use lru for dns result cache

server.go

@@ -23,8 +23,11 @@ run it
 package main
 
 import (
+	"fmt"
+	lru "github.com/hashicorp/golang-lru"
 	"github.com/miekg/dns"
 	"log"
+	"strings"
 )
 
 var client_udp *dns.Client = &dns.Client{}
@@ -39,6 +42,8 @@ var Blacklist_ips Kv = nil
 
 var debug bool = false
 
+var dns_cache *lru.Cache
+
 var hostfile string = ""
 var record_hosts Hosts = nil
 
@@ -101,6 +106,32 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 		}
 	}
 
+	key := fmt.Sprintf("%s_%s", domain, dns.TypeToString[r.Question[0].Qtype])
+
+	// reply from cache
+	if a, ok := dns_cache.Get(key); ok {
+		msg := new(dns.Msg)
+		msg.SetReply(r)
+
+		aa := strings.Split(a.(string), "|")
+		for _, a1 := range aa {
+			rr, _ := dns.NewRR(a1)
+			if rr != nil {
+				msg.Answer = append(msg.Answer, rr)
+			}
+		}
+
+		w.WriteMsg(msg)
+		logger.Debug("%s query %s %s %s, reply from cache\n",
+			w.RemoteAddr(),
+			domain,
+			dns.ClassToString[r.Question[0].Qclass],
+			dns.TypeToString[r.Question[0].Qtype],
+		)
+		return
+	}
+
+	// forward to upstream server
 	for i := 0; i < 2; i++ {
 		done = 0
 		for _, sv := range Servers {
@@ -122,6 +153,12 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 				)
 
 				if res.Rcode != dns.RcodeServerFailure && !in_blacklist(res) {
+					// add to cache
+					v := []string{}
+					for _, as := range res.Answer {
+						v = append(v, as.String())
+					}
+					dns_cache.Add(key, strings.Join(v, "|"))
 					w.WriteMsg(res)
 					done = 1
 					break
@@ -129,6 +166,7 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 			}
 		}
 
+		// fallback to default upstream server
 		if done != 1 {
 			res, err = DefaultServer.query(r)
 			if err != nil {
@@ -146,6 +184,12 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 			)
 
 			if res.Rcode != dns.RcodeServerFailure && !in_blacklist(res) {
+				// add to cache
+				v := []string{}
+				for _, as := range res.Answer {
+					v = append(v, as.String())
+				}
+				dns_cache.Add(key, strings.Join(v, "|"))
 				w.WriteMsg(res)
 				done = 1
 			}
@@ -164,6 +208,14 @@ func handleRoot(w dns.ResponseWriter, r *dns.Msg) {
 func main() {
 	parse_flags()
 
+	var err error
+
+	// create cache
+	dns_cache, err = lru.New(1000)
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	dns.HandleFunc(".", handleRoot)
 
 	logger = NewLogger(logfile, debug)
@@ -179,7 +231,7 @@ func main() {
 	}()
 
 	/* listen udp */
-	err := dns.ListenAndServe(bind_addr, "udp", nil)
+	err = dns.ListenAndServe(bind_addr, "udp", nil)
 	if err != nil {
 		log.Fatal(err)
 	}