Add utils for r/w ~/.kube/kubectx file

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

cmd/kubectx/state.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+
+	"github.com/pkg/errors"
+)
+
+func kubectxFilePath() (string, error) {
+	home := homeDir()
+	if home == "" {
+		return "", errors.New("HOME or USERPROFILE environment variable not set")
+	}
+	return filepath.Join(home, ".kube", "kubectx"), nil
+}
+
+// readLastContext returns the saved previous context
+// if the state file exists, otherwise returns "".
+func readLastContext(path string) (string, error) {
+	b, err := ioutil.ReadFile(path)
+	if os.IsNotExist(err) {
+		return "", nil
+	}
+	return string(b), err
+}
+
+// writeLastContext saves the specified value to the state file.
+// It creates missing parent directories.
+func writeLastContext(path, value string) error {
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return errors.Wrap(err, "failed to create parent directories")
+	}
+	return ioutil.WriteFile(path, []byte(value), 0644)
+}

cmd/kubectx/state_test.go

@@ -0,0 +1,88 @@
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func Test_readLastContext_nonExistingFile(t *testing.T) {
+	s, err := readLastContext(filepath.FromSlash("/non/existing/file"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if s != "" {
+		t.Fatalf("expected empty string; got=%q", s)
+	}
+}
+
+func Test_readLastContext(t *testing.T) {
+	path, cleanup := testfile(t, "foo")
+	defer cleanup()
+
+	s, err := readLastContext(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if expected := "foo"; s != expected {
+		t.Fatalf("expected=%q; got=%q", expected, s)
+	}
+}
+
+func Test_writeLastContext_err(t *testing.T) {
+	path := filepath.Join(os.DevNull, "foo", "bar")
+	err := writeLastContext(path, "foo")
+	if err == nil {
+		t.Fatal("got empty error")
+	}
+}
+
+func Test_writeLastContext(t *testing.T) {
+	dir, err := ioutil.TempDir(os.TempDir(), "state-file-test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(dir, "foo", "bar")
+
+	if err := writeLastContext(path, "ctx1"); err != nil {
+		t.Fatal(err)
+	}
+
+	v, err := readLastContext(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if expected := "ctx1"; v != expected {
+		t.Fatalf("read wrong value=%q; expected=%q", v, expected)
+	}
+}
+
+func Test_kubectxFilePath(t *testing.T) {
+	origHome := os.Getenv("HOME")
+	os.Setenv("HOME", filepath.FromSlash("/foo/bar"))
+	defer os.Setenv("HOME", origHome)
+
+	expected := filepath.Join(filepath.FromSlash("/foo/bar"), ".kube", "kubectx")
+	v, err := kubectxFilePath()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if v != expected {
+		t.Fatalf("expected=%q got=%q", expected, v)
+	}
+}
+
+func Test_kubectxFilePath_error(t *testing.T) {
+	origHome := os.Getenv("HOME")
+	origUserprofile := os.Getenv("USERPROFILE")
+	os.Unsetenv("HOME")
+	os.Unsetenv("USERPROFILE")
+	defer os.Setenv("HOME", origHome)
+	defer os.Setenv("USERPROFILE", origUserprofile)
+
+	_, err := kubectxFilePath()
+	if err == nil {
+		t.Fatal(err)
+	}
+}