Add an option to allow copying image indexes alone

The new --multi-arch option allows the user to select between copying the
image associated with the system platform, all images in the index, or
just the index itself without attempting to copy the images.

Signed-off-by: James Hewitt <james.hewitt@uk.ibm.com>

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)