feat: add platform flag to cosign copy command

cmd/cosign/cli/copy.go

@@ -37,12 +37,15 @@ func Copy() *cobra.Command {
   cosign copy --sig-only example.com/src example.com/dest
 
   # overwrite destination image and signatures
-  cosign copy -f example.com/src example.com/dest`,
+  cosign copy -f example.com/src example.com/dest
+
+	# copy a container image and its signatures for a specific platform
+  cosign copy --platform=linux/amd64 example.com/src:latest example.com/dest:latest`,
 
 		Args:             cobra.ExactArgs(2),
 		PersistentPreRun: options.BindViper,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			return copy.CopyCmd(cmd.Context(), o.Registry, args[0], args[1], o.SignatureOnly, o.Force)
+			return copy.CopyCmd(cmd.Context(), o.Registry, args[0], args[1], o.SignatureOnly, o.Force, o.Platform)
 		},
 	}
 

cmd/cosign/cli/copy/copy.go

@@ -28,14 +28,15 @@ import (
 	"github.com/google/go-containerregistry/pkg/v1/remote/transport"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/pkg/oci"
+	ociplatform "github.com/sigstore/cosign/v2/pkg/oci/platform"
 	ociremote "github.com/sigstore/cosign/v2/pkg/oci/remote"
 	"github.com/sigstore/cosign/v2/pkg/oci/walk"
 	"golang.org/x/sync/errgroup"
 )
 
 // CopyCmd implements the logic to copy the supplied container image and signatures.
 // nolint
-func CopyCmd(ctx context.Context, regOpts options.RegistryOptions, srcImg, dstImg string, sigOnly, force bool) error {
+func CopyCmd(ctx context.Context, regOpts options.RegistryOptions, srcImg, dstImg string, sigOnly, force bool, platform string) error {
 	no := regOpts.NameOptions()
 	srcRef, err := name.ParseReference(srcImg, no...)
 	if err != nil {
@@ -71,6 +72,11 @@ func CopyCmd(ctx context.Context, regOpts options.RegistryOptions, srcImg, dstIm
 		return err
 	}
 
+	root, err = ociplatform.SignedEntityForPlatform(root, platform)
+	if err != nil {
+		return err
+	}
+
 	if err := walk.SignedEntity(gctx, root, func(ctx context.Context, se oci.SignedEntity) error {
 		// Both of the SignedEntity types implement Digest()
 		h, err := se.Digest()

cmd/cosign/cli/copy/copy_test.go

@@ -33,8 +33,20 @@ func TestCopyAttachmentTagPrefix(t *testing.T) {
 
 	err := CopyCmd(ctx, options.RegistryOptions{
 		RefOpts: refOpts,
-	}, srcImg, destImg, false, true)
+	}, srcImg, destImg, false, true, "")
 	if err == nil {
 		t.Fatal("failed to copy with attachment-tag-prefix")
 	}
 }
+
+func TestCopyPlatformOpt(t *testing.T) {
+	ctx := context.Background()
+
+	srcImg := "alpine"
+	destImg := "test-alpine"
+
+	err := CopyCmd(ctx, options.RegistryOptions{}, srcImg, destImg, false, true, "linux/amd64")
+	if err == nil {
+		t.Fatal("failed to copy with platform")
+	}
+}

cmd/cosign/cli/download/attestation.go

@@ -21,10 +21,9 @@ import (
 	"fmt"
 
 	"github.com/google/go-containerregistry/pkg/name"
-	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/pkg/cosign"
-	"github.com/sigstore/cosign/v2/pkg/oci"
+	"github.com/sigstore/cosign/v2/pkg/oci/platform"
 	ociremote "github.com/sigstore/cosign/v2/pkg/oci/remote"
 )
 
@@ -51,42 +50,9 @@ func AttestationCmd(ctx context.Context, regOpts options.RegistryOptions, attOpt
 		return err
 	}
 
-	idx, isIndex := se.(oci.SignedImageIndex)
-
-	// We only allow --platform on multiarch indexes
-	if attOptions.Platform != "" && !isIndex {
-		return fmt.Errorf("specified reference is not a multiarch image")
-	}
-
-	if attOptions.Platform != "" && isIndex {
-		targetPlatform, err := v1.ParsePlatform(attOptions.Platform)
-		if err != nil {
-			return fmt.Errorf("parsing platform: %w", err)
-		}
-		platforms, err := getIndexPlatforms(idx)
-		if err != nil {
-			return fmt.Errorf("getting available platforms: %w", err)
-		}
-
-		platforms = matchPlatform(targetPlatform, platforms)
-		if len(platforms) == 0 {
-			return fmt.Errorf("unable to find an attestation for %s", targetPlatform.String())
-		}
-		if len(platforms) > 1 {
-			return fmt.Errorf(
-				"platform spec matches more than one image architecture: %s",
-				platforms.String(),
-			)
-		}
-
-		nse, err := idx.SignedImage(platforms[0].hash)
-		if err != nil {
-			return fmt.Errorf("searching for %s image: %w", platforms[0].hash.String(), err)
-		}
-		if nse == nil {
-			return fmt.Errorf("unable to find image %s", platforms[0].hash.String())
-		}
-		se = nse
+	se, err = platform.SignedEntityForPlatform(se, attOptions.Platform)
+	if err != nil {
+		return err
 	}
 
 	attestations, err := cosign.FetchAttestations(se, predicateType)

cmd/cosign/cli/download/sbom.go

@@ -21,28 +21,14 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"strings"
 
 	"github.com/google/go-containerregistry/pkg/name"
-	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/sigstore/cosign/v2/cmd/cosign/cli/options"
 	"github.com/sigstore/cosign/v2/pkg/oci"
+	"github.com/sigstore/cosign/v2/pkg/oci/platform"
 	ociremote "github.com/sigstore/cosign/v2/pkg/oci/remote"
 )
 
-type platformList []struct {
-	hash     v1.Hash
-	platform *v1.Platform
-}
-
-func (pl *platformList) String() string {
-	r := []string{}
-	for _, p := range *pl {
-		r = append(r, p.platform.String())
-	}
-	return strings.Join(r, ", ")
-}
-
 func SBOMCmd(
 	ctx context.Context, regOpts options.RegistryOptions,
 	dnOpts options.SBOMDownloadOptions, imageRef string, out io.Writer,
@@ -62,51 +48,20 @@ func SBOMCmd(
 		return nil, err
 	}
 
-	idx, isIndex := se.(oci.SignedImageIndex)
-
-	// We only allow --platform on multiarch indexes
-	if dnOpts.Platform != "" && !isIndex {
-		return nil, fmt.Errorf("specified reference is not a multiarch image")
+	se, err = platform.SignedEntityForPlatform(se, dnOpts.Platform)
+	if err != nil {
+		return nil, err
 	}
 
-	if dnOpts.Platform != "" && isIndex {
-		targetPlatform, err := v1.ParsePlatform(dnOpts.Platform)
-		if err != nil {
-			return nil, fmt.Errorf("parsing platform: %w", err)
-		}
-		platforms, err := getIndexPlatforms(idx)
-		if err != nil {
-			return nil, fmt.Errorf("getting available platforms: %w", err)
-		}
-
-		platforms = matchPlatform(targetPlatform, platforms)
-		if len(platforms) == 0 {
-			return nil, fmt.Errorf("unable to find an SBOM for %s", targetPlatform.String())
-		}
-		if len(platforms) > 1 {
-			return nil, fmt.Errorf(
-				"platform spec matches more than one image architecture: %s",
-				platforms.String(),
-			)
-		}
-
-		nse, err := idx.SignedImage(platforms[0].hash)
-		if err != nil {
-			return nil, fmt.Errorf("searching for %s image: %w", platforms[0].hash.String(), err)
-		}
-		if nse == nil {
-			return nil, fmt.Errorf("unable to find image %s", platforms[0].hash.String())
-		}
-		se = nse
-	}
+	idx, isIndex := se.(oci.SignedImageIndex)
 
 	file, err := se.Attachment("sbom")
 	if errors.Is(err, ociremote.ErrImageNotFound) {
 		if !isIndex {
 			return nil, errors.New("no sbom attached to reference")
 		}
 		// Help the user with the available architectures
-		pl, err := getIndexPlatforms(idx)
+		pl, err := platform.GetIndexPlatforms(idx)
 		if len(pl) > 0 && err == nil {
 			fmt.Fprintf(
 				os.Stderr,
@@ -139,57 +94,3 @@ func SBOMCmd(
 
 	return sboms, nil
 }
-
-func getIndexPlatforms(idx oci.SignedImageIndex) (platformList, error) {
-	im, err := idx.IndexManifest()
-	if err != nil {
-		return nil, fmt.Errorf("fetching index manifest: %w", err)
-	}
-
-	platforms := platformList{}
-	for _, m := range im.Manifests {
-		if m.Platform == nil {
-			continue
-		}
-		platforms = append(platforms, struct {
-			hash     v1.Hash
-			platform *v1.Platform
-		}{m.Digest, m.Platform})
-	}
-	return platforms, nil
-}
-
-// matchPlatform filters a list of platforms returning only those matching
-// a base. "Based" on ko's internal equivalent while it moves to GGCR.
-// https://github.com/google/ko/blob/e6a7a37e26d82a8b2bb6df991c5a6cf6b2728794/pkg/build/gobuild.go#L1020
-func matchPlatform(base *v1.Platform, list platformList) platformList {
-	ret := platformList{}
-	for _, p := range list {
-		if base.OS != "" && base.OS != p.platform.OS {
-			continue
-		}
-		if base.Architecture != "" && base.Architecture != p.platform.Architecture {
-			continue
-		}
-		if base.Variant != "" && base.Variant != p.platform.Variant {
-			continue
-		}
-
-		if base.OSVersion != "" && p.platform.OSVersion != base.OSVersion {
-			if base.OS != "windows" {
-				continue
-			} else { //nolint: revive
-				if pcount, bcount := strings.Count(base.OSVersion, "."), strings.Count(p.platform.OSVersion, "."); pcount == 2 && bcount == 3 {
-					if base.OSVersion != p.platform.OSVersion[:strings.LastIndex(p.platform.OSVersion, ".")] {
-						continue
-					}
-				} else {
-					continue
-				}
-			}
-		}
-		ret = append(ret, p)
-	}
-
-	return ret
-}

cmd/cosign/cli/options/copy.go

@@ -23,6 +23,7 @@ import (
 type CopyOptions struct {
 	SignatureOnly bool
 	Force         bool
+	Platform      string
 	Registry      RegistryOptions
 }
 
@@ -37,4 +38,7 @@ func (o *CopyOptions) AddFlags(cmd *cobra.Command) {
 
 	cmd.Flags().BoolVarP(&o.Force, "force", "f", false,
 		"overwrite destination image(s), if necessary")
+
+	cmd.Flags().StringVar(&o.Platform, "platform", "",
+		"only copy container image and its signatures for a specific platform image")
 }