Add image.copy.digestOptions

for now, purely to let us internally work on implementing digest
choice / conversions; there is no way for a caller to set it.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

Author: mtrmac

image/copy/copy.go

@@ -14,6 +14,7 @@ import (
 	"github.com/sirupsen/logrus"
 	"go.podman.io/image/v5/docker/reference"
 	internalblobinfocache "go.podman.io/image/v5/internal/blobinfocache"
+	"go.podman.io/image/v5/internal/digests"
 	"go.podman.io/image/v5/internal/image"
 	"go.podman.io/image/v5/internal/imagedestination"
 	"go.podman.io/image/v5/internal/imagesource"
@@ -155,6 +156,15 @@ type Options struct {
 	// In oci-archive: destinations, this will set the create/mod/access timestamps in each tar entry
 	// (but not a timestamp of the created archive file).
 	DestinationTimestamp *time.Time
+
+	// FIXME:
+	// - this reference to an internal type is unusable from the outside even if we made the field public
+	// - what is the actual semantics? Right now it is probably “choices to use when writing to the destination”, TBD
+	// - anyway do we want to expose _all_ of the digests.Options tunables, or fewer?
+	// - … do we want to expose _more_ granularity than that?
+	//   - (“must have at least sha512 integrity when reading”, what does “at least” mean for random pairs of algorithms?)
+	//   - should some of this be in config files, maybe ever per-registry?
+	digestOptions digests.Options
 }
 
 // OptionCompressionVariant allows to supply information about
@@ -200,6 +210,12 @@ func Image(ctx context.Context, policyContext *signature.PolicyContext, destRef,
 	if options == nil {
 		options = &Options{}
 	}
+	// FIXME: Currently, digestsOptions is not implemented at all, and exists in the codebase
+	// only to allow gradually building the feature set.
+	// After c/image/copy consistently implements it, provide a public digest options API of some kind.
+	optionsCopy := *options
+	optionsCopy.digestOptions = digests.CanonicalDefault()
+	options = &optionsCopy
 
 	if err := validateImageListSelection(options.ImageListSelection); err != nil {
 		return nil, err