Implement facilities to parse kubeconfig file

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

cmd/kubectx/kubeconfig.go

@@ -1,9 +1,11 @@
 package main
 
 import (
-	"errors"
 	"os"
 	"path/filepath"
+
+	"github.com/pkg/errors"
+	"gopkg.in/yaml.v3"
 )
 
 func kubeconfigPath() (string, error) {
@@ -27,3 +29,15 @@ func kubeconfigPath() (string, error) {
 	}
 	return filepath.Join(home, ".kube", "config"), nil
 }
+
+func parseKubeconfig(path string) (kubeconfig, error) {
+	// TODO refactor to accept io.Reader instead of file
+	var v kubeconfig
+
+	f, err := os.Open(path)
+	if err != nil {
+		return v, errors.Wrap(err, "file open error")
+	}
+	err = yaml.NewDecoder(f).Decode(&v)
+	return v, errors.Wrap(err, "yaml parse error")
+}

cmd/kubectx/kubeconfig_test.go

@@ -1,10 +1,13 @@
 package main
 
 import (
+	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
 	"testing"
+
+	"github.com/google/go-cmp/cmp"
 )
 
 func Test_kubeconfigPath_homePath(t *testing.T) {
@@ -72,5 +75,79 @@ func Test_kubeconfigPath_envOvverideDoesNotSupportPathSeparator(t *testing.T) {
 
 	_, err := kubeconfigPath()
 	if err == nil { t.Fatal("expected error")}
-
+}
+
+
+func Test_parseKubeconfig_openError(t *testing.T) {
+	_, err := parseKubeconfig("/non/existing/path")
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+	msg := err.Error()
+	expected := `file open error`
+	if !strings.Contains(msg, expected) {
+		t.Fatalf("expected=%q, got=%q", expected, msg)
+	}
+}
+
+func Test_parseKubeconfig_yamlFormatError(t *testing.T) {
+	file, cleanup := testfile(t, `a: [1,2 `) // supposed to be invalid yaml
+	defer cleanup()
+
+	_, err := parseKubeconfig(file)
+	if err == nil {
+		t.Fatal("expected error")
+	}
+	expected := "yaml parse error"
+	if got := err.Error(); !strings.Contains(got, expected) {
+		t.Fatalf("expected=%q; got=%q", expected, got)
+	}
+}
+
+func Test_parseKubeconfig(t *testing.T) {
+	file, cleanup := testfile(t,
+		`
+apiVersion: v1
+current-context: foo
+contexts:
+- name: c3
+- name: c2
+- name: c1`)
+	defer cleanup()
+
+	got, err := parseKubeconfig(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	expected := kubeconfig{
+		APIVersion:     "v1",
+		CurrentContext: "foo",
+		Contexts: []context{
+			{Name:"c3"},{Name:"c2"},{Name:"c1"},
+		},
+	}
+
+	diff := cmp.Diff(expected, got)
+	if diff != "" {
+		t.Fatalf("got wrong object:\n%s", diff)
+	}
+}
+
+func testfile(t *testing.T, contents string) (path string, cleanup func()) {
+	t.Helper()
+
+	f, err := ioutil.TempFile(os.TempDir(), "test-file")
+	if err != nil {
+		t.Fatalf("failed to create test file: %v", err)
+	}
+	path = f.Name()
+	if _, err := f.Write([]byte(contents)); err != nil {
+		t.Fatalf("failed to write to test file: %v", err)
+	}
+
+	return path, func() {
+		f.Close()
+		os.Remove(path)
+	}
 }

cmd/kubectx/list.go

@@ -1 +1,36 @@
 package main
+
+import (
+	"io"
+
+	"github.com/pkg/errors"
+)
+
+type context struct {
+	Name string `yaml:"name"`
+}
+
+type kubeconfig struct {
+	APIVersion     string    `yaml:"apiVersion"`
+	CurrentContext string    `yaml:"current-context"`
+	Contexts       []context `yaml:"contexts"`
+}
+
+func printListContexts(out io.Writer) error {
+	cfgPath, err := kubeconfigPath()
+	if err != nil {
+		return errors.Wrap(err, "failed to determine kubeconfig path")
+	}
+
+	cfg, err := parseKubeconfig(cfgPath)
+	if err != nil {
+		return errors.Wrap(err, "failed to read kubeconfig file")
+	}
+	_ = cfg
+	
+	// print each context
+	//  - natural sort
+	//  - highlight current context
+
+	return nil
+}

cmd/kubectx/main.go

@@ -13,12 +13,12 @@ func main() {
 	var op Op
 	op = parseArgs(os.Args[1:])
 
+	// TODO consider addin Run() operation to each operation type
 	switch v := op.(type) {
 	case HelpOp:
 		printHelp(os.Stdout)
 	case ListOp:
-		// TODO implement
-		panic("not implemented")
+		printListContexts(os.Stdout)
 	case SwitchOp:
 		// TODO implement
 		panic("not implemented")

go.mod

@@ -5,4 +5,6 @@ go 1.14
 require (
 	github.com/fatih/color v1.9.0
 	github.com/google/go-cmp v0.4.0
+	github.com/pkg/errors v0.9.1
+	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c
 )

go.sum

@@ -7,7 +7,12 @@ github.com/mattn/go-colorable v0.1.4/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVc
 github.com/mattn/go-isatty v0.0.8/go.mod h1:Iq45c/XA43vh69/j3iqttzPXn0bhXyGjM0Hdxcsrc5s=
 github.com/mattn/go-isatty v0.0.11 h1:FxPOTFNqGkuDUGi3H/qkUbQO4ZiBa2brKq5r0l8TGeM=
 github.com/mattn/go-isatty v0.0.11/go.mod h1:PhnuNfih5lzO57/f3n+odYbM4JtupLOxQOAqxQCu2WE=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037 h1:YyJpGZS1sBuBCzLAR1VEpK193GlqGZbnPFnPV/5Rsb4=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=