diff --git a/main.go b/main.go
index 4ca98ff..6c2f0e0 100644
--- a/main.go
+++ b/main.go
@@ -52,8 +52,12 @@ func main() {
 	if cfg.UpstreamTimeout == 0 {
 		cfg.UpstreamTimeout = 5
 	}
+
 	initDNSClient(cfg)
+
 	log.Debugf("%+v", cfg)
+
 	makeServers(cfg)
+
 	select {}
 }
diff --git a/middleware.go b/middleware.go
index 3b9e877..ee8177b 100644
--- a/middleware.go
+++ b/middleware.go
@@ -35,6 +35,8 @@ func (lh *logHandler) Status() int {
 
 var _ http.ResponseWriter = &logHandler{}
 
+// LogHandler is a log middleware
+// record request log
 func LogHandler(handler http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		defer func() {
@@ -50,6 +52,5 @@ func LogHandler(handler http.Handler) http.Handler {
 		handler.ServeHTTP(lh, r)
 		log.Infof("\"%s %s %s\" - %d %d \"%s\"",
 			r.Method, r.RequestURI, r.Proto, lh.Status(), lh.size, r.UserAgent())
-
 	})
 }
diff --git a/server_https.go b/server_https.go
index 722a814..a784bf7 100644
--- a/server_https.go
+++ b/server_https.go
@@ -9,10 +9,12 @@ import (
 	"github.com/miekg/dns"
 )
 
+const dnsMsgType = "application/dns-message"
+
 func (srv *server) handleHTTPReq(w http.ResponseWriter, r *http.Request) {
 	ctype := r.Header.Get("content-type")
-	if !strings.HasPrefix(ctype, "application/dns-message") {
-		log.Errorf("request type %s, require application/dns-message", ctype)
+	if !strings.HasPrefix(ctype, dnsMsgType) {
+		log.Errorf("request type %s, require %s", ctype, dnsMsgType)
 		http.Error(w, "dns message is required", http.StatusBadRequest)
 		return
 	}
@@ -45,7 +47,7 @@ func (srv *server) handleHTTPReq(w http.ResponseWriter, r *http.Request) {
 	for _, a := range m.Answer {
 		log.Debugln("result", a.String())
 	}
-	w.Header().Set("content-type", "application/dns-message")
+	w.Header().Set("content-type", dnsMsgType)
 	d, _ := m.Pack()
 	w.Write(d)
 }
diff --git a/upstream.go b/upstream.go
index b41c77a..38fa477 100644
--- a/upstream.go
+++ b/upstream.go
@@ -10,7 +10,6 @@ import (
 	"time"
 
 	"github.com/fangdingjun/go-log"
-	//nghttp2 "github.com/fangdingjun/nghttp2-go"
 	"github.com/miekg/dns"
 	"golang.org/x/net/http2"
 )