Add SVCB dohpath key

[ainar-g]

The parameter is being added in its own IETF draft and also being used in
the IETF draft about Discovery of Designated Resolvers.

Additionally, the mappings of the numeric key values to strings are exported,
under names consistent with the already existing exported mappings, to make it
easier for the clients of the module to validate and print SVCB keys.

Testing was done by sending SVCB queries for the "_dns.resolver.arpa" domain to
OpenDNS's 146.112.41.2 server.

[ainar-g]

@miekg, thanks for the review, ptal!

[tmthrgd]

I have to say I really dislike that we’re pulling in so many draft standards for SVCB. We’ve already seen them change in ways bordering on backwards-incompatible. I’d personally rather wait for these to be actually published as RFCs.

[tmthrgd]

I should clarify, I don’t object to implementing drafts where they can be kept as internal implementation details, but I do object when they become part of our public API.

[miekg]

[ Quoting ***@***.***> in "Re: [miekg/dns] Add SVCB dohpath ke..." ]

I should clarify, I don’t object to implementing drafts where they can be kept as internal implementation details, but I do object when they become part of our public API.

I hear you. We should indeed be careful. OTOH this new RR has gained popularity quickly and there seems to be some experimentation going on. Waiting for these I-Ds to be RFC can take multiple years, so we should be a bit lenient here. My position is: you know you're dealing with a pre-RFC RR here, so it's fine for us to break things when the actual RFC turns out to be different. (We could put such a warning in the code, but I don't think we have something prominent enough where folks would actually read it)

[ainar-g]

@miekg, the Go standard library has a few spots where it explicitly says that something is experimental and is likely to change in the future. For example, package syscall/js. I could send a PR where I go through all exported SVCB identifiers and add a warning regarding the draft status of this functionality.

[miekg]

[ Quoting ***@***.***> in "Re: [miekg/dns] Add SVCB dohpath ke..." ] ***@***.***, the Go standard library has a few spots where it explicitly says that

something is experimental and is likely to change in the future. For example, package syscall/js. I could send a PR where I go through all exported SVCB identifiers and add a warning regarding the draft status of this functionality.

As ugly as that is, it might "solve" some of Tom's conerns (and mine - frankly)