add ability to read input file from stdin

cmd/print.go

@@ -327,7 +327,7 @@ func newPrintCommand() *cobra.Command {
 		"Output format. One of: (yaml, json, kyaml).")
 
 	cmd.Flags().StringVar(&pr.inputFile, "input-file", "",
-		`Path to the manifest file. When set, the tool will read ingresses from the file instead of reading from the cluster. Supported files are yaml and json.`)
+		`Path to the manifest file. Use "-" to read from stdin. When set, the tool will read ingresses from the file instead of reading from the cluster. Supported files are yaml and json.`)
 
 	cmd.Flags().StringVarP(&pr.namespace, "namespace", "n", "",
 		`If present, the namespace scope for this CLI request.`)

pkg/i2gw/providers/common/resource_reader.go

@@ -23,6 +23,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"sync"
 
 	apiv1 "k8s.io/api/core/v1"
 	networkingv1 "k8s.io/api/networking/v1"
@@ -34,6 +35,12 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
 
+var (
+	stdin     []byte
+	stdinOnce sync.Once
+	stdinErr  error
+)
+
 func ReadIngressesFromCluster(ctx context.Context, client client.Client, ingressClasses sets.Set[string]) (map[types.NamespacedName]*networkingv1.Ingress, error) {
 	var ingressList networkingv1.IngressList
 	err := client.List(ctx, &ingressList)
@@ -52,11 +59,32 @@ func ReadIngressesFromCluster(ctx context.Context, client client.Client, ingress
 	return ingresses, nil
 }
 
-func ReadIngressesFromFile(filename, namespace string, ingressClasses sets.Set[string]) (map[types.NamespacedName]*networkingv1.Ingress, error) {
+// readFileOrStdin reads content from a file or stdin based on the filename.
+// If filename is "-", it reads from stdin, otherwise from the specified file.
+// Stdin content is stored in memory after the first read to allow multiple calls.
+func readFileOrStdin(filename string) ([]byte, error) {
+	if filename == "-" {
+		stdinOnce.Do(func() {
+			stdin, stdinErr = io.ReadAll(os.Stdin)
+			if stdinErr != nil {
+				stdinErr = fmt.Errorf("failed to read from stdin: %w", stdinErr)
+			}
+		})
+		return stdin, stdinErr
+	}
+
 	stream, err := os.ReadFile(filename)
 	if err != nil {
 		return nil, fmt.Errorf("failed to read file %v: %w", filename, err)
 	}
+	return stream, nil
+}
+
+func ReadIngressesFromFile(filename, namespace string, ingressClasses sets.Set[string]) (map[types.NamespacedName]*networkingv1.Ingress, error) {
+	stream, err := readFileOrStdin(filename)
+	if err != nil {
+		return nil, err
+	}
 
 	unstructuredObjects, err := ExtractObjectsFromReader(bytes.NewReader(stream), namespace)
 	if err != nil {
@@ -98,9 +126,9 @@ func ReadServicesFromCluster(ctx context.Context, client client.Client) (map[typ
 }
 
 func ReadServicesFromFile(filename, namespace string) (map[types.NamespacedName]*apiv1.Service, error) {
-	stream, err := os.ReadFile(filename)
+	stream, err := readFileOrStdin(filename)
 	if err != nil {
-		return nil, fmt.Errorf("failed to read file %v: %w", filename, err)
+		return nil, err
 	}
 
 	unstructuredObjects, err := ExtractObjectsFromReader(bytes.NewReader(stream), namespace)