allow public routes to be served from a different base url path

README.md

@@ -196,6 +196,10 @@ The following environment variables can be used to configure Livebook on boot:
   * `LIVEBOOK_BASE_URL_PATH` - sets the base url path the web application is
     served on. Useful when deploying behind a reverse proxy.
 
+  * `LIVEBOOK_PUBLIC_BASE_URL_PATH_OVERRIDE` - overrides the base url path for the public
+    asset routes only. Useful to create exceptions when deploying behind a reverse proxy 
+    that requires authentication.
+
   * `LIVEBOOK_CACERTFILE` - path to a local file containing CA certificates.
     Those certificates are used during for server authentication when Livebook
     accesses files from external sources.

assets/js/hooks/js_view.js

@@ -507,7 +507,7 @@ const JSView = {
  * once and the response is cached.
  */
 function cachedPublicEndpointCheck() {
-  const healthUrl = window.LIVEBOOK_BASE_URL_PATH + "/public/health";
+  const healthUrl = window.LIVEBOOK_PUBLIC_BASE_URL_PATH + "/public/health";
 
   cachedPublicEndpointCheck.promise =
     cachedPublicEndpointCheck.promise ||

lib/livebook.ex

@@ -114,6 +114,11 @@ defmodule Livebook do
       config :livebook, LivebookWeb.Endpoint, url: [path: base_url_path]
     end
 
+    if public_base_url_path_override =
+         Livebook.Config.public_base_url_path_override!("LIVEBOOK_PUBLIC_BASE_URL_PATH_OVERRIDE") do
+      config :livebook, :public_base_url_path_override, public_base_url_path_override
+    end
+
     if password = Livebook.Config.password!("LIVEBOOK_PASSWORD") do
       config :livebook, :authentication, {:password, password}
     else

lib/livebook/config.ex

@@ -212,6 +212,17 @@ defmodule Livebook.Config do
     String.trim_trailing(path, "/")
   end
 
+  @doc """
+  Returns the base url path for Livebook public endpoints (health & assets)
+  """
+  @spec public_base_url_path() :: String.t()
+  def public_base_url_path() do
+    case Application.get_env(:livebook, :public_base_url_path_override) do
+      nil -> base_url_path()
+      path -> String.trim_trailing(path, "/")
+    end
+  end
+
   @doc """
   Returns the configured port for the iframe endpoint.
   """
@@ -518,6 +529,15 @@ defmodule Livebook.Config do
     end
   end
 
+  @doc """
+  Parses and validates the public base url path override from env
+  """
+  def public_base_url_path_override!(env) do
+    if override = System.get_env(env) do
+      String.trim_trailing(override, "/")
+    end
+  end
+
   @doc """
   Parses and validates the ip from env.
   """

lib/livebook_web/components/layouts/root.html.heex

@@ -13,6 +13,7 @@
     <link phx-track-static rel="stylesheet" href={~p"/assets/app.css"} />
     <script>
       window.LIVEBOOK_BASE_URL_PATH = "<%= Livebook.Config.base_url_path() %>";
+      window.LIVEBOOK_PUBLIC_BASE_URL_PATH = "<%= Livebook.Config.public_base_url_path() %>"
     </script>
     <LivebookWeb.LayoutComponents.dev_script />
     <%!-- This prevents the script to be loaded twice in Chrome --%>

lib/livebook_web/controllers/session_controller.ex

@@ -127,7 +127,14 @@ defmodule LivebookWeb.SessionController do
       conn
       |> cache_permanently()
       |> put_status(:moved_permanently)
-      |> redirect(to: ~p"/public/sessions/node/#{node_id}/assets/#{hash}/#{file_parts}")
+      |> redirect(
+        to:
+          ~p"/public/sessions/node/#{node_id}/assets/#{hash}/#{file_parts}"
+          |> String.replace(
+            Livebook.Config.base_url_path(),
+            Livebook.Config.public_base_url_path()
+          )
+      )
     else
       send_resp(conn, 404, "Not found")
     end

lib/livebook_web/live/js_view_component.ex

@@ -11,15 +11,20 @@ defmodule LivebookWeb.JSViewComponent do
 
   @impl true
   def render(assigns) do
+    assets_base_path =
+      ~p"/public/sessions/#{assigns.session_id}/assets/#{assigns.js_view.assets.hash}/"
+      |> String.replace(Livebook.Config.base_url_path(), Livebook.Config.public_base_url_path())
+
+    assigns =
+      assign(assigns, :js_view, Map.put(assigns.js_view, :assets_base_path, assets_base_path))
+
     ~H"""
     <div
       id={"js-output-#{@id}-#{@js_view.ref}"}
       phx-hook="JSView"
       phx-update="ignore"
       data-p-ref={hook_prop(@js_view.ref)}
-      data-p-assets-base-path={
-        hook_prop(~p"/public/sessions/#{@session_id}/assets/#{@js_view.assets.hash}/")
-      }
+      data-p-assets-base-path={hook_prop(@js_view.assets_base_path)}
       data-p-assets-cdn-url={hook_prop(cdn_url(@js_view.assets[:cdn_url]))}
       data-p-js-path={hook_prop(@js_view.assets.js_path)}
       data-p-session-token={hook_prop(session_token(@session_id, @client_id))}