?(reply_depth) do
+          for reply_id <- replies(object) do
+            Pleroma.Workers.RemoteFetcherWorker.enqueue("fetch_remote", %{
+              "id" => reply_id,
+              "depth" => reply_depth
+            })
+          end
         end
 
         {:ok, created_activity}
@@ -448,7 +455,8 @@ def handle_incoming(
       |> fix_addressing
 
     with {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
-      options = Keyword.put(options, :depth, (options[:depth] || 0) + 1)
+      reply_depth = (options[:depth] || 0) + 1
+      options = Keyword.put(options, :depth, reply_depth)
       object = fix_object(object, options)
 
       params = %{

lib/pleroma/web/federator/federator.ex

@@ -15,13 +15,19 @@ defmodule Pleroma.Web.Federator do
 
   require Logger
 
-  @doc "Addresses [memory leaks on recursive replies fetching](https://git.pleroma.social/pleroma/pleroma/issues/161)"
+  @doc """
+  Returns `true` if the distance to target object does not exceed max configured value.
+  Serves to prevent fetching of very long threads, especially useful on smaller instances.
+  Addresses [memory leaks on recursive replies fetching](https://git.pleroma.social/pleroma/pleroma/issues/161).
+  Applies to fetching of both ancestor (reply-to) and child (reply) objects.
+  """
   # credo:disable-for-previous-line Credo.Check.Readability.MaxLineLength
-  def allowed_incoming_reply_depth?(depth) do
-    max_replies_depth = Pleroma.Config.get([:instance, :federation_incoming_replies_max_depth])
+  def allowed_thread_distance?(distance) do
+    max_distance = Pleroma.Config.get([:instance, :federation_incoming_replies_max_depth])
 
-    if max_replies_depth do
-      (depth || 1) <= max_replies_depth
+    if max_distance && max_distance >= 0 do
+      # Default depth is 0 (an object has zero distance from itself in its thread)
+      (distance || 0) <= max_distance
     else
       true
     end

lib/pleroma/workers/remote_fetcher_worker.ex

@@ -12,9 +12,9 @@ def perform(
         %{
           "op" => "fetch_remote",
           "id" => id
-        },
+        } = args,
         _job
       ) do
-    {:ok, _object} = Fetcher.fetch_object_from_id(id)
+    {:ok, _object} = Fetcher.fetch_object_from_id(id, depth: args["depth"])
   end
 end

test/object/fetcher_test.exs

@@ -26,6 +26,31 @@ defmodule Pleroma.Object.FetcherTest do
     :ok
   end
 
+  describe "max thread distance restriction" do
+    @ap_id "http://mastodon.example.org/@admin/99541947525187367"
+
+    clear_config([:instance, :federation_incoming_replies_max_depth])
+
+    test "it returns thread depth exceeded error if thread depth is exceeded" do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 0)
+
+      assert {:error, "Max thread distance exceeded."} =
+               Fetcher.fetch_object_from_id(@ap_id, depth: 1)
+    end
+
+    test "it fetches object if max thread depth is restricted to 0 and depth is not specified" do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 0)
+
+      assert {:ok, _} = Fetcher.fetch_object_from_id(@ap_id)
+    end
+
+    test "it fetches object if requested depth does not exceed max thread depth" do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 10)
+
+      assert {:ok, _} = Fetcher.fetch_object_from_id(@ap_id, depth: 10)
+    end
+  end
+
   describe "actor origin containment" do
     test "it rejects objects with a bogus origin" do
       {:error, _} = Fetcher.fetch_object_from_id("https://info.pleroma.site/activity.json")

test/web/activity_pub/transmogrifier_test.exs

@@ -42,7 +42,7 @@ test "it ignores an incoming notice if we already have it" do
     end
 
     @tag capture_log: true
-    test "it fetches replied-to activities if we don't have them" do
+    test "it fetches reply-to activities if we don't have them" do
       data =
         File.read!("test/fixtures/mastodon-post-activity.json")
         |> Poison.decode!()
@@ -63,7 +63,7 @@ test "it fetches replied-to activities if we don't have them" do
       assert returned_object.data["inReplyToAtomUri"] == "https://shitposter.club/notice/2827873"
     end
 
-    test "it does not fetch replied-to activities beyond max_replies_depth" do
+    test "it does not fetch reply-to activities beyond max replies depth limit" do
       data =
         File.read!("test/fixtures/mastodon-post-activity.json")
         |> Poison.decode!()
@@ -75,7 +75,7 @@ test "it does not fetch replied-to activities beyond max_replies_depth" do
       data = Map.put(data, "object", object)
 
       with_mock Pleroma.Web.Federator,
-        allowed_incoming_reply_depth?: fn _ -> false end do
+        allowed_thread_distance?: fn _ -> false end do
         {:ok, returned_activity} = Transmogrifier.handle_incoming(data)
 
         returned_object = Object.normalize(returned_activity, false)
@@ -1350,12 +1350,14 @@ test "it accepts Move activities" do
     end
   end
 
-  describe "handle_incoming/2: `replies` handling:" do
+  describe "`handle_incoming/2`, Mastodon format `replies` handling" do
     clear_config([:activitypub, :note_replies_output_limit]) do
       Pleroma.Config.put([:activitypub, :note_replies_output_limit], 5)
     end
 
-    test "with Mastodon-formatted `replies` collection, it schedules background fetching of items" do
+    clear_config([:instance, :federation_incoming_replies_max_depth])
+
+    setup do
       data =
         "test/fixtures/mastodon-post-activity.json"
         |> File.read!()
@@ -1364,15 +1366,41 @@ test "with Mastodon-formatted `replies` collection, it schedules background fetc
       items = get_in(data, ["object", "replies", "first", "items"])
       assert length(items) > 0
 
+      %{data: data, items: items}
+    end
+
+    test "schedules background fetching of `replies` items if max thread depth limit allows", %{
+      data: data,
+      items: items
+    } do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 10)
+
       {:ok, _activity} = Transmogrifier.handle_incoming(data)
 
       for id <- items do
-        job_args = %{"op" => "fetch_remote", "id" => id}
+        job_args = %{"op" => "fetch_remote", "id" => id, "depth" => 1}
         assert_enqueued(worker: Pleroma.Workers.RemoteFetcherWorker, args: job_args)
       end
     end
 
-    test "with Pleroma-formatted `replies` collection, it schedules background fetching of items" do
+    test "does NOT schedule background fetching of `replies` beyond max thread depth limit allows",
+         %{data: data} do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 0)
+
+      {:ok, _activity} = Transmogrifier.handle_incoming(data)
+
+      assert all_enqueued(worker: Pleroma.Workers.RemoteFetcherWorker) == []
+    end
+  end
+
+  describe "`handle_incoming/2`, Pleroma format `replies` handling" do
+    clear_config([:activitypub, :note_replies_output_limit]) do
+      Pleroma.Config.put([:activitypub, :note_replies_output_limit], 5)
+    end
+
+    clear_config([:instance, :federation_incoming_replies_max_depth])
+
+    setup do
       user = insert(:user)
 
       {:ok, activity} = CommonAPI.post(user, %{"status" => "post1"})
@@ -1390,13 +1418,31 @@ test "with Pleroma-formatted `replies` collection, it schedules background fetch
       Repo.delete(activity.object)
       Repo.delete(activity)
 
+      %{federation_output: federation_output, replies_uris: replies_uris}
+    end
+
+    test "schedules background fetching of `replies` items if max thread depth limit allows", %{
+      federation_output: federation_output,
+      replies_uris: replies_uris
+    } do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 1)
+
       {:ok, _activity} = Transmogrifier.handle_incoming(federation_output)
 
       for id <- replies_uris do
-        job_args = %{"op" => "fetch_remote", "id" => id}
+        job_args = %{"op" => "fetch_remote", "id" => id, "depth" => 1}
         assert_enqueued(worker: Pleroma.Workers.RemoteFetcherWorker, args: job_args)
       end
     end
+
+    test "does NOT schedule background fetching of `replies` beyond max thread depth limit allows",
+         %{federation_output: federation_output} do
+      Pleroma.Config.put([:instance, :federation_incoming_replies_max_depth], 0)
+
+      {:ok, _activity} = Transmogrifier.handle_incoming(federation_output)
+
+      assert all_enqueued(worker: Pleroma.Workers.RemoteFetcherWorker) == []
+    end
   end
 
   describe "prepare outgoing" do