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  • Ivan 165 posts 543 karma points
    Oct 25, 2012 @ 14:58
    Ivan
    0

    Does it respect "Expires" header when image is changed.

    Hi guys.

    I understand that pro version supports client side caching, meaning that images respond with Expires header.

    The problem comes out when cached images are updated. Client won't see changes due to browser caching (according to Expires period).

    Is that problem solved in ImageGen?

     

  • Douglas Robar 3570 posts 4711 karma points MVP ∞ admin c-trib
    Oct 25, 2012 @ 17:18
    Douglas Robar
    0

    Hi, Ivan,

    The problem has nothing to do with ImageGen, it's just the way the web works. If you set an expires header the browser won't even ask the server if the original file has changed. Used carefully this is extremely powerful and a huge performance boost to your sites. 

    With ImageGen Professional you can set how long you want for the expires headers in each class. So you can decide what is best for each kind of image served up by ImageGen.

    When the expiration has passed (or if you're using ImageGen Basic since it doesn't have client-side caching) the browser will request the image from ImageGen on the server. ImageGen will compare the image the browser already has with what's on the server and if it's the same will send a tiny 304 Not Modified response to tell the browser to use what it already has in its local cache rather than downloading an identical image again. 

    Whenever this comparison is done on the server ImageGen will look to see if the original image has changed from the last time it sent the image and will automatically re-create the image as needed. So if you have a file called photo.jpg of you and resize it with ImageGen the website visitor will get that resized image. If you subsequently update the photo.jpg file with a different image the next request for it via ImageGen will create a new resized image and send that to the browser. If the source image (photo.jpg) hasn't changed then ImageGen will immediately send either the already-cached image from the server or a 304 response if the browser already has the correct image.

    Hope this helps.

    cheers,
    doug. 

  • Ivan 165 posts 543 karma points
    Oct 26, 2012 @ 05:40
    Ivan
    0

    Thanks, Douglas.

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