Custom Error Pages

[terrytrent]

I may be missing a way to do this, but as far as I can see error pages are generated from nicegui.error.error_content

I would like the ability to fully customize the error page, or entirely overwrite the error_content function.

I see this as the error function being converted into a class, allowing inheritance and modification. A new argument could be added ui.run specifying the new class to generate the error pages.

[rodja]

Thanks. I like the idea. An alternative to passing a builder to ui.run we introduce a new decorator:

@ui.error_page(404)
def page_not_found():
    ui.label('Sorry, this page does not exist')

[iron3oxide]

This would be a great addition! I find myself raising different HTTPExceptions quite a bit and having the sleek nicegui error page for 404s but an ugly text response for 401s is a bit meh. Of course I could use the solution below, but it is not as nice to use as a decorator would be.

[rodja]

You can already overwrite the error handling of NiceGUI by doing something like this:

from nicegui import ui, Client
from nicegui.page import page

@app.exception_handler(404)
async def exception_handler_404(request: Request, exception: Exception) -> Response:
    with Client(page('')) as client:
        ui.label('Sorry, this page does not exist')
    return client.build_response(request, 404)

[kleynjan]

For those trying this at home in 2024, note that to create the Client object you now have to pass the request object:

from nicegui import ui, Client
from nicegui.page import page

@app.exception_handler(404)
async def exception_handler_404(request: Request, exception: Exception) -> Response:
    with Client(page(''), request=request) as client:
        ui.label('Sorry, this page does not exist')
    return client.build_response(request, 404)

My 500 handler is based on this -- which thanks to theme.py (see modularization example) keeps the user nicely in the app context rather than "throw them out" of the app, while sending the stack trace to support:

@app.exception_handler(500)
async def exception_handler_500(request: Request, exception: Exception) -> Response:
    stack_trace = traceback.format_exc()
    msg_to_user = f"**{exception}**\n\nStack trace: \n<pre>{stack_trace}"

    if OTAP == 'P':   # production -> send trace by mail & nice soothing message
        mailres = send_mail_somehow(from, to, etc, etc, msg_to_user)
        msg_to_user = _("Incident has been reported, repair is underway.")

    with Client(page(''), request=request) as client:
        with theme.frame("error"):
            with ui.card().classes("error-card"):
                ui.label(_("500 Application Error")).classes("heading")
                ui.markdown(msg_to_user).classes("message")
    return client.build_response(request, 500)