copy: add support for ForceCompressionFormat

ForceCompressionFormat allows end users to force selected compression format
(set in DestinationCtx.CompressionFormat) which ensures that while copying
blobs of other compression algorithms are not reused.

Following flag is a frontend wrapper for: containers#2023
Will help in:
* containers/buildah#4613
* containers/podman#18660

Signed-off-by: Aditya R <arajan@redhat.com>

copy/copy.go

@@ -133,6 +133,11 @@ type Options struct {
 	// Invalid when copying a non-multi-architecture image. That will probably
 	// change in the future.
 	EnsureCompressionVariantsExist []OptionCompressionVariant
+
+	// ForceCompressionFormat allows end users to force selected compression format
+	// (set in DestinationCtx.CompressionFormat) which ensures that while copying
+	// blobs of other compression algorithms are not reused.
+	ForceCompressionFormat bool
 }
 
 // OptionCompressionVariant allows to supply information about

copy/multiple.go

@@ -230,6 +230,16 @@ 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)
+			singleImageOpts := copySingleImageOptions{requireCompressionFormatMatch: false}
+			if c.options.ForceCompressionFormat {
+				singleImageOpts.requireCompressionFormatMatch = true
+				// If CompressionFormat is nil set it to `Gzip` as default,
+				// since requireCompressionFormatMatch is pretty much `no-op`
+				// for `nil` CompressionFormat.
+				if c.options.DestinationCtx.CompressionFormat == nil {
+					singleImageOpts.compressionFormat: &compression.Gzip
+				}
+			}
 			updated, err := c.copySingleImage(ctx, unparsedInstance, &instanceCopyList[i].sourceDigest, copySingleImageOptions{requireCompressionFormatMatch: false})
 			if err != nil {
 				return nil, fmt.Errorf("copying image %d/%d from manifest list: %w", i+1, len(instanceCopyList), err)