Extract RSS Feed functionality from OStatus

lib/pleroma/web/metadata/feed.ex

@@ -0,0 +1,23 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Web.Metadata.Providers.Feed do
+  alias Pleroma.Web.Endpoint
+  alias Pleroma.Web.Metadata.Providers.Provider
+  alias Pleroma.Web.Router.Helpers
+
+  @behaviour Provider
+
+  @impl Provider
+  def build_tags(%{user: user}) do
+    [
+      {:link,
+       [
+         rel: "alternate",
+         type: "application/atom+xml",
+         href: Helpers.feed_path(Endpoint, :feed, user.nickname) <> ".atom"
+       ], []}
+    ]
+  end
+end