[LON-CAPA-users] dynamic plots not generated

[Stuart Raeburn]

Hi,

Correction:

> ... you should have a URL of the form:
>
> http://loncapa.mines.edu/adm/roles/cgi-bin/plot.png?file=username_domain_1359314655_14857241_plot.data

should be:

... a URL of the form:

http://loncapa.mines.edu/cgi-bin/plot.png?file=username_domain_1359314655_14857241_plot.data

Stuart Raeburn
LON-CAPA Academic Consortium


Quoting Stuart Raeburn <raeburn at msu.edu>:

> Hi Todd,
>
>> This happens only on his personal laptop (it works fine for him on other
>> machines), running Windows7.  It happens with firefox, chrome, and ie.
>> It's clearly some kind of issue with the configuration on his machine.
>
> /res/csm/csmphyslib/Mechanics/Kinematics/Graphical_Analysis/PosAndAccelFromVel1.problem
>
> If you mouse over the location of one of the dynamic plots (which are
> failing to render) and right click, and use "Copy Image Location" you
> should have a URL of the form:
>
> http://loncapa.mines.edu/adm/roles/cgi-bin/plot.png?file=username_domain_1359314655_14857241_plot.data
>
> where username is the username and domain correspond to the identity of
> the user for whom the plot was generated, and the first digit is the
> unix time when the page was requested, and the second digit includes
> some additional randomization.
>
> Internally within LON-CAPA, the contents of the file:
> /home/httpd/perl/tmp/username_domain_1359314655_14857241_plot.data
> are retrieved and then passed as an argument to a piped call to gnuplot.
> A header is then printed to STDOUT
>
> Content-type: image/png
>
> and then the output from gnuplot is sent.
>
> There could be a problem displaying png images if a third-party
> application had been installed, client-side, which had altered the file
> class and MIME settings for the PNG file type.
>
> If there is an issue with display of .png files specifically, the user
> could try replacing .png with .gif in the URL and resubmit the request,
> e.g.,
>
> http://loncapa.mines.edu/adm/roles/cgi-bin/plot.gif?file=username_domain_1359314655_14857241_plot.data
>
> Since the images in question are generated based on the contents of the
> query string, this issue could also be related to removal of the query
> string from the URI.
>
> A google search for issues displaying images with Windows7 found:
>
> http://support.microsoft.com/kb/283807
> http://support.microsoft.com/kb/942172
>
> which do *not* seem to be directly applicable to this case.
>
> Anyway, a couple of things to check server side would be:
> (a) look in /etc/httpd/logs/access_log for a line containing:
>
> "GET
> /cgi-bin/plot.png?file=username_domain_1359314655_14857241_plot.data
> HTTP/1.1"
>
> (replacing username and domain) to confirm that the response code and
> file size (the two numbers at the end of the line) are as expected.
>
> (b) look in /home/httpd/perl/tmp for
> username_domain_1359314655_14857241_plot.data
>
> (replacing username and domain) to see if the data file which is passed
> to gnuplot is as expected.
>
>
> Something to check client side would be to:
> -- paste the URL of the image into a separate window and try to display
> the URL.
>
> If the browser is firefox, an add-on such as httpfox
> https://addons.mozilla.org/en-US/firefox/addon/httpfox/
> could be installed (browser restart required) to allow the response
> header to be viewed.
>
> The response header should be something like:
>
> Date:
> Server: Apache/2.2.3 (CentOS)
> Connection: close
> Transfer-Encoding: chunked
> Content-Type: image/png
>
> 200 OK
>
> The httpfox add-on will also display the bytes transferred.
>
> Lastly is it possible to save the contents of the image URL to the
> desktop and open with some other application?
>
>
> Stuart Raeburn
> LON-CAPA Academic Consortium
>
>
> Quoting Todd Ruskell <todd.ruskell at gmail.com>:
>
>> Hi all,
>>
>> Here's one I don't recall seeing before.  I have one student on whose
>> computer *some* dynamically generated plots don't display.  What's more
>> interesting is that on refreshing the page, a different set of dynamically
>> generated plots are not displayed, but some of those that were originally
>> not displayed, are.
>>
>> This happens only on his personal laptop (it works fine for him on other
>> machines), running Windows7.  It happens with firefox, chrome, and ie.
>> It's clearly some kind of issue with the configuration on his machine.  I
>> know it's a shot in the dark, but if you all have any ideas of what we
>> might try to look for, I'd appreciate it.
>>
>> The resource in question is
>> /res/csmphyslib/Mechanics/Kinematics/Graphical_Analysis/PosAndAccelFromVel1.problem
>>
>> which we've used regularly without incident for the last three semesters.
>>
>> Thanks for any small leads you can provide.
>>
>> Todd