Re: Robert Wilton's No Objection on draft-ietf-httpbis-targeted-cache-control-03: (with COMMENT)

[Mark Nottingham <[e-mail]>]

Hi Rob,

> On 19 Jan 2022, at 5:15 am, Robert Wilton via Datatracker <[e-mail]> wrote:
> 
> 1.
>   Because it is often desirable to control these different classes of
>   caches separately, some means of targeting directives at them is
>   necessary.
> 
> As a reader that is not familiar with the reasons (but I could potentially
> guess), I was wondering whether it would be help to add a sentence to explain
> why this might be done?

I've added a motivating example here:
  https://github.com/httpwg/http-extensions/commit/0cfdc194517

> 2. I felt a bit ambiguous to me about what directives are actually allowed in a
> cache directive:
> 
> Section 2.1 states:
>  "Targeted fields are Dictionary Structured Fields (Section 3.2 of
>   [STRUCTURED-FIELDS]).  Each member of the dictionary is a cache
>   response directive from the Hypertext Transfer Protocol (HTTP) Cache
>   Directive Registry (https://www.iana.org/assignments/http-cache-
>   directives/)."
> 
>   and
> 
>   If a targeted field in a given response is empty, or a parsing error
>   is encountered, that field MUST be ignored by the cache (i.e., it
>   behaves as if the field were not present, likely falling back to
>   other cache control mechanisms present)
> 
> Section 3.1 states:
> 
>   Cache-Control: no-store
>   CDN-Cache-Control: none
> 
>   (note that 'none' is not a registered cache directive; it is here to
>   avoid sending a header field with an empty value, which would be
>   ignored)
> 
> It was left somewhat unclear to me whether an implementation is allowed to use
> a cache directive that is not defined in the "Cache Directive Registry", noting
> that the example in 3.1 seems to suggest this is allowed.  Perhaps the document
> would be clearer if this was explicitly stated in section 2.1?

Hm. Yes, the invocation of the registry is a bit odd there. I've attempted to improve this here:
  https://github.com/httpwg/http-extensions/commit/d1457362a509
(co-authors, please review)

> Some nits:
> 
> more of of => more of
> 
> \[CDN-Cache-Control]]) => strange escape or extra ].
> 
> "directive" to "Cache directives" in a few more places for consistency? 
> Particularly in section 2.1, I thought that this might make the text slightly
> better.

See:
  https://github.com/httpwg/http-extensions/commit/d497981c70

Thanks for the review.

--
Mark Nottingham   https://www.mnot.net/