add result.ml; polymorphic variant errors + refacto

src/api.ml

@@ -8,11 +8,19 @@
      - uri *)
 
 module DenominationHash = Hash.DenominationHash
+module Bytes32 = Signatures.Bytes32
+module Bytes64 = Signatures.Bytes64
 open Time
 open Signatures
 
-let encode jsont v = Jsont_bytesrw.encode_string jsont v
-let decode jsont v = Jsont_bytesrw.decode_string jsont v
+let encode' jsont v = Jsont_bytesrw.encode_string jsont v
+let decode' jsont v = Jsont_bytesrw.decode_string jsont v
+
+let encode jsont v =
+  encode' jsont v |> Result.map_error (fun e -> `Json_encode e)
+
+let decode jsont v =
+  decode' jsont v |> Result.map_error (fun e -> `Json_decode e)
 
 open Jsont.Object
 
@@ -57,34 +65,6 @@ module B32 = struct
       ~decode:B32.decode Caqti_type.string
 end
 
-module Bytes32 = struct
-  include Signatures.Bytes32
-
-  let jsont =
-    let decode s = Result.bind (B32.decode s) of_octets in
-    let encode b = to_octets b |> B32.encode in
-    Jsont.of_of_string ~kind:"Bytes32" decode ~enc:encode
-
-  let caqti =
-    Caqti_type.custom
-      ~encode:(fun v -> Ok (to_octets v))
-      ~decode:of_octets Caqti_type.octets
-end
-
-module Bytes64 = struct
-  include Signatures.Bytes64
-
-  let jsont =
-    let decode s = Result.bind (B32.decode s) of_octets in
-    let encode b = to_octets b |> B32.encode in
-    Jsont.of_of_string ~kind:"Bytes64" decode ~enc:encode
-
-  let caqti =
-    Caqti_type.custom
-      ~encode:(fun v -> Ok (to_octets v))
-      ~decode:of_octets Caqti_type.octets
-end
-
 module ErrorDetail = struct
   type t = {
     code: int;