Discrepancy between logged server URL and the URL in the `jpserver-*-open.html` file

[MetRonnie]

Description

When the default_url contains a hash (aka fragment) (our app uses vue-router with hash-based routing), e.g. default_url = /foo/#/workspace, there is a discrepancy between the full URL logged at startup vs the full URL in the jpserver-*-open.html file.

When the server starts up and logs the URL it is using

https://github.com/jupyter-server/jupyter_server/blob/2563baeca9575be7895930ada2b1d244f93e5163/jupyter_server/serverapp.py#L2153-L2158

https://github.com/jupyter-server/jupyter_server/blob/2563baeca9575be7895930ada2b1d244f93e5163/jupyter_server/serverapp.py#L2106-L2110

which results in

>>> parts = self._get_urlparts(include_token=True)
>>> list(parts)
[
  'http',
  'localhost:8888',
  '/foo/#/workspace',
  '',
  'token=blahblah42',
  '',
]
>>> parts.geturl()
'http://localhost:8888/foo/#/workspace?token=blahblah42'

This is incorrect as the token querystring has become part of the hash and therefore is not recognised as a querystring by the browser, and opening the URL results in the Jupyter page for logging in / entering the token manually.

Whereas the URL that gets outputted to the jpserver-xxxx-open.html file that actually gets opened is from tornado.httputil.url_concat

https://github.com/jupyter-server/jupyter_server/blob/2563baeca9575be7895930ada2b1d244f93e5163/jupyter_server/serverapp.py#L2671-L2675

which results in

>>> url = 'foo/#/workspace'
>>> url = url_concat(url, {'token': self.token})
'foo/?token=blahblah42#/workspace'
>>> url_path_join(self.connection_url, url)
'http://localhost:8888/foo/?token=blahblah42#/workspace'

which is correct as the querystring comes before the hash and everything works properly.

Reproduce

1. Use a default_url with a hash in it

Expected behavior

When handling default_url it should account for the possibility of a hash/fragment.

I should be able to come up with a quick fix for this, having debugged the issue to this extent. Otherwise I would say it would be safer to handle the URL the same way in each of the two cases, rather than the current different handling.

Context

• Operating System and version: N/A
• Browser and version: N/A
• Jupyter Server version: 2.7

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