bug#10147: HTTP "Expires" header should handle non-date values

[Andy Wingo <wingo@pobox.com>]

Hi Daniel,

So sorry for the delay.

On Sun 27 Nov 2011 05:39, Daniel Hartwig <mandyke@gmail.com> writes:

> This is definitely a bug on Guile's part, HTTP/1.1 permits such values
> for "Expires" headers [1], treating them as though they were a date in
> the past:
>
>    HTTP/1.1 clients and caches MUST treat other invalid date formats,
>    especially including the value "0", as in the past (i.e., "already
>    expired").
>
> [1] http://tools.ietf.org/html/rfc2616#section-14.21

But that's right after saying

   The format is an absolute date and time as defined by HTTP-date in
   section 3.3.1; it MUST be in RFC 1123 date format:

      Expires = "Expires" ":" HTTP-date

But, pragmatism may rule, here...

> Attached patch permits non-date values for "Expires", leaving them as
> strings (preferable, as such responses can be transparently forwarded
> to other clients). The staleness of a response could be determined
> quite crudely, e.g.
>
> (define (response-stale? r)
>   (let ((expires (response-expires r)))
>     (and expires
>          (or (not (date? expires)) ;; Indicates already expired.
>              (time<=? (date->time-utc expires)
>                       (current-time))))))

Let us assume that it is a good idea to include this hack.  Wouldn't it
be better to keep the expires header as a date?  Would any date in the
past work fine?

Would it be best to allow some special cases like "0" or "-1" instead?

I'm just trying to limit the damage here :)  WDYT?

Andy
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