Support for Websocket Denial Response

[paulo-raca]

When a websocket endpoint throws an exception (e.g., because of invalid authentication), we currently end with either with a generic 403 response (triggered by "websocket.close" message) or a generic HTTP500 response (if there is an unhandled error)

Instead, it is better to return useful HTTP error responses using the Websocket Denial Response ASGI extension, if it is available

This PR makes several changes in order to support this extension:

• Added WebsocketDenialResponse class to return a HTTP Response to a websocket request (if the extension is supported, otherwise just closes with code 403 as before)
• AuthenticationMiddleware and @requires have been updated (Fixes Wrong unauthorized WebSocket status code #1362)
• HTTPSRedirectMiddleware has been updated
  • Improved the URL mapping code
  • Added an argument to specify the port mappings (e.g., if the app is running on ports 8080/8443 instead of 80/443)
• ExceptionMiddleware and ServerErrorMiddleware have been updated to take advantage of it
  • Both classes have been refactored to share code, and a new BaseExceptionMiddleware superclass was added
  • ExceptionTypeOrStatusCode and ExceptionHandler types were added to simplify typing annotations
  • Error handlers now take a HTTPConnection instead of a Request

[paulo-raca]

Here is a simple demo (Based on FastAPI):

(It needs to be executed with hypercorn, as it is the only ASGI server currently supporting this extension)

app = FastAPI(debug=True)

@app.websocket("/ws")
async def websocket_endpoint(ws: WebSocket, err: int = None):
    if err == 500:
        raise Exception("Internal Server Error")
    elif err is not None:
        raise HTTPException(status_code=err)
    await ws.accept()
    await ws.send_text("Hello")

No error:

$python -m websockets "ws://localhost:8000/ws"
Connected to ws://localhost:8000/ws.
< Hello
Connection closed: 1000 (OK).

With custom HTTP code:

$ python -m websockets "ws://localhost:8000/ws?err=404"
Failed to connect to ws://localhost:8000/ws?err=404: server rejected WebSocket connection: HTTP 404.

Response body:
{"detail":"Not Found"}

With uncaught exception

$ python -m websockets "ws://localhost:8000/ws?err=500"
Failed to connect to ws://localhost:8000/ws?err=500: server rejected WebSocket connection: HTTP 500.

Response body:

Traceback (most recent call last):
  [...]
Exception: Internal Server Error

[paulo-raca]

Superseeded by #1315

[Kludex]

Superseded by #1535 actually.