Found an edge case issue while working on a new uvicorn rust port #383

Hypercorn’s HTTP/3 path was not propagating some QUIC disconnect events to the ASGI application.

When a client aborted an HTTP/3 request using RESET_STREAM, or when the whole QUIC connection terminated, Hypercorn could see that at the QUIC layer, but the corresponding ASGI app did not receive:

{"type": "http.disconnect"}

This means an application waiting on receive() could continue waiting even though the client was already gone.

Client
  |
  | RESET_STREAM / connection close
  v
aioquic
  |
  | QUIC event
  v
Hypercorn H3Protocol
  |
  X  event was not propagated to the request stream
  |
  v
ASGI application never receives http.disconnect

Reproduce:

async def app(scope, receive, send):
    while True:
        message = await receive()
        print(message)

Start Hypercorn with HTTP/3 enabled.
Open an HTTP/3 request.
Abort the request before it completes, causing a QUIC RESET_STREAM.
Observe the ASGI messages.

Specs

ASGI HTTP spec: closed HTTP connections are represented to the application using http.disconnect.
RFC 9114: HTTP/3 requests may be cancelled using QUIC stream mechanisms.
RFC 9000: QUIC defines RESET_STREAM and connection termination behavior.