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=item timeout => [...]

A list of timeouts to use (also determines the number of retries). To make
three retries with individual time-outs of 2, 5 and 5 seconds, use C<[2,
5, 5]>, which is also the default.

=item search => [...]

The default search list of suffixes to append to a domain name (default: none).

=item ndots => $integer

The number of dots (default: C<1>) that a name must have so that the resolver
tries to resolve the name without any suffixes first.

=item max_outstanding => $integer

Most name servers do not handle many parallel requests very well. This
option limits the number of outstanding requests to C<$integer>
(default: C<10>), that means if you request more than this many requests,
then the additional requests will be queued until some other requests have
been resolved.

=item reuse => $seconds

The number of seconds (default: C<300>) that a query id cannot be re-used
after a timeout. If there was no time-out then query ids can be reused
immediately.

=item untaint => $boolean

When true, then the resolver will automatically untaint results, and might
also ignore certain environment variables.

=back

=cut

sub new {
   my ($class, %arg) = @_;

   my $self = bless {
      server  => [],
      timeout => [2, 5, 5],
      search  => [],
      ndots   => 1,
      max_outstanding => 10,
      reuse   => 300,
      %arg,
      inhibit => 0,
      reuse_q => [],
   }, $class;

   # search should default to gethostname's domain
   # but perl lacks a good posix module

   # try to create an ipv4 and an ipv6 socket
   # only fail when we cannot create either
   my $got_socket;

   Scalar::Util::weaken (my $wself = $self);

   if (socket my $fh4, AF_INET , Socket::SOCK_DGRAM(), 0) {
      ++$got_socket;

      AnyEvent::fh_unblock $fh4;
      $self->{fh4} = $fh4;
      $self->{rw4} = AE::io $fh4, 0, sub {
         if (my $peer = recv $fh4, my $pkt, MAX_PKT, 0) {
            $wself->_recv ($pkt, $peer);
         }
      };
   }

   if (AF_INET6 && socket my $fh6, AF_INET6, Socket::SOCK_DGRAM(), 0) {
      ++$got_socket;

      $self->{fh6} = $fh6;
      AnyEvent::fh_unblock $fh6;
      $self->{rw6} = AE::io $fh6, 0, sub {
         if (my $peer = recv $fh6, my $pkt, MAX_PKT, 0) {
            $wself->_recv ($pkt, $peer);
         }
      };
   }

   $got_socket
      or Carp::croak "unable to create either an IPv4 or an IPv6 socket";

   $self->_compile;

   $self
}

# called to start asynchronous configuration
sub _config_begin {
   ++$_[0]{inhibit};
}

# called when done with async config
sub _config_done {
   --$_[0]{inhibit};
   $_[0]->_compile;
   $_[0]->_scheduler;
}

=item $resolver->parse_resolv_conf ($string)

Parses the given string as if it were a F<resolv.conf> file. The following
directives are supported (but not necessarily implemented).

C<#>- and C<;>-style comments, C<nameserver>, C<domain>, C<search>, C<sortlist>,
C<options> (C<timeout>, C<attempts>, C<ndots>).

Everything else is silently ignored.

=cut

sub parse_resolv_conf {
   my ($self, $resolvconf) = @_;