On Saturday 20 Mar 2010, Ralph Corderoy wrote:
> Yes, HTTP lets clients and servers converse over whether they need to
> fetch a new version of the page to save on needless transfers. A server
> can use it to help stop the `reload addicts' that keep reloading,
> waiting for the count to go up by one. :-)
OK. So I can see why they would want to do this.
> Here's the conversation for the first time it's fetched, some headers
> deleted. A paragraph of request, another of reply.
>
> GET /Digital-Economy/ HTTP/1.0
> Host: petitions.number10.gov.uk
> Pragma: no-cache
> Cache-Control: no-cache, max-age=259200
>
> HTTP/1.0 200 OK
> Date: Sat, 20 Mar 2010 13:12:05 GMT
> Expires: Sat, 20 Mar 2010 13:12:06 GMT
> Content-Length: 16664
> Last-Modified: Sat, 20 Mar 2010 11:31:03 GMT
> Cache-Control: max-age=1
>
> The next time the browser asks, including on a reload, it adds the
> `If-Modified-Since' header.
>
> GET /Digital-Economy/ HTTP/1.0
> If-Modified-Since: Sat, 20 Mar 2010 11:31:03 GMT
> Host: petitions.number10.gov.uk
> Cache-Control: max-age=259200
>
> HTTP/1.0 304 Not Modified
> Date: Sat, 20 Mar 2010 13:11:54 GMT
Unless I've misunderstood this, the server is lying! The browser asks if the
page has been modified since the last time it got a fresh page and the server
says no, even though it has. Seems a pretty poor approach to me, because it
will make people keep asking and wondering why a page they expect to change
isn't.
> Hold down Shift in most browsers when clicking the Reload icon to make
> it not do this and really get a fresh version of the page. But use
> sparingly. There's a reason it works as above. You don't want the
> server so heavily loaded that folks don't bother signing. :-)
That is the bit that confused me. I thought the reload button on it's own
gave that behaviour.
--
Terry Coles
64 bit computing with Kubuntu Linux
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