alt-svc from https (1.1) to https (1.1)

[reschke]

See https://lists.w3.org/Archives/Public/ietf-http-wg/2015JulSep/0193.html:

"Alternative Services MUST NOT be advertised for a protocol that is not designed to carry the scheme. In particular, HTTP/1.1 over TLS cannot carry safely requests for http resources."

...which refers to the :scheme pseudo header field in HTTP/2 (http://greenbytes.de/tech/webdav/rfc7540.html#HttpRequest).

As far as I recall the intention of the statement above is to avoid that when alt-svc is used to move http traffic to a TLSsy port such as 443, the alternative server gets confused about whether it's serving HTTP or HTTPS.

The clause seems to be less relevant when alt-svc is used to load-balance HTTP/1.1 http_s_ traffic.

[mnot]

I think this is editorial.

[reschke]

Like that?

"Special care is needed when the use of an alternative service causes a change in the URI scheme of the transport (e.g., when HTTP traffic is transferred over an HTTPS connection). In cases like these, alternative services MUST NOT be advertised for a protocol that is not designed to carry the scheme. In particular, HTTP/1.1 over TLS cannot carry safely requests for http resources.").

[icing]

Or:
"Alternative Services MUST NOT be advertised for a protocol that is not designed to carry the scheme, for resources whose scheme differs from the Alternate Service one. In particular, HTTP/1.1 over TLS cannot carry safely requests for http resources."

[martinthomson]

I think that both could be a little problematic in the sense that they confuse scheme with protocol. How about:

Alternative services MUST NOT be advertised or used if the protocol for the alternative is not designed to carry the scheme. In particular, HTTP/1.1 over TLS cannot ...

[reschke]

...but that doesn't address the problem this ticket is about...

[MikeBishop]

Maybe

...not designed to carry the scheme, unless the alternate uses the same protocol implied by the scheme.

[reschke]

proposal from @mnot in #92 (comment) would address this issue as well