Implement CBV pattern

[jordaneremieff]

Refs #27

This is an attempt to define a CBV pattern in Starlette.

Example usage:

from starlette import PlainTextResponse
from starlette.app import App
from starlette.views import View


app = App()


class HomepageView(View):
    async def get(self, request, **kwargs):
        response = PlainTextResponse(f"Hello, world!")
        return response


class UserView(View):
    async def get(self, request, **kwargs):
        username = kwargs.get("username")
        response = PlainTextResponse(f"Hello, {username}")
        return response


app.add_route("/", HomepageView())
app.add_route("/user/{username}", UserView())

[tomchristie]

I'm kinda thinking that we'll drop the asgi_application/make_asgi decorator altogether - I think it just muddies things up.

Let's leave this alone for now, but perhaps don't use it in the PR, and include any logic directly in the class.

[tomchristie]

Do we need to do the same closure .as_view() dance that Django does?

Rather than using .as_view() I figure that we just implement the endpoint/view/whatever class as an ASGI application. We're not using multi-threading so I don't think we need the same "put stuff in a closure for safety" dance, but maybe I'm not thinking it through enough.

[jordaneremieff]

I made some changes based on your comments - removed the as_view() and make_asgi methods from the view class. Still a bit more to do here when I have time, but those changes were simple enough to push for now.

[tomchristie]

I’d also suggest we drop support for the handler methods being non-awaitable. Let’s just cover async stuff in Starlette.

[jordaneremieff]

I've made the following updates to this PR:

• View class now only supports async methods
• Returns '404 Not found' if an allowed method is unimplemented on the view class rather than raising exception
• Intended to be used with App() class add_route method, previousadd_route method on Router removed
• Documentation with brief description and example code added
• Tests added

[tomchristie]

Coolio!

One observation: We’ll want to make sure that each request gets a new instance, rather than routing to an instance of the class.

Also, use 406 for the method-does-not-exist-on-this-class case.

Good stuff!

[tomchristie]

Added some further commits on top of this, in #52. Thanks so much for this!

[delijati]

hi @tomchristie can this be also added to the docs ... i found only this here

[foxmask]

@delijati that was the case before the doc changed 0.12.0...master

[tomchristie]

@foxmask @delijati https://www.starlette.io/endpoints/ (Or are we talking about something else?)

[foxmask]

@tomchristie if that were endpoints here
0.12.0...master#diff-1a523bd9fa0dbf998008b37579210e12
then yes ;)

edit the pasted URL does not work fine so ... I wanted to show you :

0.12.0...master

then > "file changed" then we can see the docs/index.md

[tomchristie]

We're not documenting a pure ASGI class, nope. We don't really need to in ASGI 3, since it's easier to write them as plain functions.

What we are documenting is the class-based HTTPEndpoint and WebSocketEndpoint implementations, which is actually what you want if you're looking for an CBV implementation.