[Webkit-unassigned] [Bug 13309] New: BrowserCache not calculating current Age correctly

[bugzilla-daemon at webkit.org]

http://bugs.webkit.org/show_bug.cgi?id=13309

           Summary: BrowserCache not calculating current Age correctly
           Product: WebKit
           Version: 522+ (nightly)
          Platform: PC
               URL: http://www.barnesandnoble.com
        OS/Version: S60 3rd edition
            Status: UNCONFIRMED
          Severity: Major
          Priority: P4
         Component: WebKit Misc.
        AssignedTo: webkit-unassigned at lists.webkit.org
        ReportedBy: anand.1.patil at nokia.com


More information is in the attached 'browser_cache_age_calc_error.doc'.

- Use case:

Cache is empty. Download a webpage. Stale HTTP::Date response headers cause the
objects to be revalidated when it need not be. 

- Steps to reproduce:

- Actual outcome:

RFC 2616, Section 13.2.3 Age Calculation defines the following algorithm and
variables for currentAge calculations. Not that the request_time and
response_time are locally computed values when the item is cached. 

/*
* age_value
* is the value of Age: header received by the cache with
* this response.
* date_value
* is the value of the origin server's Date: header
* request_time
* is the (local) time when the cache made the request
* that resulted in this cached response
* response_time
* is the (local) time when the cache received the
* response
* now
* is the current (local) time
*/
apparent_age = max(0, response_time - date_value);
corrected_received_age = max(apparent_age, age_value);
response_delay = response_time - request_time;
corrected_initial_age = corrected_received_age + response_delay;
resident_time = now - response_time;
current_age = corrected_initial_age + resident_time;

A problem is that the request_time and response_time variables must be locally
computed and not be the values received in the HTTP::Date header. By using the
HTTP::Date header values, it causes the above resident_time variable to be
extremely large and causing the current_age to exceed the Cache-Control:
max-age header value. 

The BrowserCache is incorrectly relying on the HTTP response header HTTP::Date
field in order to calculate the value of the below mentioned ‘request_time’ and
‘response_time’. Those variables need to be locally computed as described in
RFC 2616, section 13.2.3.

 This causes a revalidation and the HTTP request has to be sent over the wire
again. This can cause a performance drop in page load times. 

- Expected outcome:

The BrowserCache is incorrectly relying on the HTTP response header HTTP::Date
field in order to calculate the value of the  ‘request_time’ and
‘response_time’. Those variables need to be locally computed as described in
RFC 2616, section 13.2.3.

This should result in no need to revalidate the cached object.


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