Greetings

This is a follow-up to a previous problem I posted in SOPW (see Use of GD::Graph).

Having successfully implemented the solution proposed to me (i.e. printing images to file, and then calling them back from file using <img> tags), I am now finding that the images, rather than being updated when I click the submit button in my form, are only being updated when I hit the refresh button in my browser. I suspected this was something to do a web-server or proxy cache-ing the web page somewhere along the line, so I put the following line in my code to print to the HTTP header :

print "Cache-Control: no-cache\n";

My local webmaster also tells me that the web-server is not doing any cacheing. However, inserting this line did not solve the problem and I suspect that there is something erroneous going on with writing to and retrieving from the files.

Here are the relevant parts of my code:

#!/usr/bin/perl -w

use strict; 
use warnings;

use CGI qw/:standard *table *Tr *td/;
use CGI::Carp qw(fatalsToBrowser);
use Date::Manip; 
use DBI;
use GD::Graph;
use GD::Graph::bars;
use GD::Graph::lines;
use GD::Graph::linespoints;

my $image_directory="/var/www/html/foo/bar/";
my $image_web_path="http://(IPaddress here)/foo/bar/";
print "Cache-Control: no-cache\n";
print header;
print start_html(
        -title=>'Online search',
        -style=>'(link to style sheet)'
        );
my @imagefiles;
for (my $i=1; $i<=8; $i++){$imagefiles[$i]=$image_directory.'imagefile
+'.$i.'.gif';}
...
(form to acquire parameters specifying beginning and ending of search 
+period)
...
(database interrogation based on above search period, writing data to 
+various data structures, then preparing the data to be processed by G
+D::Graph)
...
#Output the results of the database interrogation as a graph  using GD
+::Graph and write it to file like so:

    open IMAGEFILE, ">$imagefiles[6]" or die "Couldn't open $imagefile
+s[6]:$!";
    binmode STDOUT;
    my $gd3_lines_average=$linegraph3_average->plot(\@linedata3_averag
+e)->$format3_lines_average() or die $linegraph3_average->error;
    print IMAGEFILE $gd3_lines_average;
    close IMAGEFILE;
...
Create the other image files in a similar way to the one above
...
print img({-src=>$image_web_path.'imagefile6.gif',-width=>"400",-heigh
+t=>"300",-alt=>"No of foos in month bar"})
...
Retrieve the other image files in a similar way to the one above
...
print end_html;
[download]

I've also tried retrieving the images as local files but to no avail. I could implement the second solution that was proposed to me, i.e. passing the form parameters to a second Perl script that output the images on the fly, but having gone down this route I would like to at least have a go at solving this problem before I do so.

Any ideas as to what's going on?

Thanks in advance,
Campbell

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.