static_url() is undefined in Jinja inside form.html

[luanabeckerdaluz]

Bug description

I am customizing jupyterhub templates by using images and css files stored in the jupyterhub static folder. When I need these images in the templates (page.html, login.html, spawner.html, etc.), I am accessing using the static_url() function with jinja. Nonetheless, I am not able to use this function or the functions url_for() and static() when calling it from inside kubespawner form.html. I also tried to access the STATIC_URL variable but the value was none.

Expected behaviour

The form.html file is used inside spawn.html in the object "{{spawner_options_form | safe}}". It is expected that some functions available by jinja when building jupyterhub templates also be available when building kubespawner form.html.

Actual behaviour

I think that Jinja is building the form html before insert this html in the spawner_options_form object of spawner.html. When building before, the function static_url() is undefined, while in the jupyterhub templates this function is defined. Below is shown the traceback when I tried to use this function in the html <img src="{{ static_url('images/cpu-ram.svg') }}>"

HTTPServerRequest(protocol='http', host='127.0.0.1:8081', method='GET', uri='/hub/spawn', version='HTTP/1.1', remote_ip='127.0.0.1')
Traceback (most recent call last):
File "/home/harmonize/.local/lib/python3.10/site-packages/tornado/web.py", line 1713, in _execute
  result = await result
File "/home/harmonize/.local/lib/python3.10/site-packages/jupyterhub/handlers/pages.py", line 207, in _get
  spawner_options_form = await spawner.get_options_form()
File "/home/harmonize/.local/lib/python3.10/site-packages/jupyterhub/spawner.py", line 542, in get_options_form
  options_form = await maybe_future(self.options_form(self))
File "/home/harmonize/git/jupyter-k8s/hub/config.py", line 216, in custom_options_form
  return self._options_form_default()
File "/home/harmonize/.local/lib/python3.10/site-packages/kubespawner/spawner.py", line 2974, in _options_form_default
  return self._render_options_form(self.profile_list)
File "/home/harmonize/.local/lib/python3.10/site-packages/kubespawner/spawner.py", line 2951, in _render_options_form
  return profile_form_template.render(profile_list=profile_list)
File "/home/harmonize/.local/lib/python3.10/site-packages/jinja2/environment.py", line 1301, in render
  self.environment.handle_exception()
File "/home/harmonize/.local/lib/python3.10/site-packages/jinja2/environment.py", line 936, in handle_exception
  raise rewrite_traceback_stack(source=source)
File "templates/form.html", line 72, in top-level template code
  <img  src="{{ static_url('images/cpu-ram.svg') }}">
File "/home/harmonize/.local/lib/python3.10/site-packages/jinja2/utils.py", line 83, in from_obj
  if hasattr(obj, "jinja_pass_arg"):
jinja2.exceptions.UndefinedError: 'static_url' is undefined

Your personal set up

• OS:
  • Linux Mint 21.2 Cinnamon Kernel 5.15.0-78-generic
• Version(s):
  • jupyterhub = 4.0.1.
  • I tested kubespawner versions 6.0.0 and 6.0.1-dev0.

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[yuvipanda]

We create our own jinja2 environment here:

kubespawner/kubespawner/spawner.py

Line 2943 in 6d9d9a3

profile_list = self._get_initialized_profile_list(profile_list)

. static_url and other helpers come from this jinja_env that is setup by JupyterHub (not kubespawner).

I'm not sure what exactly is the best way to move forward here.

[consideRatio]

Kubespawner renders a jinja2 template into another jinja2 template, is fix fix to ensure that static_url is parsed by the second jinja2 template rendering done by jupyterhub?

[yuvipanda]

Kubespawner renders a jinja2 template into a string, that is then passed onto JupyterHub via options_form which expects a string. That is then rendered onto a jinja2 template.

I think the cleanest way perhaps is to add templating support into upstream JupyterHub for options forms, and move #724 there.