Don't cache changed image.src?

Discussion in 'Javascript' started by jetmarc, Jun 28, 2003.

  1. jetmarc

    jetmarc Guest

    Hi.

    I have a webcam page (video surveillance) that refreshes 9 images
    once a second (1000ms rate). It uses javascript to change the
    image.src

    To trick the caching mechanism of the browser and force a fresh
    download from the IP camera, a random tag is appended to the URL.

    Unfortunately MSIE6 (WinXP) caches each and every frame ON DISK.
    That is, while the page is displayed, the harddrive stores 9*20kb
    or ~200kb per second. And worse, MSIE lets the temp folder grow
    very big, resulting in reduced system performance (especially
    when booting up after a work-day of video surveillance).


    What can I do about it? The life-time of an image is 1 second,
    it will never be used again. I don't want the browser to store
    it on the harddrive.

    I tried this on my page:

    <HEAD> <META http-equiv="Pragma" content="no-cache"> </HEAD>

    but it seems to work only for the HTML portion of the page, not
    for the image.src loading.


    I tried to locate a RAM drive where I can point the MSIE6 temp
    folder to, so that at least it won't cache on the harddrive,
    but couldn't find any solution (for WinXP) either. And also, I
    went for HTML/JavaScript to NOT have to install anything on the
    client machine :(


    Can you point me to a solution for this problem?

    Marc
     
    jetmarc, Jun 28, 2003
    #1
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  2. jetmarc

    Jim Ley Guest

    On 28 Jun 2003 10:21:06 -0700, (jetmarc) wrote:

    i.
    >I tried this on my page:
    >
    ><HEAD> <META http-equiv="Pragma" content="no-cache"> </HEAD>
    >
    >but it seems to work only for the HTML portion of the page, not
    >for the image.src loading.


    Of course, why would it work anywhere else?

    >Can you point me to a solution for this problem?


    If you'd read the FAQ, you'd've seen the link to
    http://www.mnot.net/cache_docs/

    It will not, and cannot be solved with javascript.

    Jim.
    --
    comp.lang.javascript FAQ - http://jibbering.com/faq/
     
    Jim Ley, Jun 28, 2003
    #2
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  3. jetmarc

    Jim Ley Guest

    On 28 Jun 2003 15:46:51 -0700, (jetmarc) wrote:

    >> If you'd read the FAQ, you'd've seen the link to
    >> http://www.mnot.net/cache_docs/
    >>
    >> It will not, and cannot be solved with javascript.

    >
    >Thanks for your follow-up.
    >
    >Actually I have seen that page before, when researching. The problem
    >is that I don't have any influence on the HTTP headers, because the
    >image URL is on a physically separate web cam (Axis 2100 IP network
    >camera).


    Then get some influence, simply proxy it through a real server, and
    next time choose a tool that allows you to do your job.

    >I think, actually the MSIE browser does honor the no-cache pragma in
    >that it reloads the HTML page _AND_ the initial dummy images from
    >scratch each time I open the page.


    It's unlikely that a web cam server is sending cacheable headers,
    therefore IE won't cache the image between page reloads on its default
    setting - it wll within instance.

    > I conclude that maybe Axis as a manufacturer of
    >web cams themselves did not find a way to circumvent MSIE's behaviour
    >of producing a local FILE


    IE does not _always_ save a local file.

    >Basically, I'm looking for a client-side solution.


    There is no client-side solution...

    >I can't change
    >the cameras behaviour unless I re-engineer their embedded firmware,
    >or cache all cam images on a linux server


    No, it's simple, put Apache as a proxy between the web and the camera,
    you can then control the headers and everything else in Apache.

    Jim.
    --
    comp.lang.javascript FAQ - http://jibbering.com/faq/
     
    Jim Ley, Jun 29, 2003
    #3
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