Multiple Alt-Svc parameters of the same type

[Lucas Pardue <[e-mail]>]

Hello all,

The “v” Alt-Svc parameter has seen some use in the wild, namely Google services offering the “quic” alternative service. To date this parameter was not defined anywhere but took the form of a comma-separated list of numbers e.g.

Alt-Svc: quic=":443”; v="35,34"

Mike Bishop is giving an official definition of the Alt-Svc “v” parameter, as part of https://tools.ietf.org/html/draft-ietf-quic-http-01#section-2.1, which is different than Google’s previous usage.

> When multiple versions are supported, the "v" parameter MAY be
> repeated multiple times in a single Alt-Svc entry.  For example, if a
> server supported both version "Q034" and version 0x00000001, it would
> specify the following header:

> Alt-Svc: hq=":443";v="x1";v="cQ034"

> Where multiple versions are listed, the order of the values reflects
> the server's preference (with the first value being the most
> preferred version).

This got me thinking, RFC 7838 doesn’t seem to give any direction on the handling of multiple parameters of the same type. For example, is it OK for a server to generate multiple “persist” parameters perhaps with different values, how should a client deal with that? Perhaps I’m worrying too much.

I wondered if the Alt-Svc parameter IANA registry could use some new columns to define the allowed multiplicity of each parameter, and an indication of how to treat the ordering. Any thoughts?

Regards
Lucas




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