ReactPy ASGI App and Middleware

[Archmonger]

Current Situation

Currently we perform ASGI routing via backend-specific APIs. However, it is much easier to gain broad compatibility via ASGI middleware. Additionally, we should have a "standalone" mode where ReactPy can run in a production configuration without any backend.

I originally pitched this concept a long time ago during our development of our configure() function.

Proposed Actions

Create a ReactPy ASGI application that can also function as middleware.

Interface Design

# This is "standalone mode"
from reactpy.backend import ReactPy

app = ReactPy(my_component)

# This is "middleware mode"
from reactpy.backend import ReactPy
from sanic import Sanic

sanic = Sanic()
app = ReactPy(sanic)

Implementation Draft

import re

from asgiref.compatibility import guarantee_single_callable

class ReactPy:
    def __init__(
        self,
        application=None,
        dispatcher_url="reactpy/stream/${route}${query}",
        modules_url="reactpy/modules",
        static_url="reactpy/assets",
    ) -> None:
        self.user_app = guarantee_single_callable(application)
        self.url_patterns = "|".join((dispatcher_url, modules_url, static_url))

    async def __call__(self, scope, receive, send) -> None:
        """The ASGI callable. This determines whether ReactPy should route the the
        request to ourselves or to the user application."""
        if not self.user_app or re.match(self.url_patterns, scope["path"]):
            await self.reactpy_app(scope, receive, send)
        else:
            await self.user_app(scope, receive, send)

    async def reactpy_app(self, scope, send, receive) -> None:
        """The ASGI application for ReactPy."""
        # This will handle the following: `index.html` view, component dispatcher, web modules, and static files.

[Archmonger]

@rmorshea I can also develop a WSGI variant of this. However, it will only work with WSGI webservers that have official websocket support: werkzeug, gunicorn, eventlet, and gevent.

The design of this would be largely based on flask-sock.

[rmorshea]

If we could take a similar approach to simplifying the flask/tornado backends that would be good too. If not, doesn't seem necessary. Regardless, probably should be done in a separate PR.

[Archmonger]

WSGI middleware would grant us compatibility with the following frameworks: https://wsgi.readthedocs.io/en/latest/frameworks.html

Unfortunately tornado uses its own custom API, so we would either need to drop support for tornado or keep using configure() for it. To be honest, I'm leaning towards dropping support because tornado does not have built-in integration with Jinja template tags.

[Archmonger]

I'm realizing that tornado support should almost certainly be spun off into its own package, similar to ReactPy-Django.