Caching Problems / GD Dynamically created images

Tentux

Hello there forum people - I just have a quick query - I am having troubles as I'm automatically generating a chart using the GD library. Each time a new chart is produced and used it's called 'Chart.jpg'. This is fine as I just want an on-the-fly jpeg image. The problem I'm having is that the browser caches the image and when it comes to a page displaying a chart it displays an old chart in the browsers cache. I could use a file hash solution meaning the images will always have a unique name and this would avoid hashing problems. But then I'd run into the problem of a gazzilion jpeg files...

Any ideas?

jcantrell

I see a few options,

Name the images something unique. Write a script that reads file information. Set that script to delete any files older than 30 seconds, 5 minutes, 2 weeks or whatever interval you want to use.
Name the images with a timestamp. Write a script that would read through the filenames and delete the files based on the time from the filename.

Then if you have access to set up a cron job, set a cron job to run this script every once in a while.

If you don't have acees to set up a cron job, include this script in the page that generates your map. This is how I would do it.

Hope this helps!

Weedpacket

You might also send headers specifying that the image must not be cached (an example of the sort of headers that prevent caching at various points can be found on the [man]header[/man] page). This I think is preferable, since it means the client's cache doesn't just keep filling up with multiple redundant cached copies of an obsolete image file.