DNS: TTL or GetServers?

martinheidegger · July 19, 2021, 1:38pm

Hi I have been looking for a way to get ttl numbers for dns TXT entries. As it seems the golang standard library doesn’t support ttl for entries I have been looking into miekg/dns. It works well, but for it to work out-of-the-box I need to get the systems dns servers. Since the system settings are per network interface I was assuming net.Interfaces() to have a Interface.DNS property or have a net.DNSServers() function available.

Do you know a different library that could help with this?
Do you think this should be a golang standard library issue?
Do you think it should be a feature of the golang std lib to support TTL’s for dns entries?
Should this be a feature of third party libraries like miekd/dns?

Note: From using it in Node.js it seems it should be possible to implement it in a cross-plattform manner. Possibly because Node is using c-ares in the background?

$ node -p "(new dns.Resolver).getServers()"

christophberger · July 19, 2021, 3:35pm

Hi @martinheidegger, welcome to the forum.

Regarding getting the system’s list of DNS servers, this SO answer suggests parsing /etc/resolv.conf like Ruby does.

I cannot comment on whether getting TTL data should be a feature of the stdlib or of third-party packages. This is the decision of the Go team or anyone who wrote, or plans to write, a DNS package. But I found package retryabledns that appears to include TTL data as part of a TXT response, which might suit your needs.

martinheidegger · July 19, 2021, 4:21pm

Hi @christophberger

retryabledns is a dead-end as it uses miekg/dns under the hood

The SO answer points to the right direction how to implement it, even if it has a dead link. Here is the bits of implementation that I found:

github.com

ruby/ruby/blob/036f26a4e24d7e6e8de30aa7e3cedb19f7da88b0/lib/resolv.rb#L988


          when /\Andots:(\d+)\z/
            ndots = $1.to_i
          end
        }
      end
    }
  }
  return { :nameserver => nameserver, :search => search, :ndots => ndots }
end


def Config.default_config_hash(filename="/etc/resolv.conf")
  if File.exist? filename
    config_hash = Config.parse_resolv_conf(filename)
  else
    if /mswin|cygwin|mingw|bccwin/ =~ RUBY_PLATFORM
      require 'win32/resolv'
      search, nameserver = Win32::Resolv.get_resolv_info
      config_hash = {}
      config_hash[:nameserver] = nameserver if nameserver
      config_hash[:search] = [search].flatten if search
    end

It will actually handle the windows case separately using win32/resolv - so pretty complex. Trying to support seems to be more than a quick “5 min and done” project and I am wondering where may be persons that are interested (maybe more than I am) to implement it.

christophberger · July 19, 2021, 4:49pm

Indeed, Windows can add complexity to cross-platform solutions…

system · October 17, 2021, 4:49pm

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