$h->reg_cb (
   '/test' => sub {
      my ($httpd, $req) = @_;
      $req->respond ({
         content => ['text/plain', sub {
            my ($data_cb) = @_;
            return unless $data_cb;
            $data_cb->(substr $SENT, 0, 10, '');
         }]
      });
   },
);