Set ws-url data attribute to access notebook terminal via a specific base URL for websockets

notebook/templates/terminal.html

@@ -7,6 +7,7 @@
 {% block params %}
 
 data-base-url="{{base_url | urlencode}}"
+data-ws-url="{{ws_url | urlencode}}"
 data-ws-path="{{ws_path}}"
 
 {% endblock %}