refactor(listener) refactor listener related code

Remove duplicate code around creating http listener.
Start to listen incoming http requests just before serving them.

server/listener.go

@@ -3,9 +3,35 @@ package server
 import (
 	"crypto/tls"
 	"net"
+
+	"github.com/coreos/etcd/log"
 )
 
-func NewListener(addr string) (net.Listener, error) {
+// NewListener creates a net.Listener
+// If the given scheme is "https", it will generate TLS configuration based on TLSInfo.
+// If any error happens, this function will call log.Fatal
+func NewListener(scheme, addr string, tlsInfo *TLSInfo) net.Listener {
+	if scheme == "https" {
+		cfg, err := tlsInfo.ServerConfig()
+		if err != nil {
+			log.Fatal("TLS info error: ", err)
+		}
+
+		l, err := newTLSListener(addr, cfg)
+		if err != nil {
+			log.Fatal("Failed to create TLS listener: ", err)
+		}
+		return l
+	}
+
+	l, err := newListener(addr)
+	if err != nil {
+		log.Fatal("Failed to create listener: ", err)
+	}
+	return l
+}
+
+func newListener(addr string) (net.Listener, error) {
 	if addr == "" {
 		addr = ":http"
 	}
@@ -16,7 +42,7 @@ func NewListener(addr string) (net.Listener, error) {
 	return l, nil
 }
 
-func NewTLSListener(addr string, cfg *tls.Config) (net.Listener, error) {
+func newTLSListener(addr string, cfg *tls.Config) (net.Listener, error) {
 	if addr == "" {
 		addr = ":https"
 	}