ServerSentEvent management in Granian

[ffr27]

Hi,

I'm implementing a REST API application (of course in python) using Litestar which is served by a granian web server.

Requesting a specific endpoint results in open a notification streams based on SSE. The response is a basic AsyncGenerator as described in litestar SSE response documentation.

async def notification_publisher(
        self,
        dynamic_id,
        application_service: ApplicationService,
        channels: ChannelsPlugin
    ) -> AsyncGenerator[SSEData, None]:
        # Seems to be needed to trigger the first reply (header)
        #yield ServerSentEventMessage(None)

        subscriber = await channels.subscribe(str(dynamic_id))
        async for notification in subscriber.iter_events():
            yield ServerSentEventMessage(data=f"{notification.decode()}")

When testing this endpoint, I don't get any header response while I don't get notified and then send a first SSE notification (the yield in the async for loop is not reached). I was exepecting to get at least an HTTP header response.
Is it an expected behaviour from granian ? Is it possible to set up something to change the behaviour ?

I tried the same piece of code using hypercorn and resulting in the expected behavior.

I can provide wireshark capture if needed.

Thanks.

[gi0baro]

Is it an expected behaviour from granian ? Is it possible to set up something to change the behaviour ?

This looks like a bug in the ASGI implementation. Please open an issue.