Lib: Add Typed_array.Bytes module (#1609)

Author: johnridesabike

lib/js_of_ocaml/js_of_ocaml_stubs.c

@@ -1,5 +1,9 @@
 #include <stdlib.h>
 #include <stdio.h>
+void caml_bytes_of_array () {
+  fprintf(stderr, "Unimplemented Javascript primitive caml_bytes_of_array!\n");
+  exit(1);
+}
 void caml_custom_identifier () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_custom_identifier!\n");
   exit(1);
@@ -24,6 +28,10 @@ void caml_js_on_ie () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_js_on_ie!\n");
   exit(1);
 }
+void caml_uint8_array_of_bytes () {
+  fprintf(stderr, "Unimplemented Javascript primitive caml_uint8_array_of_bytes!\n");
+  exit(1);
+}
 void caml_xmlhttprequest_create () {
   fprintf(stderr, "Unimplemented Javascript primitive caml_xmlhttprequest_create!\n");
   exit(1);

lib/js_of_ocaml/typed_array.ml

@@ -277,3 +277,13 @@ module String = struct
     let uint8 = new%js uint8Array_fromBuffer ab in
     of_uint8Array uint8
 end
+
+module Bytes = struct
+  external of_uint8Array : uint8Array Js.t -> bytes = "caml_bytes_of_array"
+
+  external to_uint8Array : bytes -> uint8Array Js.t = "caml_uint8_array_of_bytes"
+
+  let of_arrayBuffer ab =
+    let uint8 = new%js uint8Array_fromBuffer ab in
+    of_uint8Array uint8
+end

lib/js_of_ocaml/typed_array.mli

@@ -273,3 +273,20 @@ module String : sig
 
   val of_uint8Array : uint8Array Js.t -> string
 end
+
+module Bytes : sig
+  val of_uint8Array : uint8Array Js.t -> bytes
+  (** This efficiently converts a typed array to [bytes] because it will usually
+      not copy its input.
+
+      Modifying its input may also modify its output, and vice versa when
+      modifying its output. This is not a guarantee, however, since certain
+      [bytes] operations may require the runtime to make a copy. One should not
+      use this on input that is sensitive to modification. *)
+
+  val to_uint8Array : bytes -> uint8Array Js.t
+  (** See the words of caution for {!of_uint8Array}. *)
+
+  val of_arrayBuffer : arrayBuffer Js.t -> bytes
+  (** See the words of caution for {!of_uint8Array}. *)
+end