expose Response.make_void

it only has no body if the http code is compatible with it.
close #62

src/Tiny_httpd_dir.ml

@@ -249,7 +249,7 @@ let add_vfs_ ~on_fs ~top ~config ~vfs:((module VFS:VFS) as vfs) ~prefix server :
              (* redirect using path, not full path *)
              let new_path = "/" // prefix // path // "index.html" in
              S._debug (fun k->k "redirect to `%s`" new_path);
-             S.Response.make_raw ~code:301 ""
+             S.Response.make_void ~code:301 ()
                ~headers:S.Headers.(empty |> set "location" new_path)
            | Lists | Index_or_lists ->
              let body = html_list_dir ~prefix vfs path ~parent |> Html.to_string_top in

src/Tiny_httpd_server.ml

@@ -354,7 +354,9 @@ module Response = struct
     { code; headers; body=`Stream body; }
 
   let make_void ?(headers=[]) ~code () : t =
-    { code; headers; body=`Void; }
+    let is_ok = code < 200 || code = 204 || code = 304 in
+    if is_ok then { code; headers; body=`Void; }
+    else make_raw ~headers ~code "" (* invalid to not have a body *)
 
   let make_string ?headers r = match r with
     | Ok body -> make_raw ?headers ~code:200 body

src/Tiny_httpd_server.mli

@@ -232,6 +232,10 @@ module Response : sig
   (** Same as {!make_raw} but with a stream body. The body will be sent with
       the chunked transfer-encoding. *)
 
+  val make_void : ?headers:Headers.t -> code:int -> unit -> t
+  (** Return a response without a body at all.
+      @since NEXT_RELEASE *)
+
   val make :
     ?headers:Headers.t ->
     (body, Response_code.t * string) result -> t