Routing problems when using ui.sub_pages behind a reverse proxy

[SirTaros]

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Example Code

from nicegui import ui, page
from fastapi import FastAPI

app = FastAPI()

@ui.page("/")
@ui.page("/{_:path}")
def router():
    page_router = ui.sub_pages({
        '/home': home,
        '/other': other,
    }, root_path= "/mount")


#@ui.page("/other")
def other():
    ui.label("Other Site")
    ui.button(text="Go to home", on_click=lambda:ui.navigate.to("/home"))

#@ui.page("/home")
def home():
    ui.label("Home Site")
    ui.button(text="Go to other", on_click=lambda:ui.navigate.to("/other"))

ui.run_with(app, mount_path="/mount")

Description

Config

I run my NiceGUI web server with FastAPI for my API requests on a Uvicorn server. Everything runs in a Docker container.
My server has a Caddy reverse proxy and forwards any traffic with a specific URL — in this case /mount/ — through Uvicorn to NiceGUI.
I tried to create a one-site solution, where I have my main site for the header and so on, and load the pages as sub_pages. I simulated the reverse proxy here with the mount_path.

Problem

The same error occurs with both the reverse proxy and the mount_path used here for the MRE.
If I enter the URL in my browser and hit enter, it finds the site without a problem. But if I try to navigate my page with the buttons, I get a 404 page /home not found. The same happens with /other.

Additional Info

I don’t know if it’s my mistake or a problem within the sub_pages function, because it behaves as expected if you comment out the @ui.page on the router function and use the currently commented ui.page functions directly on home and other.

My tests

I tried many things, like stripping the extra path from the URL in Caddy, using --root-path in Uvicorn or
forwarding the complete URL to NiceGUI and handling it there. But every time something breaks with the URL.

I also tested ui.sub_pages with and without root_path, but the issue still occurs in all cases.

Adding the /mount/ to the navigate functions just adds a second /mount/ to the url and then it works, but it wont work for hitting enter in the Browser because of the second /mount/

I hope someone can help with my problems.

NiceGUI Version

2.23.3

Python Version

3.13.7

Browser

Safari, Firefox

Operating System

Linux

Additional Context

No response

[rodja]

Yes. There is room for improvement. I identified the issue and will prepare a PR later in the day.