AP ingest: normalize inReplyTo shapes

lib/pleroma/web/activity_pub/object_validators/common_fixes.ex

@@ -41,22 +41,34 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.CommonFixes do
   def fix_object_defaults(data) do
     data = Maps.filter_empty_values(data)
 
+    in_reply_to_id = in_reply_to_id(data["inReplyTo"])
+
     context =
       Utils.maybe_create_context(
-        data["context"] || data["conversation"] || data["inReplyTo"] || data["id"]
+        data["context"] || data["conversation"] || in_reply_to_id || data["id"]
       )
 
-    %User{follower_address: follower_collection} = User.get_cached_by_ap_id(data["attributedTo"])
+    data = Map.put(data, "context", context)
 
-    data
-    |> Map.put("context", context)
-    |> cast_and_filter_recipients("to", follower_collection)
-    |> cast_and_filter_recipients("cc", follower_collection)
-    |> cast_and_filter_recipients("bto", follower_collection)
-    |> cast_and_filter_recipients("bcc", follower_collection)
-    |> Transmogrifier.fix_implicit_addressing(follower_collection)
+    with attributed_to when is_binary(attributed_to) <- data["attributedTo"],
+         %User{follower_address: follower_collection} <- User.get_cached_by_ap_id(attributed_to) do
+      data
+      |> cast_and_filter_recipients("to", follower_collection)
+      |> cast_and_filter_recipients("cc", follower_collection)
+      |> cast_and_filter_recipients("bto", follower_collection)
+      |> cast_and_filter_recipients("bcc", follower_collection)
+      |> Transmogrifier.fix_implicit_addressing(follower_collection)
+    else
+      _ -> data
+    end
   end
 
+  defp in_reply_to_id(in_reply_to) when is_binary(in_reply_to), do: in_reply_to
+  defp in_reply_to_id(%{"id" => in_reply_to}) when is_binary(in_reply_to), do: in_reply_to
+  defp in_reply_to_id(%{"href" => in_reply_to}) when is_binary(in_reply_to), do: in_reply_to
+  defp in_reply_to_id([in_reply_to | _]), do: in_reply_to_id(in_reply_to)
+  defp in_reply_to_id(_), do: nil
+
   def fix_activity_addressing(activity) do
     %User{follower_address: follower_collection} = User.get_cached_by_ap_id(activity["actor"])
 

lib/pleroma/web/activity_pub/transmogrifier.ex

@@ -201,9 +201,29 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   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 =
+      cond do
+        is_list(in_reply_to) ->
+          if not_empty_string(in_reply_to_id) do
+            Map.put(object, "inReplyTo", in_reply_to_id)
+          else
+            Map.delete(object, "inReplyTo")
+          end
+
+        is_map(in_reply_to) and is_nil(in_reply_to["id"]) and is_binary(in_reply_to["href"]) ->
+          Map.put(object, "inReplyTo", in_reply_to["href"])
+
+        is_map(in_reply_to) and is_nil(in_reply_to["id"]) and is_nil(in_reply_to["href"]) ->
+          Map.delete(object, "inReplyTo")
+
+        true ->
+          object
+      end
+
     depth = (options[:depth] || 0) + 1
 
-    if Federator.allowed_thread_distance?(depth) do
+    if not_empty_string(in_reply_to_id) and 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
@@ -249,9 +269,17 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
       is_map(in_reply_to) && is_bitstring(in_reply_to["id"]) ->
         in_reply_to["id"]
 
+      is_map(in_reply_to) && is_bitstring(in_reply_to["href"]) ->
+        in_reply_to["href"]
+
       is_list(in_reply_to) && is_bitstring(Enum.at(in_reply_to, 0)) ->
         Enum.at(in_reply_to, 0)
 
+      is_list(in_reply_to) && is_map(Enum.at(in_reply_to, 0)) ->
+        in_reply_to
+        |> Enum.at(0)
+        |> prepare_in_reply_to()
+
       true ->
         ""
     end

test/fixtures/fedidev.fun/in_reply_to_collection.json

@@ -0,0 +1,30 @@
+{
+  "@context": [
+    "https://www.w3.org/ns/activitystreams"
+  ],
+  "type": "Create",
+  "id": "https://fedidev.fun/activity/in-reply-to-collection",
+  "actor": "https://fedidev.fun/users/alice",
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "cc": [],
+  "published": "2025-11-21T14:40:08Z",
+  "object": {
+    "type": "Note",
+    "id": "https://fedidev.fun/objects/note-in-reply-to-collection",
+    "attributedTo": "https://fedidev.fun/users/alice",
+    "to": [
+      "https://www.w3.org/ns/activitystreams#Public"
+    ],
+    "cc": [],
+    "published": "2025-11-21T14:40:08Z",
+    "content": "collection",
+    "inReplyTo": {
+      "type": "Collection",
+      "items": [
+        "https://fedidev.fun/users/alice"
+      ]
+    }
+  }
+}

test/fixtures/fedidev.fun/in_reply_to_embedded_note.json

@@ -0,0 +1,35 @@
+{
+  "@context": [
+    "https://www.w3.org/ns/activitystreams"
+  ],
+  "type": "Create",
+  "id": "https://fedidev.fun/activity/in-reply-to-embedded-note",
+  "actor": "https://fedidev.fun/users/alice",
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "cc": [],
+  "published": "2025-11-21T14:40:21Z",
+  "object": {
+    "type": "Note",
+    "id": "https://fedidev.fun/objects/note-in-reply-to-embedded-note",
+    "attributedTo": "https://fedidev.fun/users/alice",
+    "to": [
+      "https://www.w3.org/ns/activitystreams#Public"
+    ],
+    "cc": [],
+    "published": "2025-11-21T14:40:21Z",
+    "content": "embedded note",
+    "inReplyTo": {
+      "@context": "https://www.w3.org/ns/activitystreams",
+      "type": "Note",
+      "id": "https://fedidev.fun/assets/note1.jsonap",
+      "to": [
+        "https://www.w3.org/ns/activitystreams#Public"
+      ],
+      "attributedTo": "https://fedidev.fun/users/alice",
+      "content": "One",
+      "published": "2024-01-06T13:11:45Z"
+    }
+  }
+}

test/fixtures/fedidev.fun/in_reply_to_link.json

@@ -0,0 +1,28 @@
+{
+  "@context": [
+    "https://www.w3.org/ns/activitystreams"
+  ],
+  "type": "Create",
+  "id": "https://fedidev.fun/activity/in-reply-to-link",
+  "actor": "https://fedidev.fun/users/alice",
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "cc": [],
+  "published": "2025-11-21T14:39:56Z",
+  "object": {
+    "type": "Note",
+    "id": "https://fedidev.fun/objects/note-in-reply-to-link",
+    "attributedTo": "https://fedidev.fun/users/alice",
+    "to": [
+      "https://www.w3.org/ns/activitystreams#Public"
+    ],
+    "cc": [],
+    "published": "2025-11-21T14:39:56Z",
+    "content": "Link in inReplyTo",
+    "inReplyTo": {
+      "type": "Link",
+      "href": "https://fedidev.fun/assets/note1.jsonap"
+    }
+  }
+}

test/fixtures/fedidev.fun/in_reply_to_list.json

@@ -0,0 +1,28 @@
+{
+  "@context": [
+    "https://www.w3.org/ns/activitystreams"
+  ],
+  "type": "Create",
+  "id": "https://fedidev.fun/activity/in-reply-to-list",
+  "actor": "https://fedidev.fun/users/alice",
+  "to": [
+    "https://www.w3.org/ns/activitystreams#Public"
+  ],
+  "cc": [],
+  "published": "2025-11-21T14:40:08Z",
+  "object": {
+    "type": "Note",
+    "id": "https://fedidev.fun/objects/note-in-reply-to-list",
+    "attributedTo": "https://fedidev.fun/users/alice",
+    "to": [
+      "https://www.w3.org/ns/activitystreams#Public"
+    ],
+    "cc": [],
+    "published": "2025-11-21T14:40:08Z",
+    "content": "two elements in inReplyTo",
+    "inReplyTo": [
+      "https://fedidev.fun/assets/note1.jsonap",
+      "https://fedidev.fun/assets/note2.jsonap"
+    ]
+  }
+}

test/pleroma/web/activity_pub/transmogrifier/fedidev_fun_in_reply_to_test.exs

@@ -0,0 +1,72 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.ActivityPub.Transmogrifier.FedidevFunInReplyToTest do
+  use Oban.Testing, repo: Pleroma.Repo
+  use Pleroma.DataCase
+
+  alias Pleroma.Object
+  alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.Transmogrifier
+
+  import Pleroma.Factory
+
+  setup_all do
+    Tesla.Mock.mock_global(fn env -> apply(HttpRequestMock, :request, [env]) end)
+    :ok
+  end
+
+  defp ensure_remote_actor!(ap_id) when is_binary(ap_id) do
+    case User.get_cached_by_ap_id(ap_id) do
+      %User{} ->
+        :ok
+
+      _ ->
+        insert(:user,
+          local: false,
+          ap_id: ap_id,
+          follower_address: ap_id <> "/followers",
+          following_address: ap_id <> "/following",
+          featured_address: ap_id <> "/collections/featured",
+          inbox: ap_id <> "/inbox"
+        )
+
+        :ok
+    end
+  end
+
+  defp ingest_fixture!(rel_path) do
+    data = rel_path |> File.read!() |> Jason.decode!()
+    ensure_remote_actor!(data["actor"])
+
+    assert {:ok, activity} = Transmogrifier.handle_incoming(data)
+    object = Object.normalize(activity.data["object"], fetch: false)
+
+    {activity, object}
+  end
+
+  test "normalizes Link inReplyTo to a string" do
+    {_activity, object} = ingest_fixture!("test/fixtures/fedidev.fun/in_reply_to_link.json")
+    assert object.data["inReplyTo"] == "https://fedidev.fun/assets/note1.jsonap"
+  end
+
+  test "normalizes list inReplyTo to the first object ID" do
+    {_activity, object} = ingest_fixture!("test/fixtures/fedidev.fun/in_reply_to_list.json")
+    assert object.data["inReplyTo"] == "https://fedidev.fun/assets/note1.jsonap"
+  end
+
+  test "drops invalid map shapes in inReplyTo" do
+    {_activity, object} =
+      ingest_fixture!("test/fixtures/fedidev.fun/in_reply_to_collection.json")
+
+    assert object.data["inReplyTo"] == nil
+  end
+
+  test "accepts embedded objects in inReplyTo" do
+    {_activity, object} =
+      ingest_fixture!("test/fixtures/fedidev.fun/in_reply_to_embedded_note.json")
+
+    assert object.data["inReplyTo"] == "https://fedidev.fun/assets/note1.jsonap"
+  end
+end

test/pleroma/web/activity_pub/transmogrifier/note_handling_test.exs

@@ -572,11 +572,11 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier.NoteHandlingTest do
         Map.put(data["object"], "inReplyTo", ["https://shitposter.club/notice/2827873"])
 
       modified_object = Transmogrifier.fix_in_reply_to(object_with_reply)
-      assert modified_object["inReplyTo"] == ["https://shitposter.club/notice/2827873"]
+      assert modified_object["inReplyTo"] == "https://shitposter.club/notice/2827873"
 
       object_with_reply = Map.put(data["object"], "inReplyTo", [])
       modified_object = Transmogrifier.fix_in_reply_to(object_with_reply)
-      assert modified_object["inReplyTo"] == []
+      assert modified_object["inReplyTo"] == nil
     end
 
     test "returns modified object when allowed incoming reply", %{data: data} do