1 files changed, 33 insertions, 0 deletions
diff --git a/signer.go b/signer.go
new file mode 100644
index 0000000..e3ef7eb
--- /dev/null
+++ b/signer.go
@@ -0,0 +1,33 @@
+package git
+
+import (
+	"io"
+
+	"github.com/go-git/go-git/v5/plumbing"
+)
+
+// signableObject is an object which can be signed.
+type signableObject interface {
+	EncodeWithoutSignature(o plumbing.EncodedObject) error
+}
+
+// Signer is an interface for signing git objects.
+// message is a reader containing the encoded object to be signed.
+// Implementors should return the encoded signature and an error if any.
+// See https://git-scm.com/docs/gitformat-signature for more information.
+type Signer interface {
+	Sign(message io.Reader) ([]byte, error)
+}
+
+func signObject(signer Signer, obj signableObject) ([]byte, error) {
+	encoded := &plumbing.MemoryObject{}
+	if err := obj.EncodeWithoutSignature(encoded); err != nil {
+		return nil, err
+	}
+	r, err := encoded.Reader()
+	if err != nil {
+		return nil, err
+	}
+
+	return signer.Sign(r)
+}