[Django] #35703: default URLconf detection does not take a prefix into account

[Django]

#35703: default URLconf detection does not take a prefix into account
-------------------------------------+-------------------------------------
Reporter: Maarten Breddels | Type: Bug
Status: new | Component:
| Uncategorized
Version: 5.1 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Hi,

When Django runs onder a prefix (often described by SCRIPT_NAME for
cgi/wsgi or root_path in asgi land) the default URLconf is not detected.
The default page shown is then:

{{{
Page not found (404)
Request Method: GET
Request URL: http://127.0.0.1:8000/_app/m05jjd2cn5gycxqcowk/
Using the URLconf defined in mysite.urls, Django tried these URL patterns,
in this order:

admin/
The empty path didn’t match any of these.

You’re seeing this error because you have DEBUG = True in your Django
settings file. Change that to False, and Django will display a standard
404 page.
}}}

(in this case, the asgi root_path is `/_app/m05jjd2cn5gycxqcowk`)

While instead, I expected to see the nice default page with
{{{
The install worked successfully! Congratulations!
}}}

The bug was introduced in
https://github.com/maartenbreddels/django/commit/0ecb9f6e2514cfd26a678a280d471433375101a3
which uses `request.path == '/'` for comparison, while `request.path_info
== '/'` was probably the intent. This commit was part of
https://github.com/maartenbreddels/django/commit/3f1c7b70537330435e2ec2fca9550f7b7fa4372e

Note that `request.path` includes the prefix (SCRIPT_NAME or root_path),
while `request.path` does not.

I hit this bug when trying to run Django on [https://py.cafe], a platform
that can run web applications on Pyodide.

The project at:
https://py.cafe/maartenbreddels/django-start-template (which includes this
patch)
now runs fine because I monkey-patched it (see
https://py.cafe/files/maartenbreddels/django-start-
template/django_patch.py), showing this is a correct fix.

For technical reasons, we need to run under a prefix (we configure
root_path in the asgi scope), and django was giving me a 404. This gave
the (false) impression django did not support running under a prefix
(StackOverflow falsely confirmed this suspicion).

I already opened a PR at https://github.com/django/django/pull/18505
showing the change required. I'm happy to reopen that PR and do minor work
on it, but I don't think I'll have the bandwidth to add a test.


Regards,

Maarten Breddels
--
Ticket URL: <https://code.djangoproject.com/ticket/35703>
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