checker: fix GLUE search for external domains

checker/checker.go

@@ -22,7 +22,10 @@ const (
 	year68           = 1 << 31 // For RFC1982 (Serial Arithmetic) calculations in 32 bits. Taken from miekg/dns
 )
 
-var verbose = false
+var (
+	verbose           = false
+	domainsHostingMap = map[string]string{}
+)
 
 // ICMP
 
@@ -48,13 +51,82 @@ func check_ping(ip string, cb func(pkt *ping.Packet)) (err error) {
 func get_GLUE(domain string) (aaaa net.IP, err error) {
 	client := dns.Client{Net: "tcp", Timeout: time.Second * 5}
 
+	dnssrv := "[2a01:e0a:2b:2250::b]:53"
+	if strings.HasSuffix(domain, adlin.DelegatedDomainSuffix) {
+		dnssrv = "[2a01:e0a:2b:2250::b]:53"
+	} else if v, ok := domainsHostingMap[domain]; ok {
+		dnssrv = v
+	} else {
+		// Looking for root NS
+		m := new(dns.Msg)
+		m.SetQuestion(".", dns.TypeNS)
+		m.RecursionDesired = false
+		m.SetEdns0(4096, true)
+
+		var r *dns.Msg
+		r, _, err = client.Exchange(m, dnssrv)
+		if err != nil {
+			return
+		}
+
+		if r == nil {
+			return nil, errors.New("response is nil during initial recursion")
+		}
+		if r.Rcode != dns.RcodeSuccess {
+			return nil, errors.New("failed to get a valid answer during initial recursion")
+		}
+
+		for _, answer := range r.Answer {
+			if t, ok := answer.(*dns.NS); ok {
+				dnssrv = t.Ns + ":53"
+			}
+		}
+		// Do casual recursion
+		i := 0
+	recursion:
+		for i = 0; i < 10; i++ {
 			m := new(dns.Msg)
 			m.SetQuestion(domain, dns.TypeNS)
 			m.RecursionDesired = false
 			m.SetEdns0(4096, true)
 
 			var r *dns.Msg
-	r, _, err = client.Exchange(m, "[2a01:e0a:2b:2250::b]:53")
+			r, _, err = client.Exchange(m, dnssrv)
+			if err != nil {
+				return
+			}
+
+			if r == nil {
+				return nil, errors.New("response is nil during recursion")
+			}
+			if r.Rcode != dns.RcodeSuccess {
+				return nil, errors.New("failed to get a valid answer during recursion")
+			}
+
+			for _, answer := range r.Ns {
+				if t, ok := answer.(*dns.NS); ok {
+					dnssrv = t.Ns + ":53"
+					if t.Header().Name == domain {
+						break recursion
+					}
+				}
+			}
+		}
+
+		if i >= 10 {
+			return nil, fmt.Errorf("too much name recursions")
+		} else {
+			domainsHostingMap[domain] = dnssrv
+		}
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion(domain, dns.TypeNS)
+	m.RecursionDesired = false
+	m.SetEdns0(4096, true)
+
+	var r *dns.Msg
+	r, _, err = client.Exchange(m, dnssrv)
 	if err != nil {
 		return
 	}