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Re: Does no-store in request imply no-cache?

From: Eric J. Bowman <eric@bisonsystems.net>
Date: Sun, 17 Oct 2010 22:24:19 -0600
To: Adrien de Croy <adrien@qbik.com>
Cc: HTTP Working Group <ietf-http-wg@w3.org>, David Morris <dwm@xpasc.com>
Message-Id: <20101017222419.2fd97ea7.eric@bisonsystems.net>
Adrien de Croy wrote:
> 
> talking about IP and tracerts is a complete red herring.  These
> agents are the parties in TCP connections.  Sure, the IP packets may
> go via different routers between the endpoints, but the endpoints are
> the endpoints.
> 

Exactly, which is why this is no red herring...

A = user-agent
B = origin server
C = cache

The route from A to B passes through C, the route from B to A passes
through D.  User-agent A sends a GET request to the origin server B.
The request is a hit on cache C, so the response goes from C to A.

In the event of a cache miss it is not A, but C, making the request to
B -- but only for safe methods, otherwise C is not an endpoint.

The user at A changes the representation and makes a PUT request to B.
Cache C intercepts this request, and *routes* it to B.  B then sends a
200 OK response to A, which does not pass through C.

This is because caches are stand-ins for origin servers, not user-agent
proxies.  B knows nothing of C, because A made the PUT request.

So, C only knows the status of the response to the PUT if the route
from B to A is the same as the route from A to B.  When dealing with
unsafe request methods, intermediaries are not participants, only the
user-agent and origin server are endpoints.

-Eric
Received on Monday, 18 October 2010 04:24:56 GMT

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