Clarification of transport and HTTP version compatibility

[Samuel Hurst <[e-mail]>]

Hi all,

Does the quic-transport version and the HTTP mapping version have to
match? For example, could you negotiate QUIC draft-11, but the HTTP side
is still using an older version (such as draft-09 to avoid the
requirement of QPACK)?

As far as I understand it, the QUIC transport version is negotiated as
part of the TransportParams in the appropriate TLS extension, and the
HTTP mapping version is negotiated by ALPN. So in the example above,
would it be acceptable to negotiate 0xff00000a as the transport protocol
version, and then have an ALPN string of "hq-09"?

I'm then assuming that a valid Alt-Svc header for my example could be as
follows:

Alt-Svc: hq-09=":4443";quic="ff00000a"

The quic-tls draft mentions in Section 9.1 "The application-layer
protocol MAY restrict the QUIC version that it can operate over", but
none of the quic-http drafts that I've read list any such restriction.
Therefore, I'm then further assuming that it's safe to run whatever
version of the HTTP mapping I like, unless there's a compatibility
matrix between the various specs that I'm missing?

Best Regards,
Sam