query namespace exists with GET Namespace

More efficient ns switches with kubens by querying only the namespace (instead
of listing all namespaces).

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

cmd/kubens/list.go

@@ -54,15 +54,7 @@ func queryNamespaces(kc *kubeconfig.Kubeconfig) ([]string, error) {
 		return []string{"ns1", "ns2"}, nil
 	}
 
-	b, err := kc.Bytes()
-	if err != nil {
-		return nil, errors.Wrap(err, "failed to convert in-memory kubeconfig to yaml")
-	}
-	cfg, err := clientcmd.RESTConfigFromKubeConfig(b)
-	if err != nil {
-		return nil, errors.Wrap(err, "failed to initialize config")
-	}
-	clientset, err := kubernetes.NewForConfig(cfg)
+	clientset, err := newKubernetesClientSet(kc)
 	if err != nil {
 		return nil, errors.Wrap(err, "failed to initialize k8s REST client")
 	}
@@ -87,3 +79,15 @@ func queryNamespaces(kc *kubeconfig.Kubeconfig) ([]string, error) {
 	}
 	return out, nil
 }
+
+func newKubernetesClientSet(kc *kubeconfig.Kubeconfig) (*kubernetes.Clientset, error) {
+	b, err := kc.Bytes()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to convert in-memory kubeconfig to yaml")
+	}
+	cfg, err := clientcmd.RESTConfigFromKubeConfig(b)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to initialize config")
+	}
+	return kubernetes.NewForConfig(cfg)
+}

cmd/kubens/switch.go

@@ -2,8 +2,11 @@ package main
 
 import (
 	"io"
+	"os"
 
 	"github.com/pkg/errors"
+	errors2 "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
 	"github.com/ahmetb/kubectx/internal/cmdutil"
 	"github.com/ahmetb/kubectx/internal/kubeconfig"
@@ -75,14 +78,20 @@ func switchNamespace(kc *kubeconfig.Kubeconfig, ns string) (string, error) {
 }
 
 func namespaceExists(kc *kubeconfig.Kubeconfig, ns string) (bool, error) {
-	nses, err := queryNamespaces(kc)
+	// for tests
+	if os.Getenv("_MOCK_NAMESPACES") != "" {
+		return ns == "ns1" || ns == "ns2", nil
+	}
+
+	clientset, err := newKubernetesClientSet(kc)
 	if err != nil {
-		return false, err
+		return false, errors.Wrap(err, "failed to initialize k8s REST client")
 	}
-	for _, v := range nses {
-		if v == ns {
-			return true, nil
-		}
+
+	namespace, err := clientset.CoreV1().Namespaces().Get(ns, metav1.GetOptions{})
+	if errors2.IsNotFound(err) {
+		return false, nil
 	}
-	return false, nil
+	return namespace != nil, errors.Wrapf(err, "failed to query "+
+		"namespace %q from k8s API", ns)
 }