Optimize `LoopbackListenHost()` (#615)

diff --git a/listen.go b/listen.go
index 29015c100aa2e20d812a47b5a81e68cc910526b6..3840cc145a72b911438027847af806ada4ac046c 100644 (file)
--- a/listen.go
+++ b/listen.go
@@ -3,7 +3,7 @@ package torrent
 import "strings"
 
 func LoopbackListenHost(network string) string {
-       if strings.Contains(network, "4") {
+       if strings.IndexByte(network, '4') != -1 {
                return "127.0.0.1"
        } else {
                return "::1"