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From Manik Taneja <mtan...@movik.net>
Subject Re: HTTP Protocol: How frequently should browser repeat requests after 304 responses?
Date Wed, 17 Sep 2008 21:16:22 GMT

On 18-Sep-08, at 2:21 AM, Eric Covener wrote:

> On Wed, Sep 17, 2008 at 4:46 PM, Manik Taneja <mtaneja@movik.net>  
> wrote:
>> this behavior seems highly browser dependent.  There may be a few
>> possibilities as to why the browser doesn't send an IMS request.
>>
>> a. the browser cache is cleared
>> b. the browser has a limited size cache and so this object gets  
>> ejected due
>> to lack of space. you could try increasing the size of the browser  
>> cache and
>> see if that helps.
>> c. the browser prolly follows some algorithm where by it decides to  
>> send an
>> IMS only once, unlikely, but I am just guessing.
>> d. the browser is IE and is buggy :).
>
> I think in Dan's case the problem is that the IMS validation never
> gives the opportunity for a "new" expires time to be communicated to
> the client:
>
> 0) Browser gets a 200 responds for a static file along with an  
> Expires header
> 1) the browser happily uses it's local copy during the Expires window
> 2) Expires time is up
> 3) browsers sends a request with IMS
> 4) server responds with a 304
> 5) It would sure be nice if the browser had some way to find a new
> Expires: time, because now every subsequent request for the static
> file is a round-trip to get the 304.
>
> Is there any room in HTTP/1.1 for the client or server to save on the
> round-trips after the revalidation.

I speak on behalf of a proxy cache and in the past I would send out a  
304 along with a new expires header when the client sent an IMS for a  
cached response.

apparently someone reported a similar issue for squid.
http://www.squid-cache.org/bugs/show_bug.cgi?id=7

I wonder what prevents a server from sending a 304 along with new  
expires header,  what i mean is that this behavior would be no  
different from the case where a reverse proxy for a particular server  
sent back a 304 response.  The client is mostly unaware of the reverse  
proxy, unless indicated by the X-forwarded-for or Via headers but  
apart from that client shouldn't care who sent back the response.

-M


>
>
> -- 
> Eric Covener
> covener@gmail.com


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