SupportsEncryption to use bool and named errors

Signed-off-by: Brandon Lum <lumjjb@gmail.com>

copy/copy.go

@@ -44,6 +44,11 @@ type digestingReader struct {
 	skipValidation      bool
 }
 
+var (
+	// ErrDecryptParamsMissing is returned if there is missing decryption parameters
+	ErrDecryptParamsMissing = errors.New("Necessary DecryptParameters not present")
+)
+
 // maxParallelDownloads is used to limit the maxmimum number of parallel
 // downloads.  Let's follow Firefox by limiting it to 6.
 var maxParallelDownloads = 6
@@ -263,7 +268,7 @@ func (c *copier) copyOneImage(ctx context.Context, policyContext *signature.Poli
 		return nil, errors.Wrapf(err, "Error initializing image from source %s", transports.ImageName(c.rawSource.Reference()))
 	}
 
-	if err = src.SupportsEncryption(ctx); err != nil && options.EncryptLayers != nil {
+	if !src.SupportsEncryption(ctx) && options.EncryptLayers != nil {
 		return nil, errors.Wrap(err, "Encryption requested but not supported by source image type")
 	}
 
@@ -892,7 +897,7 @@ func (c *copier) copyBlobFromStream(ctx context.Context, srcStream io.Reader, sr
 		srcInfo.MediaType == manifest.DockerV2Schema2LayerEncMediaType {
 
 		if c.decryptConfig == nil {
-			return types.BlobInfo{}, errors.New("Necessary DecryptParameters not present")
+			return types.BlobInfo{}, ErrDecryptParamsMissing
 		}
 
 		dc := c.decryptConfig

copy/manifest_test.go

@@ -71,7 +71,7 @@ func (f fakeImageSource) UpdatedImageNeedsLayerDiffIDs(options types.ManifestUpd
 func (f fakeImageSource) UpdatedImage(ctx context.Context, options types.ManifestUpdateOptions) (types.Image, error) {
 	panic("Unexpected call to a mock function")
 }
-func (f fakeImageSource) SupportsEncryption(ctx context.Context) error {
+func (f fakeImageSource) SupportsEncryption(ctx context.Context) bool {
 	panic("Unexpected call to a mock function")
 }
 func (f fakeImageSource) Size() (int64, error) {

image/docker_schema1.go

@@ -201,7 +201,7 @@ func (m *manifestSchema1) convertToManifestSchema2(uploadedLayerInfos []types.Bl
 	return manifestSchema2FromComponents(configDescriptor, nil, configJSON, layers), nil
 }
 
-// SupportsEncryption returns an error if encryption is not supported for the manifest type
-func (m *manifestSchema1) SupportsEncryption(context.Context) error {
-	return errors.New("Docker Schema v1 does not support encryption")
+// SupportsEncryption returns if encryption is supported for the manifest type
+func (m *manifestSchema1) SupportsEncryption(context.Context) bool {
+	return false
 }

image/docker_schema2.go

@@ -350,7 +350,7 @@ func v1ConfigFromConfigJSON(configJSON []byte, v1ID, parentV1ID string, throwawa
 	return json.Marshal(rawContents)
 }
 
-// SupportsEncryption returns an error if encryption is not supported for the manifest type
-func (m *manifestSchema2) SupportsEncryption(context.Context) error {
-	return errors.New("Docker Schema v2 does not support encryption")
+// SupportsEncryption returns if encryption is supported for the manifest type
+func (m *manifestSchema2) SupportsEncryption(context.Context) bool {
+	return false
 }

image/manifest.go

@@ -44,8 +44,8 @@ type genericManifest interface {
 	// UpdatedImage returns a types.Image modified according to options.
 	// This does not change the state of the original Image object.
 	UpdatedImage(ctx context.Context, options types.ManifestUpdateOptions) (types.Image, error)
-	// SupportsEncryption returns an error if encryption is not supported for the manifest type
-	SupportsEncryption(ctx context.Context) error
+	// SupportsEncryption returns if encryption is supported for the manifest type
+	SupportsEncryption(ctx context.Context) bool
 }
 
 // manifestInstanceFromBlob returns a genericManifest implementation for (manblob, mt) in src.

image/oci.go

@@ -197,7 +197,7 @@ func (m *manifestOCI1) convertToManifestSchema2() (types.Image, error) {
 	return memoryImageFromManifest(m1), nil
 }
 
-// SupportsEncryption returns an error if encryption is not supported for the manifest type
-func (m *manifestOCI1) SupportsEncryption(context.Context) error {
-	return nil
+// SupportsEncryption returns if encryption is supported for the manifest type
+func (m *manifestOCI1) SupportsEncryption(context.Context) bool {
+	return true
 }

types/types.go

@@ -357,8 +357,8 @@ type Image interface {
 	// Everything in options.InformationOnly should be provided, other fields should be set only if a modification is desired.
 	// This does not change the state of the original Image object.
 	UpdatedImage(ctx context.Context, options ManifestUpdateOptions) (Image, error)
-	// SupportsEncryption errors if the image doesn't support encryption
-	SupportsEncryption(ctx context.Context) error
+	// SupportsEncryption returns an indicator that the image supports encryption
+	SupportsEncryption(ctx context.Context) bool
 	// Size returns an approximation of the amount of disk space which is consumed by the image in its current
 	// location.  If the size is not known, -1 will be returned.
 	Size() (int64, error)