Problem with PerlTransHandler

Hi all

First of all, I want to clarify that I am pretty newie in mod_perl and I'm
using mod_perl 1.

I need to write a module that allows me to capture all the requests that are
made to my server,
get a string with all the parameters stored in $r->content or $ r-> args for
each request, apply
some process and store again in $r->content or $ r->args to follow their
way.

To achieve this, I'm trying to write a PerlTransHandler:

package Test::test_filter;
use strict;
use Apache::Constants qw(:common);

sub handler {
    my $r = shift;
    my $params = $r->method eq "POST" ? $r->content:$r->args;
    print STDERR "PARAMS:$params\n";
    #DO SOMETHING WITH $params
    #$r->content($params);
    return DECLINED;
}
1;

The problem is, after showing the message with the parameters in the log
file the page with the POST form
does not change; this mean, don't show me the next page where i should see
the values of the modified parameters.

If comment my $params = $r->method eq "POST" ? $r->content:$r->args; all
works fine.

I need to do something else?, I'm using the right type of handler?

In advance thank you very much for your answers.