Add on_connect/on_disconnect hooks to ASGI app, support connection context

[rafalp]

Adds on_connect and on_disconnect options to ASGI GraphQL app and introduces connection context.

on_connect

on_connect is optional callable that is called when GraphQL client opens WebSocket connection with the server. It's called with two arguments: WebSocket instance and Any value with connection payload. It can be used to extract supported data from connection's payload to the current scope:

def on_connect(ws: WebSocket, payload: Any):
    if not isinstance(payload, dict):
        return

    ws.scope["auth"] = get_user_from_token(payload.get("auth_token"))


def get_context_value(request):
    if request.scope.type == "websocket":
        return {"auth": request.scope["auth"]}
    
    return {"auth": get_user_from_token(request.headers.get("authorization")}

As bonus, users may raise new WebSocketConnectionError from on_connect to get nice error masse sent to client:

from ariadne.asgi import WebSocketConnectionError


def on_connect(ws: WebSocket, payload: Any):
    if not isinstance(payload, dict):
        raise WebSocketConnectionError({"message": "payload object is required", "code": "payload.value_error"})

    ws.scope["auth"] = get_user_from_token(payload.get("auth_token"))

on_disconnect

on_disconnect is optional callable that is called when GraphQL client closes websocket connection. Receives one argument: WebSocket instance.

def on_disconnect(ws):
    # get some data from WS scope and maybe log it somewhere or set user from `ws.scope` to offline?

Supersedes #406, #403 and #355.

[lgtm-com]

This pull request introduces 1 alert when merging 2c0a2de into a732a7c - view on LGTM.com

new alerts:

• 1 for Unused import

[codecov]

Codecov Report

Merging #488 (1612d11) into master (903d217) will increase coverage by 0.02%.
The diff coverage is 99.24%.

@@            Coverage Diff             @@
##           master     #488      +/-   ##
==========================================
+ Coverage   98.16%   98.19%   +0.02%     
==========================================
  Files         104      104              
  Lines        5125     5253     +128     
==========================================
+ Hits         5031     5158     +127     
- Misses         94       95       +1     

Impacted Files	Coverage Δ
ariadne/asgi.py	95.49% <97.36%> (+0.28%)	⬆️
tests/asgi/test_websockets.py	100.00% <100.00%> (ø)

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[lgtm-com]

This pull request introduces 1 alert when merging 27d6071 into 903d217 - view on LGTM.com

new alerts:

• 1 for Unused import

[ammurdoch]

This is great! When can y'all get this released?