Support multiple commands in gateway binary

This commit:
- Changes the cmd package to support multiple commands in
gateway binary.
- Adds the root command, which simply prints help.
- Adds control-plane command, which starts the control plane --
the previously available functionally of the gateway binary.
- Adds provisioner command, currently not implemented.

Needed by #634

cmd/gateway/commands.go

@@ -0,0 +1,135 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+	"sigs.k8s.io/controller-runtime/pkg/log/zap"
+
+	"github.com/nginxinc/nginx-kubernetes-gateway/internal/config"
+	"github.com/nginxinc/nginx-kubernetes-gateway/internal/manager"
+)
+
+const (
+	domain                = "k8s-gateway.nginx.org"
+	gatewayClassFlag      = "gatewayclass"
+	gatewayClassNameUsage = `The name of the GatewayClass resource. ` +
+		`Every NGINX Gateway must have a unique corresponding GatewayClass resource.`
+	gatewayCtrlNameFlag     = "gateway-ctlr-name"
+	gatewayCtrlNameUsageFmt = `The name of the Gateway controller. ` +
+		`The controller name must be of the form: DOMAIN/PATH. The controller's domain is '%s'`
+)
+
+var (
+	// Backing values for common cli flags shared among all subcommands
+	// The values are managed by the Root command.
+	gatewayCtlrName = stringValidatingValue{
+		validator: validateGatewayControllerName,
+	}
+
+	gatewayClassName = stringValidatingValue{
+		validator: validateResourceName,
+	}
+)
+
+// stringValidatingValue is a string flag value with custom validation logic.
+// stringValidatingValue implements the pflag.Value interface.
+type stringValidatingValue struct {
+	validator func(v string) error
+	value     string
+}
+
+func (v *stringValidatingValue) String() string {
+	return v.value
+}
+
+func (v *stringValidatingValue) Set(param string) error {
+	if err := v.validator(param); err != nil {
+		return err
+	}
+	v.value = param
+	return nil
+}
+
+func (v *stringValidatingValue) Type() string {
+	return "string"
+}
+
+func createRootCommand() *cobra.Command {
+	rootCmd := &cobra.Command{
+		Use: "gateway",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			return cmd.Help()
+		},
+	}
+
+	rootCmd.PersistentFlags().Var(
+		&gatewayCtlrName,
+		gatewayCtrlNameFlag,
+		fmt.Sprintf(gatewayCtrlNameUsageFmt, domain),
+	)
+	utilruntime.Must(rootCmd.MarkPersistentFlagRequired(gatewayCtrlNameFlag))
+
+	rootCmd.PersistentFlags().Var(
+		&gatewayClassName,
+		gatewayClassFlag,
+		gatewayClassNameUsage,
+	)
+	utilruntime.Must(rootCmd.MarkPersistentFlagRequired(gatewayClassFlag))
+
+	return rootCmd
+}
+
+func createControlPlaneCommand() *cobra.Command {
+	return &cobra.Command{
+		Use:   "control-plane",
+		Short: "Start the control plane",
+		RunE: func(cmd *cobra.Command, args []string) error {
+			logger := zap.New()
+			logger.Info("Starting NGINX Kubernetes Gateway Control Plane",
+				"version", version,
+				"commit", commit,
+				"date", date,
+			)
+
+			podIP := os.Getenv("POD_IP")
+			if err := validateIP(podIP); err != nil {
+				return fmt.Errorf("error validating POD_IP environment variable: %w", err)
+			}
+
+			conf := config.Config{
+				GatewayCtlrName:  gatewayCtlrName.value,
+				Logger:           logger,
+				GatewayClassName: gatewayClassName.value,
+				PodIP:            podIP,
+			}
+
+			if err := manager.Start(conf); err != nil {
+				return fmt.Errorf("failed to start control loop: %w", err)
+			}
+
+			return nil
+		},
+	}
+}
+
+func createProvisionerCommand() *cobra.Command {
+	return &cobra.Command{
+		Use:    "provisioner",
+		Short:  "Start the provisioner",
+		Hidden: true,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			logger := zap.New()
+			logger.Info("Starting NGINX Kubernetes Gateway Provisioner",
+				"version", version,
+				"commit", commit,
+				"date", date,
+			)
+
+			return errors.New("not implemented yet")
+		},
+	}
+}

cmd/gateway/commands_test.go

@@ -0,0 +1,100 @@
+package main
+
+import (
+	"io"
+	"testing"
+
+	. "github.com/onsi/gomega"
+)
+
+func TestRootCmdFlagValidation(t *testing.T) {
+	tests := []struct {
+		name              string
+		expectedErrPrefix string
+		args              []string
+		wantErr           bool
+	}{
+		{
+			name: "valid flags",
+			args: []string{
+				"--gateway-ctlr-name=k8s-gateway.nginx.org/nginx-gateway",
+				"--gatewayclass=nginx",
+			},
+			wantErr: false,
+		},
+		{
+			name: "gateway-ctlr-name is not set",
+			args: []string{
+				"--gatewayclass=nginx",
+			},
+			wantErr:           true,
+			expectedErrPrefix: `required flag(s) "gateway-ctlr-name" not set`,
+		},
+		{
+			name: "gateway-ctrl-name is set to empty string",
+			args: []string{
+				"--gateway-ctlr-name=",
+				"--gatewayclass=nginx",
+			},
+			wantErr:           true,
+			expectedErrPrefix: `invalid argument "" for "--gateway-ctlr-name" flag: must be set`,
+		},
+		{
+			name: "gateway-ctlr-name is invalid",
+			args: []string{
+				"--gateway-ctlr-name=nginx-gateway",
+				"--gatewayclass=nginx",
+			},
+			wantErr: true,
+			expectedErrPrefix: `invalid argument "nginx-gateway" for "--gateway-ctlr-name" flag: invalid format; ` +
+				"must be DOMAIN/PATH",
+		},
+		{
+			name: "gatewayclass is not set",
+			args: []string{
+				"--gateway-ctlr-name=k8s-gateway.nginx.org/nginx-gateway",
+			},
+			wantErr:           true,
+			expectedErrPrefix: `required flag(s) "gatewayclass" not set`,
+		},
+		{
+			name: "gatewayclass is set to empty string",
+			args: []string{
+				"--gateway-ctlr-name=k8s-gateway.nginx.org/nginx-gateway",
+				"--gatewayclass=",
+			},
+			wantErr:           true,
+			expectedErrPrefix: `invalid argument "" for "--gatewayclass" flag: must be set`,
+		},
+		{
+			name: "gatewayclass is invalid",
+			args: []string{
+				"--gateway-ctlr-name=k8s-gateway.nginx.org/nginx-gateway",
+				"--gatewayclass=@",
+			},
+			wantErr:           true,
+			expectedErrPrefix: `invalid argument "@" for "--gatewayclass" flag: invalid format`,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			g := NewGomegaWithT(t)
+
+			rootCmd := createRootCommand()
+			// discard any output generated by cobra
+			rootCmd.SetOut(io.Discard)
+			rootCmd.SetErr(io.Discard)
+
+			rootCmd.SetArgs(test.args)
+			err := rootCmd.Execute()
+
+			if test.wantErr {
+				g.Expect(err).To(HaveOccurred())
+				g.Expect(err.Error()).To(HavePrefix(test.expectedErrPrefix))
+			} else {
+				g.Expect(err).ToNot(HaveOccurred())
+			}
+		})
+	}
+}

cmd/gateway/main.go

@@ -1,87 +1,26 @@
 package main
 
 import (
-	"errors"
 	"fmt"
-	"net"
 	"os"
-
-	flag "github.com/spf13/pflag"
-	"sigs.k8s.io/controller-runtime/pkg/log/zap"
-
-	"github.com/nginxinc/nginx-kubernetes-gateway/internal/config"
-	"github.com/nginxinc/nginx-kubernetes-gateway/internal/manager"
-)
-
-const (
-	domain                = "k8s-gateway.nginx.org"
-	gatewayClassNameUsage = `The name of the GatewayClass resource. ` +
-		`Every NGINX Gateway must have a unique corresponding GatewayClass resource.`
-	gatewayCtrlNameUsageFmt = `The name of the Gateway controller. ` +
-		`The controller name must be of the form: DOMAIN/PATH. The controller's domain is '%s'`
 )
 
 var (
 	// Set during go build
 	version string
 	commit  string
 	date    string
-
-	// Command-line flags
-	gatewayCtlrName = flag.String(
-		"gateway-ctlr-name",
-		"",
-		fmt.Sprintf(gatewayCtrlNameUsageFmt, domain),
-	)
-
-	gatewayClassName = flag.String("gatewayclass", "", gatewayClassNameUsage)
-
-	// Environment variables
-	podIP = os.Getenv("POD_IP")
 )
 
-func validateIP(ip string) error {
-	if ip == "" {
-		return errors.New("IP address must be set")
-	}
-	if net.ParseIP(ip) == nil {
-		return fmt.Errorf("%q must be a valid IP address", ip)
-	}
-
-	return nil
-}
-
 func main() {
-	flag.Parse()
-
-	MustValidateArguments(
-		flag.CommandLine,
-		GatewayControllerParam(domain),
-		GatewayClassParam(),
-	)
-
-	if err := validateIP(podIP); err != nil {
-		fmt.Printf("error validating POD_IP environment variable: %v\n", err)
-		os.Exit(1)
-	}
-
-	logger := zap.New()
-	conf := config.Config{
-		GatewayCtlrName:  *gatewayCtlrName,
-		Logger:           logger,
-		GatewayClassName: *gatewayClassName,
-		PodIP:            podIP,
-	}
+	rootCmd := createRootCommand()
 
-	logger.Info("Starting NGINX Kubernetes Gateway",
-		"version", version,
-		"commit", commit,
-		"date", date,
-	)
+	rootCmd.AddCommand(createControlPlaneCommand())
+	p := createProvisionerCommand()
+	rootCmd.AddCommand(p)
 
-	err := manager.Start(conf)
-	if err != nil {
-		logger.Error(err, "Failed to start control loop")
+	if err := rootCmd.Execute(); err != nil {
+		_, _ = fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
 }