I commend you for your coherent post but honestly I can't help you (nor can many of the monks minus the talented visualizers out there) with out seeing some if not all of your code.

Post your work and I'm sure someone (if not myself) can offer you assistance.

What you're trying to do is not what this was intended for, but you may be able to work around with QUERY_STRING

my $q = CGI->new($ENV{QUERY_STRING});
$data = $q->param('chicken');
$data = $1 if $data =~ //;# untaint chicken
$q = CGI->new(\&hook, $data);
[download]

What you're trying to do is not what this was intended for, but you may be able to work around with QUERY_STRING

Then I do wonder what it was intended for then, if not for tracking the state of uploads.

I made up a small example, using bits of your code:

The upload-form: (form.html)

<!-- using GET will make the QUERY_STRING as mentioned in the previous
+ post, but.. that's not how it's supposed to be? -->
<form action="minitest.cgi" enctype="multipart/form-data" method="GET"
+>
 <input type="file" name="file">
 <input type="submit" value="send">
 <input type="hidden" name="pregeneratedID" value="123456">
</form>
[download]

the upload-script: (minitest.cgi)

#!/usr/bin/perl -w

use strict;
use CGI qw/:standard/;
use CGI::Carp qw(fatalsToBrowser);

my $query = CGI->new($ENV{QUERY_STRING});

# I will initially save my file with this name and copy it to the corr
+ect name later (ID+original suffix)
# ID has to be passed to 'hook', to keep track of the upload-status in
+ a DB (I will just use a plain file here for testing)
# as only $filename (the originale name on the client-disk is passed t
+o the hook, there is no relation between the
# sanitized filename I will use when saving the uploaded file, and the
+ filename used in the hook, thus practically rendering
# the hook useless
my $data = $query->param('pregeneratedID');
if (!$data) { print $query->header(); print "no data?"; exit; }
$data = $1 if $data =~ //;# untaint generatedID - for some reason this
+ sets the contents of $data to .. nothing
if (!$data) { print $query->header(); print "no data?"; exit; }

$query = CGI->new(\&hook, $data);

my $fh = $query->upload('file');
# I want to save the file with the same filename as the ID (so it's ea
+sier to keep track of during download)
# for testing purposes, I will not handle renaming and moving the file
+ in this example
my $name = $data;

open ( UPLOADFILE, ">uploads/$name" ) or die ("$!");
binmode UPLOADFILE;
while ( <$fh> )
{
 print UPLOADFILE;
}
close UPLOADFILE;

print $query->header();
print "look in uploads/test.log and see if $data was passed to the hoo
+k<br>\n";
print "If the file is not there, it means hook was never called, provi
+ng the manual right (blasted!))<br>\n";
print "filetype: ".$query->uploadInfo($fh)->{'Content-Type'}; # this b
+arfs, as nothing survives the sanitizing..

####

sub hook {
 my ($filename,$buffer,$bytes_received,$data) = @_;
 open (LOG, ">>uploads/test.log");
 print LOG $filename." ".$bytes_received. " - ".$data."\n";
 close (LOG);
}
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This leaves me with an empty file in uploads/ named '123456' and no log-file, meaning the hook wasn't called.

I can only conclude, that the hook-feature makes it possible to either keep track of a specific upload by using un-sanitized filenames, giving me the option of actually using the progress-information logged by the hook, or using fully sanitized filenames in the hook as well, (by generating the ID within the upload-script, before declaring the cgi-obj), but then not having any posibilities of keeping track of the upload while it is in progress.. unless CGI.pm is modified so it will pass more information from the upload-handler. As I see it, the $data-option is nearly useless

Of course, if there is any other way of doing this in a nice way, don't keep it back :)

Then I do wonder what it was intended for then, if not for tracking the state of uploads.
Nowhere is it suggested you can get your chicken before upload hook. It says The $data field is optional; it lets you pass configuration information (e.g. a database handle) to your hook callback.

<!-- using GET will make the QUERY_STRING as mentioned in the previous post, but.. that's not how it's supposed to be? --> Who suggested you use get? I said as long as action is /foo/bar.cgi?chicken=ididid Example

#!/usr/bin/perl  -- 

use strict;
use warnings;

use CGI();

$|=1;
$ENV{QUERY_STRING}="";

{

    my $q = CGI->new("".$ENV{QUERY_STRING});
    $q->param(qw' chicken ididid ');

    print join "\n",
    $q->start_html,
    $q->start_form(
        -method=>'POST',
        -action=>  $q->self_url,
        -enctype=> &CGI::MULTIPART
    ),
    $q->filefield('file'),
    $q->hidden(pregeneratedID => 123456 ),
    $q->end_form,
    $q->end_html;
}

__END__
<!DOCTYPE html
    PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
     "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-U
+S">
<head>
<title>Untitled Document</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1
+" />
</head>
<body>

<form method="post" action="http://localhost?chicken=ididid" enctype="
+multipart/form-data">

<input type="file" name="file"  />
<input type="hidden" name="pregeneratedID" value="123456"  />
</form>

</body>
</html>
[download]