Move manifest package to schema1

As we begin our march towards multi-arch, we must prepare for the reality of
multiple manifest schemas. This is the beginning of a set of changes to
facilitate this. We are both moving this package into its target position where
it may live peacefully next to other manfiest versions.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

manifest/schema1/sign.go

@@ -0,0 +1,66 @@
+package schema1
+
+import (
+	"crypto/x509"
+	"encoding/json"
+
+	"github.com/docker/libtrust"
+)
+
+// Sign signs the manifest with the provided private key, returning a
+// SignedManifest. This typically won't be used within the registry, except
+// for testing.
+func Sign(m *Manifest, pk libtrust.PrivateKey) (*SignedManifest, error) {
+	p, err := json.MarshalIndent(m, "", "   ")
+	if err != nil {
+		return nil, err
+	}
+
+	js, err := libtrust.NewJSONSignature(p)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := js.Sign(pk); err != nil {
+		return nil, err
+	}
+
+	pretty, err := js.PrettySignature("signatures")
+	if err != nil {
+		return nil, err
+	}
+
+	return &SignedManifest{
+		Manifest: *m,
+		Raw:      pretty,
+	}, nil
+}
+
+// SignWithChain signs the manifest with the given private key and x509 chain.
+// The public key of the first element in the chain must be the public key
+// corresponding with the sign key.
+func SignWithChain(m *Manifest, key libtrust.PrivateKey, chain []*x509.Certificate) (*SignedManifest, error) {
+	p, err := json.MarshalIndent(m, "", "   ")
+	if err != nil {
+		return nil, err
+	}
+
+	js, err := libtrust.NewJSONSignature(p)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := js.SignWithChain(key, chain); err != nil {
+		return nil, err
+	}
+
+	pretty, err := js.PrettySignature("signatures")
+	if err != nil {
+		return nil, err
+	}
+
+	return &SignedManifest{
+		Manifest: *m,
+		Raw:      pretty,
+	}, nil
+}