Re: Again IMS handling (Squid PL15)

From: Henrik Nordstrom <>
Date: Mon, 10 Jun 1996 13:32:54 +0200

> I've currently asked for a more sophisticated IMS handling.
> Now I've detected that I'm unable to asked for the latest version of an
> online newspaper. I'll get a mixture of old headlines and newer pictures...
> Browser: Netscape 2.0
> Neither reload nor any key-reload combination works.

The Reload button should always work. When pressing Reload Netscape
send "Pragma: no-cache" and all cached information in Squid is ignored.
It is still a "If Modified Since" request, but all processing is done
by the original server (squid is not allowed to touch the request).

When pressing Shift-Reload, Netscape does a normal request with "Pragma: no-cache", without a If-Modified-Sice header. This request is also
sent directly to the original server.

If-Modified-Since requests is only handled directly by Squid when not
pressing reload (not sending Pragma: no-cache). (I'll check that this
is true in beta15 in a few minutes).

You can validate this it you check the access.log while trying to reload
the page.

* TCP_REFRESH: Request was sent directly to the original server, since
it contains a "Pragma: no-cache" header. If the size is small then the
server responded with a "304 Not Modified" message, if it is large then
a full object was returned.
* TCP_MISS: Cache miss (can be a "Pragma: no-cache" request too)
* TCP_HIT: Cache hit without If-Modified-Since"
* TCP_IF_MODIFIED_SINCE: Cache hit with If-Modified-Since.
"304 Not Modified" returned by Squid it the cached object is not
modified, else handled as a cache hit (sending the whole object).

Requests from a "Reload" should be TCP_REFRESH or TCP_MISS. Never

Squid 1.1 will (if the time permits) contain a much more sophisticated
IMS handling, using IMS to validate cached objects and other nice things.

Henrik Nordström
Received on Mon Jun 10 1996 - 04:32:54 MDT

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