Add CanonicalDockerReference to ImageDestination

This is necessary to resolve the canonical form of a reference for
signing it.

directory.go

@@ -36,6 +36,10 @@ func NewDirImageDestination(dir string) types.ImageDestination {
 	return &dirImageDestination{dir}
 }
 
+func (d *dirImageDestination) CanonicalDockerReference() (string, error) {
+	return "", fmt.Errorf("Can not determine canonical Docker reference for a local directory")
+}
+
 func (d *dirImageDestination) PutManifest(manifest []byte) error {
 	return ioutil.WriteFile(manifestPath(d.dir), manifest, 0644)
 }

docker.go

@@ -752,6 +752,10 @@ func NewDockerImageDestination(img, certPath string, tlsVerify bool) (types.Imag
 	}, nil
 }
 
+func (d *dockerImageDestination) CanonicalDockerReference() (string, error) {
+	return fmt.Sprintf("%s:%s", d.ref.Name(), d.tag), nil
+}
+
 func (d *dockerImageDestination) PutManifest(manifest []byte) error {
 	// FIXME: This only allows upload by digest, not creating a tag.  See the
 	// corresponding comment in NewOpenshiftImageDestination.

openshift.go

@@ -268,6 +268,10 @@ func NewOpenshiftImageDestination(imageName, certPath string, tlsVerify bool) (t
 	}, nil
 }
 
+func (d *openshiftImageDestination) CanonicalDockerReference() (string, error) {
+	return fmt.Sprintf("%s/%s/%s:%s", d.client.baseURL.Host, d.client.namespace, d.client.stream, d.client.tag), nil
+}
+
 func (d *openshiftImageDestination) PutManifest(manifest []byte) error {
 	// Note: This does absolutely no kind/version checking or conversions.
 	manifestDigest, err := dockerutils.ManifestDigest(manifest)

types/types.go

@@ -37,6 +37,8 @@ type ImageSource interface {
 
 // ImageDestination is a service, possibly remote (= slow), to store components of a single image.
 type ImageDestination interface {
+	// CanonicalDockerReference returns the full, unambiguous, Docker reference for this image (even if the user referred to the image using some shorthand notation).
+	CanonicalDockerReference() (string, error)
 	PutManifest([]byte) error
 	PutLayer(digest string, stream io.Reader) error
 	PutSignatures(signatures [][]byte) error