chase.go

package main

import (
	"log"
	"strings"

	"github.com/miekg/dns"
)

func main() {
	qname := "github.com."
	ns_path := []string{"g.root-servers.net."}
	client := new(dns.Client)
	q := new(dns.Msg).SetQuestion(qname, dns.TypeNS)
	q.MsgHdr.RecursionDesired = false
	var ns, extra []dns.RR

query_loop:
	for {
		q.Id = dns.Id()
		target := ns_path[len(ns_path)-1]
		r, _, err := client.Exchange(q, target+":53")

		switch {
		case err != nil:
			log.Fatalf("error querying %s: %s", err, target)
		case r.MsgHdr.Rcode != dns.RcodeSuccess:
			log.Fatalf("unexpected rcode from %s:\n%s", target, r)
		case r.MsgHdr.Authoritative:
			log.Fatalf("ran into an authoritative server. problem with lookup logic?\n%s", r)
		case len(r.Ns) == 0:
			log.Fatalf("expected referral from %s:\n%s", target, r)
		default:
			ns, extra = r.Ns, r.Extra
			if rr, ok := ns[0].(*dns.NS); ok {
				if rr.Hdr.Name == qname {
					break query_loop
				}
				ns_path = append(ns_path, rr.Ns)
			} else {
				log.Fatalf("expected an NS rr - message:\n%s", target, r)
			}
		}
	}

	glue := make(map[string][]string)
	for _, rr := range extra {
		switch rr := rr.(type) {
		case *dns.A:
			glue[rr.Hdr.Name] = append(glue[rr.Hdr.Name], rr.A.String())
		case *dns.AAAA:
			glue[rr.Hdr.Name] = append(glue[rr.Hdr.Name], rr.AAAA.String())
		}
	}

	log.Printf("followed path: %s\n", strings.Join(ns_path, " -> "))
	for _, rr := range ns {
		if rr, ok := rr.(*dns.NS); ok {
			if len(glue[rr.Ns]) == 0 {
				log.Printf(" * %s <no glue supplied>\n", rr.Ns)
			} else {
				log.Printf(" * %s %v\n", rr.Ns, glue[rr.Ns])
			}
		}
	}
}