Instance/Static runtime plug

This allows to set-up an arbitrary directory which overrides most of the
static files: index.html static/ emoji/ packs/ sounds/ images/ instance/
favicon.png.

If the files are not present in the directory, the bundled ones in
priv/static will be used.

lib/pleroma/plugs/instance_static.ex

@@ -0,0 +1,54 @@
+defmodule Pleroma.Plugs.InstanceStatic do
+  @moduledoc """
+  This is a shim to call `Plug.Static` but with runtime `from` configuration.
+
+  Mountpoints are defined directly in the module to avoid calling the configuration for every request including non-static ones.
+  """
+  @behaviour Plug
+
+  def file_path(path) do
+    instance_path =
+      Path.join(Pleroma.Config.get([:instance, :static_dir], "instance/static/"), path)
+
+    if File.exists?(instance_path) do
+      instance_path
+    else
+      Path.join(Application.app_dir(:pleroma, "priv/static/"), path)
+    end
+  end
+
+  @only ~w(index.html static emoji packs sounds images instance favicon.png)
+
+  def init(opts) do
+    opts
+    |> Keyword.put(:from, "__unconfigured_instance_static_plug")
+    |> Keyword.put(:at, "/__unconfigured_instance_static_plug")
+    |> Plug.Static.init()
+  end
+
+  for only <- @only do
+    at = Plug.Router.Utils.split("/")
+
+    def call(conn = %{request_path: "/" <> unquote(only) <> _}, opts) do
+      call_static(
+        conn,
+        opts,
+        unquote(at),
+        Pleroma.Config.get([:instance, :static_dir], "instance/static")
+      )
+    end
+  end
+
+  def call(conn, _) do
+    conn
+  end
+
+  defp call_static(conn, opts, at, from) do
+    opts =
+      opts
+      |> Map.put(:from, from)
+      |> Map.put(:at, at)
+
+    Plug.Static.call(conn, opts)
+  end
+end

lib/pleroma/web/endpoint.ex

@@ -12,6 +12,10 @@ defmodule Pleroma.Web.Endpoint do
 
   plug(Pleroma.Plugs.UploadedMedia)
 
+  # InstanceStatic needs to be before Plug.Static to be able to override shipped-static files
+  # If you're adding new paths to `only:` you'll need to configure them in InstanceStatic as well
+  plug(Pleroma.Plugs.InstanceStatic, at: "/")
+
   plug(
     Plug.Static,
     at: "/",

lib/pleroma/web/ostatus/ostatus_controller.ex

@@ -136,7 +136,7 @@ defmodule Pleroma.Web.OStatus.OStatusController do
         "html" ->
           conn
           |> put_resp_content_type("text/html")
-          |> send_file(200, Application.app_dir(:pleroma, "priv/static/index.html"))
+          |> send_file(200, Pleroma.Plugs.InstanceStatic.file_path("index.html"))
 
         _ ->
           represent_activity(conn, format, activity, user)

lib/pleroma/web/router.ex

@@ -459,7 +459,7 @@ defmodule Fallback.RedirectController do
   def redirector(conn, _params) do
     conn
     |> put_resp_content_type("text/html")
-    |> send_file(200, Application.app_dir(:pleroma, "priv/static/index.html"))
+    |> send_file(200, Pleroma.Plugs.InstanceStatic.file_path("index.html"))
   end
 
   def registration_page(conn, params) do