Render with Panel button breaks with Jupyterlab root_dir

[govinda18]

ALL software version info

Jupyterlab 3.2.8
Panel master

Description of expected behavior and the observed behavior

Hi team, jupyterlab allows you to set a custom root_dir and preferred_dir config for your server app. You can set it using the following:

$ jupyter notebook --generate-config

Then in your ~/.jupyter folder you should find jupyter_notebook_config.py and there we can set a configuration like:

## The directory to use for notebooks and kernels.
#  Default: ''
c.ServerApp.root_dir = '/'
## Preferred starting directory to use for notebooks and kernels.
#  Default: ''
import os
c.ServerApp.preferred_dir = os.getcwd()

Now when you launch jupyter, the jupyter extensions get file path relative to the root_dir. So suppose you launch your lab from /home/gt and root dir is set to / and we try to render a panel preview for a file located at /home/gt/notebook.ipynb, this will break as the path passed to the PanelHandler.get is actually home/gt/notebook.ipynb but the bokeh utility here tries to get abspath which is relative to cwd (which is /home/gt) and it turns out to be /home/gt/home/gt/notebook.ipynb.

Here, what the PanelHandler should be doing is setting the path to bokeh as root_dir + path. A good example is the FileContentsManager of jupyter extension. As you can see here, for all the utility it evaluates the path relative to the root dir.

Complete, minimal, self-contained example code that reproduces the issue

import panel as pn
pn.extension()
pn.pane.Markdown("# Test").servable()

This simple code throws 500 Internal server errors if the following configuration is done -

c.ServerApp.root_dir = '/'
import os
c.ServerApp.preferred_dir = os.getcwd()

and the lab is launched from a directory other than the root_dir. What the above config does is it allows you to access files outside your cwd as well from the lab.

Stack traceback and/or browser JavaScript console output

ERROR 00:22:44 Uncaught exception GET /panel-preview/render/home/totla/Untitled.ipynb (10.218.24.254)

    HTTPServerRequest(protocol='https', host='myhost.com', method='GET', uri='/panel-preview/render/home/totla/Untitled.ipynb', version='HTTP/1.1', remote_ip='10.218.24.254')
    Traceback (most recent call last):
      File "/usr/local/python/python-3.9/std/lib64/python3.9/site-packages/tornado/web.py", line 1704, in _execute
        result = await result
      File "/usr/local/python/python-3.9/std/lib64/python3.9/site-packages/panel/io/jupyter_server_extension.py", line 93, in get
        app = build_single_handler_application(path)
      File "/usr/local/python/python-3.9/std/lib64/python3.9/site-packages/bokeh/command/util.py", line 135, in build_single_handler_application
        raise ValueError("Path for Bokeh server application does not exist: %s" % path)
    ValueError: Path for Bokeh server application does not exist: /home/totla/home/totla/Untitled.ipynb

Proposed Fix

A simple fix here would be similar to what FileContentManager does:

def get_abs_path(self, path):
    try:
        # May be there is a better way to do this
        root_dir = self.application._app.settings['config']['ServerApp']['root_dir']
    except:
        import os
        root_dir = os.getcwd()
    return root_dir + path  

# To be added here https://github.com/holoviz/panel/blob/master/panel/io/jupyter_server_extension.py#L84
path = self.get_abs_path(path)

Similarly, this should be done for PanelWSHandler as well. I was able to make it work with the above change. If this looks fine, I would be happy to raise a PR too. Please let me know if you feel there is a better way to achieve the same.

[philippjfr]

Thanks @govinda18! Would absolutely love to see a PR with your suggested changes.

[govinda18]

Done.