Use reference package internally

Most places in the registry were using string types to refer to
repository names. This changes them to use reference.Named, so the type
system can enforce validation of the naming rules.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

manifest/schema1/config_builder.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/docker/distribution"
 	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/reference"
 	"github.com/docker/libtrust"
 
 	"github.com/docker/distribution/digest"
@@ -39,10 +40,8 @@ type configManifestBuilder struct {
 	// configJSON is configuration supplied when the ManifestBuilder was
 	// created.
 	configJSON []byte
-	// name is the name provided to NewConfigManifestBuilder
-	name string
-	// tag is the tag provided to NewConfigManifestBuilder
-	tag string
+	// ref contains the name and optional tag provided to NewConfigManifestBuilder.
+	ref reference.Named
 	// descriptors is the set of descriptors referencing the layers.
 	descriptors []distribution.Descriptor
 	// emptyTarDigest is set to a valid digest if an empty tar has been
@@ -54,13 +53,12 @@ type configManifestBuilder struct {
 // schema version from an image configuration and a set of descriptors.
 // It takes a BlobService so that it can add an empty tar to the blob store
 // if the resulting manifest needs empty layers.
-func NewConfigManifestBuilder(bs distribution.BlobService, pk libtrust.PrivateKey, name, tag string, configJSON []byte) distribution.ManifestBuilder {
+func NewConfigManifestBuilder(bs distribution.BlobService, pk libtrust.PrivateKey, ref reference.Named, configJSON []byte) distribution.ManifestBuilder {
 	return &configManifestBuilder{
 		bs:         bs,
 		pk:         pk,
 		configJSON: configJSON,
-		name:       name,
-		tag:        tag,
+		ref:        ref,
 	}
 }
 
@@ -190,12 +188,17 @@ func (mb *configManifestBuilder) Build(ctx context.Context) (m distribution.Mani
 
 	history[0].V1Compatibility = string(transformedConfig)
 
+	tag := ""
+	if tagged, isTagged := mb.ref.(reference.Tagged); isTagged {
+		tag = tagged.Tag()
+	}
+
 	mfst := Manifest{
 		Versioned: manifest.Versioned{
 			SchemaVersion: 1,
 		},
-		Name:         mb.name,
-		Tag:          mb.tag,
+		Name:         mb.ref.Name(),
+		Tag:          tag,
 		Architecture: img.Architecture,
 		FSLayers:     fsLayerList,
 		History:      history,