URL rewrite + internal development server: how to?

[the-vindicar]

I'm running a small Quart project behind an nginx proxy. The project makes use of internal server via app.run_task(), since its load is expected to be very low (a single user thing). nginx is doing a simple proxying and URL rewrite, sending all requests starting with /prefix to the app, but also removing said /prefix.

The problem is, since the app itself has no idea about the rewrite, url_for() generates URLs without the /prefix. How do I configure the app to do otherwise? Basically, I don't want any incoming URLs to change - only what's generated via code.

I've tried setting SCRIPT_NAME, both via nginx config and directly as app environment, to no avail.

An example to clarify what I'm looking for:

import quart

app = quart.Quart(__name__)
app.config['SERVER_NAME'] = '127.0.0.1:8080'
app.config['APPLICATION_ROOT'] = '/foo'


@app.get('/test')
async def test():
    return 'This is a test, lol!'


@app.get('/')
async def root():
    # I want this to return "http://127.0.0.1:8080/foo/test"
    # Instead it returns "http://127.0.0.1:8080/test"
    return quart.url_for('test', _external=True)


async def main():
    from pprint import pprint
    pprint(dict(app.config))
    await app.run_task('127.0.0.1', 8080)


if __name__ == '__main__':
    import asyncio
    asyncio.run(main())

[the-vindicar]

I also tried this approach:
myapp.py

import quart
from hypercorn.middleware import ProxyFixMiddleware

app = quart.Quart(__name__)
app.asgi_app = ProxyFixMiddleware(app.asgi_app, mode='legacy', trusted_hops=1)
...  # same things after that

Nginx config:

    location /foo/ {
        proxy_pass http://127.0.0.1:8080/;  # trailing / equals rewrite of '/foo/' into '/'. This part works.
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-Forwarded-Prefix /foo;
    }

Still no luck. Test app shows that headers are being passed, but middleware doesn't seem to do anything...

[the-vindicar]

So after picking the framework apart over a couple of days, I've come to the conclusion that the dev server does not support this.
Which is a shame, since switching over to hypercorn would be pointless, as I would be stuck with maxworkers=1 anyway because of the way my app is structured (webserver is not its main component, but other components register blueprints of their own).

As such, I've come up with this hack. I replace url map class to enforce it always returns a prefixed map adapter. This way only URL building is affected, but not URL routing. You might want to

import quart
from quart.routing import QuartMap
from werkzeug.routing import MapAdapter


class CustomQuartMap(QuartMap):
    PREFIX = ''

    def bind_to_request(self, *args, **kwargs) -> MapAdapter:
        adapter = super().bind_to_request(*args, **kwargs)
        adapter.script_name = self.PREFIX + adapter.script_name
        return adapter

    def bind_to_environ(self, *args, **kwargs) -> MapAdapter:
        adapter = super().bind_to_environ(*args, **kwargs)
        adapter.script_name = self.PREFIX + adapter.script_name
        return adapter


quart.Quart.url_map_class = CustomQuartMap
app = quart.Quart(__name__)

You can configure CustomQuartMap.PREFIX any way you want, as long as you're only running one app in your script.
If it's not the case, you will have to find a way to pass app reference to your custom map, maybe via an attribute you set immediately after creating the app.

[aenglander]

You should be able to add a middleware to accomplish this.

[the-vindicar]

Yeah I have attempted that. However, as far as I was able to get, it appears that via middleware (such as DispatcherMiddleware or its ASGI equivalent) I can only modify the scope, which adds the prefix to both incoming query URLs and outgoing generated URLs. As in, instead of / and /test I need to route /foo/ and /foo/test.
I don't want that, but it is indeed a possible solution, if I reconfigure Nginx to use the prefix to match URLs without actually rewriting them. At this point I'm not entirely sure which way is preferable.

But still, thanks for your response.