better module for BytesXX

src/signatures.ml

@@ -33,16 +33,40 @@ open Aliases
 
 let size_of_int32 = 4
 
-module Bytes32 = struct
-  type t = string
+module type BYTES = sig
+  type t
 
-  let bin = Bin.bytes 32
+  val of_octets : string -> (t, string) result
+  val to_octets : t -> string
+  val bin : t Bin.t
 end
 
-module Bytes64 = struct
+module Bytes32 : BYTES = struct
+  let n = 32
+
   type t = string
 
-  let bin = Bin.bytes 64
+  let of_octets s =
+    match String.length s = n with
+    | false -> Error "invalid bytes length"
+    | true -> Ok s
+
+  let to_octets = Fun.id
+  let bin = Bin.bytes n
+end
+
+module Bytes64 : BYTES = struct
+  let n = 64
+
+  type t = string
+
+  let of_octets s =
+    match String.length s = n with
+    | false -> Error "invalid bytes length"
+    | true -> Ok s
+
+  let to_octets = Fun.id
+  let bin = Bin.bytes n
 end
 
 module TransferSecretP = Bytes64