add method cat & md5

storage.go

@@ -0,0 +1,16 @@
+package registry
+
+import "crypto/md5"
+
+type Storage struct {
+	Md5 [md5.Size]byte
+	m   map[string]string
+}
+
+func (s *Storage) Get(key string) (string, error) {
+	v, ok := s.m[key]
+	if ok {
+		return v, nil
+	}
+	return "", ErrNoSuchKey
+}