update conditional metrics usage

metrics/metrics.go

@@ -29,7 +29,7 @@ var (
 	global Metrics = Noop()
 )
 
-func SetGlobal(m Metrics) {
+func Init(m Metrics) {
 	if m != nil {
 		global = m
 	} else {
@@ -37,8 +37,8 @@ func SetGlobal(m Metrics) {
 	}
 }
 
-func Global() Metrics {
-	return global
+func IsEnabled() bool {
+	return global != Noop()
 }
 
 type Gauge interface {

metrics/wrapper/conn.go

@@ -20,6 +20,9 @@ type serverConn struct {
 }
 
 func WrapConn(service string, c net.Conn) net.Conn {
+	if !metrics.IsEnabled() {
+		return c
+	}
 	return &serverConn{
 		service: service,
 		Conn:    c,
@@ -65,6 +68,9 @@ type packetConn struct {
 }
 
 func WrapPacketConn(service string, pc net.PacketConn) net.PacketConn {
+	if !metrics.IsEnabled() {
+		return pc
+	}
 	return &packetConn{
 		PacketConn: pc,
 		service:    service,

metrics/wrapper/listener.go

@@ -12,6 +12,10 @@ type listener struct {
 }
 
 func WrapListener(service string, ln net.Listener) net.Listener {
+	if !metrics.IsEnabled() {
+		return ln
+	}
+
 	return &listener{
 		service:  service,
 		Listener: ln,
@@ -24,9 +28,5 @@ func (ln *listener) Accept() (net.Conn, error) {
 		return nil, err
 	}
 
-	// metrics is not enabled
-	if metrics.Global() == metrics.Noop() {
-		return c, nil
-	}
 	return WrapConn(ln.service, c), nil
 }