Feature: add custom DNS support (#56)

dns/server.go

@@ -0,0 +1,62 @@
+package dns
+
+import (
+	"net"
+
+	D "github.com/miekg/dns"
+)
+
+var (
+	address string
+	server  = &Server{}
+)
+
+type Server struct {
+	*D.Server
+	r *Resolver
+}
+
+func (s *Server) ServeDNS(w D.ResponseWriter, r *D.Msg) {
+	msg, err := s.r.Exchange(r)
+
+	if err != nil {
+		D.HandleFailed(w, r)
+		return
+	}
+	msg.SetReply(r)
+	w.WriteMsg(msg)
+}
+
+func ReCreateServer(addr string, resolver *Resolver) error {
+	if server.Server != nil {
+		server.Shutdown()
+	}
+
+	if addr == address {
+		return nil
+	}
+
+	_, port, err := net.SplitHostPort(addr)
+	if port == "0" || port == "" || err != nil {
+		return nil
+	}
+
+	udpAddr, err := net.ResolveUDPAddr("udp", addr)
+	if err != nil {
+		return err
+	}
+
+	p, err := net.ListenUDP("udp", udpAddr)
+	if err != nil {
+		return err
+	}
+
+	address = addr
+	server = &Server{r: resolver}
+	server.Server = &D.Server{Addr: addr, PacketConn: p, Handler: server}
+
+	go func() {
+		server.ActivateAndServe()
+	}()
+	return nil
+}