File Coverage

blib/lib/Mail/DKIM/DNS.pm

Criterion	Covered	Total	%
statement	61	80	76.2
branch	18	34	52.9
condition	4	6	66.6
subroutine	7	11	63.6
pod	2	4	50.0
total	92	135	68.1

package Mail::DKIM::DNS;
use strict;
use warnings;
our $VERSION = '1.20230630'; # VERSION
# ABSTRACT: performs DNS queries for Mail::DKIM

# Copyright 2007, 2012 Messiah College. All rights reserved.
# Jason Long


# This class contains a method to perform synchronous DNS queries.
# Hopefully some day it will have a method to perform
# asynchronous DNS queries.

use Net::DNS;
our $TIMEOUT = 10;
our $RESOLVER;

sub resolver {
    if (@_) {
        $RESOLVER = $_[0];
    }
    return $RESOLVER;
}

sub enable_EDNS0 {

    # enable EDNS0, set acceptable UDP packet size to a
    # conservative payload size that should fit into a single
    # packet (MTU less the IP header size) in most cases;
    # See also draft-andrews-dnsext-udp-fragmentation
    # and RFC 3542 section 11.3.

    my $res = Net::DNS::Resolver->new();
    $res->udppacketsize( 1280 - 40 );
    resolver($res);
}

# 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 ) = @_;

    if ( !$RESOLVER ) {
        $RESOLVER = Net::DNS::Resolver->new()
          or die "Internal error: can't create DNS resolver";
    }

    my $rslv = $RESOLVER;

    #
    # perform the DNS query
    #   if the query takes too long, we should generate an error
    #
    my $resp;
    my $remaining_time = alarm(0);    # check time left, stop the timer
    my $deadline = time + $remaining_time;
    my $E;
    eval {
        local $SIG{__DIE__};

        # set a timeout, 10 seconds by default
        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
        my $E2;
        eval {
            local $SIG{__DIE__};
            $resp = $rslv->send( $domain, $type );
            1;
        } or do {
            $E2 = $@;
        };
        alarm 0;
        if ($E2) { chomp $E2; die "$E2\n" }    # no line number here
        1;
    } or do {
        $E = $@;    # the $@ only makes sense if eval returns a false
    };
    alarm 0;

    # restart the timer if it was active
    if ( $remaining_time > 0 ) {
        my $dt = $deadline - time;

        # make sure the timer expiration will trigger a signal,
        # even at the expense of stretching the interval by one second
        alarm( $dt < 1 ? 1 : $dt );
    }
    if ($E) { chomp $E; die $E }    # ensure a line number

    # RFC 2308: NODATA is indicated by an answer with the RCODE set to NOERROR
    # and no relevant answers in the answer section.  The authority section
    # will contain an SOA record, or there will be no NS records there.
    # NODATA responses have to be algorithmically determined from the
    # response's contents as there is no RCODE value to indicate NODATA.
    # In some cases to determine with certainty that NODATA is the correct
    # response it can be necessary to send another query.

    if ($resp) {
        my $header = $resp->header;
        if ($header) {

            # NOERROR, NXDOMAIN, SERVFAIL, FORMERR, REFUSED, ...
            my $rcode = $header->rcode;

            $@ = $rcode;
            if ( $rcode eq 'NOERROR' ) {

                # may or may not contain RRs in the answer sect
                my @result = grep { lc $_->type eq lc $type } $resp->answer;
                $@ = 'NODATA' if !@result;
                return @result;    # possibly empty
            }
            elsif ( $rcode eq 'NXDOMAIN' ) {
                return;            # empty list, rcode in $@
            }
        }
    }
    if ( $rslv->errorstring eq 'NOERROR' ) {
        return;
    }
    if ( $rslv->errorstring =~ /\bno error\b/ ) {
        return;
    }
    die 'DNS error: ' . $rslv->errorstring . "\n";
}

# query_async() - perform a DNS query asynchronously
#
#   my $waiter = query_async('example.org', 'TXT',
#                        Callbacks => {
#                                Success => \&on_success,
#                                Error => \&on_error,
#                                },
#                            );
#   my $result = $waiter->();
#
sub query_async {
    my ( $domain, $type, %prms ) = @_;

    my $callbacks = $prms{Callbacks} || {};
    my $on_success = $callbacks->{Success} || sub { $_[0] };
    my $on_error   = $callbacks->{Error}   || sub { die $_[0] };

    my $waiter = sub {
        my @resp;
        my $rcode;
        eval {
            local $SIG{__DIE__};
            @resp = query( $domain, $type );
            $rcode = $@;
            1;
        } or do {
            return $on_error->($@);
        };
        $@ = $rcode;
        return $on_success->(@resp);
    };
    return $waiter;
}

1;

__END__