Why http.response.start exists?

[Kludex]

I've been wondering... Uvicorn is the only ASGI server that sends http.response.start, and then processes the body. The problem with this approach, is that the successful response may be a lie, if there's an error when processing the body.

And... I was thinking about changing the behavior on Uvicorn.

I was wondering, why do we allow http.response.start to be sent before the body?

[andrewgodwin]

The idea was to emulate the WSGI behaviour, where you can begin the HTTP response before you then start streaming the body contents (start_response versus the contents of an iterator).