Add 500 response codes on errors

lib/app/app.go

@@ -18,8 +18,8 @@ import (
 // App context
 type App struct {
 	cli    *cli.App
-	client *client.Client
-	out    io.Writer
+	Client *client.Client
+	Out    io.Writer
 }
 
 var (
@@ -60,7 +60,7 @@ var (
 func New() *App {
 	cliapp := cli.NewApp()
 	app := &App{
-		out: os.Stdout,
+		Out: os.Stdout,
 		cli: cliapp,
 	}
 
@@ -79,19 +79,19 @@ func New() *App {
 		cli.Command{
 			Name:   "print",
 			Usage:  "pretty prints api result",
-			Action: app.actionPrint,
+			Action: app.ActionPrint,
 		},
 		cli.Command{
 			Name:   "export",
 			Usage:  "runs http exporter for prometheus",
-			Action: app.actionMetrics,
+			Action: app.ActionMetrics,
 			Flags: []cli.Flag{
 				FlagInterface,
 			},
 		},
 	}
 
-	app.cli.Before = app.before
+	app.cli.Before = app.Before
 	return app
 }
 
@@ -101,8 +101,8 @@ func (a *App) Run(args []string) error {
 }
 
 // Before sets up app
-func (a *App) before(ctx *cli.Context) error {
-	a.client = &client.Client{
+func (a *App) Before(ctx *cli.Context) error {
+	a.Client = &client.Client{
 		URL: url.URL{
 			Scheme: ctx.String("scheme"),
 			Host:   ctx.String("host"),
@@ -112,30 +112,41 @@ func (a *App) before(ctx *cli.Context) error {
 	return nil
 }
 
-func (a *App) actionPrint(_ *cli.Context) error {
-	node, err := a.client.Fetch()
+// ActionPrint prints api result
+func (a *App) ActionPrint(_ *cli.Context) error {
+	node, err := a.Client.Fetch()
 	if err != nil {
 		return err
 	}
-	fmt.Fprint(a.out, node.Stringify())
+	fmt.Print(a.Out, node.Stringify())
 	return nil
 }
 
-func (a *App) actionMetrics(ctx *cli.Context) error {
+// ActionMetrics serves http
+func (a *App) ActionMetrics(ctx *cli.Context) error {
 	addr := ctx.String("http")
-	http.HandleFunc("/metrics", func(resp http.ResponseWriter, req *http.Request) {
+	http.HandleFunc("/metrics", a.HandleMetrics)
+	log.Println(a.Out, "listen on: "+addr)
+	return http.ListenAndServe(addr, nil)
+}
+
+// HandleMetrics handler
+func (a *App) HandleMetrics(resp http.ResponseWriter, req *http.Request) {
 	log.Println("GET /metrics")
-		root, err := a.client.Fetch()
+	root, err := a.Client.Fetch()
 	if err != nil {
+		http.Error(resp, err.Error(), http.StatusInternalServerError)
 		return
 	}
 	vals, err := root.Values()
 	if err != nil {
+		http.Error(resp, err.Error(), http.StatusInternalServerError)
 		return
 	}
 	collection := metrics.FromVals(vals)
 	registry := prometheus.NewRegistry()
 	if err := registry.Register(collection); err != nil {
+		http.Error(resp, err.Error(), http.StatusInternalServerError)
 		return
 	}
 
@@ -145,7 +156,4 @@ func (a *App) actionMetrics(ctx *cli.Context) error {
 
 	handler.ServeHTTP(resp, req)
 	registry.Unregister(collection)
-	})
-	log.Println("listen on: " + addr)
-	return http.ListenAndServe(addr, nil)
 }