RFC 7838 ALTSVC Frame

All,

I’m implementing support in hyper-h2 for the ALTSVC frame as specified in RFC 7838. However, a detailed read of RFC 7838 does not appear to define what stream state the ALTSVC frame may be sent in. This is in contrast to the frames in RFC 7540 which explicitly list in which stream states they are acceptable.

The closest I can see is an allusion in the text that says "Receiving an ALTSVC frame is semantically equivalent to receiving an Alt-Svc header field”, which suggests that the correct answer may be the open and half-closed remote states, but it’s still unclear. Can I send ALTSVC on closed streams? On idle streams? What about half-closed (local) streams? Can they be sent at any time?

Can I get some clarification from this WG about what the consensus is here? I know that nghttp2 has implemented support already, so in the absence of any further information I’ll take the now-traditional route of “just do what nghttp2 does”, but I’d like a bit more clarity than that!

Thanks

Cory