在Apache配置中有条件地设置到期标头

Question

I would like to conditionally set expires headers on images so that they will not cache while a project is in development but will when it is in production. Ideally this would just be a modification of the apache conf file. I have a perl script that will return the status of the project, which can be used with mod_rewrite as follows:

rewritemap  PSTAT prg:/bin/pstat.pl
...skipping...
rewritecond ${PSTAT:$site:$1} =devel
rewriterule ^/run/$site/p(\d+)/(\w+) /logout.pl/$2 [NS,L]

It would be nice if I could do something like:

rewritecond ${PSTAT:$site:$1} =devel
ExpiresByType image/jpg "now plus 1 second"

Though of course that wouldn't work.

Is there any solution?

Answer 1

A trick that worked for me is to first set the headers unconditionally:

ExpiresByType image/jpg "now plus 1 second"
...

And then to unset the header in case we are in devel mode:

Header set Cache-control "no-cache" env=devel
Header unset expires env=devel

This requires that you have a boolean env devel previously initialized based on your mode. In our case we decide on the host name whether we want to be devel or not (devel.domain.com vs. www.domain.com).

Answer 2

Starting from what alienhard said I managed to come up with an answer to my problem.

rewritemap  PSTAT prg:/bin/pstat.pl
...skipping...
rewritecond ${PSTAT:$site:$1} =devel
rewriterule ^/images/(\d+)/(\w+) - [E=devel:1]

header set cache-control "no-cache" env=devel
header unset expires env=devel

( /images/(\\d+) is the folder of images for a particular project number (\\d+) )

The E flag of rewriterule lets you set an environment variable in the case that the rule matches. - doesn't actually rewrite anything. Thus, this checks the output of the script using rewritecond sending it the project number from the rewriterule , and then sets the environment variable in the case that both conditions match. Then header conditionally gets set based on the presence of that environment variable.