Trio support.

[tomchristie]

Via https://gitter.im/python-trio/general?at=5e2fe9b940da694c5edc8d70

It'd be nice to have Starlette support both Trio and Asyncio.

Currently it's an asyncio-only framework, but there's actually not many places where we're tied to asyncio, with the exception of a bunch of "if this callable is a plain function then call into with with run_in_threadpool, otherwise await it.".

I think the other places are:

• The WSGI middleware (optional). Currently has an asyncio-based implementation.
• The BaseHTTPMiddleware class (optional), that provides a request/response middleware interface to develop against, rather than directly writing against ASGI. Again, currently has an asyncio-based implemention.
• One weird part of the request model, .is_disconnected - that I think is structured as an anti-pattern and probably needs rethinking.
• The graphene-based GraphQL async executor, which probably ought to come out of the core package anyways.
• The existing TestClient, which we oughta replace with httpx now anyways, which does have trio+asyncio.

Short: Tweaking our run_in_threadpool function to use sniffio and then either call trio's threadpooling or asyncio's threadpooling would be sufficient as a starting point to start using Starlette with Trio.

[gdhameeja]

I'm taking this up.

[jtrakk]

@gdhameeja Can you share a link to your repo so we can follow along?

[tammoippen]

Also, FileResponse uses aiofiles, which is asyncio based. Here the trio i/o could be used?

Edit: And StaticFiles.

[parity3]

I figured these possible alternatives / POC / intermediate steps are worth mentioning here.

• trio-asyncio
• anyio

[pquentin]

For what it's worth, here's an example of Uvicorn + Starlette + FastAPI running with trio-asyncio: python-trio/trio-asyncio#84

[uSpike]

I'm taking this up.

@gdhameeja any updates? I'd like to take a stab at using anyio if nobody else is working on this.

[uSpike]

I took an initial stab at using anyio in #1157

It was surprisingly easy but I'd like some feedback if anyone would be so kind. There's a few things left to do/fix. All done!

[espetro]

Hi! Thanks for such an amazing work 🙌🏼 , I cannot wait to try trio with Starlette. How are we supposed to enable it? There's only documentation for TestClient.

[Sxderp]

@espetro For a very simple web server. In this I use hypercorn (runs the server) + starlette (handles the processing). 90% of Starlette worked on trio before the anyio patch. There were just a few bits (error handling is one I can think of) that failed / cashed. You really don't have to do anything to "enable" trio. Your web server (in my case hypercorn) is doing most of the heavy lifting.

import trio
from hypercorn.config import Config
from hypercorn.trio import serve
from starlette.applications import Starlette
from starlette.responses import JSONResponse
from starlette.routing import Route

class IPC(Starlette):
    def __init__(self):
        super().__init__(routes=[Route('/index', self._index)])

    async def _index(self, request):
        return JSONResponse({'foo': 'bar'}, status_code=200)


async def bootstrap():
    hyper_config = Config.from_mapping({'bind': '127.0.0.1:56601'})
    async with trio.open_nursery() as nursery:
        nursery.start_soon(serve, IPC(), hyper_config)


if __name__ == '__main__':
    trio.run(bootstrap)

And then

$ curl http://127.0.0.1:56601/index
{"foo":"bar"}