#!/usr/bin/perl
# $Id: mresolv 1815 2020-10-14 21:55:18Z willem $

=head1 NAME

mresolv - Perform multiple DNS lookups in parallel

=head1 SYNOPSIS

B<mresolv> S<[ B<-d> ]> S<[ B<-n> I<number> ]> S<[ B<-t> I<timeout> ]>
S<[ I<filename>... ]>

=head1 DESCRIPTION

B<mresolv> performs multiple DNS lookups in parallel.  Names to query
are read from the list of files given on the command line, or from the
standard input.

=head1 OPTIONS

=over 4

=item B<-d>

Turn on debugging output.

=item B<-n> I<number>

Set the number of queries to have outstanding at any time.

=item B<-t> I<timeout>

Set the timeout in seconds.  If no replies are received for this
amount of time, all outstanding queries will be flushed and new
names will be read from the input stream.

=back

=head1 COPYRIGHT

Copyright (c) 1997-2000 Michael Fuhr.  All rights reserved.

=head1 SEE ALSO

L<perl(1)>, L<axfr>, L<check_soa>, L<check_zone>, L<mx>, L<perldig>,
L<Net::DNS>

=cut

use strict;
use warnings;
use Net::DNS;
use IO::Select;
use Getopt::Std;
use vars qw($opt_d $opt_n $opt_t);

local $| = 1;

$opt_n = 32;	# number of requests to have outstanding at any time
$opt_t = 15;	# timeout (seconds)

getopts("dn:t:");

my $res = Net::DNS::Resolver->new;
my $sel = IO::Select->new;
my $eof = 0;

while (1) {
	my $name;
	my $sock;

	#----------------------------------------------------------------------
	# Read names until we've filled our quota of outstanding requests.
	#----------------------------------------------------------------------

	while (!$eof && $sel->count < $opt_n) {
		print "DEBUG: reading..." if defined $opt_d;
		$name = <>;
		unless ($name) {
			print "EOF.\n" if defined $opt_d;
			$eof = 1;
			last;
		}
		chomp $name;
		$sock = $res->bgsend($name);
		$sel->add($sock);
		print "name = $name, outstanding = ", $sel->count, "\n"
			if defined $opt_d;
	}

	#----------------------------------------------------------------------
	# Wait for any replies.  Remove any replies from the outstanding pool.
	#----------------------------------------------------------------------

	my @ready;
	my $timed_out = 1;

	print "DEBUG: waiting for replies\n" if defined $opt_d;

	for (@ready = $sel->can_read($opt_t);
	     @ready;
	     @ready = $sel->can_read(0)) {

		$timed_out = 0;

		print "DEBUG: replies received: ", scalar @ready, "\n"
			if defined $opt_d;

		foreach my $sock (@ready) {
			print "DEBUG: handling a reply\n" if defined $opt_d;
			$sel->remove($sock);
			my $ans = $res->bgread($sock);
			next unless $ans;
			my $rr;
			foreach my $rr ($ans->answer) {
				$rr->print;
			}
		}
	}

	#----------------------------------------------------------------------
	# If we timed out waiting for replies, remove all entries from the
	# outstanding pool.
	#----------------------------------------------------------------------

	if ($timed_out) {
		print "DEBUG: timeout: clearing the outstanding pool.\n"
			if defined $opt_d;
		my $sock;
		foreach my $sock ($sel->handles) {
			$sel->remove($sock);
		}
	}

	print "DEBUG: outstanding = ", $sel->count, ", eof = $eof\n"
		if defined $opt_d;

	#----------------------------------------------------------------------
	# We're done if there are no outstanding queries and we've read EOF.
	#----------------------------------------------------------------------

	last if ($sel->count == 0) && $eof;
}