Make types.Image Docker-independent

The remaining uses of the dependencies, in (skopeo inspect), now check
whether their types.Image is a docker.Image and call the docker.Image
functions directly.

This does not change behavior for Docker images.

For non-Docker images (which can't happen yet), the Name field is
removed; RepoTags remain and are reported as empty, because using
json:",omitempty" would also omit an empty list for Docker images.

cmd/skopeo/inspect.go

@@ -7,12 +7,13 @@ import (
 
 	"github.com/Sirupsen/logrus"
 	"github.com/codegangsta/cli"
+	"github.com/projectatomic/skopeo/docker"
 	"github.com/projectatomic/skopeo/docker/utils"
 )
 
 // inspectOutput is the output format of (skopeo inspect), primarily so that we can format it with a simple json.MarshalIndent.
 type inspectOutput struct {
-	Name          string
+	Name          string `json:",omitempty"`
 	Tag           string
 	Digest        string
 	RepoTags      []string
@@ -51,10 +52,10 @@ var inspectCmd = cli.Command{
 			logrus.Fatal(err)
 		}
 		outputData := inspectOutput{
-			// Name is set below.
-			Tag: imgInspect.Tag,
+			Name: "", // Possibly overridden for a docker.Image.
+			Tag:  imgInspect.Tag,
 			// Digest is set below.
-			// RepoTags are set below.
+			RepoTags:      []string{}, // Possibly overriden for a docker.Image.
 			Created:       imgInspect.Created,
 			DockerVersion: imgInspect.DockerVersion,
 			Labels:        imgInspect.Labels,
@@ -66,13 +67,15 @@ var inspectCmd = cli.Command{
 		if err != nil {
 			logrus.Fatalf("Error computing manifest digest: %s", err.Error())
 		}
-		outputData.Name, err = img.SourceRefFullName()
-		if err != nil {
-			logrus.Fatalf("Error getting expanded repository name: %s", err.Error())
-		}
-		outputData.RepoTags, err = img.GetRepositoryTags()
-		if err != nil {
-			logrus.Fatalf("Error determining repository tags: %s", err.Error())
+		if dockerImg, ok := img.(*docker.Image); ok {
+			outputData.Name, err = dockerImg.SourceRefFullName()
+			if err != nil {
+				logrus.Fatalf("Error getting expanded repository name: %s", err.Error())
+			}
+			outputData.RepoTags, err = dockerImg.GetRepositoryTags()
+			if err != nil {
+				logrus.Fatalf("Error determining repository tags: %s", err.Error())
+			}
 		}
 		out, err := json.MarshalIndent(outputData, "", "    ")
 		if err != nil {

docker/image.go

@@ -26,6 +26,14 @@ type genericImage struct {
 	cachedSignatures [][]byte // Private cache for Signatures(); nil if not yet known.
 }
 
+// GenericImageFromSource returns a types.Image implementation for source.
+// NOTE: This is currently an internal testing helper, do not rely on this as
+// a stable API. There might be an ImageFromSource eventually, but it would not be
+// in the skopeo/docker package.
+func GenericImageFromSource(src types.ImageSource) types.Image {
+	return &genericImage{src: src}
+}
+
 // IntendedDockerReference returns the full, unambiguous, Docker reference for this image, _as specified by the user_
 // (not as the image itself, or its underlying storage, claims).  This can be used e.g. to determine which public keys are trusted for this image.
 // May be "" if unknown.

types/types.go

@@ -59,15 +59,9 @@ type Image interface {
 	// Signatures is like ImageSource.GetSignatures, but the result is cached; it is OK to call this however often you need.
 	Signatures() ([][]byte, error)
 	Layers(layers ...string) error // configure download directory? Call it DownloadLayers?
-	// SourceRefFullName returns a fully expanded name for the repository this image is in.
-	SourceRefFullName() (string, error)
 	// Inspect returns various information for (skopeo inspect) parsed from the manifest and configuration.
 	Inspect() (*ImageInspectInfo, error)
 	DockerTar() ([]byte, error) // ??? also, configure output directory
-	// GetRepositoryTags list all tags available in the repository. Note that this has no connection with the tag(s) used for this specific image, if any.
-	// Eventually we should move this away from the generic Image interface, and move it into a Docker-specific case within the (skopeo inspect) command,
-	// see https://github.com/projectatomic/skopeo/pull/58#discussion_r63411838 .
-	GetRepositoryTags() ([]string, error)
 }
 
 // ImageInspectInfo is a set of metadata describing Docker images, primarily their manifest and configuration.