handle CNAME records (#13)

* handle CNAME records

* Type cast cname record

dns/dns.go

@@ -107,6 +107,25 @@ func HandleSingleQuestion(name string, qType uint16, r *dns.Msg, s *dnsStore) bo
 				}
 			}
 		}
+
+		// handle CNAME record
+		if !hasPreciseMatch && qType != dns.TypeCNAME {
+			cnameList := typeMap[dns.TypeCNAME]
+			if cnameList != nil && len(cnameList) != 0 {
+				// should only have one CNAME RR
+				cnameRR, err := dns.NewRR(cnameList[0])
+				if err == nil && cnameRR != nil {
+					r.Answer = append(r.Answer, cnameRR)
+					// get the canonical name for this request domain name
+					realCNameRR, ok := cnameRR.(*dns.CNAME)
+					if ok {
+						cnameData := realCNameRR.Target
+						// retry with canonical name
+						return HandleSingleQuestion(cnameData, qType, r, s)
+					}
+				}
+			}
+		}
 	}
 
 	// Has precise match, no need to scan further