support more than one upstream dns server

arguments.go

@@ -9,7 +9,7 @@ import (
 
 var bind_addr string
 
-var default_server string
+var default_server ArgSrvs
 
 var srv ArgSrvs
 
@@ -17,7 +17,7 @@ var logfile string
 
 type ArgSrvs []string
 
-var DefaultServer *UpstreamServer
+var DefaultServer []*UpstreamServer
 
 var blacklist_file string
 
@@ -44,7 +44,8 @@ func parse_flags() {
 		}
 	}
 
-	proto, addr, err := parse_addr(default_server)
+	for _, dsvr := range default_server {
+		proto, addr, err := parse_addr(dsvr)
 		if err != nil {
 			log.Fatal(err)
 		}
@@ -56,11 +57,17 @@ func parse_flags() {
 			c = client_tcp
 		}
 
-	DefaultServer = &UpstreamServer{
+		upsrv := &UpstreamServer{
 			Addr:   addr,
 			Proto:  proto,
 			client: c,
 		}
+		DefaultServer = append(DefaultServer, upsrv)
+	}
+
+	if len(DefaultServer) == 0 {
+		log.Fatal("please special a -upstream")
+	}
 
 	a, err := load_domain(blacklist_file)
 	if err != nil {
@@ -93,7 +100,7 @@ func init() {
         `)
 
 	flag.StringVar(&bind_addr, "bind", ":53", "the address bind to")
-	flag.StringVar(&default_server, "upstream", "udp:114.114.114.114:53", "the default upstream server to use")
+	flag.Var(&default_server, "upstream", "special the upstream server to use")
 	flag.StringVar(&logfile, "logfile", "", "the logfile, default stdout")
 	flag.StringVar(&blacklist_file, "blacklist", "", "the blacklist file")
 	flag.BoolVar(&debug, "debug", false, "output debug log, default false")

server.go

@@ -168,7 +168,8 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 
 		// fallback to default upstream server
 		if done != 1 {
-			res, err = DefaultServer.query(r)
+			for _, dfsrv := range DefaultServer {
+				res, err = dfsrv.query(r)
 				if err != nil {
 					logger.Error("%s", err)
 					continue
@@ -179,7 +180,7 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 					domain,
 					dns.ClassToString[r.Question[0].Qclass],
 					dns.TypeToString[r.Question[0].Qtype],
-				DefaultServer.Proto, DefaultServer.Addr,
+					dfsrv.Proto, dfsrv.Addr,
 					dns.RcodeToString[res.Rcode],
 				)
 
@@ -192,6 +193,8 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 					dns_cache.Add(key, strings.Join(v, "|"))
 					w.WriteMsg(res)
 					done = 1
+					break
+				}
 			}
 		}