net: extract HTTPProxy.listen() to MultiListener

http_proxy.go

@@ -566,38 +566,35 @@ func (hp *HTTPProxy) run(ctx context.Context) error {
 	return g.Wait()
 }
 
-func (hp *HTTPProxy) listen() (_ []net.Listener, ferr error) {
+func (hp *HTTPProxy) listen() ([]net.Listener, error) {
 	switch hp.config.Protocol {
 	case HTTPScheme, HTTPSScheme, HTTP2Scheme:
 	default:
 		return nil, fmt.Errorf("invalid protocol %q", hp.config.Protocol)
 	}
 
-	prototype := Listener{
-		TLSConfig: hp.tlsConfig,
-		metrics:   newListenerMetrics(hp.config.PromRegistry, hp.config.PromNamespace),
-	}
-
-	listeners := make([]net.Listener, 0, len(hp.config.ExtraListeners)+1)
-	defer func() {
-		if ferr != nil {
-			for _, l := range listeners {
-				l.Close()
-			}
+	if len(hp.config.ExtraListeners) == 0 {
+		l := &Listener{
+			ListenerConfig: hp.config.ListenerConfig,
+			TLSConfig:      hp.tlsConfig,
+			PromConfig: PromConfig{
+				PromNamespace: hp.config.PromNamespace,
+				PromRegistry:  hp.config.PromRegistry,
+			},
 		}
-	}()
-
-	for _, lc := range append([]NamedListenerConfig{{ListenerConfig: hp.config.ListenerConfig}}, hp.config.ExtraListeners...) {
-		l := new(Listener)
-		*l = prototype
-		l.ListenerConfig = lc.ListenerConfig
 		if err := l.Listen(); err != nil {
 			return nil, err
 		}
-		listeners = append(listeners, l)
+		return []net.Listener{l}, nil
 	}
 
-	return listeners, nil
+	return MultiListener{
+		ListenerConfigs: append([]NamedListenerConfig{{ListenerConfig: hp.config.ListenerConfig}}, hp.config.ExtraListeners...),
+		TLSConfig: func(lc NamedListenerConfig) *tls.Config {
+			return hp.tlsConfig
+		},
+		PromConfig: hp.config.PromConfig,
+	}.Listen()
 }
 
 // Addr returns the address the server is listening on.

net.go

@@ -196,6 +196,43 @@ type NamedListenerConfig struct {
 	ListenerConfig
 }
 
+// MultiListener is a builder for multiple listeners sharing the same prometheus configuration.
+type MultiListener struct {
+	ListenerConfigs []NamedListenerConfig
+	TLSConfig       func(NamedListenerConfig) *tls.Config
+	PromConfig
+}
+
+func (ml MultiListener) Listen() (_ []net.Listener, ferr error) {
+	prototype := Listener{
+		metrics: newListenerMetrics(ml.PromRegistry, ml.PromNamespace),
+	}
+
+	listeners := make([]net.Listener, 0, len(ml.ListenerConfigs))
+	defer func() {
+		if ferr != nil {
+			for _, l := range listeners {
+				l.Close()
+			}
+		}
+	}()
+
+	for _, lc := range ml.ListenerConfigs {
+		l := new(Listener)
+		*l = prototype
+		l.ListenerConfig = lc.ListenerConfig
+		if ml.TLSConfig != nil {
+			l.TLSConfig = ml.TLSConfig(lc)
+		}
+		if err := l.Listen(); err != nil {
+			return nil, err
+		}
+		listeners = append(listeners, l)
+	}
+
+	return listeners, nil
+}
+
 type Listener struct {
 	ListenerConfig
 	TLSConfig *tls.Config