dns: support AXFR queries

[silverwind]

Now that we support ANY queries (#13137), I think the foundation is laid to support zone transfers and we can likely share most of the code that is used to parse the ANY response and parse the AXFR response with it.

cc: @XadillaX

[XadillaX]

The principle of ANY queries is to parse the packet time by time by calling ares_parse_a_reply, ares_parse_aaaa_reply, etc.

But it seems C-ARES does not support to parse AXFR query.

[tniessen]

The main difference between "normal" queries and AXFR queries is that AXFR queries can have their answers spread across any number of messages. @XadillaX might be correct, I am not sure whether c-ares supports this 😕

[silverwind]

Yeah, looks like c-ares can indeed not parse a AXFR response. Using the adig utility that comes with it, I only see the initial SOA response being parsed, but not the AXFR content:

$ ./adig -t axfr -s 127.0.0.1 domain.com
DNS server returned answer with no data
id: 18388
flags: qr aa rd
opcode: QUERY
rcode: NOERROR
Questions:
  domain.com.   AXFR
Answers:
NS records:
  domain.com. 3600  SOA ...

[bnoordhuis]

@silverwind Is the conclusion that this isn't possible? If yes, can you close it out?

(Aside: adig -- like c-ares -- indeed doesn't support AXFR, it only recognizes the tag.)

[silverwind]

Yes, we can close it, I just don't want it to be forgotten. Let's see what comes out of #14713, otherwise I'll open an issue on the c-ares tracker.

[Trott]

Yes, we can close it, I just don't want it to be forgotten. Let's see what comes out of #14713, otherwise I'll open an issue on the c-ares tracker.

@silverwind Did you ever open that issue on the c-ares tracker?

[silverwind]

No, I don't think so. Nowadays, I just use https://github.com/mafintosh/dns-packet/ for advanced DNS use cases.