GNU bug report logs - #10147
HTTP "Expires" header should handle non-date values

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Andy Wingo <wingo <at> pobox.com>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#10147: closed (HTTP "Expires" header should handle non-date
 values)
Date: Mon, 09 Jan 2012 22:38:02 +0000

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Your message dated Mon, 09 Jan 2012 23:36:44 +0100
with message-id <87mx9w4i6b.fsf <at> pobox.com>
and subject line Re: bug#10147: HTTP "Expires" header should handle non-date values
has caused the debbugs.gnu.org bug report #10147,
regarding HTTP "Expires" header should handle non-date values
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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From: Daniel Hartwig <mandyke <at> gmail.com>
To: "R. P. Dillon" <rpdillon <at> gmail.com>
Cc: bug-guile <at> gnu.org, guile-user <at> gnu.org
Subject: HTTP "Expires" header should handle non-date values
Date: Sun, 27 Nov 2011 18:39:12 +0800

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Package: guile
Version: 2.0.3
Tags: patch

On 6 November 2011 13:49, R. P. Dillon <rpdillon <at> gmail.com> wrote:
> (use-modules (web request) (web response) (web uri) (rnrs bytevectors))
> (define port (socket PF_INET SOCK_STREAM 0))
> (define address (addrinfo:addr (car (getaddrinfo "www.google.com" "http"))))
> (connect port address)
> (define request (build-request (build-uri 'http #:host "www.google.com")))
> (write-request request port)
> (define response (read-response port))
> (read-response ...) consistently fails with Google:
> web/http.scm:754:6: In procedure parse-asctime-date:
> web/http.scm:754:6: Throw to key `bad-header' with args `(date "-1")'.
> The expiration is set to -1 in the headers, and this seems to cause a
> problem for the web libraries in Guile.
> This same request seems to work well for my own domain (killring.org).

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

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))))))

This approach completely ignores the recommended way of determining
whether a response has expired.  See section 13.2.4 of the RFC for
calculations involving various factors such as the time that a request
was sent, "Cache-Control" directives, etc.


Regards

Daniel

[0001-Permit-non-date-values-for-Expires-header.patch (text/x-patch, attachment)]

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From: Andy Wingo <wingo <at> pobox.com>
To: Daniel Hartwig <mandyke <at> gmail.com>
Cc: guile-user <at> gnu.org, 10147-done <at> debbugs.gnu.org
Subject: Re: bug#10147: HTTP "Expires" header should handle non-date values
Date: Mon, 09 Jan 2012 23:36:44 +0100

Hi Daniel,

Thanks very much for the thorough analysis!

On Tue 27 Dec 2011 16:49, Daniel Hartwig <mandyke <at> gmail.com> writes:

> Given those points, I have attached a patch implementing the suggested
> handling for "Expires" and will take a look at perhaps relaxing
> parse-date (and others).  Anyone have ideas on that?

I applied your patch, and I think some sensible parse-date relaxations
are a good idea too.

Regards,

Andy
-- 
http://wingolog.org/

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