add backendDNS opt

cmd/main.go

@@ -55,6 +55,7 @@ type CmdArgs struct {
 	FakeDNSAddr   *string
 	FakeDNSHosts  *string
 	HijackDNS     *string
+	BackendDNS    *string
 
 	// Session Statistics Monitor
 	EnableMonitor *bool

cmd/main_fakedns.go

@@ -4,6 +4,7 @@ package main
 
 import (
 	"flag"
+	"strings"
 
 	"github.com/xjasonlyu/tun2socks/component/fakedns"
 	"github.com/xjasonlyu/tun2socks/log"
@@ -15,6 +16,7 @@ func init() {
 	args.FakeIPRange = flag.String("fakeIPRange", "198.18.0.0/15", "Fake IP CIDR range for DNS")
 	args.FakeDNSHosts = flag.String("fakeDNSHosts", "", "DNS hosts mapping, e.g. 'example.com=1.1.1.1,example.net=2.2.2.2'")
 	args.HijackDNS = flag.String("hijackDNS", "", "Hijack the DNS query to get a fake ip, e.g. '*:53' or '8.8.8.8:53,8.8.4.4:53'")
+	args.BackendDNS = flag.String("backendDNS", "8.8.8.8:53", "Backend DNS to resolve !TypeA or !ClassINET query. (must support tcp)")
 
 	registerInitFn(func() {
 		if *args.EnableFakeDNS {
@@ -26,6 +28,7 @@ func init() {
 
 			// Set fakeDNS variables
 			fakedns.ServeAddr = *args.FakeDNSAddr
+			fakedns.BackendDNS = strings.Split(*args.BackendDNS, ",")
 
 			// Start fakeDNS server
 			if err := fakeDNS.Start(); err != nil {

component/fakedns/middleware.go

@@ -11,14 +11,12 @@ import (
 )
 
 var (
-	nameserver = "8.8.8.8:53"
+	BackendDNS = []string{}
 )
 
-func dnsExchange(r *D.Msg) *D.Msg {
-	c := new(D.Client)
-	c.Net = "tcp"
-	msg, _, err := c.Exchange(r, nameserver)
-	if err != nil {
+func dnsExchange(r *D.Msg) (msg *D.Msg) {
+	defer func() {
+		if msg == nil {
 			// empty DNS response
 			rr := &D.A{}
 			rr.Hdr = D.RR_Header{Name: r.Question[0].Name, Rrtype: D.TypeA, Class: D.ClassINET, Ttl: dnsDefaultTTL}
@@ -26,6 +24,16 @@ func dnsExchange(r *D.Msg) *D.Msg {
 			msg.Answer = []D.RR{rr}
 			setMsgTTL(msg, dnsDefaultTTL)
 		}
+	}()
+
+	c := new(D.Client)
+	c.Net = "tcp"
+	for _, dns := range BackendDNS {
+		msg, _, _ = c.Exchange(r, dns)
+		if msg != nil {
+			break
+		}
+	}
 	return msg
 }