Expose Signatures() on Repository

Add a SignatureService and expose it via Signatures() on Repository so
external integrations wrapping the registry can access signatures.

Move signature related code from revisionstore.go to signaturestore.go.

Signed-off-by: Andy Goldstein <agoldste@redhat.com>

docs/storage/signaturestore.go

@@ -0,0 +1,75 @@
+package storage
+
+import (
+	"path"
+
+	"github.com/docker/distribution"
+	"github.com/docker/distribution/digest"
+)
+
+type signatureStore struct {
+	*repository
+}
+
+var _ distribution.SignatureService = &signatureStore{}
+
+func (s *signatureStore) Get(dgst digest.Digest) ([][]byte, error) {
+	signaturesPath, err := s.pm.path(manifestSignaturesPathSpec{
+		name:     s.Name(),
+		revision: dgst,
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	// Need to append signature digest algorithm to path to get all items.
+	// Perhaps, this should be in the pathMapper but it feels awkward. This
+	// can be eliminated by implementing listAll on drivers.
+	signaturesPath = path.Join(signaturesPath, "sha256")
+
+	signaturePaths, err := s.driver.List(signaturesPath)
+	if err != nil {
+		return nil, err
+	}
+
+	var signatures [][]byte
+	for _, sigPath := range signaturePaths {
+		// Append the link portion
+		sigPath = path.Join(sigPath, "link")
+
+		// TODO(stevvooe): These fetches should be parallelized for performance.
+		p, err := s.blobStore.linked(sigPath)
+		if err != nil {
+			return nil, err
+		}
+
+		signatures = append(signatures, p)
+	}
+
+	return signatures, nil
+}
+
+func (s *signatureStore) Put(dgst digest.Digest, signatures ...[]byte) error {
+	for _, signature := range signatures {
+		signatureDigest, err := s.blobStore.put(signature)
+		if err != nil {
+			return err
+		}
+
+		signaturePath, err := s.pm.path(manifestSignatureLinkPathSpec{
+			name:      s.Name(),
+			revision:  dgst,
+			signature: signatureDigest,
+		})
+
+		if err != nil {
+			return err
+		}
+
+		if err := s.blobStore.link(signaturePath, signatureDigest); err != nil {
+			return err
+		}
+	}
+	return nil
+}