Fix importing notebook via livebook.dev/run to download attachments

lib/livebook_web/live/open_live.ex

@@ -159,12 +159,13 @@ defmodule LivebookWeb.OpenLive do
   def handle_params(%{"url" => url}, _url, socket)
       when socket.assigns.live_action == :public_import do
     origin = Notebook.ContentLoader.url_to_location(url)
+    files_url = Livebook.Utils.expand_url(url, "files/")
 
     origin
     |> Notebook.ContentLoader.fetch_content_from_location()
     |> case do
       {:ok, content} ->
-        socket = import_source(socket, content, origin: origin)
+        socket = import_source(socket, content, origin: origin, files_source: {:url, files_url})
         {:noreply, socket}
 
       {:error, _message} ->

test/livebook_web/live/open_live_test.exs

@@ -232,13 +232,23 @@ defmodule LivebookWeb.OpenLiveTest do
   end
 
   describe "public import endpoint" do
-    test "imports notebook from the given url and redirects to the new session", %{conn: conn} do
+    test "imports notebook from the given url and downloads its files", %{conn: conn} do
       bypass = Bypass.open()
 
       Bypass.expect_once(bypass, "GET", "/notebook", fn conn ->
         conn
         |> Plug.Conn.put_resp_content_type("text/plain")
-        |> Plug.Conn.resp(200, "# My notebook")
+        |> Plug.Conn.resp(200, """
+        <!-- livebook:{"file_entries":[{"name":"image.jpg","type":"attachment"}]} -->
+
+        # My notebook
+        """)
+      end)
+
+      Bypass.expect_once(bypass, "GET", "/files/image.jpg", fn conn ->
+        conn
+        |> Plug.Conn.put_resp_content_type("text/plain")
+        |> Plug.Conn.resp(200, "content")
       end)
 
       notebook_url = "http://localhost:#{bypass.port}/notebook"
@@ -248,6 +258,12 @@ defmodule LivebookWeb.OpenLiveTest do
       {:ok, view, _} = live(conn, to)
       assert render(view) =~ "My notebook"
 
+      "/sessions/" <> session_id = to
+      {:ok, session} = Sessions.fetch_session(session_id)
+
+      assert FileSystem.File.resolve(session.files_dir, "image.jpg") |> FileSystem.File.read() ==
+               {:ok, "content"}
+
       close_session_by_path(to)
     end