Fix Go Idioms

- DRY out SchemaVersion literals
- Better name the predefined Versioned struct for the Image Index
- Var names, declarations, else cases.

Co-authored-by: Milos Gajdos <milosthegajdos@gmail.com>
Signed-off-by: Bracken Dawson <abdawson@gmail.com>

manifest/manifestlist/manifestlist.go

@@ -129,7 +129,7 @@ func FromDescriptors(descriptors []ManifestDescriptor) (*DeserializedManifestLis
 func fromDescriptorsWithMediaType(descriptors []ManifestDescriptor, mediaType string) (*DeserializedManifestList, error) {
 	m := ManifestList{
 		Versioned: manifest.Versioned{
-			SchemaVersion: 2,
+			SchemaVersion: SchemaVersion.SchemaVersion,
 			MediaType:     mediaType,
 		},
 	}

manifest/ocischema/index.go

@@ -11,9 +11,9 @@ import (
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
-// OCISchemaVersion provides a pre-initialized version structure for this
-// packages OCIschema version of the manifest.
-var OCISchemaVersion = manifest.Versioned{
+// IndexSchemaVersion provides a pre-initialized version structure for OCI Image
+// Indices.
+var IndexSchemaVersion = manifest.Versioned{
 	SchemaVersion: 2,
 	MediaType:     v1.MediaTypeImageIndex,
 }
@@ -69,13 +69,13 @@ type ImageIndex struct {
 // References returns the distribution descriptors for the referenced image
 // manifests.
 func (ii ImageIndex) References() []distribution.Descriptor {
-	dependencies := make([]distribution.Descriptor, len(ii.Manifests))
+	references := make([]distribution.Descriptor, len(ii.Manifests))
 	for i := range ii.Manifests {
-		dependencies[i] = ii.Manifests[i].Descriptor
-		dependencies[i].Platform = ii.Manifests[i].Platform
+		references[i] = ii.Manifests[i].Descriptor
+		references[i].Platform = ii.Manifests[i].Platform
 	}
 
-	return dependencies
+	return references
 }
 
 // DeserializedImageIndex wraps ManifestList with a copy of the original
@@ -96,10 +96,10 @@ func FromDescriptors(descriptors []ManifestDescriptor, annotations map[string]st
 }
 
 // fromDescriptorsWithMediaType is for testing purposes, it's useful to be able to specify the media type explicitly
-func fromDescriptorsWithMediaType(descriptors []ManifestDescriptor, annotations map[string]string, mediaType string) (*DeserializedImageIndex, error) {
+func fromDescriptorsWithMediaType(descriptors []ManifestDescriptor, annotations map[string]string, mediaType string) (_ *DeserializedImageIndex, err error) {
 	m := ImageIndex{
 		Versioned: manifest.Versioned{
-			SchemaVersion: 2,
+			SchemaVersion: IndexSchemaVersion.SchemaVersion,
 			MediaType:     mediaType,
 		},
 		Annotations: annotations,
@@ -112,7 +112,6 @@ func fromDescriptorsWithMediaType(descriptors []ManifestDescriptor, annotations
 		ImageIndex: m,
 	}
 
-	var err error
 	deserialized.canonical, err = json.MarshalIndent(&m, "", "   ")
 	return &deserialized, err
 }
@@ -147,11 +146,9 @@ func (m *DeserializedImageIndex) MarshalJSON() ([]byte, error) {
 // Payload returns the raw content of the manifest list. The contents can be
 // used to calculate the content identifier.
 func (m DeserializedImageIndex) Payload() (string, []byte, error) {
-	var mediaType string
+	mediaType := m.MediaType
 	if m.MediaType == "" {
 		mediaType = v1.MediaTypeImageIndex
-	} else {
-		mediaType = m.MediaType
 	}
 
 	return mediaType, m.canonical, nil

manifest/ocischema/manifest.go

@@ -11,10 +11,10 @@ import (
 	v1 "github.com/opencontainers/image-spec/specs-go/v1"
 )
 
-// SchemaVersion provides a pre-initialized version structure for this
-// packages version of the manifest.
+// SchemaVersion provides a pre-initialized version structure for OCI Image
+// Manifests
 var SchemaVersion = manifest.Versioned{
-	SchemaVersion: 2, // historical value here.. does not pertain to OCI or docker version
+	SchemaVersion: 2,
 	MediaType:     v1.MediaTypeImageManifest,
 }
 

registry/storage/manifestlisthandler.go

@@ -34,17 +34,19 @@ func (ms *manifestListHandler) Unmarshal(ctx context.Context, dgst digest.Digest
 func (ms *manifestListHandler) Put(ctx context.Context, manifestList distribution.Manifest, skipDependencyVerification bool) (digest.Digest, error) {
 	dcontext.GetLogger(ms.ctx).Debug("(*manifestListHandler).Put")
 
-	var schemaVersion int
+	var schemaVersion, expectedSchemaVersion int
 	switch m := manifestList.(type) {
 	case *manifestlist.DeserializedManifestList:
+		expectedSchemaVersion = manifestlist.SchemaVersion.SchemaVersion
 		schemaVersion = m.SchemaVersion
 	case *ocischema.DeserializedImageIndex:
+		expectedSchemaVersion = ocischema.IndexSchemaVersion.SchemaVersion
 		schemaVersion = m.SchemaVersion
 	default:
 		return "", fmt.Errorf("wrong type put to manifestListHandler: %T", manifestList)
 	}
-	if schemaVersion != 2 {
-		return "", fmt.Errorf("unrecognized manifest list schema version %d", schemaVersion)
+	if schemaVersion != expectedSchemaVersion {
+		return "", fmt.Errorf("unrecognized manifest list schema version %d, expected %d", schemaVersion, expectedSchemaVersion)
 	}
 
 	if err := ms.verifyManifest(ms.ctx, manifestList, skipDependencyVerification); err != nil {