copy: add --multi-arch=sparse:...

Add a "sparse:..." value for the copy --multi-arch option, where the
"..." is a comma-separated list of instance digests, platform
specifications, or the literal word "system" to signify the local
platform.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

cmd/skopeo/copy.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"strings"
 
+	"github.com/containerd/containerd/platforms"
 	commonFlag "github.com/containers/common/pkg/flag"
 	"github.com/containers/common/pkg/retry"
 	"github.com/containers/image/v5/copy"
@@ -19,6 +20,8 @@ import (
 	"github.com/containers/image/v5/transports/alltransports"
 	encconfig "github.com/containers/ocicrypt/config"
 	enchelpers "github.com/containers/ocicrypt/helpers"
+	"github.com/opencontainers/go-digest"
+	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/spf13/cobra"
 )
 
@@ -99,23 +102,40 @@ See skopeo(1) section "IMAGE NAMES" for the expected format
 }
 
 // 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.
+// It returns the copy.ImageListSelection, instance list, and platform list to use in image.Copy option
+func parseMultiArch(multiArch string) (copy.ImageListSelection, []digest.Digest, []imgspecv1.Platform, error) {
+	switch {
+	case multiArch == "system":
+		return copy.CopySystemImage, nil, nil, nil
+	case multiArch == "all":
+		return copy.CopyAllImages, nil, nil, nil
+	case multiArch == "index-only":
+		// There is no CopyNoImages value in copy.ImageListSelection per se, but
+		// we can get the desired effect by using CopySpecificImages.
+		return copy.CopySpecificImages, nil, nil, nil
+	case strings.HasPrefix(multiArch, "sparse:"):
+		sparseArg := strings.TrimPrefix(multiArch, "sparse:")
+		platformSpecs := strings.Split(sparseArg, ",")
+		var platformList []imgspecv1.Platform
+		var instanceList []digest.Digest
+		for _, platformSpec := range platformSpecs {
+			if instanceDigest, err := digest.Parse(platformSpec); err == nil {
+				instanceList = append(instanceList, instanceDigest)
+				continue
+			}
+			if platformSpec == "system" {
+				platformList = append(platformList, imgspecv1.Platform{})
+			} else {
+				p, err := platforms.Parse(platformSpec)
+				if err != nil {
+					return copy.CopySpecificImages, nil, nil, fmt.Errorf("while parsing platform specifier %q: %w", platformSpec, err)
+				}
+				platformList = append(platformList, p)
+			}
+		}
+		return copy.CopySpecificImages, instanceList, platformList, nil
 	default:
-		return copy.CopySystemImage, fmt.Errorf("unknown multi-arch option %q. Choose one of the supported options: 'system', 'all', or 'index-only'", multiArch)
+		return copy.CopySystemImage, nil, nil, fmt.Errorf("unknown multi-arch option %q. Choose one of the supported options: 'system', 'sparse:...', 'all', or 'index-only'", multiArch)
 	}
 }
 
@@ -186,11 +206,13 @@ func (opts *copyOptions) run(args []string, stdout io.Writer) (retErr error) {
 	}
 
 	imageListSelection := copy.CopySystemImage
+	var instanceDigests []digest.Digest
+	var instancePlatforms []imgspecv1.Platform
 	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())
+		imageListSelection, instanceDigests, instancePlatforms, err = parseMultiArch(opts.multiArch.Value())
 		if err != nil {
 			return err
 		}
@@ -296,6 +318,8 @@ func (opts *copyOptions) run(args []string, stdout io.Writer) (retErr error) {
 			DestinationCtx:                   destinationCtx,
 			ForceManifestMIMEType:            manifestType,
 			ImageListSelection:               imageListSelection,
+			Instances:                        instanceDigests,
+			InstancePlatforms:                instancePlatforms,
 			PreserveDigests:                  opts.preserveDigests,
 			OciDecryptConfig:                 decConfig,
 			OciEncryptLayers:                 encLayers,

docs/skopeo-copy.1.md

@@ -79,9 +79,10 @@ Print usage statement
 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
+- "system": Copy only the image that matches the system architecture
+- "all": Copy the full multi-architecture image
+- "index-only": Copy only the index
+- "sparse:_list_": Copy the index and images which match the comma-separated list of platform specifications, digests, or the local system ("system")
 
 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.
 

go.mod

@@ -3,6 +3,7 @@ module github.com/containers/skopeo
 go 1.18
 
 require (
+	github.com/containerd/containerd v1.7.0
 	github.com/containers/common v0.52.0
 	github.com/containers/image/v5 v5.25.0
 	github.com/containers/ocicrypt v1.1.7

go.sum

@@ -28,6 +28,8 @@ github.com/cncf/udpa/go v0.0.0-20191209042840-269d4d468f6f/go.mod h1:M8M6+tZqaGX
 github.com/containerd/cgroups v1.1.0 h1:v8rEWFl6EoqHB+swVNjVoCJE8o3jX7e8nqBGPLaDFBM=
 github.com/containerd/cgroups v1.1.0/go.mod h1:6ppBcbh/NOOUU+dMKrykgaBnK9lCIBxHqJDGwsa1mIw=
 github.com/containerd/console v1.0.3/go.mod h1:7LqA/THxQ86k76b8c/EMSiaJ3h1eZkMkXar0TQ1gf3U=
+github.com/containerd/containerd v1.7.0 h1:G/ZQr3gMZs6ZT0qPUZ15znx5QSdQdASW11nXTLTM2Pg=
+github.com/containerd/containerd v1.7.0/go.mod h1:QfR7Efgb/6X2BDpTPJRvPTYDE9rsF0FsXX9J8sIs/sc=
 github.com/containerd/stargz-snapshotter/estargz v0.14.3 h1:OqlDCK3ZVUO6C3B/5FSkDwbkEETK84kQgEeFwDC+62k=
 github.com/containerd/stargz-snapshotter/estargz v0.14.3/go.mod h1:KY//uOCIkSuNAHhJogcZtrNHdKrA99/FCCRjE3HD36o=
 github.com/containers/common v0.52.0 h1:S5GApgpNEGBuPhDHTFgMc55y5gsuxHcQeElvUpO5kp4=