Add support for remote favicons

lib/pleroma/user.ex

@@ -2253,4 +2253,34 @@ defmodule Pleroma.User do
     |> Map.put(:bio, HTML.filter_tags(user.bio, filter))
     |> Map.put(:fields, fields)
   end
+
+  def get_cached_favicon(%User{} = user) do
+    key = "favicon:#{user.ap_id}"
+    Cachex.fetch!(:user_cache, key, fn _ -> get_favicon(user) end)
+  end
+
+  def get_cached_favicon(_user) do
+    nil
+  end
+
+  def get_favicon(user) do
+    try do
+      with url <- user.ap_id,
+           true <- is_binary(url),
+           {:ok, %Tesla.Env{body: html}} <- Pleroma.HTTP.get(url),
+           favicon_rel <-
+             html
+             |> Floki.parse_document!()
+             |> Floki.attribute("link[rel=icon]", "href")
+             |> List.first(),
+           favicon_url <- URI.merge(URI.parse(url), favicon_rel) |> to_string(),
+           true <- is_binary(favicon_url) do
+        favicon_url
+      else
+        _ -> nil
+      end
+    rescue
+      _ -> nil
+    end
+  end
 end

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

@@ -245,7 +245,8 @@ defmodule Pleroma.Web.MastodonAPI.AccountView do
         hide_favorites: user.hide_favorites,
         relationship: relationship,
         skip_thread_containment: user.skip_thread_containment,
-        background_image: image_url(user.background) |> MediaProxy.url()
+        background_image: image_url(user.background) |> MediaProxy.url(),
+        favicon: User.get_cached_favicon(user) |> MediaProxy.url()
       }
     }
     |> maybe_put_role(user, opts[:for])