Net::DNS::ToolKit::RR::NULL - Resource Record Handler

  DO NOT use Net::DNS::ToolKit::RR::NULL
  DO NOT require Net::DNS::ToolKit::RR::NULL

  Net::DNS::ToolKit::RR::NULL is autoloaded by 
  class Net::DNS::ToolKit::RR and its methods
  are instantiated in a 'special' manner.

  use Net::DNS::ToolKit::RR;
  ($get,$put,$parse) = new Net::DNS::ToolKit::RR;

  ($newoff,$name,$type,$class,$ttl,$rdlength,
        $anydata) = $get->NULL(\$buffer,$offset);

  Note: the $get->NULL method is normally called
  via:  @stuff = $get->next(\$buffer,$offset);

  ($newoff,@dnptrs)=$put->NULL(\$buffer,$offset,\@dnptrs,
	$name,$type,$class,$ttl,$rdlength,$anydata);

  $NAME,$TYPE,$CLASS,$TTL,$rdlength,$anydata) 
    = $parse->NULL($name,$type,$class,$ttl,$rdlength,
        $anydata);

Net::DNS::ToolKit::RR:NULL appends an NULL resource record to a DNS packet under construction, recovers an NULL resource record from a packet being decoded, and converts the numeric/binary portions of the resource record to human readable form.

  Description from RFC1035.txt

  3.2.1. Format

  All RRs have the same top level format shown below:

                                    1  1  1  1  1  1
      0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                      NAME                     |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                      TYPE                     |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                     CLASS                     |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                      TTL                      |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    |                   RDLENGTH                    |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
    |                     RDATA                     |
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

  NAME	an owner name, i.e., the name of the node to which this
	resource record pertains.

  TYPE	two octets containing one of the RR TYPE codes.

  CLASS	two octets containing one of the RR CLASS codes.

  TTL	a 32 bit signed integer that specifies the time interval
	that the resource record may be cached before the source
	of the information should again be consulted.  Zero
	values are interpreted to mean that the RR can only be
	used for the transaction in progress, and should not be
	cached.  For example, SOA records are always distributed
	with a zero TTL to prohibit caching.  Zero values can
	also be used for extremely volatile data.

  RDLENGTH an unsigned 16 bit integer that specifies the length
	in octets of the RDATA field.

  RDATA	a variable length string of octets that describes the
	resource.  The format of this information varies
	according to the TYPE and CLASS of the resource record.

  3.3.10. NULL RDATA format (EXPERIMENTAL)

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
    /                  <anything>                   /
    /                                               /
    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

Anything at all may be in the RDATA field so long as it is 65535 octets or less.

This is probably not correct. An entire resource record + question, etc... info must fit inside the 65535 record because that is the limitation imposed by TCP window size. See: extra_docs/draft-ietf-dnsext-axfr-clarify-05.txt section 3.1

NULL records cause no additional section processing. NULL RRs are not allowed in master files. NULLs are used as placeholders in some experimental extensions of the DNS.

* @stuff = $get->NULL(\$buffer,$offset);

  Get the contents of the resource record.

  USE: @stuff = $get->next(\$buffer,$offset);

  where: @stuff = (
  $newoff $name,$type,$class,$ttl,$rdlength,
  $anydata );

All except the last item, $anydata, is provided by the class loader, Net::DNS::ToolKit::RR. The code in this method knows how to retrieve $anydata.

  input:        pointer to buffer,
                offset into buffer
  returns:      offset to next resource,
                @common RR elements,
		lots of bytes

* ($newoff,@dnptrs)=$put->NULL(\$buffer,$offset,\@dnptrs, $name,$type,$class,$ttl,$rdlength,$anydata);

Append a NULL record to $buffer.

  where @common = (
	$name,$type,$class,$ttl);

The method will insert the $rdlength and $anydata, then pass through the updated pointer to the array of compressed names

The class loader, Net::DNS::ToolKit::RR, inserts the @common elements and returns updated @dnptrs. This module knows how to insert its RDATA and calculate the $rdlength.

  input:        pointer to buffer,
                offset (normally end of buffer), 
                pointer to compressed name array,
                @common RR elements,
		lots of bytes
  output:       offset to next RR,
                new compressed name pointer array,
           or   empty list () on error.

* (@COMMON,$anydata) = $parse->NULL(@common,$anydata);

Converts binary/numeric field data into human readable form. The common RR elements are supplied by the class loader, Net::DNS::ToolKit::RR. For NULL RR's, this is a null operation.

  input:	lots of bytes
  returns:	the same bytes

	Net::DNS::ToolKit
	Net::DNS::Codes
	Net::DNS::ToolKit::RR::TXT

	none

Michael Robinton <michael@bizsystems.com>

Copyright 2003, Michael Robinton <michael@bizsystems.com>

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.

Net::DNS::Codes(3), Net::DNS::ToolKit(3)