diff --git a/src/node/net/p2p_connection.ml b/src/node/net/p2p_connection.ml
index b00c7619b..b4e439f9d 100644
--- a/src/node/net/p2p_connection.ml
+++ b/src/node/net/p2p_connection.ml
@@ -292,19 +292,18 @@ module Writer = struct
     canceler: Canceler.t ;
     conn: connection ;
     encoding: 'msg Data_encoding.t ;
-    messages: ('msg * unit tzresult Lwt.u option) Lwt_pipe.t ;
+    messages: (MBytes.t * unit tzresult Lwt.u option) Lwt_pipe.t ;
     mutable worker: unit Lwt.t ;
   }
 
   let encode_message st msg =
-    try return (Data_encoding.Binary.to_bytes st.encoding msg)
-    with _ -> fail Encoding_error
+    try ok (Data_encoding.Binary.to_bytes st.encoding msg)
+    with _ -> error Encoding_error
 
   let rec worker_loop st =
     Lwt_unix.yield () >>= fun () ->
     Lwt_utils.protect ~canceler:st.canceler begin fun () ->
-      Lwt_pipe.pop st.messages >>= fun (msg, wakener) ->
-      encode_message st msg >>=? fun buf ->
+      Lwt_pipe.pop st.messages >>= fun (buf, wakener) ->
       lwt_debug "writing %d bytes to %a"
         (MBytes.length buf) Connection_info.pp st.conn.info >>= fun () ->
       Crypto.write_chunk st.conn.fd st.conn.cryptobox_data buf >>= fun res ->
@@ -326,10 +325,8 @@ module Writer = struct
 
   let run ?size conn encoding canceler =
     let compute_size = function
-      | msg, None ->
-          10 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
-      | msg, Some _ ->
-          18 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
+      | buf, None -> Sys.word_size + MBytes.length buf
+      | buf, Some _ -> 2 * Sys.word_size + MBytes.length buf
     in
     let size = map_option size ~f:(fun max -> max, compute_size) in
     let st =
@@ -403,18 +400,28 @@ let catch_closed_pipe f =
 
 let write { writer } msg =
   catch_closed_pipe begin fun () ->
-    Lwt_pipe.push writer.messages (msg, None) >>= return
+    Lwt.return (Writer.encode_message writer msg) >>=? fun buf ->
+    Lwt_pipe.push writer.messages (buf, None) >>= return
   end
 let write_sync { writer } msg =
   catch_closed_pipe begin fun () ->
     let waiter, wakener = Lwt.wait () in
-    Lwt_pipe.push writer.messages (msg, Some wakener) >>= fun () ->
+    Lwt.return (Writer.encode_message writer msg) >>=? fun buf ->
+    Lwt_pipe.push writer.messages (buf, Some wakener) >>= fun () ->
     waiter
   end
 let write_now { writer } msg =
-  try Ok (Lwt_pipe.push_now writer.messages (msg, None))
+  Writer.encode_message writer msg >>? fun buf ->
+  try Ok (Lwt_pipe.push_now writer.messages (buf, None))
   with Lwt_pipe.Closed -> Error [P2p_io_scheduler.Connection_closed]
 
+let raw_write_sync { writer } bytes =
+  catch_closed_pipe begin fun () ->
+    let waiter, wakener = Lwt.wait () in
+    Lwt_pipe.push writer.messages (bytes, Some wakener) >>= fun () ->
+    waiter
+  end
+
 let is_readable { reader } =
   not (Lwt_pipe.is_empty reader.messages)
 let wait_readable { reader } =
diff --git a/src/node/net/p2p_connection.mli b/src/node/net/p2p_connection.mli
index 60aa6dbf5..4ec769413 100644
--- a/src/node/net/p2p_connection.mli
+++ b/src/node/net/p2p_connection.mli
@@ -112,3 +112,8 @@ val stat: 'msg t -> Stat.t
     [conn]. *)
 
 val close: ?wait:bool -> 'msg t -> unit Lwt.t
+
+(**/**)
+
+(** for testing only *)
+val raw_write_sync: 'msg t -> MBytes.t -> unit tzresult Lwt.t
diff --git a/src/node/net/p2p_connection_pool.ml b/src/node/net/p2p_connection_pool.ml
index 61bab5608..ad5abb600 100644
--- a/src/node/net/p2p_connection_pool.ml
+++ b/src/node/net/p2p_connection_pool.ml
@@ -509,6 +509,9 @@ let write { conn } msg =
 let write_sync { conn } msg =
   P2p_connection.write_sync conn (Message msg)
 
+let raw_write_sync { conn } buf =
+  P2p_connection.raw_write_sync conn buf
+
 let write_now { conn } msg =
   P2p_connection.write_now conn (Message msg)
 
diff --git a/src/node/net/p2p_connection_pool.mli b/src/node/net/p2p_connection_pool.mli
index 43d13fafb..ce645156d 100644
--- a/src/node/net/p2p_connection_pool.mli
+++ b/src/node/net/p2p_connection_pool.mli
@@ -253,6 +253,10 @@ val write_sync:  ('msg, 'meta) connection -> 'msg -> unit tzresult Lwt.t
 (** [write_sync conn msg] is [P2p_connection.write_sync conn' msg]
     where [conn'] is the internal [P2p_connection.t] inside [conn]. *)
 
+(**/**)
+val raw_write_sync:  ('msg, 'meta) connection -> MBytes.t -> unit tzresult Lwt.t
+(**/**)
+
 val write_now:  ('msg, 'meta) connection -> 'msg -> bool tzresult
 (** [write_now conn msg] is [P2p_connection.write_now conn' msg] where
     [conn'] is the internal [P2p_connection.t] inside [conn]. *)