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Re: #292: Pragma

From: Mark Nottingham <mnot@mnot.net>
Date: Fri, 20 May 2011 12:29:08 +1000
Cc: Roy Fielding <fielding@gbiv.com>, Poul-Henning Kamp <phk@phk.freebsd.dk>
Message-Id: <60B8F941-3A27-42BE-81F8-A69FFE8E7A2B@mnot.net>
To: HTTP Working Group <ietf-http-wg@w3.org>
Incorporated with:
  http://trac.tools.ietf.org/wg/httpbis/trac/changeset/1284


On 12/05/2011, at 12:37 PM, Mark Nottingham wrote:

> OK, I've split this into a separate ticket <http://trac.tools.ietf.org/wg/httpbis/trac/ticket/292>.
> 
> I think this is where we're at (incorporating feedback to date):
> 
> """
> 3.4.  Pragma
> 
> The "Pragma" header field allows backwards compatibility with HTTP/1.0 caches, so that clients can specify a "no-cache" request that they will understand (as Cache-Control was not defined until HTTP/1.1). When the Cache-Control header is also present and understood in a request, Pragma is ignored. 
> 
> In HTTP/1.0, Pragma was defined as an extensible field for implementation-specified directives for recipients. This specification deprecates such extensions to improve interoperability. 
> 
>    Pragma           = 1#pragma-directive
>    pragma-directive = "no-cache" / extension-pragma
>    extension-pragma = token [ "=" ( token / quoted-string ) ]
> 
> When the Cache-Control header is not present in a request, the no-cache request pragma-directive MUST have the same effect on caches as if "Cache-Control: no-cache" were present.
> 
> When sending a no-cache request, a client SHOULD include both pragma and cache-control directives unless Cache-Control: no-cache is purposefully omitted to target other Cache-Control response directives at HTTP/1.1 caches. For example:
> 
> GET / HTTP/1.1
> Host: www.example.com
> Cache-Control: max-age=30
> Pragma: no-cache
> 
> will constrain HTTP/1.1 caches to serve a response no older than 30 seconds, while precluding implementations that do not understand Cache-Control from serving a cached response.
> 
> Note: Because the meaning of "Pragma: no-cache" in responses is not specified, it does not provide a reliable replacement for "Cache-Control: no-cache" in them.
> 
> """
> 
> Look OK?
> 
> 
> --
> Mark Nottingham   http://www.mnot.net/
> 
> 
> 
> 

--
Mark Nottingham   http://www.mnot.net/
Received on Friday, 20 May 2011 02:29:36 GMT

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