Add an option to allow copying image indexes alone

cmd/skopeo/copy.go

@@ -32,6 +32,7 @@ type copyOptions struct {
 	format              commonFlag.OptionalString // Force conversion of the image to a specified format
 	quiet               bool                      // Suppress output information when copying images
 	all                 bool                      // Copy all of the images if the source is a list
+	multiArch           commonFlag.OptionalString // How to handle multi architecture images
 	encryptLayer        []int                     // The list of layers to encrypt
 	encryptionKeys      []string                  // Keys needed to encrypt the image
 	decryptionKeys      []string                  // Keys needed to decrypt the image
@@ -72,6 +73,7 @@ See skopeo(1) section "IMAGE NAMES" for the expected format
 	flags.StringSliceVar(&opts.additionalTags, "additional-tag", []string{}, "additional tags (supports docker-archive)")
 	flags.BoolVarP(&opts.quiet, "quiet", "q", false, "Suppress output information when copying images")
 	flags.BoolVarP(&opts.all, "all", "a", false, "Copy all images if SOURCE-IMAGE is a list")
+	flags.Var(commonFlag.NewOptionalStringValue(&opts.multiArch), "multi-arch", `How to handle multi-architecture images (system, all, or index-only)`)
 	flags.BoolVar(&opts.removeSignatures, "remove-signatures", false, "Do not copy signatures from SOURCE-IMAGE")
 	flags.StringVar(&opts.signByFingerprint, "sign-by", "", "Sign the image using a GPG key with the specified `FINGERPRINT`")
 	flags.StringVar(&opts.digestFile, "digestfile", "", "Write the digest of the pushed image to the specified file")
@@ -82,6 +84,27 @@ See skopeo(1) section "IMAGE NAMES" for the expected format
 	return cmd
 }
 
+// parseMultiArch parses the list processing selection
+// It returns the copy.ImageListSelection to use with image.Copy option
+func parseMultiArch(multiArch string) (copy.ImageListSelection, error) {
+	switch multiArch {
+	case "system":
+		return copy.CopySystemImage, nil
+	case "all":
+		return copy.CopyAllImages, nil
+	// There is no CopyNoImages value in copy.ImageListSelection, but because we
+	// don't provide an option to select a set of images to copy, we can use
+	// CopySpecificImages.
+	case "index-only":
+		return copy.CopySpecificImages, nil
+	// We don't expose CopySpecificImages other than index-only above, because
+	// we currently don't provide an option to choose the images to copy. That
+	// could be added in the future.
+	default:
+		return copy.CopySystemImage, fmt.Errorf("unknown multi-arch option %q. Choose one of the supported options: 'system', 'all', or 'index-only'", multiArch)
+	}
+}
+
 func (opts *copyOptions) run(args []string, stdout io.Writer) error {
 	if len(args) != 2 {
 		return errorShouldDisplayUsage{errors.New("Exactly two arguments expected")}
@@ -143,7 +166,17 @@ func (opts *copyOptions) run(args []string, stdout io.Writer) error {
 	if opts.quiet {
 		stdout = nil
 	}
+
 	imageListSelection := copy.CopySystemImage
+	if opts.multiArch.Present() && opts.all {
+		return fmt.Errorf("Cannot use --all and --multi-arch flags together")
+	}
+	if opts.multiArch.Present() {
+		imageListSelection, err = parseMultiArch(opts.multiArch.Value())
+		if err != nil {
+			return err
+		}
+	}
 	if opts.all {
 		imageListSelection = copy.CopyAllImages
 	}

completions/bash/skopeo

@@ -40,6 +40,7 @@ _skopeo_copy() {
     --src-authfile
     --dest-authfile
     --format -f
+    --multi-arch
     --sign-by
     --src-creds --screds
     --src-cert-dir

docs/skopeo-copy.1.md

@@ -66,6 +66,17 @@ MANIFEST TYPE (oci, v2s1, or v2s2) to use in the destination (default is manifes
 
 Print usage statement
 
+**--multi-arch**
+
+Control what is copied if _source-image_ refers to a multi-architecture image. Default is system.
+
+Options:
+- system: Copy only the image that matches the system architecture
+- all: Copy the full multi-architecture image
+- index-only: Copy only the index
+
+The index-only option usually fails unless the referenced per-architecture images are already present in the destination, or the target registry supports sparse indexes.
+
 **--quiet**, **-q**
 
 Suppress output information when copying images.

integration/copy_test.go

@@ -123,10 +123,10 @@ func (s *CopySuite) TestCopyAllWithManifestListRoundTrip(c *check.C) {
 	dir2, err := ioutil.TempDir("", "copy-all-manifest-list-dir")
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(dir2)
-	assertSkopeoSucceeds(c, "", "copy", "--all", knownListImage, "oci:"+oci1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "oci:"+oci1, "dir:"+dir1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "dir:"+dir1, "oci:"+oci2)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "oci:"+oci2, "dir:"+dir2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", knownListImage, "oci:"+oci1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "oci:"+oci1, "dir:"+dir1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "dir:"+dir1, "oci:"+oci2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "oci:"+oci2, "dir:"+dir2)
 	assertDirImagesAreEqual(c, dir1, dir2)
 	out := combinedOutputOfCommand(c, "diff", "-urN", oci1, oci2)
 	c.Assert(out, check.Equals, "")
@@ -145,15 +145,30 @@ func (s *CopySuite) TestCopyAllWithManifestListConverge(c *check.C) {
 	dir2, err := ioutil.TempDir("", "copy-all-manifest-list-dir")
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(dir2)
-	assertSkopeoSucceeds(c, "", "copy", "--all", knownListImage, "oci:"+oci1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "oci:"+oci1, "dir:"+dir1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "--format", "oci", knownListImage, "dir:"+dir2)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "dir:"+dir2, "oci:"+oci2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", knownListImage, "oci:"+oci1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "oci:"+oci1, "dir:"+dir1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "--format", "oci", knownListImage, "dir:"+dir2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "dir:"+dir2, "oci:"+oci2)
 	assertDirImagesAreEqual(c, dir1, dir2)
 	out := combinedOutputOfCommand(c, "diff", "-urN", oci1, oci2)
 	c.Assert(out, check.Equals, "")
 }
 
+func (s *CopySuite) TestCopyNoneWithManifestList(c *check.C) {
+	dir1, err := ioutil.TempDir("", "copy-all-manifest-list-dir")
+	c.Assert(err, check.IsNil)
+	defer os.RemoveAll(dir1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=index-only", knownListImage, "dir:"+dir1)
+
+	manifestPath := filepath.Join(dir1, "manifest.json")
+	readManifest, err := ioutil.ReadFile(manifestPath)
+	c.Assert(err, check.IsNil)
+	mimeType := manifest.GuessMIMEType(readManifest)
+	c.Assert(mimeType, check.Equals, "application/vnd.docker.distribution.manifest.list.v2+json")
+	out := combinedOutputOfCommand(c, "ls", "-1", dir1)
+	c.Assert(out, check.Equals, "manifest.json\nversion\n")
+}
+
 func (s *CopySuite) TestCopyWithManifestListConverge(c *check.C) {
 	oci1, err := ioutil.TempDir("", "copy-all-manifest-list-oci")
 	c.Assert(err, check.IsNil)
@@ -168,9 +183,9 @@ func (s *CopySuite) TestCopyWithManifestListConverge(c *check.C) {
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(dir2)
 	assertSkopeoSucceeds(c, "", "copy", knownListImage, "oci:"+oci1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "oci:"+oci1, "dir:"+dir1)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "oci:"+oci1, "dir:"+dir1)
 	assertSkopeoSucceeds(c, "", "copy", "--format", "oci", knownListImage, "dir:"+dir2)
-	assertSkopeoSucceeds(c, "", "copy", "--all", "dir:"+dir2, "oci:"+oci2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", "dir:"+dir2, "oci:"+oci2)
 	assertDirImagesAreEqual(c, dir1, dir2)
 	out := combinedOutputOfCommand(c, "diff", "-urN", oci1, oci2)
 	c.Assert(out, check.Equals, "")
@@ -181,7 +196,7 @@ func (s *CopySuite) TestCopyAllWithManifestListStorageFails(c *check.C) {
 	c.Assert(err, check.IsNil)
 	defer os.RemoveAll(storage)
 	storage = fmt.Sprintf("[vfs@%s/root+%s/runroot]", storage, storage)
-	assertSkopeoFails(c, `.*destination transport .* does not support copying multiple images as a group.*`, "copy", "--all", knownListImage, "containers-storage:"+storage+"test")
+	assertSkopeoFails(c, `.*destination transport .* does not support copying multiple images as a group.*`, "copy", "--multi-arch=all", knownListImage, "containers-storage:"+storage+"test")
 }
 
 func (s *CopySuite) TestCopyWithManifestListStorage(c *check.C) {
@@ -239,7 +254,7 @@ func (s *CopySuite) TestCopyWithManifestListDigest(c *check.C) {
 	c.Assert(err, check.IsNil)
 	digest := manifestDigest.String()
 	assertSkopeoSucceeds(c, "", "copy", knownListImage+"@"+digest, "dir:"+dir1)
-	assertSkopeoSucceeds(c, "", "copy", "--all", knownListImage+"@"+digest, "dir:"+dir2)
+	assertSkopeoSucceeds(c, "", "copy", "--multi-arch=all", knownListImage+"@"+digest, "dir:"+dir2)
 	assertSkopeoSucceeds(c, "", "copy", "dir:"+dir1, "oci:"+oci1)
 	assertSkopeoSucceeds(c, "", "copy", "dir:"+dir2, "oci:"+oci2)
 	out := combinedOutputOfCommand(c, "diff", "-urN", oci1, oci2)