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Re: Calculating Age Question

From: Henrik Frystyk Nielsen <frystyk@w3.org>
Date: Mon, 25 Nov 1996 22:01:25 -0500
Message-Id: <3.0.32.19961125220059.007bac70@pop.w3.org>
To: Paul Hethmon <phethmon@utk.edu>, HTTP-WG <http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com>
At 08:46 PM 11/25/96 EST, Paul Hethmon wrote:
>I don't mean to bring this up for discusion, rather clarification. 
>In going through the mailing list archives and over draft 07, I  
>wanted to be sure I understood the calculations of the Age value 
>correctly.

I have included how I implement it libwww 5.0a which is available from

	http://www.w3.org/pub/WWW/Library/

The function is part of the HTCache.c module.

Hope this helps,

Henrik

-----------------------------------------------------------------

/*
**  Calculate the corrected_initial_age of the object. We use the time
**  when this function is called as the response_time as this is when
**  we have received the complete response. This may cause a delay if
**  the reponse header is very big but should not cause any incorrect
**  behavior.
*/
PRIVATE BOOL calculate_time (HTCache * me, HTRequest * request,
                             HTResponse * response)
{
    if (me && request) {
        HTParentAnchor * anchor = HTRequest_anchor(request);
        time_t date = HTAnchor_date(anchor);
        me->response_time = time(NULL);
        me->expires = HTAnchor_expires(anchor);
        {
            time_t apparent_age = HTMAX(0, me->response_time - date);
            time_t corrected_received_age = HTMAX(apparent_age,
HTAnchor_age(anchor));
            time_t response_delay = me->response_time -
HTRequest_date(request);
            me->corrected_initial_age = corrected_received_age +
response_delay;
        }

        /*
        **  Estimate an expires time using the max-age and expires time. If we
        **  don't have an explicit expires time then set it to 10% of the LM
        **  date. If no LM date is available then use 24 hours.
        */
        {
            time_t freshness_lifetime = HTResponse_maxAge(response);
            if (freshness_lifetime < 0) {
                if (me->expires < 0) {
                    time_t lm = HTAnchor_lastModified(anchor);
                    if (lm < 0)
                        freshness_lifetime = 24*3600;           /* 24 hours */
                    else 
                        freshness_lifetime = (date - lm) / 10;
                } else
                    freshness_lifetime = me->expires - date;
            }
            me->freshness_lifetime = HTMAX(0, freshness_lifetime);
        }
        if (CACHE_TRACE) {
            HTTrace("Cache....... Received Age %d, corrected %d, freshness
lifetime %d\n",
                    HTAnchor_age(anchor),
                    me->corrected_initial_age,
                    me->freshness_lifetime);
        }
        return YES;
    }
    return NO;
}
Received on Monday, 25 November 1996 19:06:07 EST

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