404 error page not rendered on static file routes

[falkoschindler]

Description

As noticed by @Anindya088 (#2568), the 404 error page isn't rendered correctly when accessed via a (sub-)path of a static route. Take this code for example:

app.add_static_files('/static', '.')
ui.link('Static', '/static')

When visiting /static or /static/subpage, the HTML page is displayed, but without any CSS and JS assets. They are requested from a wrong path and, thus, not used for rendering the page.

[rodja]

Thanks for the PR, @Lucas-lyh. It made me dig a bit deeper into the issue. I think the problem was introduced with #848 which sets the path prefix to scope['root_path'] -- which is correct in my opinion:

nicegui/nicegui/client.py

Line 116 in cc7770e

prefix = request.headers.get('X-Forwarded-Prefix', request.scope.get('root_path', ''))

But, app.add_static_files uses app.mount internally:

nicegui/nicegui/app/app.py

Line 156 in cc7770e

self.mount(url_path, StaticFiles(directory=str(local_directory), follow_symlink=follow_symlink))

This is defined in the ASGI standard to alter the scope['root_path'] -- which is not desired in this case. Because there is no way to tell the FastAPI/Starlette (which implements ASGI) to not alter scope['root_path'], we may be forced to implement app.add_static_files in some other way :-(