diff --git a/src/utils/lwt_utils.ml b/src/utils/lwt_utils.ml
index cee2b3f7b..399045db6 100644
--- a/src/utils/lwt_utils.ml
+++ b/src/utils/lwt_utils.ml
@@ -224,3 +224,36 @@ let stable_sort cmp l =
   if len < 2 then Lwt.return l else sort len l
 
 let sort = stable_sort
+
+let rec read_bytes ?(pos = 0) ?len fd buf =
+  let len = match len with None -> Bytes.length buf - pos | Some l -> l in
+  let rec inner pos len =
+    if len = 0 then
+      Lwt.return_unit
+    else
+      Lwt_unix.read fd buf pos len >>= fun nb_read ->
+      inner (pos + nb_read) (len - nb_read)
+  in
+  inner pos len
+
+let read_mbytes ?(pos=0) ?len fd buf =
+  let len = match len with None -> MBytes.length buf - pos | Some l -> l in
+  let rec inner pos len =
+    if len = 0 then
+      Lwt.return_unit
+    else
+      Lwt_bytes.read fd buf pos len >>= fun nb_read ->
+      inner (pos + nb_read) (len - nb_read)
+  in
+  inner pos len
+
+let write_mbytes ?(pos=0) ?len descr buf =
+  let len = match len with None -> MBytes.length buf - pos | Some l -> l in
+  let rec inner pos len =
+    if len = 0 then
+      Lwt.return_unit
+    else
+      Lwt_bytes.write descr buf pos len >>= fun nb_written ->
+      inner (pos + nb_written) (len - nb_written) in
+  inner pos len
+
diff --git a/src/utils/lwt_utils.mli b/src/utils/lwt_utils.mli
index b3ddc40fa..96c77b86a 100644
--- a/src/utils/lwt_utils.mli
+++ b/src/utils/lwt_utils.mli
@@ -24,3 +24,12 @@ val worker:
 val trigger: unit -> (unit -> unit) * (unit -> unit Lwt.t)
 val queue: unit -> ('a -> unit) * (unit -> 'a list Lwt.t)
 val sort: ('a -> 'a -> int Lwt.t) -> 'a list -> 'a list Lwt.t
+
+val read_bytes:
+  ?pos:int -> ?len:int -> Lwt_unix.file_descr -> bytes -> unit Lwt.t
+
+val read_mbytes:
+  ?pos:int -> ?len:int -> Lwt_unix.file_descr -> MBytes.t -> unit Lwt.t
+
+val write_mbytes:
+  ?pos:int -> ?len:int -> Lwt_unix.file_descr -> MBytes.t -> unit Lwt.t