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Re: Caching of cgi results

From: Andy Coles - WEB developer <Andrew.Coles@it.newsint.co.uk>
Date: Fri, 31 May 1996 10:07:15 +0100
Message-Id: <9605310907.AA05633@dogi.newsint.com>
To: www-talk@w3.org
If I telnet into my server port and issue the following http request i get

HEAD /cgi-bin/image?block.gif HTTP/1.0

HTTP/1.0 200 OK
Server: Netscape-Commerce/1.1
Date: Friday, 31-May-96 08:48:24 GMT
Expires: Friday, 31-May-96 08:48:24 GMT
Content-type: image/gif

Connection closed by foreign host.

which looks okay to me

The http 1.0 spec says that if the Expires date is equal to or less than the Date date then the content should not be cached. Either:-

a) this isn't true for Netscape 2.0

or

b) more likely it something to do with my cgi. To expand on my methods:-

I have an html form, generated from a cgi, which calls another cgi in an IMG SRC tag. every time the form is submitted it is recreated along with the IMG SRC tag which references the other cgi program. although the image data which is produced by the second cgi changes every time the form is submitted the URL to it doesn't! The problem I'm having is that the image displayed is always the first one and never updates itself.

> 
> There's an infrequent server misconfiguration error that can sometimes
> cause a page not to refresh.  Check to see if your server returns
> a proper response to a HEAD (not GET) request for that URL
> (http://your.server/cgi-bin/image?block.gif).  If it doesn't respond
> with a correct HEAD request, some (though not all) browsers may
> refuse to refresh the page.  Some browsers, notably some of the
> newer versions of Netscape, do a HEAD request to check to find out
> whether a page is newer than a cashed version.  If they get nonsense
> from a HEAD request, the usual fallback is to simply not update the
> page.
> 
> Rare, but possible...
> 
Received on Friday, 31 May 1996 05:07:07 GMT

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