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package Net::DNS::Header;
#
# $Id: Header.pm 1527 2017-01-18 21:42:48Z willem $
#
our $VERSION = (qw$LastChangedRevision: 1527 $)[1];
=head1 NAME
Net::DNS::Header - DNS packet header
=head1 SYNOPSIS
use Net::DNS;
$packet = new Net::DNS::Packet;
$header = $packet->header;
=head1 DESCRIPTION
C<Net::DNS::Header> represents the header portion of a DNS packet.
=cut
use strict;
use warnings;
use integer;
use Carp;
use Net::DNS::Parameters;
=head1 METHODS
=head2 $packet->header
$packet = new Net::DNS::Packet;
$header = $packet->header;
Net::DNS::Header objects emanate from the Net::DNS::Packet header()
method, and contain an opaque reference to the parent Packet object.
Header objects may be assigned to suitably scoped lexical variables.
They should never be stored in global variables or persistent data
structures.
=head2 string
print $packet->header->string;
Returns a string representation of the packet header.
=cut
sub string {
my $self = shift;
my $id = $self->id;
my $qr = $self->qr;
my $opcode = $self->opcode;
my $rcode = $self->rcode;
my $qd = $self->qdcount;
my $an = $self->ancount;
my $ns = $self->nscount;
my $ar = $self->arcount;
my $opt = $$self->edns;
my $edns = $opt->_specified ? $opt->string : '';
return <<END . $edns if $opcode eq 'UPDATE';
;; id = $id
;; qr = $qr opcode = $opcode rcode = $rcode
;; zocount = $qd prcount = $an upcount = $ns adcount = $ar
END
my $aa = $self->aa;
my $tc = $self->tc;
my $rd = $self->rd;
my $ra = $self->ra;
my $zz = $self->z;
my $ad = $self->ad;
my $cd = $self->cd;
my $do = $self->do;
return <<END . $edns;
;; id = $id
;; qr = $qr aa = $aa tc = $tc rd = $rd opcode = $opcode
;; ra = $ra z = $zz ad = $ad cd = $cd rcode = $rcode
;; qdcount = $qd ancount = $an nscount = $ns arcount = $ar
;; do = $do
END
}
=head2 print
$packet->header->print;
Prints the string representation of the packet header.
=cut
sub print { print &string; }
=head2 id
print "query id = ", $packet->header->id, "\n";
$packet->header->id(1234);
Gets or sets the query identification number.
A random value is assigned if the argument value is undefined.
=cut
sub id {
my $self = shift;
$$self->{id} = shift if scalar @_;
return $$self->{id} if defined $$self->{id};
$$self->{id} = int rand(0xffff);
}
=head2 opcode
print "query opcode = ", $packet->header->opcode, "\n";
$packet->header->opcode("UPDATE");
Gets or sets the query opcode (the purpose of the query).
=cut
sub opcode {
my $self = shift;
for ( $$self->{status} ) {
return opcodebyval( ( $_ >> 11 ) & 0x0f ) unless scalar @_;
my $opcode = opcodebyname(shift);
$_ = ( $_ & 0x87ff ) | ( $opcode << 11 );
return $opcode;
}
}
=head2 rcode
print "query response code = ", $packet->header->rcode, "\n";
$packet->header->rcode("SERVFAIL");
Gets or sets the query response code (the status of the query).
=cut
sub rcode {
my $self = shift;
for ( $$self->{status} ) {
my $arg = shift;
my $opt = $$self->edns;
unless ( defined $arg ) {
my $rcode = $opt->rcode;
return rcodebyval( $_ & 0x0f ) unless $opt->_specified;
$rcode = ( $rcode & 0xff0 ) | ( $_ & 0x00f );
$opt->rcode($rcode); # write back full 12-bit rcode
return $rcode == 16 ? 'BADVERS' : rcodebyval($rcode);
}
my $rcode = rcodebyname($arg);
$opt->rcode($rcode); # full 12-bit rcode
$_ &= 0xfff0; # low 4-bit rcode
$_ |= ( $rcode & 0x000f );
return $rcode;
}
}
=head2 qr
print "query response flag = ", $packet->header->qr, "\n";
$packet->header->qr(0);
Gets or sets the query response flag.
=cut
sub qr {
shift->_dnsflag( 0x8000, @_ );
}
=head2 aa
print "answer is ", $packet->header->aa ? "" : "non-", "authoritative\n";
$packet->header->aa(0);
Gets or sets the authoritative answer flag.
=cut
sub aa {
shift->_dnsflag( 0x0400, @_ );
}
=head2 tc
print "packet is ", $packet->header->tc ? "" : "not ", "truncated\n";
$packet->header->tc(0);
Gets or sets the truncated packet flag.
=cut
sub tc {
shift->_dnsflag( 0x0200, @_ );
}
=head2 rd
print "recursion was ", $packet->header->rd ? "" : "not ", "desired\n";
$packet->header->rd(0);
Gets or sets the recursion desired flag.
=cut
sub rd {
shift->_dnsflag( 0x0100, @_ );
}
=head2 ra
print "recursion is ", $packet->header->ra ? "" : "not ", "available\n";
$packet->header->ra(0);
Gets or sets the recursion available flag.
=cut
sub ra {
shift->_dnsflag( 0x0080, @_ );
}
=head2 z
Unassigned bit, should always be zero.
=cut
sub z {
shift->_dnsflag( 0x0040, @_ );
}
=head2 ad
print "The result has ", $packet->header->ad ? "" : "not", "been verified\n";
Relevant in DNSSEC context.
(The AD bit is only set on answers where signatures have been
cryptographically verified or the server is authoritative for the data
and is allowed to set the bit by policy.)
=cut
sub ad {
shift->_dnsflag( 0x0020, @_ );
}
=head2 cd
print "checking was ", $packet->header->cd ? "not" : "", "desired\n";
$packet->header->cd(0);
Gets or sets the checking disabled flag.
=cut
sub cd {
shift->_dnsflag( 0x0010, @_ );
}
=head2 qdcount, zocount
print "# of question records: ", $packet->header->qdcount, "\n";
Returns the number of records in the question section of the packet.
In dynamic update packets, this field is known as C<zocount> and refers
to the number of RRs in the zone section.
=cut
our $warned;
sub qdcount {
my $self = shift;
return $$self->{count}[0] || scalar @{$$self->{question}} unless scalar @_;
carp 'header->qdcount attribute is read-only' unless $warned++;
}
=head2 ancount, prcount
print "# of answer records: ", $packet->header->ancount, "\n";
Returns the number of records in the answer section of the packet
which may, in the case of corrupt packets, differ from the actual
number of records.
In dynamic update packets, this field is known as C<prcount> and refers
to the number of RRs in the prerequisite section.
=cut
sub ancount {
my $self = shift;
return $$self->{count}[1] || scalar @{$$self->{answer}} unless scalar @_;
carp 'header->ancount attribute is read-only' unless $warned++;
}
=head2 nscount, upcount
print "# of authority records: ", $packet->header->nscount, "\n";
Returns the number of records in the authority section of the packet
which may, in the case of corrupt packets, differ from the actual
number of records.
In dynamic update packets, this field is known as C<upcount> and refers
to the number of RRs in the update section.
=cut
sub nscount {
my $self = shift;
return $$self->{count}[2] || scalar @{$$self->{authority}} unless scalar @_;
carp 'header->nscount attribute is read-only' unless $warned++;
}
=head2 arcount, adcount
print "# of additional records: ", $packet->header->arcount, "\n";
Returns the number of records in the additional section of the packet
which may, in the case of corrupt packets, differ from the actual
number of records.
In dynamic update packets, this field is known as C<adcount>.
=cut
sub arcount {
my $self = shift;
return $$self->{count}[3] || scalar @{$$self->{additional}} unless scalar @_;
carp 'header->arcount attribute is read-only' unless $warned++;
}
sub zocount { &qdcount; }
sub prcount { &ancount; }
sub upcount { &nscount; }
sub adcount { &arcount; }
=head1 EDNS Protocol Extensions
=head2 do
print "DNSSEC_OK flag was ", $packet->header->do ? "not" : "", "set\n";
$packet->header->do(1);
Gets or sets the EDNS DNSSEC OK flag.
=cut
sub do {
shift->_ednsflag( 0x8000, @_ );
}
=head2 Extended rcode
EDNS extended rcodes are handled transparently by $packet->header->rcode().
=head2 UDP packet size
$udp_max = $packet->header->size;
$udp_max = $packet->edns->size;
EDNS offers a mechanism to advertise the maximum UDP packet size
which can be assembled by the local network stack.
UDP size advertisement can be viewed as either a header extension or
an EDNS feature. Endless debate is avoided by supporting both views.
=cut
sub size {
my $self = shift;
return $$self->edns->size(@_);
}
=head2 edns
$header = $packet->header;
$version = $header->edns->version;
@options = $header->edns->options;
$option = $header->edns->option(n);
$udp_max = $packet->edns->size;
Auxiliary function which provides access to the EDNS protocol
extension OPT RR.
=cut
sub edns {
my $self = shift;
return $$self->edns;
}
########################################
sub _dnsflag {
my $self = shift;
my $flag = shift;
for ( $$self->{status} ) {
my $set = $_ | $flag;
my $not = $set - $flag;
$_ = (shift) ? $set : $not if scalar @_;
return ( $_ & $flag ) ? 1 : 0;
}
}
sub _ednsflag {
my $self = shift;
my $flag = shift;
my $edns = $$self->edns->flags || 0;
return $flag & $edns ? 1 : 0 unless scalar @_;
my $set = $flag | $edns;
my $not = $set - $flag;
my $new = (shift) ? $set : $not;
$$self->edns->flags($new) unless $new == $edns;
return ( $new & $flag ) ? 1 : 0;
}
1;
__END__
########################################
=head1 COPYRIGHT
Copyright (c)1997 Michael Fuhr.
Portions Copyright (c)2002,2003 Chris Reinhardt.
Portions Copyright (c)2012 Dick Franks.
All rights reserved.
=head1 LICENSE
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted, provided
that the above copyright notice appear in all copies and that both that
copyright notice and this permission notice appear in supporting
documentation, and that the name of the author not be used in advertising
or publicity pertaining to distribution of the software without specific
prior written permission.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
=head1 SEE ALSO
L<perl>, L<Net::DNS>, L<Net::DNS::Packet>, L<Net::DNS::RR::OPT>
RFC 1035 Section 4.1.1
=cut
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