Endpoint class decorators

I need to implement a decorator for an endpoint, and for some technical reasons, I would like to implement it with a class. I also would like my decorator to not need parenthesis when called. (i.e. prefer @my_decorator over @my_decorator()).

Here is a simple implementation:

from starlette.responses import JSONResponse
from starlette.applications import Starlette
from starlette.routing import Route


class foobar:
    def __init__(self, func):
        self.func = func

    def __call__(self, *args, **kwargs):
        return self.func(*args, **kwargs)


@foobar
def my_endpoint(request):
    return JSONResponse({"response": "my_endpoint"})


app = Starlette(
    debug=True,
    routes=[
        Route('/my_endpoint', my_endpoint),
    ],
)

But accessing to /my_endpoint produces this traceback:

Traceback (most recent call last):
  File "~/myproject/env/lib/python3.8/site-packages/uvicorn/protocols/http/httptools_impl.py", line 385, in run_asgi
    result = await app(self.scope, self.receive, self.send)
  File "~/myproject/env/lib/python3.8/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
    return await self.app(scope, receive, send)
  File "~/myproject/env/lib/python3.8/site-packages/starlette/applications.py", line 102, in __call__
    await self.middleware_stack(scope, receive, send)
  File "~/myproject/env/lib/python3.8/site-packages/starlette/middleware/errors.py", line 178, in __call__
    raise exc from None
  File "~/myproject/env/lib/python3.8/site-packages/starlette/middleware/errors.py", line 156, in __call__
    await self.app(scope, receive, _send)
  File "~/myproject/env/lib/python3.8/site-packages/starlette/exceptions.py", line 82, in __call__
    raise exc from None
  File "~/myproject/env/lib/python3.8/site-packages/starlette/exceptions.py", line 71, in __call__
    await self.app(scope, receive, sender)
  File "~/myproject/env/lib/python3.8/site-packages/starlette/routing.py", line 551, in __call__
    await route.handle(scope, receive, send)
  File "~/myproject/env/lib/python3.8/site-packages/starlette/routing.py", line 228, in handle
    await self.app(scope, receive, send)
  File "./app.py", line 11, in __call__
    return self.func(*args, **kwargs)
TypeError: my_endpoint() takes 1 positional argument but 3 were given

I am not really sure what is going wrong here. I also did not find documentation about endpoint decorators with starlette. Do I make mistakes when defining my decorator or is it something not supported by starlette?

PS: I used starlette 0.13 and python 3.8

[Davmuz]

It’s still relevant to me, I used a nasty workaround in several projects.

[tomchristie]

AFAIU the purpose of the ASGI part of Route() is to support HTTPEndpoint and others — i.e. class-based views, which do implement ASGI.

Right. And actually thinking about it, we don’t need to be doing that.

The request/response function to Route needs to accept a request and return a response. I’d assumed we can do that on CBV’s because eg init just returns the class instance. (So eg in Django there’s a ViewClass.as_view() hoop that users jump through.)

My solution had been “okay, let’s have Route accept either a request/response function, or an ASGI app. Then CBVs can be implemented as mini ASGI apps)

Happily, in our case I think instantiating the CBV can be the request/response function, because “response” here just means, an ASGI callable. So… if the CBV init method accepts a request, and if call implements the ASGI interface and handles dispatch, then the classes are request/response callables.

We can then drop the “Route can also be an ASGI app” case, because we don’t really need it. Mount is appropriate for pointing at apps, Route is appropriate for pointing as req/response callables.