Don't cache changed image.src?

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  • jetmarc
    #1

    Don't cache changed image.src?

    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
    Tags: None
    • Jim Ley
      #2
      Re: Don't cache changed image.src?

      On 28 Jun 2003 10:21:06 -0700, jetmarc@hotmail .com (jetmarc) wrote:

      i.[color=blue]
      >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.[/color]

      Of course, why would it work anywhere else?
      [color=blue]
      >Can you point me to a solution for this problem?[/color]

      If you'd read the FAQ, you'd've seen the link to
      Caching Tutorial for Web Authors and Webmasters
      http://www.mnot.net/cache_docs/
      Covers the how's and why's of Web caching for people who publish on the Web. With FAQs.


      It will not, and cannot be solved with javascript.

      Jim.
      --
      comp.lang.javas cript FAQ - http://jibbering.com/faq/

        Comment

        • Jim Ley
          #3
          Re: Don't cache changed image.src?

          On 28 Jun 2003 15:46:51 -0700, jetmarc@hotmail .com (jetmarc) wrote:
          [color=blue][color=green]
          >> 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.[/color]
          >
          >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).[/color]

          Then get some influence, simply proxy it through a real server, and
          next time choose a tool that allows you to do your job.
          [color=blue]
          >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.[/color]

          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.
          [color=blue]
          > 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[/color]

          IE does not _always_ save a local file.
          [color=blue]
          >Basically, I'm looking for a client-side solution.[/color]

          There is no client-side solution...
          [color=blue]
          >I can't change
          >the cameras behaviour unless I re-engineer their embedded firmware,
          >or cache all cam images on a linux server[/color]

          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.javas cript FAQ - http://jibbering.com/faq/

            Comment

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