[net-dns-users] SVCB

[Dick Franks]

On Sun, 10 Nov 2024 at 02:36, Doug Barton via net-dns-users
<net-dns-users at lists.nlnetlabs.nl> wrote:
>
> I have two questions about the SVCB/HTTPS implementation.
>
> First, how does one decode the "presentation format" data that's
> returned by the svcparam methods? I tried every combination of unpack
> that I could think of, including those used for pack and unpack in the
> pm file, and all I get is gibberish. None of the standard RR methods
> work either, including print, string, etc.; and I'm pretty sure I tried
> them all.

SVCB RRs are intended to be interpreted by browsers and similar
software elements.

The mnemonic presentation format described in RFC9460 facilitates
construction of SVCB RRs in zone files.
Subsequent representation of the SVCB RRs so constructed uses RFC3597 format.

There is no credible use-case which involves resurrection of the
mnemonic presentation format from the wire-format representation.

RFC9460(7.1.1 para 3) refers to "opaque key format" (e.g.,
key1=\002h2), the data being indistinguishable from the character
string representation of arbitrary data prescribed by RFC1035(5.1).
The keyNN methods (and also, by extension, alpn etc.) currently return
data in the same form.

script:

 use Net::DNS;
 my $svcb = Net::DNS::RR->new( <<'END' );
 svcb.example.    IN    SVCB    ( 1 .
     alpn=h2,h3
     ipv6hint=2001:db8::1
 END

 $svcb->print;
 print $svcb->alpn, "\n";
 print $svcb->ipv6hint, "\n";
 print $svcb->key1, "\n";
 print $svcb->key6, "\n";

produces:

 svcb.example.    IN    SVCB    ( \# 33 0001 00    ; .
    0001 0006 026832026833
    0006 0010 20010db8000000000000000000000001 )
 \002h2\002h3
 " \001\013\184\000\000\000\000\000\000\000\000\000\000\000\001"
 \002h2\002h3
 " \001\013\184\000\000\000\000\000\000\000\000\000\000\000\001"

>
>
> Second, what's the rationale for this substitution on line 190 of the
> current version of SVCB.pm:
>
>          return ( $target eq '.' ) ? $self->owner : $target;
>

RFC9460(2.5.2)

--rwf


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