copy.Options: add an InstancePlatforms field

Add an InstancePlatforms field to the copy.Options structure.  When
asked to copy only a specific subset of instances, combine the Instances
list with the instances which match the platforms given in the
InstancePlatforms list, returning an error if we're unable to find an
instance which matches any of the InstancePlatforms.

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

copy/copy.go

@@ -23,6 +23,7 @@ import (
 	"github.com/containers/image/v5/types"
 	encconfig "github.com/containers/ocicrypt/config"
 	digest "github.com/opencontainers/go-digest"
+	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/exp/slices"
 	"golang.org/x/sync/semaphore"
@@ -91,8 +92,9 @@ type Options struct {
 	PreserveDigests bool
 	// manifest MIME type of image set by user. "" is default and means use the autodetection to the manifest MIME type
 	ForceManifestMIMEType string
-	ImageListSelection    ImageListSelection // set to either CopySystemImage (the default), CopyAllImages, or CopySpecificImages to control which instances we copy when the source reference is a list; ignored if the source reference is not a list
-	Instances             []digest.Digest    // if ImageListSelection is CopySpecificImages, copy only these instances and the list itself
+	ImageListSelection    ImageListSelection   // set to either CopySystemImage (the default), CopyAllImages, or CopySpecificImages to control which instances we copy when the source reference is a list; ignored if the source reference is not a list
+	Instances             []digest.Digest      // if ImageListSelection is CopySpecificImages, copy only these instances, instances matching the InstancePlatforms list, and the list itself
+	InstancePlatforms     []imgspecv1.Platform // if ImageListSelection is CopySpecificImages, copy only matching instances, instances listed in the Instances list, and the list itself
 	// Give priority to pulling gzip images if multiple images are present when configured to OptionalBoolTrue,
 	// prefers the best compression if this is configured as OptionalBoolFalse. Choose automatically (and the choice may change over time)
 	// if this is set to OptionalBoolUndefined (which is the default behavior, and recommended for most callers).

copy/multiple.go

@@ -12,6 +12,8 @@ import (
 	internalManifest "github.com/containers/image/v5/internal/manifest"
 	"github.com/containers/image/v5/manifest"
 	"github.com/containers/image/v5/signature"
+	"github.com/containers/image/v5/types"
+	digest "github.com/opencontainers/go-digest"
 	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/exp/slices"
@@ -87,17 +89,43 @@ func (c *copier) copyMultipleImages(ctx context.Context, policyContext *signatur
 	}
 
 	// Copy each image, or just the ones we want to copy, in turn.
+	optionsInstances := options.Instances
 	instanceDigests := updatedList.Instances()
+	if len(options.InstancePlatforms) > 0 {
+		// Build a map for helping us avoid duplication of instance digests.
+		instanceDigestMap := make(map[digest.Digest]struct{})
+		for _, instanceDigest := range optionsInstances {
+			instanceDigestMap[instanceDigest] = struct{}{}
+		}
+		// Choose the best match for each platform we were asked to also copy.
+		for _, platform := range options.InstancePlatforms {
+			platformContext := types.SystemContext{
+				OSChoice:           platform.OS,
+				ArchitectureChoice: platform.Architecture,
+				VariantChoice:      platform.Variant,
+			}
+			instanceDigest, err := updatedList.ChooseInstance(&platformContext)
+			if err != nil {
+				return nil, fmt.Errorf("No instance in list matched platform spec %v", platform)
+			}
+			instanceDigestMap[instanceDigest] = struct{}{}
+		}
+		// Deduplicate the set of digests.
+		optionsInstances = nil
+		for instanceDigest := range instanceDigestMap {
+			optionsInstances = append(optionsInstances, instanceDigest)
+		}
+	}
 	imagesToCopy := len(instanceDigests)
 	if options.ImageListSelection == CopySpecificImages {
-		imagesToCopy = len(options.Instances)
+		imagesToCopy = len(optionsInstances)
 	}
 	c.Printf("Copying %d of %d images in list\n", imagesToCopy, len(instanceDigests))
 	updates := make([]manifest.ListUpdate, len(instanceDigests))
 	instancesCopied := 0
 	for i, instanceDigest := range instanceDigests {
 		if options.ImageListSelection == CopySpecificImages &&
-			!slices.Contains(options.Instances, instanceDigest) {
+			!slices.Contains(optionsInstances, instanceDigest) {
 			update, err := updatedList.Instance(instanceDigest)
 			if err != nil {
 				return nil, err