how to invalidate an object in the cache?
I am working with photo rotating/resizing, via PIL on external method. All the images are kept on LocalFS. There is a thumbnail bonanza page, when I select a thumbnail a form is shown, and I can adjust rotation/contrast/brightness. Upon submit, the new image+thumbnail is calculated and written to the filesystem. Then the method calls RESPONSE.redirect to show the index page again. When I go back to the index thumbnail page, the image I've just rotated is displayed with the right size (which means that Zope gets it right), but not rotated (which means that Netscape reads the old image from the cache). I mean, if it was 320x200 and is now 200x320, the browser displays the old 320x200 image stretched to 200x320. I'm not digging into contrast and brightness, but the same happens. Is there a way to force the browser to discard the cache for that image? If I go "right-button, view image, shift+reload" the new image is displayed. Any idea? I'm not very knowledgeable on this matter, I don't design pages for a living. Might javascript help? Thank you. -- "This company has performed an illegal operation and will be shut down. If the problem persists, contact your vendor or appeal to a higher court." - Signal11 on slashdot
Sounds like you need to manipulate the expiry time for the objects. I'd suggest that that can either be done in the RESPONSE or via meta tags in the standard_html_header to mark the page and the image as non-cacheable. I'm actually interested in a Guru's response on this as I will need to set the expiry explicitly to save load on the server for content that is dynamically generated but doesn't change often. Marc
-----Original Message----- From: zope-admin@zope.org [mailto:zope-admin@zope.org]On Behalf Of Marco Mariani Sent: Sunday, 2 July 2000 9:08 AM To: zope@zope.org Subject: [Zope] how to invalidate an object in the cache?
I am working with photo rotating/resizing, via PIL on external method.
All the images are kept on LocalFS.
There is a thumbnail bonanza page, when I select a thumbnail a form is shown, and I can adjust rotation/contrast/brightness. Upon submit, the new image+thumbnail is calculated and written to the filesystem.
Then the method calls RESPONSE.redirect to show the index page again.
When I go back to the index thumbnail page, the image I've just rotated is displayed with the right size (which means that Zope gets it right), but not rotated (which means that Netscape reads the old image from the cache). I mean, if it was 320x200 and is now 200x320, the browser displays the old 320x200 image stretched to 200x320.
I'm not digging into contrast and brightness, but the same happens.
Is there a way to force the browser to discard the cache for that image? If I go "right-button, view image, shift+reload" the new image is displayed.
Any idea? I'm not very knowledgeable on this matter, I don't design pages for a living.
Might javascript help?
Thank you.
-- "This company has performed an illegal operation and will be shut down. If the problem persists, contact your vendor or appeal to a higher court." - Signal11 on slashdot
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On Sun, Jul 02, 2000 at 03:56:39PM +1000, Marc Boschma wrote:
Sounds like you need to manipulate the expiry time for the objects. I'd suggest that that can either be done in the RESPONSE or via meta tags in the standard_html_header to mark the page and the image as non-cacheable.
I'm actually interested in a Guru's response on this as I will need to set the expiry explicitly to save load on the server for content that is dynamically generated but doesn't change often.
It would work, but I'd have to set up meta tags for LocalFS objects.. I've found a better kludge: when I call the index page, I pass a "refresh" variable along the URL which contains the number of the modified image. Within the index method, I then call: <dtml-call "REQUEST.set('id2',id+'_0.jpg')"> <dtml-let img="store[id][id2]"> <A HREF="imageForm?fnum=&dtml.url_quote-id;"><IMG SRC="<dtml-var "img.absolute_url()+['','?%s'%_.random.random()][REQUEST.get('refresh')==id]">" ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ WIDTH="<dtml-var "img.width">" HEIGHT="<dtml-var "img.height">" ALT="&dtml-id;"></A> </dtml-let> This way, the refreshed image is called with a trailing "?0.283759872" that tricks Netscape to think it's a new object, and reloads. This could work for you too, maybe. -- "This company has performed an illegal operation and will be shut down. If the problem persists, contact your vendor or appeal to a higher court." - Signal11 on slashdot
Marc Boschma wrote:
Sounds like you need to manipulate the expiry time for the objects. I'd suggest that that can either be done in the RESPONSE or via meta tags in the standard_html_header to mark the page and the image as non-cacheable.
Read the Cacheability Howto - http://www.mnot.net/cache_docs/ You can set the HTTP headers described there using RESPONSE.setHeader: RESPONSE.setHeader('Cache-Control', 'no-cache') -- Itamar S.T. itamar@maxnm.com Fingerprint = D365 7BE8 B81E 2B18 6534 025E D0E7 92DB E441 411C
Hi, Itamar Shtull-Trauring wrote:
Marc Boschma wrote:
Sounds like you need to manipulate the expiry time for the objects. I'd suggest that that can either be done in the RESPONSE or via meta tags in the standard_html_header to mark the page and the image as non-cacheable.
Read the Cacheability Howto - http://www.mnot.net/cache_docs/
You can set the HTTP headers described there using RESPONSE.setHeader: RESPONSE.setHeader('Cache-Control', 'no-cache')
Yeah, but you have to do this in the image, not the document. So one has to patch the image-object as I did for this case. Regards Tino Wildenhain
participants (4)
-
Itamar Shtull-Trauring -
Marc Boschma -
Marco Mariani -
Tino Wildenhain