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Filename : Header.pm
back
package Net::DNS::Header;

use strict;
use warnings;

our $VERSION = (qw$Id: Header.pm 2042 2025-12-24 10:23:11Z willem $)[2];


=head1 NAME

Net::DNS::Header - DNS packet header

=head1 SYNOPSIS

	use Net::DNS;

	$packet = Net::DNS::Packet->new();
	$header = $packet->header;


=head1 DESCRIPTION

C<Net::DNS::Header> represents the header portion of a DNS packet.

=cut


use integer;
use Carp;

use Net::DNS::Parameters qw(:opcode :rcode);


=head1 METHODS


=head2 $packet->header

	$packet = Net::DNS::Packet->new();
	$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 $dispid = defined $id ? $id : 'undef';
	return <<"QQ" if $opcode eq 'DSO';
;;	id = $dispid	qr = $qr
;;	opcode = $opcode	rcode = $rcode
QQ
	return <<"QQ" if $opcode eq 'UPDATE';
;;	id = $dispid	qr = $qr
;;	opcode = $opcode	rcode = $rcode
;;	zocount = $qd	prcount = $an
;;	upcount = $ns	adcount = $ar
QQ
	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;
	my $co = $self->co;
	my $de = $self->de;
	return <<"QQ";
;;	id = $dispid
;;	qr = $qr	aa = $aa	tc = $tc	rd = $rd	opcode = $opcode
;;	ra = $ra	z  = $zz	ad = $ad	cd = $cd	rcode  = $rcode
;;	do = $do	co = $co	de = $de
;;	qdcount = $qd	ancount = $an
;;	nscount = $ns	arcount = $ar
QQ
}


=head2 print

	$packet->header->print;

Prints the string representation of the packet header.

=cut

sub print {
	print &string;
	return;
}


=head2 id

	print "query id = ", $packet->header->id, "\n";
	$packet->header->id(1234);

Gets or sets the query identification number.

=cut

sub id {
	my ( $self, @value ) = @_;
	for (@value) { $$self->{id} = $_ }
	return $$self->{id};
}


=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, $arg ) = @_;
	my $opcode;
	for ( $$self->{status} ) {
		return opcodebyval( ( $_ >> 11 ) & 0x0f ) unless defined $arg;
		$opcode = opcodebyname($arg);
		$_	= ( $_ & 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, $arg ) = @_;
	my $rcode;
	for ( $$self->{status} ) {
		my $opt = $$self->edns;
		unless ( defined $arg ) {
			$rcode = ( $opt->rcode & 0xff0 ) | ( $_ & 0x00f );
			$opt->rcode($rcode);			# write back full 12-bit rcode
			return $rcode == 16 ? 'BADVERS' : rcodebyval($rcode);
		}
		$rcode = rcodebyname($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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x8000, @value );
}


=head2 aa

	print "response is ", $packet->header->aa ? "" : "non-", "authoritative\n";
	$packet->header->aa(0);

Gets or sets the authoritative answer flag.

=cut

sub aa {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0400, @value );
}


=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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0200, @value );
}


=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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0100, @value );
}


=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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0080, @value );
}


=head2 z

Unassigned bit, should always be zero.

=cut

sub z {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0040, @value );
}


=head2 ad

	print "The response has ", $packet->header->ad ? "" : "not", "been verified\n";

Relevant in DNSSEC context.

(The AD bit is only set on a response 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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0020, @value );
}


=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 {
	my ( $self, @value ) = @_;
	return $self->_dnsflag( 0x0010, @value );
}


=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

sub qdcount {
	my ( $self, @value ) = @_;
	for (@value) { $self->_warn('packet->header->qdcount is read-only') }
	return $$self->{count}[0] || scalar @{$$self->{question}};
}


=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, @value ) = @_;
	for (@value) { $self->_warn('packet->header->ancount is read-only') }
	return $$self->{count}[1] || scalar @{$$self->{answer}};
}


=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, @value ) = @_;
	for (@value) { $self->_warn('packet->header->nscount is read-only') }
	return $$self->{count}[2] || scalar @{$$self->{authority}};
}


=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, @value ) = @_;
	for (@value) { $self->_warn('packet->header->arcount is read-only') }
	return $$self->{count}[3] || scalar @{$$self->{additional}};
}

sub zocount { return &qdcount; }
sub prcount { return &ancount; }
sub upcount { return &nscount; }
sub adcount { return &arcount; }


=head1 EDNS Protocol Extensions

=head2 do, co, de

	print "DNSSEC_OK flag was ", $packet->header->do ? "not" : "", "set\n";
	$packet->header->do(1);

Gets or sets the named EDNS flag.

=cut

sub do {
	my ( $self, @value ) = @_;
	return $self->_ednsflag( 0x8000, @value );
}

sub co {
	my ( $self, @value ) = @_;
	return $self->_ednsflag( 0x4000, @value );
}

sub de {
	my ( $self, @value ) = @_;
	return $self->_ednsflag( 0x2000, @value );
}


=head2 Extended rcode

EDNS extended rcodes are handled transparently by $packet->header->rcode().


=head2 UDP packet size

	$udp_max = $packet->edns->UDPsize;

EDNS offers a mechanism to advertise the maximum UDP packet size
which can be assembled by the local network stack.

=cut

sub size {				## historical
	my ( $self, @value ) = @_;
	return $$self->edns->UDPsize(@value);
}


=head2 edns

	$header  = $packet->header;
	$version = $header->edns->version;
	@options = $header->edns->options;
	$option  = $header->edns->option(n);
	$udp_max = $packet->edns->UDPsize;

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, $flag, @value ) = @_;
	for ( $$self->{status} ) {
		my $set = $_ | $flag;
		$_ = ( shift @value ) ? $set : ( $set ^ $flag ) if @value;
		$flag &= $_;
	}
	return $flag ? 1 : 0;
}


sub _ednsflag {
	my ( $self, $flag, @value ) = @_;
	my $edns = $$self->edns;
	for ( $edns->flags ) {
		my $set = $_ | $flag;
		$edns->flags( $_ = ( shift @value ) ? $set : ( $set ^ $flag ) ) if @value;
		$flag &= $_;
	}
	return $flag ? 1 : 0;
}


my %warned;

sub _warn {
	my ( undef, @note ) = @_;
	return carp "usage; @note" unless $warned{"@note"}++;
}


1;
__END__


########################################

=head1 COPYRIGHT

Copyright (c)1997 Michael Fuhr.

Portions Copyright (c)2002,2003 Chris Reinhardt.

Portions Copyright (c)2012,2022 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 original copyright notices appear in all copies and that both
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>
L<RFC1035(4.1.1)|https://iana.org/go/rfc1035#section-4.1.1>

=cut