feat: --output for oras manifest index create

cmd/oras/root/manifest/index/create.go

@@ -20,6 +20,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/opencontainers/image-spec/specs-go"
@@ -44,9 +45,11 @@ var maxConfigSize int64 = 4 * 1024 * 1024 // 4 MiB
 type createOptions struct {
 	option.Common
 	option.Target
+	option.Pretty
 
-	sources   []string
-	extraRefs []string
+	sources    []string
+	extraRefs  []string
+	outputPath string
 }
 
 func createCmd() *cobra.Command {
@@ -70,6 +73,12 @@ Example - create an index and push it with multiple tags:
 
 Example - create an index and push to an OCI image layout folder 'layout-dir' and tag with 'v1':
   oras manifest index create layout-dir:v1 linux-amd64 sha256:99e4703fbf30916f549cd6bfa9cdbab614b5392fbe64fdee971359a77073cdf9
+
+Example - create an index and save it locally to index.json, auto push will be disabled:
+  oras manifest index create --output index.json localhost:5000/hello linux-amd64 linux-arm64
+
+Example - create an index and output the index to stdout, auto push will be disabled:
+  oras manifest index create localhost:5000/hello linux-arm64 --output - --pretty
 `,
 		Args: oerrors.CheckArgs(argument.AtLeast(1), "the destination index to create."),
 		PreRunE: func(cmd *cobra.Command, args []string) error {
@@ -84,6 +93,7 @@ Example - create an index and push to an OCI image layout folder 'layout-dir' an
 			return createIndex(cmd, opts)
 		},
 	}
+	cmd.Flags().StringVarP(&opts.outputPath, "output", "o", "", "file `path` to write the created index to, use - for stdout")
 	option.ApplyFlags(&opts, cmd.Flags())
 	return oerrors.Command(cmd, &opts.Target)
 }
@@ -108,7 +118,18 @@ func createIndex(cmd *cobra.Command, opts createOptions) error {
 	indexBytes, _ := json.Marshal(index)
 	desc := content.NewDescriptorFromBytes(ocispec.MediaTypeImageIndex, indexBytes)
 	opts.Println(status.IndexPromptPacked, descriptor.ShortDigest(desc), ocispec.MediaTypeImageIndex)
-	return pushIndex(ctx, target, desc, indexBytes, opts.Reference, opts.extraRefs, opts.AnnotatedReference(), opts.Printer)
+
+	switch opts.outputPath {
+	case "":
+		err = pushIndex(ctx, target, desc, indexBytes, opts.Reference, opts.extraRefs, opts.AnnotatedReference(), opts.Printer)
+	case "-":
+		opts.Println("Digest:", desc.Digest)
+		err = opts.Output(os.Stdout, indexBytes)
+	default:
+		opts.Println("Digest:", desc.Digest)
+		err = os.WriteFile(opts.outputPath, indexBytes, 0666)
+	}
+	return err
 }
 
 func fetchSourceManifests(ctx context.Context, target oras.ReadOnlyTarget, opts createOptions) ([]ocispec.Descriptor, error) {

test/e2e/internal/testdata/multi_arch/const.go

@@ -97,3 +97,8 @@ var (
 		},
 	}
 )
+
+// exported index
+var (
+	CreatedIndex = `{"schemaVersion":2,"mediaType":"application/vnd.oci.image.index.v1+json","manifests":[{"mediaType":"application/vnd.oci.image.manifest.v1+json","digest":"sha256:9d84a5716c66a1d1b9c13f8ed157ba7d1edfe7f9b8766728b8a1f25c0d9c14c1","size":458,"platform":{"architecture":"amd64","os":"linux"}}]}`
+)

test/e2e/suite/command/manifest_index.go

@@ -18,6 +18,7 @@ package command
 import (
 	"encoding/json"
 	"fmt"
+	"path/filepath"
 
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
@@ -130,6 +131,21 @@ var _ = Describe("1.1 registry users:", func() {
 			ValidateIndex(content, expectedManifests)
 		})
 
+		It("should output created index to file", func() {
+			testRepo := indexTestRepo("create", "output-to-file")
+			CopyZOTRepo(ImageRepo, testRepo)
+			filePath := filepath.Join(GinkgoT().TempDir(), "createdIndex")
+			ORAS("manifest", "index", "create", RegistryRef(ZOTHost, testRepo, ""), string(multi_arch.LinuxAMD64.Digest), "--output", filePath).Exec()
+			MatchFile(filePath, multi_arch.CreatedIndex, DefaultTimeout)
+		})
+
+		It("should output created index to stdout", func() {
+			testRepo := indexTestRepo("create", "output-to-stdout")
+			CopyZOTRepo(ImageRepo, testRepo)
+			ORAS("manifest", "index", "create", RegistryRef(ZOTHost, testRepo, ""), string(multi_arch.LinuxAMD64.Digest),
+				"--output", "-").MatchKeyWords(multi_arch.CreatedIndex).Exec()
+		})
+
 		It("should fail if given a reference that does not exist in the repo", func() {
 			testRepo := indexTestRepo("create", "nonexist-ref")
 			CopyZOTRepo(ImageRepo, testRepo)
@@ -211,6 +227,21 @@ var _ = Describe("OCI image layout users:", func() {
 			ValidateIndex(content, expectedManifests)
 		})
 
+		It("should output created index to file", func() {
+			root := PrepareTempOCI(ImageRepo)
+			indexRef := LayoutRef(root, "output-to-file")
+			filePath := filepath.Join(GinkgoT().TempDir(), "createdIndex")
+			ORAS("manifest", "index", "create", Flags.Layout, indexRef, string(multi_arch.LinuxAMD64.Digest), "--output", filePath).Exec()
+			MatchFile(filePath, multi_arch.CreatedIndex, DefaultTimeout)
+		})
+
+		It("should output created index to stdout", func() {
+			root := PrepareTempOCI(ImageRepo)
+			indexRef := LayoutRef(root, "output-to-stdout")
+			ORAS("manifest", "index", "create", Flags.Layout, indexRef, string(multi_arch.LinuxAMD64.Digest),
+				"--output", "-").MatchKeyWords(multi_arch.CreatedIndex).Exec()
+		})
+
 		It("should fail if given a reference that does not exist in the repo", func() {
 			root := PrepareTempOCI(ImageRepo)
 			indexRef := LayoutRef(root, "latest")