rekor server validation via custom type

This retargets #67 at main instead of openapi branch

cmd/cli/app/root.go

@@ -55,7 +55,7 @@ func init() {
 
 	rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default is $HOME/.rekor.yaml)")
 
-	rootCmd.PersistentFlags().String("rekor_server", "http://localhost:3000", "Server address:port")
+	rootCmd.PersistentFlags().Var(&UrlFlag{url: "http://localhost:3000"}, "rekor_server", "Server address:port")
 
 	// these are bound here and not in PreRun so that all child commands can use them
 	if err := viper.BindPFlags(rootCmd.PersistentFlags()); err != nil {
@@ -212,22 +212,33 @@ func buildRekorEntryFromPFlags() (*types.RekorEntry, error) {
 	return &rekorEntry, nil
 }
 
-func validateRekorServerURL() error {
-	rekorServerURL := viper.GetString("rekor_server")
-	if rekorServerURL != "" {
-		url, err := url.Parse(rekorServerURL)
-		if err != nil {
-			return fmt.Errorf("malformed rekor_server URL: %w", err)
-		}
-		if !url.IsAbs() {
-			return errors.New("rekor_server URL must be absolute")
-		}
-		lowercaseScheme := strings.ToLower(url.Scheme)
-		if lowercaseScheme != "http" && lowercaseScheme != "https" {
-			return errors.New("rekor_server must be a valid HTTP or HTTPS URL")
-		}
-	} else {
-		return errors.New("rekor_server must be specified")
+type UrlFlag struct {
+	url string
+}
+
+func (u *UrlFlag) String() string {
+	return u.url
+}
+
+func (u *UrlFlag) Set(s string) error {
+	if s == "" {
+		return errors.New("flag must be specified")
+	}
+	url, err := url.Parse(s)
+	if err != nil {
+		return fmt.Errorf("malformed URL: %w", err)
+	}
+	if !url.IsAbs() {
+		return fmt.Errorf("URL must be absolute, got %s", s)
 	}
+	lowercaseScheme := strings.ToLower(url.Scheme)
+	if lowercaseScheme != "http" && lowercaseScheme != "https" {
+		return fmt.Errorf("URL must be a valid HTTP or HTTPS URL, got %s", s)
+	}
+	u.url = s
 	return nil
 }
+
+func (u *UrlFlag) Type() string {
+	return "url"
+}

cmd/cli/app/root_test.go

@@ -198,9 +198,7 @@ func TestValidateRekorServerURL(t *testing.T) {
 	}
 
 	for _, tc := range tests {
-		viper.Reset()
-		viper.Set("rekor_server", tc.rekorServer)
-		if err := validateRekorServerURL(); (err == nil) != tc.expectSuccess {
+		if err := rootCmd.PersistentFlags().Set("rekor_server", tc.rekorServer); (err == nil) != tc.expectSuccess {
 			t.Errorf("unexpected result in '%v': %v", tc.caseDesc, err)
 		}
 	}

cmd/cli/app/upload.go

@@ -49,11 +49,6 @@ var uploadCmd = &cobra.Command{
 		if err := viper.BindPFlags(cmd.Flags()); err != nil {
 			log.Logger.Fatal("Error initializing cmd line args: ", err)
 		}
-		if err := validateRekorServerURL(); err != nil {
-			log.Logger.Error(err)
-			_ = cmd.Help()
-			os.Exit(1)
-		}
 		if err := validateArtifactPFlags(); err != nil {
 			log.Logger.Error(err)
 			_ = cmd.Help()

cmd/cli/app/verify.go

@@ -55,11 +55,6 @@ var verifyCmd = &cobra.Command{
 		if err := viper.BindPFlags(cmd.Flags()); err != nil {
 			log.Logger.Fatal("Error initializing cmd line args: ", err)
 		}
-		if err := validateRekorServerURL(); err != nil {
-			log.Logger.Error(err)
-			_ = cmd.Help()
-			os.Exit(1)
-		}
 		if err := validateArtifactPFlags(); err != nil {
 			log.Logger.Error(err)
 			_ = cmd.Help()