I am not sure what's going on anymore so I'll just commit and reset all the other files to HEAD

lib/pleroma/html.ex

@@ -5,18 +5,8 @@
 defmodule Pleroma.HTML do
   alias HtmlSanitizeEx.Scrubber
 
-  defp get_scrubbers(scrubber) when is_atom(scrubber), do: [scrubber]
-  defp get_scrubbers(scrubbers) when is_list(scrubbers), do: scrubbers
-  defp get_scrubbers(_), do: [Pleroma.HTML.Scrubber.Default]
-
-  def get_scrubbers() do
-    Pleroma.Config.get([:markup, :scrub_policy])
-    |> get_scrubbers
-  end
-
-  def filter_tags(html, nil) do
-    get_scrubbers()
-    |> Enum.reduce(html, fn scrubber, html ->
+  def filter_tags(html, scrubbers) when is_list(scrubbers) do
+    Enum.reduce(scrubbers, html, fn scrubber, html ->
       filter_tags(html, scrubber)
     end)
   end
@@ -39,6 +29,10 @@ defmodule Pleroma.HTML.Scrubber.TwitterText do
   require HtmlSanitizeEx.Scrubber.Meta
   alias HtmlSanitizeEx.Scrubber.Meta
 
+  def version do
+    0
+  end
+
   Meta.remove_cdata_sections_before_scrub()
   Meta.strip_comments()
 
@@ -77,6 +71,10 @@ defmodule Pleroma.HTML.Scrubber.Default do
   require HtmlSanitizeEx.Scrubber.Meta
   alias HtmlSanitizeEx.Scrubber.Meta
 
+  def version do
+    0
+  end
+
   @markup Application.get_env(:pleroma, :markup)
   @uri_schemes Application.get_env(:pleroma, :uri_schemes, [])
   @valid_schemes Keyword.get(@uri_schemes, :valid_schemes, [])
@@ -152,6 +150,10 @@ end
 defmodule Pleroma.HTML.Transform.MediaProxy do
   @moduledoc "Transforms inline image URIs to use MediaProxy."
 
+  def version do
+    0
+  end
+
   alias Pleroma.Web.MediaProxy
 
   def before_scrub(html), do: html

lib/pleroma/user.ex

@@ -733,7 +733,9 @@ defmodule Pleroma.User do
     Pleroma.HTML.Scrubber.TwitterText
   end
 
-  def html_filter_policy(_), do: nil
+  @default_scrubbers Pleroma.Config.get([:markup, :scrub_policy])
+
+  def html_filter_policy(_), do: @default_scrubbers
 
   def get_or_fetch_by_ap_id(ap_id) do
     user = get_by_ap_id(ap_id)

lib/pleroma/web/common_api/common_api.ex

@@ -128,7 +128,8 @@ defmodule Pleroma.Web.CommonAPI do
              |> Enum.reduce(%{}, fn {name, file}, acc ->
                Map.put(acc, name, "#{Pleroma.Web.Endpoint.static_url()}#{file}")
              end)
-           ) do
+           ),
+         object <- Map.put(object, "scrubber_cache", %{}) do
       res =
         ActivityPub.create(%{
           to: to,

lib/pleroma/web/common_api/utils.ex

@@ -5,7 +5,7 @@
 defmodule Pleroma.Web.CommonAPI.Utils do
   alias Calendar.Strftime
   alias Comeonin.Pbkdf2
-  alias Pleroma.{Activity, Formatter, Object, Repo}
+  alias Pleroma.{Activity, Formatter, Object, Repo, HTML}
   alias Pleroma.User
   alias Pleroma.Web
   alias Pleroma.Web.ActivityPub.Utils
@@ -261,4 +261,63 @@ defmodule Pleroma.Web.CommonAPI.Utils do
       }
     end)
   end
+
+  @doc """
+  Get sanitized HTML from cache, or scrub it and save to cache.
+  """
+  def get_scrubbed_html(
+        content,
+        scrubbers,
+        %{data: %{"object" => object}} = activity
+      ) do
+    scrubber_cache =
+      if object["scrubber_cache"] != nil and is_list(object["scrubber_cache"]) do
+        object["scrubber_cache"]
+      else
+        []
+      end
+
+    key = generate_scrubber_key(scrubbers)
+
+    {new_scrubber_cache, scrubbed_html} =
+      Enum.map_reduce(scrubber_cache, nil, fn %{
+                                                :scrubbers => current_key,
+                                                :content => current_content
+                                              },
+                                              _ ->
+        if Map.keys(current_key) == Map.keys(key) do
+          if scrubbers == key do
+            {current_key, current_content}
+          else
+            # Remove the entry if scrubber version is outdated
+            {nil, nil}
+          end
+        end
+      end)
+
+    new_scrubber_cache = Enum.reject(new_scrubber_cache, &is_nil/1)
+
+    if !(new_scrubber_cache == scrubber_cache) or scrubbed_html == nil do
+      scrubbed_html = HTML.filter_tags(content, scrubbers)
+      new_scrubber_cache = [%{:scrubbers => key, :content => scrubbed_html} | new_scrubber_cache]
+
+      activity =
+        Map.merge(activity, %{
+          data: %{"object" => %{"scrubber_cache" => new_scrubber_cache}}
+        })
+
+      cng = Ecto.Changeset.change(activity)
+      Repo.update(cng)
+      scrubbed_html
+    else
+      IO.puts("got the post from cache")
+      scrubbed_html
+    end
+  end
+
+  defp generate_scrubber_key(scrubbers) do
+    Enum.reduce(scrubbers, %{}, fn scrubber, acc ->
+      Map.put(acc, to_string(scrubber), scrubber.version)
+    end)
+  end
 end

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -120,7 +120,7 @@ defmodule Pleroma.Web.MastodonAPI.StatusView do
     content =
       object
       |> render_content()
-      |> HTML.filter_tags(User.html_filter_policy(opts[:for]))
+      |> Utils.get_scrubbed_html(User.html_filter_policy(opts[:for]), activity)
 
     %{
       id: to_string(activity.id),

lib/pleroma/web/twitter_api/views/activity_view.ex

@@ -245,7 +245,7 @@ defmodule Pleroma.Web.TwitterAPI.ActivityView do
 
     html =
       content
-      |> HTML.filter_tags(User.html_filter_policy(opts[:for]))
+      |> Utils.get_scrubbed_html(User.html_filter_policy(opts[:for]), activity)
       |> Formatter.emojify(object["emoji"])
 
     text =