> -----Original Message-----
> From: Simon Hook [mailto:simon.j.hook@xxxxxxxxxxxx]
> Sent: Donnerstag, 10. März 2005 17:01
> To: Boyle Owen
> Subject: Re: [users@httpd] When an image is replaced in the htdocs
> directory through a cgi script and incorporated into a new
> html page the
> new image does not get displayed
>
>
> Hi Owen
Please keep on list...
>
> mod_file_cache is disabled:
>
> #LoadModule file_cache_module modules/mod_file_cache.so
>
> I get the same problem with either Firefox or IE so while it
> could be a
> browser cache problem it seems like and Apache problem.
This is not convincing. Both these browsers have extensive caching capabilities. In Firefox, you can clear the cache with Tools -> Options -> Privacy -> Cache -> Clear. Do this between requests to eliminate the browser cache.
Also, to investigate further, look in the apache access_log while you request the page. You should see a GET for the HTML page and then another GET for the embedded image. If you don't see a second GET, then the browser is deciding not to request it because it thinks it already has it.
If you do see a second GET, look at the response code; if it's 200 then apache fetched the image again, if it's 304 then apache is replying "Not Modified" (which would be bad).
>
> I am not sure what you mean by connected directly to the
> server. Apache
> is installed on my machine and I am accessing files with a
> webrowser on
> my machine i.e.
>
> http://mymachine/cgin-bin/noupdate.py
>
> so I think I am directly connected to my server.
If both browser and server are running on the same physical machine then you're directly connected :-) If your server had been, say, on a remote hosting location and your browser on a desktop inside a corporate LAN, there would almost certainly have been a caching proxy somewhere in between..
>
> Any other ideas its a complete showstopper for using Apache!
My guess is it is certainly a browser cache problem. You have to convince the browser to re-issue the request no matter what. You could try ExpiresByType (see http://httpd.apache.org/docs-2.0/mod/mod_expires.html#expiresbytype) to do this, eg.
ExpiresByType image/png A0
Rgds,
Owen Boyle
Disclaimer: Any disclaimer attached to this message may be ignored.
>
> Thanks, Simon
>
> Boyle Owen wrote:
>
> >
> >
> >>-----Original Message-----
> >>From: Simon Hook [mailto:simon.j.hook@xxxxxxxxxxxx]
> >>Sent: Donnerstag, 10. März 2005 07:23
> >>To: users@xxxxxxxxxxxxxxxx
> >>Subject: [users@httpd] When an image is replaced in the
> >>htdocs directory
> >>through a cgi script and incorporated into a new html page
> >>the new image
> >>does not get incorporated.
> >>
> >>
> >>PROBLEM: When an image is replaced in the htdocs directory
> >>through a cgi
> >>script and incorporated into a new html page the new image
> >>does not get
> >>incorporated.
> >>
> >>Hi All,
> >>
> >>I am trying to write a web app where a variable, passed with
> >>a form, is
> >>used to generate a plot, which is saved and then displayed
> >>as a static
> >>image in an html page. I am using the webform from pythonweb and
> >>generating the plot with matplotlib. I am using Apache 2.053 under
> >>Windows XP. I am keeping it real simple by simply passing
> an integer.
> >>The whole process works, HOWEVER, when I back page and submit a new
> >>integer value which generates a new plot and new static
> >>image, the new
> >>image does not get displayed, instead the last version of
> the static
> >>image (plot) is displayed (presumably from the cache).
> >>
> >>
> >
> >Rather, "...presumably from *a* cache..."
> >
> >There are several points where data are cached in a typical
> >browser-server configuration:
> >
> >- in the server: Are you using mod_cache? If so, try CacheDisable the
> >path to the cgi, or just switch off (don't Load it).
> >
> >- in the network: Are the browser and server connected via a
> network? If
> >there are proxies in the route, they will certainly cache
> things.. Can
> >you connect directly?
> >
> >- in the browser: disable caching (thought his will make
> pages slow to
> >load - it'll have to reload images every time
> >
> >To check if it's really the server, use a browser with caching turned
> >off and connected directly to the server..
> >
> >Rgds,
> >Owen Boyle
> >Disclaimer: Any disclaimer attached to this message may be ignored.
> >
> >
> >
> >
> >>If I
> >>reload the
> >>page with the browser the updated image gets displayed
> otherwise the
> >>previous plot gets displayed with 2 or 3 re-submits and then
> >>eventually
> >>an updated one is displayed. It seems like Apache does not
> >>recognize a
> >>changed image and still uses the first plot I created for 2
> >>or 3 submits
> >>or the submit does not force Apache to look for a changed file.
> >>
> >>I am new to Apache, Pythonweb and MatplotLib although I have done
> >>similar stuff with ASP and IIS and some Python work. I have waded
> >>through the Apache and Pythonweb documentation and got
> >>nowhere. I have
> >>tried using the MOD_EXPIRES directive with Apache but this has no
> >>effect. I think this is because a new image (PNG) has been
> generated
> >>rather than an old one has expired. I cannot see any way with
> >>pythonweb
> >>forms to load a static html page (i.e. with cgi). I think
> if I had a
> >>static html page I could write out maybe I could expire that
> >>which would
> >>force Apache to load the new image file.
> >>
> >>I have tried
> >>
> >><META HTTP-EQUIV=Refresh CONTENT=1>
> >>
> >>which refreshes the page every second - this works but who
> >>would want it!
> >>
> >>I have tried
> >>
> >><META HTTP-EQUIV=expires CONTENT=0>
> >>
> >>but this does not work.
> >>
> >>I have attached the code below, its a rework of one of the
> >>examples in
> >>pythonweb. Just copy this to the cgi-bin directory and it
> >>should work,
> >>provided matplotlib is installed. Matplotlib is available from:
> >>
> >>http://matplotlib.sourceforge.net/
> >>
> >>Pythonweb is available from:
> >>
> >>http://www.pythonweb.org
> >>
> >>Despite hours of trying I cannot get this to work, which
> >>would seem like
> >>a necessity for Pythonweb and Apache. Any help would be much
> >>appreciated.
> >>
> >>Thanks,
> >>
> >>Simon
> >>
> >>---cut here
> >>
> >>#!d:/apps/Python23/python
> >>
> >>"The form that will not update"
> >>
> >>import sys, re, os
> >>sys.path.append('../')
> >>sys.path.append('../../')
> >>
> >>import web.error; web.error.handle(handler='browser',
> output='debug',
> >>format='html')
> >>import web, web.form, web.form.field.basic, web.util
> >>import web.form.field.typed
> >>from pylab import *
> >>
> >>class ExampleForm(web.form.Form):
> >>
> >> def setup(self):
> >> self.addField(web.form.field.typed.Integer('myval',
> >>default=6,
> >>required=True))
> >>
> >> # The preffered way of adding submit buttons is as
> actions so
> >>Submit buttons are normally not used.
> >> self.addAction('Validate This Form')
> >>
> >># Print the HTTP Header
> >>print web.header('text/html')
> >>
> >># Create a form
> >>exampleForm = ExampleForm('form', os.environ['SCRIPT_NAME'], 'get')
> >>
> >>if len(web.cgi) > 0: # Form submitted
> >> # Populate form with the values from get.
> >>
> >> # Populate the form
> >> exampleForm.populate(web.cgi)
> >>
> >> # Process the form (Validate)
> >> if exampleForm.valid():
> >>
> >> # Grab the desired value, from the form
> >> myval=exampleForm['myval'].value
> >>
> >> # Create the plot, saved as a png in the htdocs directory
> >> myarray=[myval,4,9,16]
> >> print myarray
> >> plot([1,2,3,4], myarray, 'ro')
> >> axis([0, 6, 0, 20])
> >> savefig('../htdocs/plot.png')
> >>
> >> print "<hmtl><body><div align=center><img src=/plot.png
> >>alt=theplot></div></body></html>"
> >>
> >>else:
> >> print
> >>"<html><head><title>noupdate</title></head><body>\n<h1>Input
> >>integer 0-10</h1>%s\n<hr></body></html>"%(exampleForm.html())
> >>
> >>---end cut
> >>
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> --
>
> +++++++++++++++++++++++++++++++++++++++++
> Simon J. Hook, MSc, PhD
> Jet Propulsion Laboratory
> MS 183-501
> Pasadena, CA 91109
> Office: 818-354-0974
> Fax: 818-354-0966
> Email: simon.j.hook@xxxxxxxxxxxx
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> +++++++++++++++++++++++++++++++++++++++++
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