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diff --git a/lib/pleroma/web/activity_pub/object_validator.ex b/lib/pleroma/web/activity_pub/object_validator.ex
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+# 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.ObjectValidator do
+  @moduledoc """
+  This module is responsible for validating an object (which can be an activity)
+  and checking if it is both well formed and also compatible with our view of
+  the system.
+  """
+
+  alias Pleroma.User
+  alias Pleroma.Object
+  alias Pleroma.Web.ActivityPub.Utils
+
+  def validate_id(object, meta) do
+    with {_, true} <- {:id_presence, Map.has_key?(object, "id")} do
+      {:ok, object, meta}
+    else
+      e -> {:error, e}
+    end
+  end
+
+  def validate_actor(object, meta) do
+    with {_, %User{}} <- {:actor_validation, User.get_cached_by_ap_id(object["actor"])} do
+      {:ok, object, meta}
+    else
+      e -> {:error, e}
+    end
+  end
+
+  def common_validations(object, meta) do
+    with {_, {:ok, object, meta}} <- {:validate_id, validate_id(object, meta)},
+      {_, {:ok, object, meta}} <- {:validate_actor, validate_actor(object, meta)} do
+      {:ok, object, meta}
+    else
+      e -> {:error, e}
+    end
+  end
+
+  @spec validate(map(), keyword()) :: {:ok, map(), keyword()} | {:error, any()}
+  def validate(object, meta)
+
+  def validate(%{"type" => "Like"} = object, meta) do
+    with {:ok, object, meta} <- common_validations(object, meta),
+         {_, %Object{} = liked_object} <- {:find_liked_object, Object.normalize(object["object"])},
+         {_, nil} <- {:existing_like, Utils.get_existing_like(object["actor"], liked_object)} do
+      {:ok, object, meta}
+    else
+      e -> {:error, e}
+    end
+  end
+
+  def validate(object, meta) do
+    common_validations(object, meta)
+  end
+end