refactor: Move ShortDigest out of display package (#1373)

Signed-off-by: Terry Howe <[email protected]>

cmd/oras/internal/display/status/print.go

@@ -19,6 +19,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"oras.land/oras/internal/descriptor"
 	"sync"
 
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -57,7 +58,7 @@ func (p *Printer) PrintStatus(desc ocispec.Descriptor, status string, verbose bo
 		}
 		name = desc.MediaType
 	}
-	return p.Println(status, ShortDigest(desc), name)
+	return p.Println(status, descriptor.ShortDigest(desc), name)
 }
 
 // StatusPrinter returns a tracking function for transfer status.

internal/descriptor/descriptor.go

@@ -16,6 +16,7 @@ limitations under the License.
 package descriptor
 
 import (
+	"github.com/opencontainers/go-digest"
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 
 	"oras.land/oras/internal/docker"
@@ -25,3 +26,14 @@ import (
 func IsImageManifest(desc ocispec.Descriptor) bool {
 	return desc.MediaType == docker.MediaTypeManifest || desc.MediaType == ocispec.MediaTypeImageManifest
 }
+
+// ShortDigest converts the digest of the descriptor to a short form for displaying.
+func ShortDigest(desc ocispec.Descriptor) (digestString string) {
+	digestString = desc.Digest.String()
+	if err := desc.Digest.Validate(); err == nil {
+		if algo := desc.Digest.Algorithm(); algo == digest.SHA256 {
+			digestString = desc.Digest.Encoded()[:12]
+		}
+	}
+	return digestString
+}