Introduce flags

README.md

@@ -7,7 +7,19 @@
 
 1. Setup your OpenID Connect provider, e.g. Google Identity Platform or Keycloak.
 1. Setup your Kubernetes cluster.
-1. Setup `kubectl` and `kubelogin`.
+1. Setup your `kubectl`.
+
+```
+% kubelogin --help
+2018/08/15 19:08:58 Usage:
+  kubelogin [OPTIONS]
+
+Application Options:
+      --kubeconfig= Path to the kubeconfig file. (default: ~/.kube/config) [$KUBECONFIG]
+
+Help Options:
+  -h, --help        Show this help message
+```
 
 
 ## Getting Started with Google Account

kubeconfig/kubeconfig.go

@@ -2,37 +2,11 @@ package kubeconfig
 
 import (
 	"fmt"
-	"os"
 
-	homedir "github.com/mitchellh/go-homedir"
 	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/client-go/tools/clientcmd/api"
 )
 
-const userKubeConfig = "~/.kube/config"
-
-// Find returns path to the kubeconfig file,
-// that is given by env:KUBECONFIG or ~/.kube/config.
-// This returns an error if it is not found or I/O error occurred.
-func Find() (string, error) {
-	path := os.Getenv("KUBECONFIG")
-	if path == "" {
-		var err error
-		path, err = homedir.Expand(userKubeConfig)
-		if err != nil {
-			return "", fmt.Errorf("Could not expand %s: %s", userKubeConfig, err)
-		}
-	}
-	info, err := os.Stat(path)
-	if err != nil {
-		return "", fmt.Errorf("Could not stat %s: %s", userKubeConfig, err)
-	}
-	if info.IsDir() {
-		return "", fmt.Errorf("%s should be a file", userKubeConfig)
-	}
-	return path, nil
-}
-
 // Load loads the file and returns the Config.
 func Load(path string) (*api.Config, error) {
 	config, err := clientcmd.LoadFromFile(path)

main.go

@@ -2,16 +2,48 @@ package main
 
 import (
 	"context"
+	"fmt"
 	"log"
 
 	"github.com/int128/kubelogin/authn"
 	"github.com/int128/kubelogin/kubeconfig"
+	flags "github.com/jessevdk/go-flags"
+	homedir "github.com/mitchellh/go-homedir"
 )
 
+type options struct {
+	KubeConfig string `long:"kubeconfig" default:"~/.kube/config" env:"KUBECONFIG" description:"Path to the kubeconfig file."`
+}
+
+func (o *options) ExpandKubeConfig() (string, error) {
+	d, err := homedir.Expand(o.KubeConfig)
+	if err != nil {
+		return "", fmt.Errorf("Could not expand %s", o.KubeConfig)
+	}
+	return d, nil
+}
+
+func parseOptions() (*options, error) {
+	var o options
+	parser := flags.NewParser(&o, flags.HelpFlag)
+	args, err := parser.Parse()
+	if err != nil {
+		return nil, err
+	}
+	if len(args) > 0 {
+		return nil, fmt.Errorf("Too many argument")
+	}
+	return &o, nil
+}
+
 func main() {
-	path, err := kubeconfig.Find()
+	opts, err := parseOptions()
+	if err != nil {
+		log.Fatal(err)
+	}
+	path, err := opts.ExpandKubeConfig()
 	if err != nil {
-		log.Fatalf("Could not find kubeconfig: %s", err)
+		log.Fatal(err)
 	}
 	log.Printf("Reading %s", path)
 	cfg, err := kubeconfig.Load(path)