hash: use of_raw_string_opt

src/b32.ml

@@ -29,6 +29,10 @@ let decode s =
         | c -> c)
       s
   in
+  (* restore padding for base32 lib *)
+  let n = 8 - (String.length s mod 8) in
+  let pad = String.make n '=' in
+  let s = s ^ pad in
   match Base32.decode ~alphabet ~off:0 ~len:(String.length s) s with
   | Error (`Msg e) -> Error e
   | Ok v -> Ok v