Unmounting mounted app

[matan1008]

Hey!
I thought it might be cool (and useful in my case) to unmount mounted apps.
Would be greate if you could check #2027

Thanks a lot!

[Kludex]

What's the use-case?

[matan1008]

Sure!

app = FastAPI()
subapps_manager = SubappsManager()


# Adding a subapp works fine
@app.post('/subapps/{name}')
async def add_subapp(request: Request, name: str):
    subapp = subapps_manager.get_subapp(name)
    app.mount(f'/{name}', subapp)
    return JSONResponse({})


# Deleting subapp missing API in my opinion
@app.delete('/subapps/{name}')
async def delete_subapp(request: Request, name: str):
    ...

My suggestion (and the PR that follows):

app = FastAPI()
subapps_manager = SubappsManager()
mounted_apps = {}


@app.post('/subapps/{name}')
async def add_subapp(request: Request, name: str):
    subapp = subapps_manager.get_subapp(name)
    mounted_apps[name] = app.mount(f'/{name}', subapp)
    return JSONResponse({})


@app.delete('/subapps/{name}')
async def delete_subapp(request: Request, name: str):
    app.unmount(mounted_apps[name])
    del mounted_apps[name]
    return JSONResponse({})

[alex-oleshkevich]

Thanks! This is a very untypical use case. Not sure it this should be a part of Starlette.

Alternatively you can:

1. subclass Mount and modify app.routes.routes
2. or, have a middleware that properly routes users to a specific route branches

I would personally go with 2 as the most flexible and error-prone solution.

[matan1008]

Thanks a lot!
I am facing a similar problem - how to remove an added middleware?

[alex-oleshkevich]

I mean, you don't need to remove it. In the middleware, check who is the user and allow/deny access to the sub route.

It may look like this:

def can_access(user, subapp) -> bool:
    """some logic to test if user can access subapp"""

def GuardMiddleware:
    def __init__(self, app):
        self.app = app

    async def __call__(self, scope, receive, send):
        request = Request(scope, receive, send)

        if 'subapps/admin' in request.url.path and can_access(request.user, 'admin'):
            return await self.app(scope, receive, send) # grant

        if 'subapps/anotherapp' in request.url.path and can_access(request.user, 'anotherapp'):
            return await self.app(scope, receive, send) # grant

		response = PlainTextResponse('Forbidden', 403)
        await response(scope, receive, send) # forbid

[matan1008]

Sorry, I didn't explain the use case well enough. First, I want load the sub application dynamically (literally, using importlib) - in my example the get_subapp would return different app each time. Second, after loading the app all users should be able to access it and after removing it no one should be able to access it