http header / browser caching issues

d_i_r_t_y has asked for the wisdom of the Perl Monks concerning the following question:

i'm currently having issues with browsers apparently caching the output of my cgi scripts, such that hitting 'back' or following a link to a script that has been called previously does not re-call the cgi script.

naturally, this often ends up with the old (and usually incorrect) information being shown.i have tried setting the http 'expires' header to 'now' and '-10d' (using the CGI::header method), and then verified the http headers by telnet'ing to port 80 and issuing manual http 1.1 GET's... all looks well - the expires header is there and set to the correct date/time etc...

one thing i've done which is perhaps a little unusual is that all my scripts do not have suffixes - they are simply named 'query', 'results' etc -- i have accordingly setup apache to execute as CGI anything in a particular directory (and kept all my library *.pm's elsewhere...).

can any web monk(-ey) provide any explanation or pointers as to why the silly browser (any browser) continues to cache the output of my cgi's?

d_i_r_t_y

Comment on http header / browser caching issues

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Re: http header / browser caching issues by echo (Pilgrim) on Aug 30, 2001 at 12:15 UTC
Using the `expires` header is not always sufficient, if only because of clients that have their clock set wrong. I have had good results with the following headers, which is what the Apache API `r->no_cache` emits: `Cache-Control: no-cache Pragma: no-cache` [download] in combination with the <code>expires now<code> header you already send out.	[reply] [d/l] [select]
Re: http header / browser caching issues by tachyon (Chancellor) on Aug 30, 2001 at 17:34 UTC
There is a demo of how to do this here: How can i do a expires to my page or here How to code security for Expires Page or here printing header method. Hope that helps. Sadly some browsers don't play fair and ignore expires, cache-control and pragma no cache directives but what can you do. Only so much and this is it. cheers tachyon s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print	[reply]
Re: http header / browser caching issues by earthboundmisfit (Chaplain) on Aug 30, 2001 at 18:14 UTC
The above info is all excellent. However, for anyone who needs a more basic explanation of document caching, I've found this resource to be of great value. `Cache control: proxy-revalidate` might apply to your situation.	[reply]