sub handler {

   my $r=shift;

   # generate your Spreadsheet binary and put it in, oh
   # $sheet, ok?

   $r->content_type('application/vnd.ms-excel');
   $r->header_out('Content-disposition' => "attachment; filename=\"$filename"");
   $r->send_http_header;

   $r->print($sheet);

   return DONE;

}