From 0349e372ac7ecfe02b8952272fe6fcc4f904a3d1 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Sat, 2 Oct 2021 16:59:20 +0200
Subject: [PATCH] collector: move net.InterfaceByName() call out of
 getUnicastAddr()

Preparation for setting IPV6_MULTICAST_IF in listenUDP().
---
 respond/collector.go | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/respond/collector.go b/respond/collector.go
index d2cc54d..97037d7 100644
--- a/respond/collector.go
+++ b/respond/collector.go
@@ -59,16 +59,20 @@ func (coll *Collector) listenUDP(iface InterfaceConfig) {
 
 	var addr net.IP
 
-	var err error
-	if iface.IPAddress != "" {
-		addr = net.ParseIP(iface.IPAddress)
-	} else {
-		addr, err = getUnicastAddr(iface.InterfaceName)
-		if err != nil {
-			log.WithField("iface", iface.InterfaceName).Panic(err)
+	ifaceInfo, err := net.InterfaceByName(iface.InterfaceName)
+
+	if err == nil {
+		if iface.IPAddress != "" {
+			addr = net.ParseIP(iface.IPAddress)
+		} else {
+			addr, err = getUnicastAddr(ifaceInfo)
 		}
 	}
 
+	if err != nil {
+		log.WithField("iface", iface.InterfaceName).Panic(err)
+	}
+
 	multicastAddress := MulticastAddressDefault
 	if iface.MulticastAddress != "" {
 		multicastAddress = iface.MulticastAddress
@@ -96,12 +100,7 @@ func (coll *Collector) listenUDP(iface InterfaceConfig) {
 }
 
 // Returns a unicast address of given interface (linklocal or global unicast address)
-func getUnicastAddr(ifname string) (net.IP, error) {
-	iface, err := net.InterfaceByName(ifname)
-	if err != nil {
-		return nil, err
-	}
-
+func getUnicastAddr(iface *net.Interface) (net.IP, error) {
 	addresses, err := iface.Addrs()
 	if err != nil {
 		return nil, err