Re: RFC 9113 and :authority header field

["Roy T. Fielding" <[e-mail]>]

> On Jun 30, 2022, at 2:02 AM, Willy Tarreau <[e-mail]> wrote:
> 
> On Thu, Jun 30, 2022 at 09:01:23AM +0200, Willy Tarreau wrote:
>>>> What we're
>>>> doing in haproxy is that both Host and :authority are used interchangeably
>>>> after having been checked for proper matching, and are modified at the
>>>> same time if needed, and we have a flag indicating if an authority was
>>>> present in the incoming request to know if we have to produce one on
>>>> output or not. That's in the end what seems to preserve the most accurate
>>>> representation along a chain of multiple versions. This allows us to emit
>>>> a Host field only if one was present, and an authority only if one was
>>>> present, regardless of the HTTP version. I don't think that RFC9113 brings
>>>> any changes regarding this, it might only be a matter of what constitutes
>>>> "control data".
>>> 
>>> Sorry, that is a broken implementation. You need to send Host regardless
>>> of the original request version.
>> 
>> I can guarantee you that each time we accidently failed to do this because
>> of a tiny change or some strengthening of the checks of host vs authority,
>> we got instant reports of various 1.0 applications getting broken. And
>> actually I did verify carefully that the updated set of RFCs continued to
>> cover that compatibility requirement with these old components, i.e. Host
>> remains Host and :authority remains :authority along all the chain, and
>> only when both are set, they must match and we can simplify (e.g. drop
>> authority when passing to an HTTP/1.x server).
> 
> BTW, I think I just understood the case that concerned you and I was
> partially incorrect above, as we do *always* create a Host header on
> output since it's obviously always valid, we only make the difference
> on the authority to decide whether to rebuild and absolute or origin
> form for the URI.
> 
> Sorry for this confusion.
> 
> Willy

Heh, no worries ... I was wondering how it could possibly work, unless
you happened to be testing on single-origin default servers. It makes me
wonder what happens when a hostless request hits a CDN -- I haven't
even tested that in ages.

Cheers,

....Roy