Add copy.CopyOnlyInstances

Add copy.CopyOnlyInstances to the copy.MultipleImagesOption enumerated
type, add Instance() to the manifest.List interface, and add an
Instances field top copy.Options.

Signed-off-by: Nalin Dahyabhai <[email protected]>

copy/copy.go

@@ -123,6 +123,12 @@ const (
 	// source reference refers to a list of images, but the target reference
 	// can only accept one image, an error should be returned.
 	CopyAllImages
+	// CopyOnlyInstances is a value which, when set in Options.MultipleImages,
+	// indicates that the caller expects the source reference to be a list
+	// of images, and wants only specific instances from it copied, along with
+	// the list itself.  If the target reference can only accept one image
+	// (i.e., it cannot accept lists), an error should be returned.
+	CopyOnlyInstances
 )
 
 // MultipleImagesOption is either CopyOnlyCurrentRuntimeImage or CopyAllImages, to control
@@ -141,7 +147,8 @@ type Options struct {
 	Progress         chan types.ProgressProperties // Reported to when ProgressInterval has arrived for a single artifact+offset.
 	// manifest MIME type of image set by user. "" is default and means use the autodetection to the the manifest MIME type
 	ForceManifestMIMEType string
-	MultipleImages        MultipleImagesOption // set to either CopyOnlyCurrentRuntimeImage or CopyAllImages
+	MultipleImages        MultipleImagesOption // set to either CopyOnlyCurrentRuntimeImage, CopyAllImages, or CopyOnlyInstances
+	Instances             []digest.Digest      // if MultipleImages is CopyOnlyInstances, copy only these instances and the list itself
 }
 
 // Image copies image from srcRef to destRef, using policyContext to validate
@@ -157,7 +164,7 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 		options = &Options{}
 	}
 
-	if options.MultipleImages != CopyAllImages && options.MultipleImages != CopyOnlyCurrentRuntimeImage {
+	if options.MultipleImages != CopyAllImages && options.MultipleImages != CopyOnlyCurrentRuntimeImage && options.MultipleImages != CopyOnlyInstances {
 		return nil, errors.Errorf("Invalid value for options.MultipleImages: %d", options.MultipleImages)
 	}
 	reportWriter := ioutil.Discard
@@ -260,13 +267,18 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 			if copiedManifest, _, _, err = c.copyOneImage(ctx, policyContext, options, unparsedInstance, nil); err != nil {
 				return nil, err
 			}
-		} else { /* options.MultipleImages == CopyAllImages */
+		} else { /* options.MultipleImages == CopyAllImages or options.MultipleImages == CopyOnlyInstances, */
 			// If we were asked to copy multiple images and can't, that's an error.
 			if !supportsMultipleImages(c.dest) {
 				return nil, errors.Errorf("Error copying multiple images: destination reference %q does not support multiple images", transports.ImageName(destRef))
 			}
-			// Copy all of the images.
-			logrus.Debugf("Source is a manifest list; copying all instances")
+			// Copy some or all of the images.
+			switch options.MultipleImages {
+			case CopyAllImages:
+				logrus.Debugf("Source is a manifest list; copying all instances")
+			case CopyOnlyInstances:
+				logrus.Debugf("Source is a manifest list; copying some instances")
+			}
 			if copiedManifest, _, err = c.copyMultipleImages(ctx, policyContext, options, unparsedToplevel); err != nil {
 				return nil, err
 			}
@@ -329,10 +341,28 @@ func (c *copier) copyMultipleImages(ctx context.Context, policyContext *signatur
 		}
 	}
 
-	// Copy each image, in turn.
+	// Copy each image, or just the ones we want to copy, in turn.
 	instanceDigests := list.Instances()
 	updates := make([]manifest.ListUpdate, len(instanceDigests))
 	for i, instanceDigest := range instanceDigests {
+		if options.MultipleImages == CopyOnlyInstances {
+			skip := true
+			for _, instance := range options.Instances {
+				if instance == instanceDigest {
+					skip = false
+					break
+				}
+			}
+			if skip {
+				update, err := list.Instance(instanceDigest)
+				if err != nil {
+					return nil, "", err
+				}
+				logrus.Debugf("Skipping instance %s (%d/%d)", instanceDigest, i+1, len(instanceDigests))
+				updates[i] = update
+				continue
+			}
+		}
 		logrus.Debugf("Copying instance %s (%d/%d)", instanceDigest, i+1, len(instanceDigests))
 		unparsedInstance := image.UnparsedInstance(c.rawSource, &instanceDigest)
 		updatedManifest, updatedManifestType, updatedManifestDigest, err := c.copyOneImage(ctx, policyContext, options, unparsedInstance, &instanceDigest)

manifest/docker_list.go

@@ -49,6 +49,20 @@ func (list *Schema2List) Instances() []digest.Digest {
 	return results
 }
 
+// Instance returns the size and MIME type of a particular instance in the list.
+func (list *Schema2List) Instance(instanceDigest digest.Digest) (ListUpdate, error) {
+	for _, manifest := range list.Manifests {
+		if manifest.Digest == instanceDigest {
+			return ListUpdate{
+				Digest:    manifest.Digest,
+				Size:      manifest.Size,
+				MediaType: manifest.MediaType,
+			}, nil
+		}
+	}
+	return ListUpdate{}, errors.Errorf("unable to find instance %s passed to Schema2List.Instances", instanceDigest)
+}
+
 // UpdateInstances updates the sizes, digests, and media types of the manifests
 // which the list catalogs.
 func (list *Schema2List) UpdateInstances(updates []ListUpdate) error {

manifest/list.go

@@ -33,6 +33,9 @@ type List interface {
 	// must be specified.
 	UpdateInstances([]ListUpdate) error
 
+	// Instance returns the size and MIME type of a particular instance in the list.
+	Instance(digest.Digest) (ListUpdate, error)
+
 	// ChooseInstance selects which manifest is most appropriate for the platform described by the
 	// SystemContext, or for the current platform if the SystemContext doesn't specify any details.
 	ChooseInstance(ctx *types.SystemContext) (digest.Digest, error)

manifest/oci_index.go

@@ -32,6 +32,20 @@ func (index *OCI1Index) Instances() []digest.Digest {
 	return results
 }
 
+// Instance returns the size and MIME type of a particular instance in the index.
+func (index *OCI1Index) Instance(instanceDigest digest.Digest) (ListUpdate, error) {
+	for _, manifest := range index.Manifests {
+		if manifest.Digest == instanceDigest {
+			return ListUpdate{
+				Digest:    manifest.Digest,
+				Size:      manifest.Size,
+				MediaType: manifest.MediaType,
+			}, nil
+		}
+	}
+	return ListUpdate{}, errors.Errorf("unable to find instance %s in OCI1Index", instanceDigest)
+}
+
 // UpdateInstances updates the sizes, digests, and media types of the manifests
 // which the list catalogs.
 func (index *OCI1Index) UpdateInstances(updates []ListUpdate) error {