fix(activitypub): deduplicate account favourites

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -1025,6 +1025,20 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
   defp restrict_assigned_account(query, _), do: query
 
   defp restrict_favorited_by(query, %{favorited_by: ap_id}) do
+    newer_favorite =
+      from(newer_favorite in Activity,
+        where: newer_favorite.actor == ^ap_id,
+        where: newer_favorite.id > parent_as(:favorited_activity).id,
+        where: fragment("?->>'type' = ?", newer_favorite.data, "Like"),
+        where:
+          fragment(
+            "associated_object_id(?) = associated_object_id(?)",
+            newer_favorite.data,
+            parent_as(:favorited_activity).data
+          ),
+        select: 1
+      )
+
     from(
       [activity, object: object] in query,
       join: favorited_activity in Activity,
@@ -1033,6 +1047,8 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
         favorited_activity.actor == ^ap_id and
           fragment("?->>'type' = ?", favorited_activity.data, "Like") and
           fragment("associated_object_id(?) = (?)->>'id'", favorited_activity.data, object.data),
+      where: fragment("(?)->'likes' \\? (?)", object.data, ^ap_id),
+      where: not exists(subquery(newer_favorite)),
       select: %Activity{activity | pagination_id: favorited_activity.id}
     )
   end

priv/repo/migrations/20260725000000_add_activity_favorites_lookup_index.exs

@@ -0,0 +1,20 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Repo.Migrations.AddActivityFavoritesLookupIndex do
+  use Ecto.Migration
+
+  @disable_ddl_transaction true
+  @disable_migration_lock true
+
+  def change do
+    create_if_not_exists(
+      index(:activities, [:actor, "associated_object_id(data)", "id DESC"],
+        name: :activities_favorites_lookup_index,
+        where: "data->>'type' = 'Like'",
+        concurrently: true
+      )
+    )
+  end
+end

test/pleroma/web/pleroma_api/controllers/account_controller_test.exs

@@ -5,9 +5,12 @@
 defmodule Pleroma.Web.PleromaAPI.AccountControllerTest do
   use Pleroma.Web.ConnCase
 
+  alias Pleroma.Activity
   alias Pleroma.Config
+  alias Pleroma.Repo
   alias Pleroma.Tests.ObanHelpers
   alias Pleroma.User
+  alias Pleroma.Web.ActivityPub.Utils
   alias Pleroma.Web.CommonAPI
 
   import Pleroma.Factory
@@ -127,6 +130,49 @@ defmodule Pleroma.Web.PleromaAPI.AccountControllerTest do
       assert Enum.map(response, & &1["id"]) == [second_post.id, first_post.id, third_post.id]
     end
 
+    test "returns a status once when duplicate favorite activities exist", %{
+      conn: conn,
+      user: user
+    } do
+      older_activity = insert(:note_activity)
+      {:ok, _} = CommonAPI.favorite(older_activity.id, user)
+
+      activity = insert(:note_activity)
+      {:ok, favorite} = CommonAPI.favorite(activity.id, user)
+
+      duplicate =
+        Repo.insert!(%Activity{
+          actor: favorite.actor,
+          data: Map.put(favorite.data, "id", Utils.generate_activity_id()),
+          local: favorite.local,
+          recipients: favorite.recipients
+        })
+
+      conn = get(conn, "/api/v1/pleroma/accounts/#{user.id}/favourites?limit=1")
+      response = json_response_and_validate_schema(conn, :ok)
+
+      assert Enum.map(response, & &1["id"]) == [activity.id]
+      assert [link_header] = get_resp_header(conn, "link")
+      assert link_header =~ "max_id=#{duplicate.id}"
+      assert link_header =~ "min_id=#{duplicate.id}"
+
+      response =
+        conn
+        |> get("/api/v1/pleroma/accounts/#{user.id}/favourites?max_id=#{duplicate.id}&limit=1")
+        |> json_response_and_validate_schema(:ok)
+
+      assert Enum.map(response, & &1["id"]) == [older_activity.id]
+
+      {:ok, _} = CommonAPI.unfavorite(activity.id, user)
+
+      response =
+        conn
+        |> get("/api/v1/pleroma/accounts/#{user.id}/favourites")
+        |> json_response_and_validate_schema(:ok)
+
+      assert Enum.map(response, & &1["id"]) == [older_activity.id]
+    end
+
     test "returns favorited DM only when user is logged in and he is one of recipients", %{
       current_user: current_user,
       user: user