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Document: draft-ietf-httpbis-cache-header-08
Reviewer: Paul Kyzivat
Review Date: 2021-07-07
IETF LC End Date: 2021-07-01
IESG Telechat date: ?
Summary:
This draft is on the right track but has open issues, described in the
review.
General:
What I read in Security Considerations section scares me, but I'm not
competent to express an opinion. I am going to leave this to the
security review.
Issues:
Major: 0
Minor: 4
Nits: 0
1) Minor: Is a hit or fwd parameter required?
Is it required that an entry contain one of "hit" or "fwd"? Section 2.1
makes it clear that you can't use both, but is less clear that one of
them must be included. But logically it seems that an entry without
either wouldn't be very useful.
I suggest that this be stated explicitly.
2) Minor: ttl for other caches
I'm not clear about the following in section 3:
Going through two separate layers of caching, where the cache closest
to the origin responded to an earlier request with a stored response,
and a second cache stored that response and later reused it to
satisfy the current request:
Cache-Status: OriginCache; hit; ttl=1100,
"CDN Company Here"; hit; ttl=545
When "CDN Company Here" replies with a hit is it responsible for
updating the ttl for the OriginCache? (Based on the time that has
elapsed since it cached the value.) If not, does that ttl have any
relevance?
3) Minor: registration of parameters
IMO the process of registration is underspecified.
For one thing, IANA is not instructed as to what the registry itself
should look like. Given that a specification document is optional, the
registry presumably must contain everything specified by the template in
section 4 for new parameter registrations. But the instructions for
pre-populating the registry from section 2 would mean copying a *lot*
free formatted text into the registry.
ISTM that it would be more straightforward to always require a
specification and have the IANA registry refer to it.
Alternatively, you could have different templates for registering
with/without a specification and different registry formats for each.
I suggest you provide IANA with a template for the registry, and provide
authors of extension parameters with a template for what should be
included in a specification document.
4) Minor: Applicability of this header field is confusing
Section 2 says:
The Cache-Status header field is only applicable to responses that
are generated by an origin server. An intermediary SHOULD NOT append
a Cache-Status member to responses that it generates, even if that
intermediary contains a cache, except when the generated response is
based upon a stored response (e.g., a 304 Not Modified or 206 Partial
Content).
The use of "are" implies to me that the cache received the response from
the origin server just now. Using "were" (or even more explicit
language) would tell me that this was a response received by the cache
either now or in the past.
Also, IIUC the cache can't ever really distinguish if it received a
response from the origin server or another cache. So how can it know if
this response *ever* was created by the origin server? All it can know
is that it received it from a server closer to the origin.
Can you clarify the language?
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