[Webtransport] Draining WebTransport connections

[Lucas Pardue <[e-mail]>]

Hi WebTranport enthusiasts,

I might have missed it but it seems that WebTranport doesn't have a
capability to drain connections, similar to how GOAWAY works for H2 or H3.
The crux of draining here is being able to tell a peer that creating new
streams is no longer wanted (and possibly that they should move to a new
connection to do that).

draft-ietf-webtrans-http3-03 Section 4.6 [1] does say something but I don't
think it helps:

> HTTP/3 defines a graceful shutdown mechanism (Section 5.2 of [HTTP3
<https://www.ietf.org/archive/id/draft-ietf-webtrans-http3-03.html#HTTP3>])
that allows a peer to send a GOAWAY frame indicating that it will no longer
accept any new incoming requests or pushes. This mechanism applies to the
CONNECT requests for new WebTransport sessions. A GOAWAY frame does not
affect data streams for existing WebTransport sessions; those can continue
to be opened even after the GOAWAY frame has been sent or received.

The text is clear that H3's GOAWAY won't stop the peer creating new
WebTransport streams. Absent explicit draining notification for
WebTransport streams, the outcome seems to be to either expect spontaneous
connection termination, or delegate it to applications on top of
WebTransport to make their own solution up. Maybe we should just solve it
in the WebTransport protocol, so that the WebTransport API factors it in?

Cheers,
Lucas

[1] -
https://www.ietf.org/archive/id/draft-ietf-webtrans-http3-03.html#section-4.6