"Rich-F" <RichF@d...> wrote in message
news:EE64C55B-B026-46E7-8974-FE8FAAE1C0A4@m......
> "Anthony Jones" wrote:
>
> >
> > "Rich-F" <RichF@d...> wrote in message
> > news:61C826B1-E1F2-4E6F-87FF-83C675E9FDF4@m......
> > > "Anthony Jones" wrote:
> > > <snip>
> > >
> > > > The point I was trying to communicate is that a browser offers the
user
> > the
> > > > opportunity to override the normal operation of the local cache by
using
> > the
> > > > refresh button.  This causes all requests to fulfill the page to
pass
> > > > through local cache to the origin server regardless of whether there
is
> > > > fresh instance of the resource in the cache.
> > > >
> > > > I'm trying to implement a similar feature for resources that have
been
> > > > fetched with XMLHTTP.  For performance reasons I do not want to send
a
> > > > request every time it's needed however I want to offer the user the
same
> > > > 'refresh' option.
> > > <snip>
> > >
> > > Just considering this last point.....
> > >
> > > The only method that worked reliably for me was adding the
> > If-Modified-Since
> > > header and making sure that the date I used was definitely older than
any
> > > timestamp that might be associated with the file.  (I used IE6 and
> > > XMLHTTP.3.0)
> >
> > Ok thanks for the input.  However since changing the If-Modified-Since
in
> > that way would always result in 200 response from the server and never a
304
> > it's the same is simply using the the load method on a DOM with
ForceResync
> > enabled which is what I was hoping to avoid.
>
> (we're going round in circles here)

Yes we are

>
> If you want to absolutely force the request to go to the server then set
> If-Modified-Since to something really old.
>
> If you want to give the server a chance to reply with a 304 then set
> If-Modified-Since to the 'real' modified date as per my previous code
example.

Your previous code example knew what the 'real' modified date is from a
previous fetch. As I pointed out in response to that; trapping, persisting
and retrieving that piece of information is a complication way beyond the
worth of the feature.

I've also already stated that I'm not seeing the results in my testing that
you appear to be.
I've tried setting the If-Modified-Since header but it doesn't force a round
trip to the server.  This is as I would expect, the modification date of a
resource has no bearing on the resources age in the cache.