#!/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
    }
}
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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"'