pkg/netutil: stop resolving in place

It helps to copy out a and b, and not modify the original a and b.

pkg/netutil/netutil.go

@@ -35,15 +35,24 @@ var (
 )
 
 // resolveTCPAddrs is a convenience wrapper for net.ResolveTCPAddr.
-// resolveTCPAddrs resolves all DNS hostnames in-place for the given set of
-// url.URLs.
-func resolveTCPAddrs(urls ...[]url.URL) error {
+// resolveTCPAddrs return a new set of url.URLs, in which all DNS hostnames
+// are resolved.
+func resolveTCPAddrs(urls [][]url.URL) ([][]url.URL, error) {
+	newurls := make([][]url.URL, 0)
 	for _, us := range urls {
+		nus := make([]url.URL, len(us))
 		for i, u := range us {
+			nu, err := url.Parse(u.String())
+			if err != nil {
+				return nil, err
+			}
+			nus[i] = *nu
+		}
+		for i, u := range nus {
 			host, _, err := net.SplitHostPort(u.Host)
 			if err != nil {
 				plog.Errorf("could not parse url %s during tcp resolving", u.Host)
-				return err
+				return nil, err
 			}
 			if host == "localhost" {
 				continue
@@ -54,13 +63,14 @@ func resolveTCPAddrs(urls ...[]url.URL) error {
 			tcpAddr, err := resolveTCPAddr("tcp", u.Host)
 			if err != nil {
 				plog.Errorf("could not resolve host %s", u.Host)
-				return err
+				return nil, err
 			}
 			plog.Infof("resolving %s to %s", u.Host, tcpAddr.String())
-			us[i].Host = tcpAddr.String()
+			nus[i].Host = tcpAddr.String()
 		}
+		newurls = append(newurls, nus)
 	}
-	return nil
+	return newurls, nil
 }
 
 // urlsEqual checks equality of url.URLS between two arrays.
@@ -69,7 +79,11 @@ func urlsEqual(a []url.URL, b []url.URL) bool {
 	if len(a) != len(b) {
 		return false
 	}
-	resolveTCPAddrs(a, b)
+	urls, err := resolveTCPAddrs([][]url.URL{a, b})
+	if err != nil {
+		return false
+	}
+	a, b = urls[0], urls[1]
 	sort.Sort(types.URLs(a))
 	sort.Sort(types.URLs(b))
 	for i := range a {