net/dns: dns_get_addr_info() cannot "resolve" (parse) numeric IP addresses

[zephyrbot]

Reported by Paul Sokolovsky:

I thought that Zephyr's DNS resolver is able to deal with numeric addresses like "192.0.2.1", but turned out it doesn't, it's my local dnsmasq what "resolved" them, only for IPv4.

On the other hand, BSD Sockets' getaddrinfo() must resolve them, which leads to the question where it should be implemented - in native DNS resolver, or on BSD Sockets level. I usually try to push as much functionality as possible down the native stack, but here I'm not sure - one of the idea might be to keep DNS resolver minimal, and well, make it resolve only DNS name, of which numeric numbers aren't. But from usability point of view, numeric addresses can be used anywhere a domain name can, so it either leads to gap in the functionality (where numeric address suddenly doesn't work), or puts extra burden on each and every app.

Please suggest.

(Imported from Jira ZEP-2562)

[zephyrbot]

by Jukka Rissanen:

I think this should be handled in DNS resolver, otherwise it is very confusing for the user. We could probably use the new net_ipaddr_parse() API to try to parse the address in resolver, and only if that fails, we can try to resolve it from the net.

[zephyrbot]

by Paul Sokolovsky:

Sounds good, thanks. DNS resolver actually accepts just a host name/address, so existing net_addr_pton() will be enough, apparently with pre-check for numeric address and IPv4 vs IPv6 family.

[zephyrbot]

by Paul Sokolovsky:

Well, actually as the port is optional for net_ipaddr_parse(), maybe reusing it makes sense.

[zephyrbot]

by Jukka Rissanen:

I have a fix for this, see #1198 for details.