Creating an RR instance with empty RDATA

[mattias-p]

I have a domain name and an rrtype and I want to construct a corresponding fully functional dns.RR instance with empty RDATA. This is required for dns.Msg.RemoveRRset(), and I also need to perform some other processing on these records. However, I couldn’t find any documentation on the intended way to do this.

I tried using a plain *dns.RR_Header. This mostly works since *dns.RR_Header formally implements dns.RR, but its dns.RR.copy implementation just returns nil, so dns.Copy doesn't work with such instances.

I also tried using dns.NewRR(fmt.Sprintf("%s %d IN %s", domain, ttl, dns.TypeToString[rrtype])). This also mostly works but for TXT records it seems dns.PackRR needs a larger buffer than what's reported by dns.Len.

I had a look at the source code for dns.RemoveRRset and realized that wrapping the dns.RR_Header in a dns.ANY might be a solution. So far I haven't stumbled on any surprising behaviors with this solution, but I'm not confident about its robustness either.

What is the recommended way to construct a dns.RR instance with empty RDATA?