From 5eb8d0077a26e448ddd37709a7da0dc9e110f3d6 Mon Sep 17 00:00:00 2001
From: Vincent Bernardoff <vb@luminar.eu.org>
Date: Sat, 14 Jan 2017 13:13:41 +0100
Subject: [PATCH] Shell: add `Data_encoding.Binary.fixed_length`

---
 src/minutils/data_encoding.ml  | 10 ++++++++++
 src/minutils/data_encoding.mli |  3 +++
 2 files changed, 13 insertions(+)

diff --git a/src/minutils/data_encoding.ml b/src/minutils/data_encoding.ml
index 3de84af44..2da130d06 100644
--- a/src/minutils/data_encoding.ml
+++ b/src/minutils/data_encoding.ml
@@ -1178,4 +1178,14 @@ let rec length : type x. x t -> x -> int = fun e ->
   let to_bytes = to_bytes
 
   let length = length
+
+  let fixed_length e =
+    match classify e with
+    | `Fixed n -> Some n
+    | `Dynamic | `Variable -> None
+  let fixed_length_exn e =
+    match fixed_length e with
+    | Some n -> n
+    | None -> invalid_arg "Data_encoding.Binary.fixed_length_exn"
+
 end
diff --git a/src/minutils/data_encoding.mli b/src/minutils/data_encoding.mli
index be410b820..8bac5d62f 100644
--- a/src/minutils/data_encoding.mli
+++ b/src/minutils/data_encoding.mli
@@ -236,4 +236,7 @@ module Binary : sig
   val to_bytes : 'a encoding -> 'a -> MBytes.t
   val of_bytes : 'a encoding -> MBytes.t -> 'a option
 
+  val fixed_length : 'a encoding -> int option
+  val fixed_length_exn : 'a encoding -> int
+
 end