copy: add support for ForceCompressionFormat

copy/copy.go

@@ -133,6 +133,10 @@ type Options struct {
 	// Invalid when copying a non-multi-architecture image. That will probably
 	// change in the future.
 	EnsureCompressionVariantsExist []OptionCompressionVariant
+	// ForceCompressionFormat ensures that the compression algorithm set in
+	// DestinationCtx.CompressionFormat is used exclusively, and blobs of other
+	// compression algorithms are not reused.
+	ForceCompressionFormat bool
 }
 
 // OptionCompressionVariant allows to supply information about
@@ -163,6 +167,14 @@ type copier struct {
 	signersToClose                []*signer.Signer    // Signers that should be closed when this copier is destroyed.
 }
 
+// Internal function to validate `requireCompressionFormatMatch` for copySingleImageOptions
+func shouldRequireCompressionFormatMatch(options *Options) (bool, error) {
+	if options.ForceCompressionFormat && (options.DestinationCtx == nil || options.DestinationCtx.CompressionFormat == nil) {
+		return false, fmt.Errorf("cannot use ForceCompressionFormat with undefined default compression format")
+	}
+	return options.ForceCompressionFormat, nil
+}
+
 // Image copies image from srcRef to destRef, using policyContext to validate
 // source image admissibility.  It returns the manifest which was written to
 // the new copy of the image.
@@ -269,8 +281,12 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 		if len(options.EnsureCompressionVariantsExist) > 0 {
 			return nil, fmt.Errorf("EnsureCompressionVariantsExist is not implemented when not creating a multi-architecture image")
 		}
+		requireCompressionFormatMatch, err := shouldRequireCompressionFormatMatch(options)
+		if err != nil {
+			return nil, err
+		}
 		// The simple case: just copy a single image.
-		single, err := c.copySingleImage(ctx, c.unparsedToplevel, nil, copySingleImageOptions{requireCompressionFormatMatch: false})
+		single, err := c.copySingleImage(ctx, c.unparsedToplevel, nil, copySingleImageOptions{requireCompressionFormatMatch: requireCompressionFormatMatch})
 		if err != nil {
 			return nil, err
 		}
@@ -279,6 +295,10 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 		if len(options.EnsureCompressionVariantsExist) > 0 {
 			return nil, fmt.Errorf("EnsureCompressionVariantsExist is not implemented when not creating a multi-architecture image")
 		}
+		requireCompressionFormatMatch, err := shouldRequireCompressionFormatMatch(options)
+		if err != nil {
+			return nil, err
+		}
 		// This is a manifest list, and we weren't asked to copy multiple images.  Choose a single image that
 		// matches the current system to copy, and copy it.
 		mfest, manifestType, err := c.unparsedToplevel.Manifest(ctx)
@@ -295,7 +315,7 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 		}
 		logrus.Debugf("Source is a manifest list; copying (only) instance %s for current system", instanceDigest)
 		unparsedInstance := image.UnparsedInstance(rawSource, &instanceDigest)
-		single, err := c.copySingleImage(ctx, unparsedInstance, nil, copySingleImageOptions{requireCompressionFormatMatch: false})
+		single, err := c.copySingleImage(ctx, unparsedInstance, nil, copySingleImageOptions{requireCompressionFormatMatch: requireCompressionFormatMatch})
 		if err != nil {
 			return nil, fmt.Errorf("copying system image from manifest list: %w", err)
 		}

copy/multiple.go

@@ -32,6 +32,10 @@ type instanceCopy struct {
 	op           instanceCopyKind
 	sourceDigest digest.Digest
 
+	// Fields which can be used by callers when operation
+	// is `instanceCopyCopy`
+	copyForceCompressionFormat bool
+
 	// Fields which can be used by callers when operation
 	// is `instanceCopyClone`
 	cloneCompressionVariant OptionCompressionVariant
@@ -122,9 +126,14 @@ func prepareInstanceCopies(list internalManifest.List, instanceDigests []digest.
 		if err != nil {
 			return res, fmt.Errorf("getting details for instance %s: %w", instanceDigest, err)
 		}
+		forceCompressionFormat, err := shouldRequireCompressionFormatMatch(options)
+		if err != nil {
+			return nil, err
+		}
 		res = append(res, instanceCopy{
-			op:           instanceCopyCopy,
-			sourceDigest: instanceDigest,
+			op:                         instanceCopyCopy,
+			sourceDigest:               instanceDigest,
+			copyForceCompressionFormat: forceCompressionFormat,
 		})
 		platform := platformV1ToPlatformComparable(instanceDetails.ReadOnly.Platform)
 		compressionList := compressionsByPlatform[platform]
@@ -230,7 +239,7 @@ func (c *copier) copyMultipleImages(ctx context.Context) (copiedManifest []byte,
 			logrus.Debugf("Copying instance %s (%d/%d)", instance.sourceDigest, i+1, len(instanceCopyList))
 			c.Printf("Copying image %s (%d/%d)\n", instance.sourceDigest, i+1, len(instanceCopyList))
 			unparsedInstance := image.UnparsedInstance(c.rawSource, &instanceCopyList[i].sourceDigest)
-			updated, err := c.copySingleImage(ctx, unparsedInstance, &instanceCopyList[i].sourceDigest, copySingleImageOptions{requireCompressionFormatMatch: false})
+			updated, err := c.copySingleImage(ctx, unparsedInstance, &instanceCopyList[i].sourceDigest, copySingleImageOptions{requireCompressionFormatMatch: instance.copyForceCompressionFormat})
 			if err != nil {
 				return nil, fmt.Errorf("copying image %d/%d from manifest list: %w", i+1, len(instanceCopyList), err)
 			}

copy/multiple_test.go

@@ -32,7 +32,7 @@ func TestPrepareCopyInstancesforInstanceCopyCopy(t *testing.T) {
 
 	for _, instance := range sourceInstances {
 		compare = append(compare, instanceCopy{op: instanceCopyCopy,
-			sourceDigest: instance})
+			sourceDigest: instance, copyForceCompressionFormat: false})
 	}
 	assert.Equal(t, instancesToCopy, compare)
 
@@ -42,6 +42,9 @@ func TestPrepareCopyInstancesforInstanceCopyCopy(t *testing.T) {
 	compare = []instanceCopy{{op: instanceCopyCopy,
 		sourceDigest: sourceInstances[1]}}
 	assert.Equal(t, instancesToCopy, compare)
+
+	_, err = prepareInstanceCopies(list, sourceInstances, &Options{Instances: []digest.Digest{sourceInstances[1]}, ImageListSelection: CopySpecificImages, ForceCompressionFormat: true})
+	require.EqualError(t, err, "cannot use ForceCompressionFormat with undefined default compression format")
 }
 
 // Test `instanceCopyClone` cases.