#!/usr/bin/perl
# Copyright 2007 Messiah College. All rights reserved.
# Jason Long <jlong@messiah.edu>
use strict;
use warnings;
# This class contains a method to perform synchronous DNS queries.
# Hopefully some day it will have a method to perform
# asynchronous DNS queries.
package Mail::DKIM::DNS;
use Net::DNS;
our $TIMEOUT = 10;
# query- returns a list of RR objects
# or an empty list if the domain record does not exist
# (e.g. in the case of NXDOMAIN or NODATA)
# or throws an error on a DNS query time-out or other transient error
# (e.g. SERVFAIL)
#
# if an empty list is returned, $@ is also set to a string explaining
# why no records were returned (e.g. "NXDOMAIN").
#
sub query
{
my ($domain, $type) = @_;
my $rslv = Net::DNS::Resolver->new()
or die "can't create DNS resolver";
#
# perform the DNS query
# if the query takes too long, we should generate an error
#
my $resp;
eval
{
# set a 10 second timeout
local $SIG{ALRM} = sub { die "DNS query timeout for $domain\n" };
alarm $TIMEOUT;
# the query itself could cause an exception, which would prevent
# us from resetting the alarm before leaving the eval {} block
# so we wrap the query in a nested eval {} block
eval
{
$resp = $rslv->query($domain, $type);
};
my $E = $@;
alarm 0;
die $E if $E;
};
my $E = $@;
alarm 0; #FIXME- restore previous alarm?
die $E if $E;
if ($resp)
{
my @result = grep { lc $_->type eq lc $type } $resp->answer;
return @result if @result;
}
$@ = $rslv->errorstring;
return () if ($@ eq "NOERROR" || $@ eq "NXDOMAIN");
die "DNS error: $@\n";
}
1;
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