Re: [squid-users] Pragma: no-cache

On 23/02/2013 2:53 a.m., FredB wrote:
> Hello,
>
> With latest version squid 3.2.7, pragma: no-cache seem doesn't work like before, it's very annoying with some admin page ...
> Sites with this values are in cache, with previous version no.
>
> Hypertext Transfer Protocol
> HTTP/1.1 200 OK
> Server: nginx/0.7.6
> Date: Fri, 22 Feb 2013 08:58:12 GMT
> Content-Type: text/html; charset=iso-8859-1
> Connection: keep-alive
> Expires: Sat, 23 Feb 2013 08:58:12 GMT
> Cache-Control: max-age=86400
> Pragma: no-cache
> Last-Modified: Fri, 22 Feb 2013 08:58:12
> Content-Encoding: gzip
> Content-Length: 2799
> X-Varnish: 1263601159
> Age: 0
> Via: 1.1 varnish
> X-Cache: Miss from Varnish
>
> It's a bug ? Or a voluntary change in behaviour ?

This is an intentional change in behaviour which comes from upgrading
Squid to perform the HTTP/1.1 protocol properly.
http://squidproxy.wordpress.com/2012/10/16/squid-3-2-pragma-cache-control-no-cache-versus-storage/

Please note the detail:
"
When sent on a server response:

  * /Pragma/ in all its forms *has no meaning whatsoever.* It must be
    ignored.

"

Looking at the above header with my HTTP/1.1 glasses on...

* it contains HTTP/1.1 tag indicating that the sender supports HTTP/1.1
properly.

* it contains Cache-Control: indicating that an HTTP/1.1 recipient (ie
Squid 3.2+) MAY store the response for up to 86400 seconds.

* it contains Date:, Expires: and Last-Modified: headers confirming what
Cache-Control has just indicated.
     eg. Last-Modified + 86400 sec == Date -Age + 86400 sec == Expires.
  ... so all three HTTP/1.0 and HTTP/1.1 methods of calculating storage
time come up with the 24hr caching permission for Squid.

* Pragma is not defined by any of the HTTP RFCs and therefore must be
considered to be a Entity header relating to how the end-user agent (ie
browser) is supposed to display or manage that entity. It is not
supposed to be related to Squid or other HTTP/1.1 proxies.

Amos
Received on Sat Feb 23 2013 - 03:10:35 MST