[net-dns-users] IXFR methods

[Wessels, Duane]

Chris,

Looks good, but I don't understand why you're discarding the DNSSEC types?  Isn't it
possible that the caller would want those records?

DW

On Dec 18, 2012, at 12:22 PM, Chris Buxton wrote:

> Hello all,
> 
> As Doug said, it's very nice to have a list.
> 
> Has anyone else created an IXFR method for Net::DNS::Resolver? I have, and I think it's pretty good, but I think it could probably be improved.
> 
> Here's my code -- requires perl 5.10 or later:
> 
> # Hack IXFR capability into Net::DNS::Resolver
> sub Net::DNS::Resolver::Base::ixfr($$$)
> {
>    my( $res, $zone, $serial ) = @_;
>    local $_;
> 
>    # Send IXFR requests over TCP
>    $res->usevc(1);
> 
>    # Construct the request. It contains an abbreviated SOA record in
>    # the authority section, where the only fields that matter are name,
>    # class, type, and old serial number.
>    my $packet = new Net::DNS::Packet( $zone, 'IXFR' );
>    my $soa = Net::DNS::RR->new(
>        name    => $zone,
>        type    => 'SOA',
>        mname   => '',
>        rname   => '',
>        serial  => $serial,
>        refresh => 0,
>        retry   => 0,
>        expire  => 0,
>        minimum => 0
>    );
>    $packet->push( authority => $soa );
> 
>    # Send the request and store the result in an array reference.
>    my $result = $res->send( $packet );
> 
>    # The method here is, we're going to accumulate records into arrays
>    # of @$items, and then put those into @$hunks like [ $mode, $items
>    # ]. We then push each $hunk onto @diff. $mode will switch from '+'
>    # to '-' and back again for each new @$hunk. Therefore:
>    #
>    # @diff = (
>    #   [ $mode, [ $rr, ... ] ],
>    #   ...
>    # )
>    #
>    # Each @$hunk ends with an SOA record. Every time we encounter an
>    # SOA record, we start a new hunk right afterward (with the next
>    # record) and switch the $mode (the operator for each hunk).
>    #
>    # If you look carefully, you'll see that the very first SOA record
>    # is inserted into an empty @$items, but this @$items array doesn't
>    # get attached to @diff before being replaced with a fresh array. So
>    # we're processing it to set the $mode, but we're otherwise throwing
>    # it away.
>    #
>    # The last hunk (started after the final SOA record of the IXFR) has
>    # no records. Always. So we remove it before returning @diff.
>    # Therefore, an IXFR that requests changes since the current serial
>    # will return an empty array; an AXFR-style IXFR will contain
>    # exactly one hunk. To summarize:
>    #
>    # @diff == 1 # no changes since the presented serial number
>    # @diff == 2 # AXFR-style IXFR
>    # @diff >  2 # Normal IXFR containing changes
>    #
>    # Algorithm to interpret an IXFR courtesy of Mark Andrews @ISC, via
>    # a quick and dirty awk script he posted to BIND Users.
> 
>    # Get ready to parse the result.
>    my( @diff, $hunk, $items );
>    my $mode = '-';
> 
>    for my $rr ( $result->answer )
>    {
>        given( $rr->type )
>        {
>            when( 'SOA' )
>            {
>                push @$items, $rr;
>                $mode = ( $mode eq '-' ? '+' : '-' );
>                $hunk = [ $mode, [] ];
>                $items = $hunk->[1];
>                push @diff, $hunk;
>            }
>            when( [ qw( RRSIG NSEC NSEC3 NSEC3PARAM ) ] )
>            {
>                # Strip out DNSSEC records like this, as we can't really
>                # do anything useful with them
>            }
>            when( 'TSIG' )
>            {
>                # TODO: Add some error checking here
>                # For now, strip these out also
>            }
>            default
>            {
>                # Anything else gets added to @$items
>                push @$items, $rr;
>            }
>        }
>    }
> 
>    # Discard the empty hunk from the end and return everything else
>    pop @diff;
>    return @diff;
> }
> 
> Chris
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