#!/usr/bin/perl -Tw

use CGI;
use strict;

BEGIN {
    my $POST_MAX = 512 * 1024;

    my $content_length = defined $ENV{'CONTENT_LENGTH'} ? $ENV{'CONTEN
+T_LENGTH'} : 0;
    if ( ($POST_MAX > 0) && ($content_length > $POST_MAX) ) {
        #   custom request entity too large error handling
    }
}
[download]

This code block uses the same logic employed by CGI for the handling of the oversize HTTP requests, however, whereas CGI returns a 413 error, this code block can be customised in its return output.

BTW - CGI::Application rocks! :-)

perl -le 'print+unpack"N",pack"B32","00000000000000000000001001011111"'

 An attempt to send a POST larger than $POST_MAX bytes will cause para
+m() to return an empty CGI parameter list.  You can test for this eve
+nt by checking cgi_error()...
<snip>
...If the POST was intercepted, then cgi_error() will return the messa
+ge "413 POST too large".
[download]

I have an upload script that relies *solely* on the CGI.pm module, and the script incorporates a "maximum size" testing feature that has worked for me. Here's the snippet I use as the uploaded file is being "read in" during the upload:

$max_size = '100000'; #set your max size value
$totalbytes=0;
open (IMAGESAVE,">$image_upload_directory/$final_name");
while ($bytesread=read ($file,$data,1024)) {
    $totalbytes+=$bytesread;
    if ($totalbytes > $max_size) {
        unlink ("$image_upload_directory/$file_name");
        &FileTooLarge; #call your error sub 
        exit;
    }
    print IMAGESAVE $data;
}
close IMAGESAVE;
[download]

just realized .... $final_name should be $file_name in the file open line above.