Re: [lwip-users] DNS look-up of name that is already RFC 1035 encoded

[Craig McQueen]

address@hidden wrote:
> On 12.11.2018 01:04, Craig McQueen wrote:
> > DHCP option 120 provides SIP server address(es), which may be an IP
> address or a DNS name. If it's a DNS name, then it is already encoded in the
> encoding used for DNS look-ups (RFC 1035). See RFC 3361 section 3.1.
> >
> > What is the best way to look up such a name via lwIP?
> 
> The only lookup lwIP supports is the normal dotted string notation.
> 
> > Shall I convert it from the RFC 1035 encoding to the normal dotted string
> notation, and not fret about the perceived inefficiency that lwIP will just
> convert it back to RFC 1035 encoding? (it's converted in dns_send().)
> Alternatively, core/dns.c could be modified to provide an API function that
> takes a hostname in the RFC 1035 encoding.
> 
> dns.c implements a cache. Taking one name as RFC1035 is not enough:
> future comparisons must match it, too. So either we're buffering in
> RFC1035 or in dotted strings. I'd say given the length of such names (and
> unless there's a different point in keeping names in RFC1035 format), it's
> probably not worth changing anything from the current state...

I looked into DNS internationalization and Punycode. I can't see any problem 
with internationalization with either RFC1035 encoding or dotted string 
notation. So I think that's not a concern, regardless of what RFC3361 stated 
about internationalization.

So, I think the most straight-forward solution is for my code to just convert 
from the RFC 1035 encoding to dotted string notation, and avoid fretting about 
the double conversion.

-- 
Craig McQueen