# in case of success: return a 'true' value   (1 or a useful value)
# in case of error:   return a 'false' value  (0 or undef)
sub verify_port {
  my $value = shift;

  # user provided input should be viewed as toxic - do not
  # trust until proven to contain a sane value
  if (defined $value and $value =~ /\A (\d+) \z/xms) {
    my $port = $1;

    if ($MIN_TCP_PORT <= $port and $port <= $MAX_TCP_PORT) {
      return 1;  # or TRUE or $port
    }
  }

  return 0;  # or FALSE or undef
}