Adding CLI validation (nginx#8)

* Adding CLI validation

Validate input parameter.

Users can input entire DOMAIN/NS/NAME path, or leave some elements
off. Gateway will require all elements.

Created Validator pattern. Each argument requiring Validation should provide a Validator. The callback will be provided a FlagSet for referencing other arguments and the particular flag value for validation.

Author: miledxz

cmd/gateway/gateway_suite_test.go

@@ -0,0 +1,13 @@
+package main_test
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+
+	"testing"
+)
+
+func TestGateway(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Gateway Suite")
+}

cmd/gateway/main.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/nginxinc/nginx-gateway-kubernetes/internal/config"
@@ -10,30 +11,38 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/log/zap"
 )
 
+const (
+	domain string = "gateway.nginx.org"
+)
+
 var (
 	// Set during go build
 	version string
 	commit  string
 	date    string
 
 	// Command-line flags
-	gatewayCtlrName = flag.String("gateway-ctlr-name", "", "The name of the Gateway controller")
+	gatewayCtlrName = flag.String(
+		"gateway-ctlr-name",
+		"",
+		fmt.Sprintf("The name of the Gateway controller. The controller name must be of the form: DOMAIN/NAMESPACE/NAME. The controller's domain is '%s'.", domain),
+	)
 )
 
 func main() {
 	flag.Parse()
 
-	if *gatewayCtlrName == "" {
-		flag.PrintDefaults()
-		os.Exit(1)
-	}
-
 	logger := zap.New()
 	conf := config.Config{
 		GatewayCtlrName: *gatewayCtlrName,
 		Logger:          logger,
 	}
 
+	MustValidateArguments(
+		flag.CommandLine,
+		GatewayControllerParam(domain, "nginx-gateway" /* TODO dynamically set */),
+	)
+
 	logger.Info("Starting NGINX Gateway",
 		"version", version,
 		"commit", commit,

cmd/gateway/setup.go

@@ -0,0 +1,95 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	flag "github.com/spf13/pflag"
+)
+
+const (
+	errTmpl = "failed validation - flag: '--%s' reason: '%s'\n"
+)
+
+type Validator func(*flag.FlagSet) error
+type ValidatorContext struct {
+	Key string
+	V   Validator
+}
+
+func GatewayControllerParam(domain string, namespace string) ValidatorContext {
+	name := "gateway-ctlr-name"
+	return ValidatorContext{
+		name,
+		func(flagset *flag.FlagSet) error {
+			// FIXME(yacobucci) this does not provide the same regex validation as
+			// GatewayClass.ControllerName. provide equal and then specific validation
+			param, err := flagset.GetString(name)
+			if err != nil {
+				return err
+			}
+
+			if len(param) == 0 {
+				return errors.New("flag must be set")
+			}
+
+			fields := strings.Split(param, "/")
+			l := len(fields)
+			if l != 3 {
+				return errors.New("unsupported path length, must be form DOMAIN/NAMESPACE/NAME")
+			}
+
+			for i := len(fields); i > 0; i-- {
+				switch i {
+				case 3:
+					if fields[0] != domain {
+						return fmt.Errorf("invalid domain: %s", fields[0])
+					}
+					fields = fields[1:]
+				case 2:
+					if fields[0] != namespace {
+						return fmt.Errorf("cross namespace unsupported: %s", fields[0])
+					}
+					fields = fields[1:]
+				case 1:
+					if fields[0] == "" {
+						return errors.New("must provide a name")
+					}
+				}
+			}
+
+			return nil
+		},
+	}
+}
+
+func ValidateArguments(flagset *flag.FlagSet, validators ...ValidatorContext) []string {
+	var msgs []string
+	for _, v := range validators {
+		if flagset.Lookup(v.Key) != nil {
+			err := v.V(flagset)
+			if err != nil {
+				msgs = append(msgs, fmt.Sprintf(errTmpl, v.Key, err.Error()))
+			}
+		}
+	}
+
+	return msgs
+}
+
+func MustValidateArguments(flagset *flag.FlagSet, validators ...ValidatorContext) {
+	msgs := ValidateArguments(flagset, validators...)
+	if msgs != nil {
+		for i := range msgs {
+			fmt.Fprintf(os.Stderr, "%s", msgs[i])
+		}
+		fmt.Fprintln(os.Stderr, "")
+
+		fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
+		flag.PrintDefaults()
+
+		os.Exit(1)
+	}
+}