kubens: implement namespace switching

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

internal/kubeconfig/contextmodify.go

@@ -6,12 +6,9 @@ import (
 )
 
 func (k *Kubeconfig) DeleteContextEntry(deleteName string) error {
-	contexts := valueOf(k.rootNode, "contexts")
-	if contexts == nil {
-		return errors.New("there are no contexts in kubeconfig")
-	}
-	if contexts.Kind != yaml.SequenceNode {
-		return errors.New("'contexts' key is not a sequence")
+	contexts, err := k.contextsNode()
+	if err != nil {
+		return err
 	}
 
 	i := -1
@@ -51,11 +48,9 @@ func (k *Kubeconfig) ModifyCurrentContext(name string) error {
 }
 
 func (k *Kubeconfig) ModifyContextName(old, new string) error {
-	contexts := valueOf(k.rootNode, "contexts")
-	if contexts == nil {
-		return errors.New("\"contexts\" entry is nil")
-	} else if contexts.Kind != yaml.SequenceNode {
-		return errors.New("\"contexts\" is not a sequence node")
+	contexts, err := k.contextsNode()
+	if err != nil {
+		return err
 	}
 
 	var changed bool

internal/kubeconfig/contexts.go

@@ -1,9 +1,35 @@
 package kubeconfig
 
 import (
+	"github.com/pkg/errors"
 	"gopkg.in/yaml.v3"
 )
 
+func (k *Kubeconfig) contextsNode() (*yaml.Node, error) {
+	contexts := valueOf(k.rootNode, "contexts")
+	if contexts == nil {
+		return nil, errors.New("\"contexts\" entry is nil")
+	} else if contexts.Kind != yaml.SequenceNode {
+		return nil, errors.New("\"contexts\" is not a sequence node")
+	}
+	return contexts, nil
+}
+
+func (k *Kubeconfig) contextNode(name string) (*yaml.Node, error) {
+	contexts, err := k.contextsNode()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, contextNode := range contexts.Content {
+		nameNode := valueOf(contextNode, "name")
+		if nameNode.Kind == yaml.ScalarNode && nameNode.Value == name {
+			return contextNode, nil
+		}
+	}
+	return nil, errors.Errorf("context with name %q not found", name)
+}
+
 func (k *Kubeconfig) ContextNames() []string {
 	contexts := valueOf(k.rootNode, "contexts")
 	if contexts == nil {

internal/kubeconfig/namespace.go

@@ -1,31 +1,11 @@
 package kubeconfig
 
-import (
-	"github.com/pkg/errors"
-	"gopkg.in/yaml.v3"
-)
+import "gopkg.in/yaml.v3"
 
 const (
 	defaultNamespace = "default"
 )
 
-func (k *Kubeconfig) contextNode(name string) (*yaml.Node, error) {
-	contexts := valueOf(k.rootNode, "contexts")
-	if contexts == nil {
-		return nil, errors.New("\"contexts\" entry is nil")
-	} else if contexts.Kind != yaml.SequenceNode {
-		return nil, errors.New("\"contexts\" is not a sequence node")
-	}
-
-	for _, contextNode := range contexts.Content {
-		nameNode := valueOf(contextNode, "name")
-		if nameNode.Kind == yaml.ScalarNode && nameNode.Value == name {
-			return contextNode, nil
-		}
-	}
-	return nil, errors.Errorf("context with name %q not found", name)
-}
-
 func (k *Kubeconfig) NamespaceOfContext(contextName string) (string, error) {
 	ctx, err := k.contextNode(contextName)
 	if err != nil {
@@ -37,3 +17,26 @@ func (k *Kubeconfig) NamespaceOfContext(contextName string) (string, error) {
 	}
 	return ns.Value, nil
 }
+
+func (k *Kubeconfig) SetNamespace(ctxName string, ns string) error {
+	ctx, err := k.contextNode(ctxName)
+	if err != nil {
+		return err
+	}
+	nsNode := valueOf(ctx, "namespace")
+	if nsNode != nil {
+		nsNode.Value = ns
+		return nil
+	}
+
+	keyNode := &yaml.Node{
+		Kind:  yaml.ScalarNode,
+		Value: "namespace",
+		Tag:   "!!str"}
+	valueNode := &yaml.Node{
+		Kind:  yaml.ScalarNode,
+		Value: ns,
+		Tag:   "!!str"}
+	ctx.Content = append(ctx.Content, keyNode, valueNode)
+	return nil
+}

internal/kubeconfig/namespace_test.go

@@ -3,6 +3,8 @@ package kubeconfig
 import (
 	"testing"
 
+	"github.com/google/go-cmp/cmp"
+
 	"github.com/ahmetb/kubectx/internal/testutil"
 )
 
@@ -44,3 +46,35 @@ func TestKubeconfig_NamespaceOfContext(t *testing.T) {
 		t.Fatalf("c2: expected=%q got=%q", expected, v2)
 	}
 }
+
+func TestKubeconfig_SetNamespace(t *testing.T) {
+	l := WithMockKubeconfigLoader(testutil.KC().
+		WithCtxs(
+			testutil.Ctx("c1"),
+			testutil.Ctx("c2").Ns("c2n1")).ToYAML(t))
+	kc := new(Kubeconfig).WithLoader(l)
+	if err := kc.Parse(); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := kc.SetNamespace("c3", "foo"); err == nil {
+		t.Fatalf("expected error for non-existing ctx")
+	}
+
+	if err := kc.SetNamespace("c1", "c1n1"); err != nil {
+		t.Fatal(err)
+	}
+	if err := kc.SetNamespace("c2", "c2n2"); err != nil {
+		t.Fatal(err)
+	}
+	if err := kc.Save(); err != nil {
+		t.Fatal(err)
+	}
+
+	expected := testutil.KC().WithCtxs(
+		testutil.Ctx("c1").Ns("c1n1"),
+		testutil.Ctx("c2").Ns("c2n2")).ToYAML(t)
+	if diff := cmp.Diff(l.Output(), expected); diff != "" {
+		t.Fatal(diff)
+	}
+}