Re: [EXTERNAL] Re: Response for unsupported conditional request

Mike,

I think it's also a requirement to point out that many RFC's are not always
well-written and some make numerous assumptions. Despite the best efforts
of the IETF.

To go back to your original point:

> Is there a required or recommended response that a server should give if
it receives a request with a conditional header (If-Match, If-No-Match,
If-Modified, If-Unmodified) that it does not support?

There is clearly a required or recommended response if the server supports
the header, as defined in the RFC - we all agree on that.

If the server doesn't support the field, then the RFC may suggest a
response, but there's obviously a good chance that the server was written
without referring to the RFC, so the server has no idea what that suggested
response is.

To use your example, if a server was written to follow RFC9110, but prior
to the RFC which defines your hypothetical If-YouFeelLikeIt field, then not
only does it obviously not support If-YouFeelLikeIt, but it has no idea
that If-YouFeelLikeIt even exists, so it has no idea what to respond
with... So all you can do in your RFC is include instructions for what a
user agent should do if it sends the If-YouFeelLikeIt field and gets
nothing specific in the response.

AFAIAC, there's basically no reason (IMO) to include a "If a server does
not support header If-YouFeelLikeIt, then it SHOULD respond with X" section
in the RFC which defines If-YouFeelLikeIt - it will never be used by
servers that don't support If-YouFeelLikeIt.

On Tue, Feb 4, 2025 at 1:54 PM Mike Kistler <mikekistler@microsoft.com>
wrote:

> > I think you may have a misguided assumption that all RFCs are
>
> > somehow strictly enforced everywhere.  They are not.
>
>
> I do not have this assumption. I am simply trying to understand what it
> means to be compliant with the RFC. When I read the language I cited, it
> seems to me that origin servers "MUST" implement the behavior described or
> they are not compliant with the RFC. If that is not the case, I would
> appreciate being educated on why that is not the case. What wording have I
> missed or misunderstood?
>
>
> > Multiple reasons have already been given.  I'll repeat one:
>
>
> > This is the nature of a heterogeneous internet with clients and servers
>
> > of widely varying ages, protocol support, and simplicity/complexity.
>
>
> I can understand that this is why some origin servers do not comply with
> the RFC. But this is not what I'm asking. i want to know what it means to
> be compliant. But maybe you mean that for this reason it is not necessary
> to follow the "MUST" provisions to be compliant with the RFC. I hope you
> don't mean that, because in that case it seems that all servers are
> vacuously compliant which is not particularly useful.
>
>
> Mike
>
>

-- 
Rory Hewitt

https://www.linkedin.com/in/roryhewitt