commit 60703b621feba1f8aff3879589ef37a0b466801a
from: Oliver Lowe <o@olowe.co>
date: Sat Dec 18 07:22:45 2021 UTC

cmd/recursor: return error when no more servers to ask

So we eturn SERVFAIL correctly to clients, the same way that
Cloudflare, quad9 et al. do.

commit - 2cf560f78905b6f035e5eb06dfeae712d2346370
commit + 60703b621feba1f8aff3879589ef37a0b466801a
blob - 2cf269043af39ad5bc96455d62d39b1003a85d18
blob + 488d1259cf272dbd1ab4b106310b589b3a37e1e4
--- cmd/recursor/resolve.go
+++ cmd/recursor/resolve.go
@@ -37,19 +37,6 @@ func filterRRs(rrs []dnsmessage.Resource, n dnsmessage
 	return matches
 }
 
-func nextServerAddrs(resources []dnsmessage.Resource) []net.IP {
-	var next []net.IP
-	for _, r := range resources {
-		switch b := r.Body.(type) {
-		case *dnsmessage.AResource:
-			next = append(next, net.IP(b.A[:]))
-		case *dnsmessage.AAAAResource:
-			next = append(next, net.IP(b.AAAA[:]))
-		}
-	}
-	return next
-}
-
 func resolveFromRoot(q dnsmessage.Question) (dnsmessage.Message, error) {
 	return resolve(q, roots, 0)
 }
@@ -116,15 +103,15 @@ func resolve(q dnsmessage.Question, next []net.IP, dep
 					continue
 				}
 				if len(rmsg.Answers) > 0 {
-					return resolve(q, nextServerAddrs(rmsg.Answers), depth+1)
+					return resolve(q, dns.ExtractIPs(rmsg.Answers), depth+1)
 				}
-				return resolve(q, nextServerAddrs(rmsg.Additionals), depth+1)
+				return resolve(q, dns.ExtractIPs(rmsg.Additionals), depth+1)
 			default:
 				return rmsg, fmt.Errorf("unexpected authority resource type %s", a.Header.Type)
 			}
 		}
 	}
 
-	// No real answer, no more servers to ask; return our best guess
-	return rmsg, nil
+	// return our best guess anyway
+	return rmsg, fmt.Errorf("resolve %s: no more nameservers to ask", q.Name)
 }
blob - c94e6c8eed57383a0421ce6130875cbda6a3c033
blob + 14d4fe846cd63d5fbe3031e0e11446a2b4242c0c
--- server.go
+++ server.go
@@ -148,3 +148,18 @@ func DefaultHandler(w ResponseWriter, msg *dnsmessage.
 	rmsg.Header.RCode = dnsmessage.RCodeNotImplemented
 	w.WriteMsg(rmsg)
 }
+
+// ExtractIPs extracts any IP addresses from resources. An empty slice is
+// returned if there are no addresses.
+func ExtractIPs(resources []dnsmessage.Resource) []net.IP {
+	var ips []net.IP
+	for _, r := range resources {
+		switch b := r.Body.(type) {
+		case *dnsmessage.AResource:
+			ips = append(ips, net.IP(b.A[:]))
+		case *dnsmessage.AAAAResource:
+			ips = append(ips, net.IP(b.AAAA[:]))
+		}
+	}
+	return ips
+}