image caching

[Lea H]

Hi,
I have an image like that <img src='controller/action' /> that calls
action in controller. This action creates a PIL and sends it to the
browser. It seems that once the action was called the resulting image
is cached and reused every time the image is shown (the action is not
called anymore). Since the image contains dynamic data I need it to be
re-created every time I go on that page. Can I somehow tell the
browser not to cache that specific image?

Thanks for you help.

Cheers,
Lea

[Stephen Emslie]

How about adding a unique query string to the request? e.g.

<img src="/controller/action?<timestamp>"/>

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[Lea Hänsenberger]

That's simple ;-). Thank you.

[Alexandre Conrad]

Hi,

I don't know the answer as I haven't really used caching, but I guess
the correct way to do it is to play with the HTTP headers, tweaking
the Cache-Control setting.

The headers can be changed with the response object, available in your
controller:

# Set HTTP response headers before returning
response.headers['Cache-Control'] = 'some value here'

Here's the RFC about Cache-Control:

http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9

Regards,
Alex

2009/11/25 Lea H <baer...@gmail.com>:

[vince spicer]

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Lea,

There are a few things you can do to disable caching, the oldest way is to append a timestamp into the url so the image url is different on every request.

EX: 

"""<img src="/controller/image?time=%s">""" % time.time()
then in your controller ensure you except the time argument

or you can use cache-control/max-age headers on the returning image, to tell the browser to refresh.  However this does tend to be browser specific and can be fun finding the right headers to return for all browsers.

Hope this helps,

Vince