Update the excludeLosthost feature

1. Simplify the implementation
2. update readme

Signed-off-by: Benjamin Wang <benjamin.ahrtr@gmail.com>

README.md

@@ -60,6 +60,7 @@ Flags:
       --dry-run                        evaluate whether or not endpoints require defragmentation, but don't actually perform it
       --endpoints strings              comma separated etcd endpoints (default [127.0.0.1:2379])
       --etcd-storage-quota-bytes int   etcd storage quota in bytes (the value passed to etcd instance by flag --quota-backend-bytes) (default 2147483648)
+      --exclude-localhost              whether to exclude localhost endpoints (default true)
   -h, --help                           help for etcd-defrag
       --insecure-discovery             accept insecure SRV records describing cluster endpoints (default true)
       --insecure-skip-tls-verify       skip server certificate verification (CAUTION: this option should be enabled only for testing purposes)

endpoints.go

@@ -44,12 +44,12 @@ func endpoints(gcfg globalConfig) ([]string, error) {
 	return endpointsFromCluster(gcfg)
 }
 
-func IsLocalEndpoint(ep string) (bool, error) {
-
+func isLocalEndpoint(ep string) (bool, error) {
 	if strings.HasPrefix(ep, "unix:") || strings.HasPrefix(ep, "unixs:") {
 		return true, nil
 	}
 
+	hostPort := ep
 	if strings.Contains(ep, "://") {
 		url, err := url.Parse(ep)
 		if err != nil {
@@ -59,31 +59,23 @@ func IsLocalEndpoint(ep string) (bool, error) {
 			return false, errBadScheme
 		}
 
-		return isLocalEndpoint(url.Host)
+		hostPort = url.Host
 	}
 
-	return isLocalEndpoint(ep)
-}
-
-func isLocalEndpoint(ep string) (bool, error) {
-
-	hostStr, _, err := net.SplitHostPort(ep)
+	hostname, _, err := net.SplitHostPort(hostPort)
 	if err != nil {
 		return false, err
 	}
 
-	// lookup localhost
-	addrs, err := net.LookupHost(hostStr)
-	if err != nil {
-		return false, nil
+	if strings.EqualFold(hostname, "localhost") {
+		return true, nil
 	}
 
-	for _, addr := range addrs {
-		ip := net.ParseIP(addr)
-		if ip != nil && ip.IsLoopback() {
-			return true, nil
-		}
+	ip := net.ParseIP(hostname)
+	if ip != nil && ip.IsLoopback() {
+		return true, nil
 	}
+
 	return false, nil
 }
 
@@ -98,9 +90,9 @@ func endpointsFromCluster(gcfg globalConfig) ([]string, error) {
 		// learner member only serves Status and SerializableRead requests, just ignore it
 		if !m.GetIsLearner() {
 			for _, ep := range m.ClientURLs {
-				// not append local endpoint when set excludeLocalhost
+				// Do not append local endpoint when `--exclude-localhost` is set.
 				if gcfg.excludeLocalhost {
-					ok, err := IsLocalEndpoint(ep)
+					ok, err := isLocalEndpoint(ep)
 					if err != nil {
 						return nil, err
 					}

endpoints_test.go

@@ -267,7 +267,7 @@ func TestIsLocalEp(t *testing.T) {
 
 	for _, testcase := range testcases {
 		t.Run(testcase.name, func(t *testing.T) {
-			if ok, err := IsLocalEndpoint(testcase.ep); err != testcase.err || ok != testcase.desire {
+			if ok, err := isLocalEndpoint(testcase.ep); err != testcase.err || ok != testcase.desire {
 				t.Errorf("expected %v, got err: %v result: %v", testcase.desire, err, ok)
 			}
 		})