sub _dotls {
   my ($self) = @_;

   if (length $self->{_tls_wbuf}) {
      while ((my $len = Net::SSLeay::write ($self->{tls}, $self->{_tls_wbuf})) > 0) {
         substr $self->{_tls_wbuf}, 0, $len, "";
      }
   }

   if (defined (my $buf = Net::SSLeay::BIO_read ($self->{_wbio}))) {
      $self->{wbuf} .= $buf;
      $self->_drain_wbuf;
   }

   while (defined (my $buf = Net::SSLeay::read ($self->{tls}))) {
      $self->{rbuf} .= $buf;
      $self->_drain_rbuf;
   }

   my $err = Net::SSLeay::get_error ($self->{tls}, -1);

   if ($err!= Net::SSLeay::ERROR_WANT_READ ()) {
      if ($err == Net::SSLeay::ERROR_SYSCALL ()) {
         return $self->_error ($!, 1);
      } elsif ($err == Net::SSLeay::ERROR_SSL ())  {
         return $self->_error (&Errno::EIO, 1);
      }

      # all others are fine for our purposes
   }
}