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

[address@hidden]

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...

Simon