From 5b7b1040b38d262b1815276f86036b50847851c7 Mon Sep 17 00:00:00 2001
From: Ivan Tashkinov <ivant.business@gmail.com>
Date: Sat, 29 Jun 2019 20:04:50 +0300
Subject: [PATCH] [#161] Limited replies depth on incoming federation in order
 to prevent memory leaks on recursive replies fetching.

---
 lib/pleroma/object.ex                         |  24 ++--
 lib/pleroma/object/fetcher.ex                 |   8 +-
 .../web/activity_pub/transmogrifier.ex        | 127 +++++++++++-------
 lib/pleroma/web/federator/federator.ex        |   6 +
 .../web/ostatus/handlers/note_handler.ex      |  13 +-
 lib/pleroma/web/ostatus/ostatus.ex            |  22 +--
 test/web/activity_pub/transmogrifier_test.exs |  37 ++++-
 test/web/ostatus/ostatus_test.exs             |  28 +++-
 8 files changed, 181 insertions(+), 84 deletions(-)

diff --git a/lib/pleroma/object.ex b/lib/pleroma/object.ex
index 4b181ec59..b8647dd26 100644
--- a/lib/pleroma/object.ex
+++ b/lib/pleroma/object.ex
@@ -44,20 +44,20 @@ def get_by_ap_id(ap_id) do
     Repo.one(from(object in Object, where: fragment("(?)->>'id' = ?", object.data, ^ap_id)))
   end
 
-  def normalize(_, fetch_remote \\ true)
+  def normalize(_, fetch_remote \\ true, options \\ [])
   # If we pass an Activity to Object.normalize(), we can try to use the preloaded object.
   # Use this whenever possible, especially when walking graphs in an O(N) loop!
-  def normalize(%Object{} = object, _), do: object
-  def normalize(%Activity{object: %Object{} = object}, _), do: object
+  def normalize(%Object{} = object, _, _), do: object
+  def normalize(%Activity{object: %Object{} = object}, _, _), do: object
 
   # A hack for fake activities
-  def normalize(%Activity{data: %{"object" => %{"fake" => true} = data}}, _) do
+  def normalize(%Activity{data: %{"object" => %{"fake" => true} = data}}, _, _) do
     %Object{id: "pleroma:fake_object_id", data: data}
   end
 
   # Catch and log Object.normalize() calls where the Activity's child object is not
   # preloaded.
-  def normalize(%Activity{data: %{"object" => %{"id" => ap_id}}}, fetch_remote) do
+  def normalize(%Activity{data: %{"object" => %{"id" => ap_id}}}, fetch_remote, _) do
     Logger.debug(
       "Object.normalize() called without preloaded object (#{ap_id}).  Consider preloading the object!"
     )
@@ -67,7 +67,7 @@ def normalize(%Activity{data: %{"object" => %{"id" => ap_id}}}, fetch_remote) do
     normalize(ap_id, fetch_remote)
   end
 
-  def normalize(%Activity{data: %{"object" => ap_id}}, fetch_remote) do
+  def normalize(%Activity{data: %{"object" => ap_id}}, fetch_remote, _) do
     Logger.debug(
       "Object.normalize() called without preloaded object (#{ap_id}).  Consider preloading the object!"
     )
@@ -78,10 +78,14 @@ def normalize(%Activity{data: %{"object" => ap_id}}, fetch_remote) do
   end
 
   # Old way, try fetching the object through cache.
-  def normalize(%{"id" => ap_id}, fetch_remote), do: normalize(ap_id, fetch_remote)
-  def normalize(ap_id, false) when is_binary(ap_id), do: get_cached_by_ap_id(ap_id)
-  def normalize(ap_id, true) when is_binary(ap_id), do: Fetcher.fetch_object_from_id!(ap_id)
-  def normalize(_, _), do: nil
+  def normalize(%{"id" => ap_id}, fetch_remote, _), do: normalize(ap_id, fetch_remote)
+  def normalize(ap_id, false, _) when is_binary(ap_id), do: get_cached_by_ap_id(ap_id)
+
+  def normalize(ap_id, true, options) when is_binary(ap_id) do
+    Fetcher.fetch_object_from_id!(ap_id, options)
+  end
+
+  def normalize(_, _, _), do: nil
 
   # Owned objects can only be mutated by their owner
   def authorize_mutation(%Object{data: %{"actor" => actor}}, %User{ap_id: ap_id}),
diff --git a/lib/pleroma/object/fetcher.ex b/lib/pleroma/object/fetcher.ex
index c422490ac..fffbf2bbb 100644
--- a/lib/pleroma/object/fetcher.ex
+++ b/lib/pleroma/object/fetcher.ex
@@ -22,7 +22,7 @@ defp reinject_object(data) do
 
   # TODO:
   # This will create a Create activity, which we need internally at the moment.
-  def fetch_object_from_id(id) do
+  def fetch_object_from_id(id, options \\ []) do
     if object = Object.get_cached_by_ap_id(id) do
       {:ok, object}
     else
@@ -38,7 +38,7 @@ def fetch_object_from_id(id) do
              "object" => data
            },
            :ok <- Containment.contain_origin(id, params),
-           {:ok, activity} <- Transmogrifier.handle_incoming(params),
+           {:ok, activity} <- Transmogrifier.handle_incoming(params, options),
            {:object, _data, %Object{} = object} <-
              {:object, data, Object.normalize(activity, false)} do
         {:ok, object}
@@ -63,8 +63,8 @@ def fetch_object_from_id(id) do
     end
   end
 
-  def fetch_object_from_id!(id) do
-    with {:ok, object} <- fetch_object_from_id(id) do
+  def fetch_object_from_id!(id, options \\ []) do
+    with {:ok, object} <- fetch_object_from_id(id, options) do
       object
     else
       _e ->
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 3bb8b40b5..d5ced2d1d 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -14,6 +14,7 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   alias Pleroma.Web.ActivityPub.ActivityPub
   alias Pleroma.Web.ActivityPub.Utils
   alias Pleroma.Web.ActivityPub.Visibility
+  alias Pleroma.Web.Federator
 
   import Ecto.Query
 
@@ -22,20 +23,20 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   @doc """
   Modifies an incoming AP object (mastodon format) to our internal format.
   """
-  def fix_object(object) do
+  def fix_object(object, options \\ []) do
     object
     |> fix_actor
     |> fix_url
     |> fix_attachments
     |> fix_context
-    |> fix_in_reply_to
+    |> fix_in_reply_to(options)
     |> fix_emoji
     |> fix_tag
     |> fix_content_map
     |> fix_likes
     |> fix_addressing
     |> fix_summary
-    |> fix_type
+    |> fix_type(options)
   end
 
   def fix_summary(%{"summary" => nil} = object) do
@@ -164,7 +165,9 @@ def fix_likes(object) do
     object
   end
 
-  def fix_in_reply_to(%{"inReplyTo" => in_reply_to} = object)
+  def fix_in_reply_to(object, options \\ [])
+
+  def fix_in_reply_to(%{"inReplyTo" => in_reply_to} = object, options)
       when not is_nil(in_reply_to) do
     in_reply_to_id =
       cond do
@@ -182,28 +185,34 @@ def fix_in_reply_to(%{"inReplyTo" => in_reply_to} = object)
           ""
       end
 
-    case get_obj_helper(in_reply_to_id) do
-      {:ok, replied_object} ->
-        with %Activity{} = _activity <-
-               Activity.get_create_by_object_ap_id(replied_object.data["id"]) do
-          object
-          |> Map.put("inReplyTo", replied_object.data["id"])
-          |> Map.put("inReplyToAtomUri", object["inReplyToAtomUri"] || in_reply_to_id)
-          |> Map.put("conversation", replied_object.data["context"] || object["conversation"])
-          |> Map.put("context", replied_object.data["context"] || object["conversation"])
-        else
-          e ->
-            Logger.error("Couldn't fetch \"#{inspect(in_reply_to_id)}\", error: #{inspect(e)}")
-            object
-        end
+    object = Map.put(object, "inReplyToAtomUri", in_reply_to_id)
 
-      e ->
-        Logger.error("Couldn't fetch \"#{inspect(in_reply_to_id)}\", error: #{inspect(e)}")
-        object
+    if (options[:depth] || 1) <= Federator.max_replies_depth() do
+      case get_obj_helper(in_reply_to_id, options) do
+        {:ok, replied_object} ->
+          with %Activity{} = _activity <-
+                 Activity.get_create_by_object_ap_id(replied_object.data["id"]) do
+            object
+            |> Map.put("inReplyTo", replied_object.data["id"])
+            |> Map.put("inReplyToAtomUri", object["inReplyToAtomUri"] || in_reply_to_id)
+            |> Map.put("conversation", replied_object.data["context"] || object["conversation"])
+            |> Map.put("context", replied_object.data["context"] || object["conversation"])
+          else
+            e ->
+              Logger.error("Couldn't fetch \"#{inspect(in_reply_to_id)}\", error: #{inspect(e)}")
+              object
+          end
+
+        e ->
+          Logger.error("Couldn't fetch \"#{inspect(in_reply_to_id)}\", error: #{inspect(e)}")
+          object
+      end
+    else
+      object
     end
   end
 
-  def fix_in_reply_to(object), do: object
+  def fix_in_reply_to(object, _options), do: object
 
   def fix_context(object) do
     context = object["context"] || object["conversation"] || Utils.generate_context_id()
@@ -336,8 +345,15 @@ def fix_content_map(%{"contentMap" => content_map} = object) do
 
   def fix_content_map(object), do: object
 
-  def fix_type(%{"inReplyTo" => reply_id} = object) when is_binary(reply_id) do
-    reply = Object.normalize(reply_id)
+  def fix_type(object, options \\ [])
+
+  def fix_type(%{"inReplyTo" => reply_id} = object, options) when is_binary(reply_id) do
+    reply =
+      if (options[:depth] || 1) <= Federator.max_replies_depth() do
+        Object.normalize(reply_id, true)
+      else
+        nil
+      end
 
     if reply && (reply.data["type"] == "Question" and object["name"]) do
       Map.put(object, "type", "Answer")
@@ -346,7 +362,7 @@ def fix_type(%{"inReplyTo" => reply_id} = object) when is_binary(reply_id) do
     end
   end
 
-  def fix_type(object), do: object
+  def fix_type(object, _), do: object
 
   defp mastodon_follow_hack(%{"id" => id, "actor" => follower_id}, followed) do
     with true <- id =~ "follows",
@@ -374,9 +390,11 @@ defp get_follow_activity(follow_object, followed) do
     end
   end
 
+  def handle_incoming(data, options \\ [])
+
   # Flag objects are placed ahead of the ID check because Mastodon 2.8 and earlier send them
   # with nil ID.
-  def handle_incoming(%{"type" => "Flag", "object" => objects, "actor" => actor} = data) do
+  def handle_incoming(%{"type" => "Flag", "object" => objects, "actor" => actor} = data, _options) do
     with context <- data["context"] || Utils.generate_context_id(),
          content <- data["content"] || "",
          %User{} = actor <- User.get_cached_by_ap_id(actor),
@@ -409,15 +427,19 @@ def handle_incoming(%{"type" => "Flag", "object" => objects, "actor" => actor} =
   end
 
   # disallow objects with bogus IDs
-  def handle_incoming(%{"id" => nil}), do: :error
-  def handle_incoming(%{"id" => ""}), do: :error
+  def handle_incoming(%{"id" => nil}, _options), do: :error
+  def handle_incoming(%{"id" => ""}, _options), do: :error
   # length of https:// = 8, should validate better, but good enough for now.
-  def handle_incoming(%{"id" => id}) when not (is_binary(id) and length(id) > 8), do: :error
+  def handle_incoming(%{"id" => id}, _options) when not (is_binary(id) and length(id) > 8),
+    do: :error
 
   # TODO: validate those with a Ecto scheme
   # - tags
   # - emoji
-  def handle_incoming(%{"type" => "Create", "object" => %{"type" => objtype} = object} = data)
+  def handle_incoming(
+        %{"type" => "Create", "object" => %{"type" => objtype} = object} = data,
+        options
+      )
       when objtype in ["Article", "Note", "Video", "Page", "Question", "Answer"] do
     actor = Containment.get_actor(data)
 
@@ -427,7 +449,8 @@ def handle_incoming(%{"type" => "Create", "object" => %{"type" => objtype} = obj
 
     with nil <- Activity.get_create_by_object_ap_id(object["id"]),
          {:ok, %User{} = user} <- User.get_or_fetch_by_ap_id(data["actor"]) do
-      object = fix_object(data["object"])
+      options = Keyword.put(options, :depth, (options[:depth] || 0) + 1)
+      object = fix_object(data["object"], options)
 
       params = %{
         to: data["to"],
@@ -452,7 +475,8 @@ def handle_incoming(%{"type" => "Create", "object" => %{"type" => objtype} = obj
   end
 
   def handle_incoming(
-        %{"type" => "Follow", "object" => followed, "actor" => follower, "id" => id} = data
+        %{"type" => "Follow", "object" => followed, "actor" => follower, "id" => id} = data,
+        _options
       ) do
     with %User{local: true} = followed <- User.get_cached_by_ap_id(followed),
          {:ok, %User{} = follower} <- User.get_or_fetch_by_ap_id(follower),
@@ -503,7 +527,8 @@ def handle_incoming(
   end
 
   def handle_incoming(
-        %{"type" => "Accept", "object" => follow_object, "actor" => _actor, "id" => _id} = data
+        %{"type" => "Accept", "object" => follow_object, "actor" => _actor, "id" => _id} = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = followed} <- User.get_or_fetch_by_ap_id(actor),
@@ -524,7 +549,8 @@ def handle_incoming(
   end
 
   def handle_incoming(
-        %{"type" => "Reject", "object" => follow_object, "actor" => _actor, "id" => _id} = data
+        %{"type" => "Reject", "object" => follow_object, "actor" => _actor, "id" => _id} = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = followed} <- User.get_or_fetch_by_ap_id(actor),
@@ -548,7 +574,8 @@ def handle_incoming(
   end
 
   def handle_incoming(
-        %{"type" => "Like", "object" => object_id, "actor" => _actor, "id" => id} = data
+        %{"type" => "Like", "object" => object_id, "actor" => _actor, "id" => id} = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
@@ -561,7 +588,8 @@ def handle_incoming(
   end
 
   def handle_incoming(
-        %{"type" => "Announce", "object" => object_id, "actor" => _actor, "id" => id} = data
+        %{"type" => "Announce", "object" => object_id, "actor" => _actor, "id" => id} = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
@@ -576,7 +604,8 @@ def handle_incoming(
 
   def handle_incoming(
         %{"type" => "Update", "object" => %{"type" => object_type} = object, "actor" => actor_id} =
-          data
+          data,
+        _options
       )
       when object_type in ["Person", "Application", "Service", "Organization"] do
     with %User{ap_id: ^actor_id} = actor <- User.get_cached_by_ap_id(object["id"]) do
@@ -614,7 +643,8 @@ def handle_incoming(
   # an error or a tombstone.  This would allow us to verify that a deletion actually took
   # place.
   def handle_incoming(
-        %{"type" => "Delete", "object" => object_id, "actor" => _actor, "id" => _id} = data
+        %{"type" => "Delete", "object" => object_id, "actor" => _actor, "id" => _id} = data,
+        _options
       ) do
     object_id = Utils.get_ap_id(object_id)
 
@@ -635,7 +665,8 @@ def handle_incoming(
           "object" => %{"type" => "Announce", "object" => object_id},
           "actor" => _actor,
           "id" => id
-        } = data
+        } = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
@@ -653,7 +684,8 @@ def handle_incoming(
           "object" => %{"type" => "Follow", "object" => followed},
           "actor" => follower,
           "id" => id
-        } = _data
+        } = _data,
+        _options
       ) do
     with %User{local: true} = followed <- User.get_cached_by_ap_id(followed),
          {:ok, %User{} = follower} <- User.get_or_fetch_by_ap_id(follower),
@@ -671,7 +703,8 @@ def handle_incoming(
           "object" => %{"type" => "Block", "object" => blocked},
           "actor" => blocker,
           "id" => id
-        } = _data
+        } = _data,
+        _options
       ) do
     with true <- Pleroma.Config.get([:activitypub, :accept_blocks]),
          %User{local: true} = blocked <- User.get_cached_by_ap_id(blocked),
@@ -685,7 +718,8 @@ def handle_incoming(
   end
 
   def handle_incoming(
-        %{"type" => "Block", "object" => blocked, "actor" => blocker, "id" => id} = _data
+        %{"type" => "Block", "object" => blocked, "actor" => blocker, "id" => id} = _data,
+        _options
       ) do
     with true <- Pleroma.Config.get([:activitypub, :accept_blocks]),
          %User{local: true} = blocked = User.get_cached_by_ap_id(blocked),
@@ -705,7 +739,8 @@ def handle_incoming(
           "object" => %{"type" => "Like", "object" => object_id},
           "actor" => _actor,
           "id" => id
-        } = data
+        } = data,
+        _options
       ) do
     with actor <- Containment.get_actor(data),
          {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
@@ -717,10 +752,10 @@ def handle_incoming(
     end
   end
 
-  def handle_incoming(_), do: :error
+  def handle_incoming(_, _), do: :error
 
-  def get_obj_helper(id) do
-    if object = Object.normalize(id), do: {:ok, object}, else: nil
+  def get_obj_helper(id, options \\ []) do
+    if object = Object.normalize(id, true, options), do: {:ok, object}, else: nil
   end
 
   def set_reply_to_uri(%{"inReplyTo" => in_reply_to} = object) when is_binary(in_reply_to) do
diff --git a/lib/pleroma/web/federator/federator.ex b/lib/pleroma/web/federator/federator.ex
index f4c9fe284..7c13ff323 100644
--- a/lib/pleroma/web/federator/federator.ex
+++ b/lib/pleroma/web/federator/federator.ex
@@ -22,6 +22,12 @@ def init do
     refresh_subscriptions()
   end
 
+  @max_replies_depth 100
+
+  @doc "Addresses [memory leaks on recursive replies fetching](https://git.pleroma.social/pleroma/pleroma/issues/161)"
+  # credo:disable-for-previous-line Credo.Check.Readability.MaxLineLength
+  def max_replies_depth, do: @max_replies_depth
+
   # Client API
 
   def incoming_doc(doc) do
diff --git a/lib/pleroma/web/ostatus/handlers/note_handler.ex b/lib/pleroma/web/ostatus/handlers/note_handler.ex
index ec6e5cfaf..6f8f3ddcb 100644
--- a/lib/pleroma/web/ostatus/handlers/note_handler.ex
+++ b/lib/pleroma/web/ostatus/handlers/note_handler.ex
@@ -10,6 +10,7 @@ defmodule Pleroma.Web.OStatus.NoteHandler do
   alias Pleroma.Web.ActivityPub.ActivityPub
   alias Pleroma.Web.ActivityPub.Utils
   alias Pleroma.Web.CommonAPI
+  alias Pleroma.Web.Federator
   alias Pleroma.Web.OStatus
   alias Pleroma.Web.XML
 
@@ -88,14 +89,15 @@ def add_external_url(note, entry) do
     Map.put(note, "external_url", url)
   end
 
-  def fetch_replied_to_activity(entry, in_reply_to) do
+  def fetch_replied_to_activity(entry, in_reply_to, options \\ []) do
     with %Activity{} = activity <- Activity.get_create_by_object_ap_id(in_reply_to) do
       activity
     else
       _e ->
-        with in_reply_to_href when not is_nil(in_reply_to_href) <-
+        with true <- (options[:depth] || 1) <= Federator.max_replies_depth(),
+             in_reply_to_href when not is_nil(in_reply_to_href) <-
                XML.string_from_xpath("//thr:in-reply-to[1]/@href", entry),
-             {:ok, [activity | _]} <- OStatus.fetch_activity_from_url(in_reply_to_href) do
+             {:ok, [activity | _]} <- OStatus.fetch_activity_from_url(in_reply_to_href, options) do
           activity
         else
           _e -> nil
@@ -104,7 +106,7 @@ def fetch_replied_to_activity(entry, in_reply_to) do
   end
 
   # TODO: Clean this up a bit.
-  def handle_note(entry, doc \\ nil) do
+  def handle_note(entry, doc \\ nil, options \\ []) do
     with id <- XML.string_from_xpath("//id", entry),
          activity when is_nil(activity) <- Activity.get_create_by_object_ap_id_with_object(id),
          [author] <- :xmerl_xpath.string('//author[1]', doc),
@@ -112,7 +114,8 @@ def handle_note(entry, doc \\ nil) do
          content_html <- OStatus.get_content(entry),
          cw <- OStatus.get_cw(entry),
          in_reply_to <- XML.string_from_xpath("//thr:in-reply-to[1]/@ref", entry),
-         in_reply_to_activity <- fetch_replied_to_activity(entry, in_reply_to),
+         options <- Keyword.put(options, :depth, (options[:depth] || 0) + 1),
+         in_reply_to_activity <- fetch_replied_to_activity(entry, in_reply_to, options),
          in_reply_to_object <-
            (in_reply_to_activity && Object.normalize(in_reply_to_activity)) || nil,
          in_reply_to <- (in_reply_to_object && in_reply_to_object.data["id"]) || in_reply_to,
diff --git a/lib/pleroma/web/ostatus/ostatus.ex b/lib/pleroma/web/ostatus/ostatus.ex
index 6ed089d84..502410c83 100644
--- a/lib/pleroma/web/ostatus/ostatus.ex
+++ b/lib/pleroma/web/ostatus/ostatus.ex
@@ -54,7 +54,7 @@ def remote_follow_path do
     "#{Web.base_url()}/ostatus_subscribe?acct={uri}"
   end
 
-  def handle_incoming(xml_string) do
+  def handle_incoming(xml_string, options \\ []) do
     with doc when doc != :error <- parse_document(xml_string) do
       with {:ok, actor_user} <- find_make_or_update_user(doc),
            do: Pleroma.Instances.set_reachable(actor_user.ap_id)
@@ -91,10 +91,12 @@ def handle_incoming(xml_string) do
               _ ->
                 case object_type do
                   'http://activitystrea.ms/schema/1.0/note' ->
-                    with {:ok, activity} <- NoteHandler.handle_note(entry, doc), do: activity
+                    with {:ok, activity} <- NoteHandler.handle_note(entry, doc, options),
+                         do: activity
 
                   'http://activitystrea.ms/schema/1.0/comment' ->
-                    with {:ok, activity} <- NoteHandler.handle_note(entry, doc), do: activity
+                    with {:ok, activity} <- NoteHandler.handle_note(entry, doc, options),
+                         do: activity
 
                   _ ->
                     Logger.error("Couldn't parse incoming document")
@@ -359,7 +361,7 @@ def get_atom_url(body) do
     end
   end
 
-  def fetch_activity_from_atom_url(url) do
+  def fetch_activity_from_atom_url(url, options \\ []) do
     with true <- String.starts_with?(url, "http"),
          {:ok, %{body: body, status: code}} when code in 200..299 <-
            HTTP.get(
@@ -367,7 +369,7 @@ def fetch_activity_from_atom_url(url) do
              [{:Accept, "application/atom+xml"}]
            ) do
       Logger.debug("Got document from #{url}, handling...")
-      handle_incoming(body)
+      handle_incoming(body, options)
     else
       e ->
         Logger.debug("Couldn't get #{url}: #{inspect(e)}")
@@ -375,13 +377,13 @@ def fetch_activity_from_atom_url(url) do
     end
   end
 
-  def fetch_activity_from_html_url(url) do
+  def fetch_activity_from_html_url(url, options \\ []) do
     Logger.debug("Trying to fetch #{url}")
 
     with true <- String.starts_with?(url, "http"),
          {:ok, %{body: body}} <- HTTP.get(url, []),
          {:ok, atom_url} <- get_atom_url(body) do
-      fetch_activity_from_atom_url(atom_url)
+      fetch_activity_from_atom_url(atom_url, options)
     else
       e ->
         Logger.debug("Couldn't get #{url}: #{inspect(e)}")
@@ -389,11 +391,11 @@ def fetch_activity_from_html_url(url) do
     end
   end
 
-  def fetch_activity_from_url(url) do
-    with {:ok, [_ | _] = activities} <- fetch_activity_from_atom_url(url) do
+  def fetch_activity_from_url(url, options \\ []) do
+    with {:ok, [_ | _] = activities} <- fetch_activity_from_atom_url(url, options) do
       {:ok, activities}
     else
-      _e -> fetch_activity_from_html_url(url)
+      _e -> fetch_activity_from_html_url(url, options)
     end
   rescue
     e ->
diff --git a/test/web/activity_pub/transmogrifier_test.exs b/test/web/activity_pub/transmogrifier_test.exs
index 68ec03c33..fc8703ca9 100644
--- a/test/web/activity_pub/transmogrifier_test.exs
+++ b/test/web/activity_pub/transmogrifier_test.exs
@@ -11,12 +11,13 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
   alias Pleroma.User
   alias Pleroma.Web.ActivityPub.ActivityPub
   alias Pleroma.Web.ActivityPub.Transmogrifier
+  alias Pleroma.Web.CommonAPI
   alias Pleroma.Web.OStatus
   alias Pleroma.Web.Websub.WebsubClientSubscription
 
+  import Mock
   import Pleroma.Factory
   import ExUnit.CaptureLog
-  alias Pleroma.Web.CommonAPI
 
   setup_all do
     Tesla.Mock.mock_global(fn env -> apply(HttpRequestMock, :request, [env]) end)
@@ -46,12 +47,10 @@ test "it fetches replied-to activities if we don't have them" do
         data["object"]
         |> Map.put("inReplyTo", "https://shitposter.club/notice/2827873")
 
-      data =
-        data
-        |> Map.put("object", object)
-
+      data = Map.put(data, "object", object)
       {:ok, returned_activity} = Transmogrifier.handle_incoming(data)
-      returned_object = Object.normalize(returned_activity.data["object"])
+
+      returned_object = Object.normalize(returned_activity.data["object"], false)
 
       assert activity =
                Activity.get_create_by_object_ap_id(
@@ -61,6 +60,32 @@ 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
+      data =
+        File.read!("test/fixtures/mastodon-post-activity.json")
+        |> Poison.decode!()
+
+      object =
+        data["object"]
+        |> Map.put("inReplyTo", "https://shitposter.club/notice/2827873")
+
+      data = Map.put(data, "object", object)
+
+      with_mock Pleroma.Web.Federator,
+        max_replies_depth: fn -> 0 end do
+        {:ok, returned_activity} = Transmogrifier.handle_incoming(data)
+
+        returned_object = Object.normalize(returned_activity.data["object"], false)
+
+        refute Activity.get_create_by_object_ap_id(
+                 "tag:shitposter.club,2017-05-05:noticeId=2827873:objectType=comment"
+               )
+
+        assert returned_object.data["inReplyToAtomUri"] ==
+                 "https://shitposter.club/notice/2827873"
+      end
+    end
+
     test "it does not crash if the object in inReplyTo can't be fetched" do
       data =
         File.read!("test/fixtures/mastodon-post-activity.json")
diff --git a/test/web/ostatus/ostatus_test.exs b/test/web/ostatus/ostatus_test.exs
index f6be16862..12627356c 100644
--- a/test/web/ostatus/ostatus_test.exs
+++ b/test/web/ostatus/ostatus_test.exs
@@ -11,8 +11,10 @@ defmodule Pleroma.Web.OStatusTest do
   alias Pleroma.User
   alias Pleroma.Web.OStatus
   alias Pleroma.Web.XML
-  import Pleroma.Factory
+
   import ExUnit.CaptureLog
+  import Mock
+  import Pleroma.Factory
 
   setup_all do
     Tesla.Mock.mock_global(fn env -> apply(HttpRequestMock, :request, [env]) end)
@@ -266,10 +268,13 @@ test "handle incoming favorites with locally available object - GS, websub" do
     assert favorited_activity.local
   end
 
-  test "handle incoming replies" do
+  test_with_mock "handle incoming replies, fetching replied-to activities if we don't have them",
+                 OStatus,
+                 [:passthrough],
+                 [] do
     incoming = File.read!("test/fixtures/incoming_note_activity_answer.xml")
     {:ok, [activity]} = OStatus.handle_incoming(incoming)
-    object = Object.normalize(activity.data["object"])
+    object = Object.normalize(activity.data["object"], false)
 
     assert activity.data["type"] == "Create"
     assert object.data["type"] == "Note"
@@ -282,6 +287,23 @@ test "handle incoming replies" do
     assert object.data["id"] == "tag:gs.example.org:4040,2017-04-25:noticeId=55:objectType=note"
 
     assert "https://www.w3.org/ns/activitystreams#Public" in activity.data["to"]
+
+    assert called(OStatus.fetch_activity_from_url(object.data["inReplyTo"], :_))
+  end
+
+  test_with_mock "handle incoming replies, not fetching replied-to activities beyond max_replies_depth",
+                 OStatus,
+                 [:passthrough],
+                 [] do
+    incoming = File.read!("test/fixtures/incoming_note_activity_answer.xml")
+
+    with_mock Pleroma.Web.Federator,
+      max_replies_depth: fn -> 0 end do
+      {:ok, [activity]} = OStatus.handle_incoming(incoming)
+      object = Object.normalize(activity.data["object"], false)
+
+      refute called(OStatus.fetch_activity_from_url(object.data["inReplyTo"], :_))
+    end
   end
 
   test "handle incoming follows" do