Shell: fix unhandled exception in io_scheduler.

src/node/net/p2p_connection.ml

@@ -236,21 +236,25 @@ module Reader = struct
       let size = 6 * (Sys.word_size / 8) + MBytes.length buf in
       lwt_debug "reading %d bytes from %a"
         size Connection_info.pp st.conn.info >>= fun () ->
-      read_message st buf >>|? fun msg ->
-      size, msg
-    end >>= function
-    | Ok (_, None) ->
+      read_message st buf >>=? fun msg ->
+      match msg with
+      | None ->
           Lwt_pipe.push st.messages (Error [Decoding_error]) >>= fun () ->
-        worker_loop st
-    | Ok (size, Some msg) ->
+          return false
+      | Some msg ->
           Lwt_pipe.push st.messages (Ok (size, msg)) >>= fun () ->
+          return true
+    end >>= function
+    | Ok true ->
         worker_loop st
+    | Ok false ->
+        Lwt.return_unit
     | Error [Lwt_utils.Canceled | Exn Lwt_pipe.Closed] ->
       lwt_debug "connection closed to %a"
         Connection_info.pp st.conn.info >>= fun () ->
         Lwt.return_unit
     | Error _ as err ->
-        Lwt_pipe.push st.messages err >>= fun () ->
+        Lwt_pipe.safe_push_now st.messages err ;
         Canceler.cancel st.canceler >>= fun () ->
         Lwt.return_unit
 

src/utils/lwt_pipe.ml

@@ -108,6 +108,10 @@ exception Full
 let push_now_exn q elt =
   if not (push_now q elt) then raise Full
 
+let safe_push_now q elt =
+  try push_now_exn q elt
+  with _ -> ()
+
 let rec pop ({ closed ; queue ; empty ; current_size } as q) =
   if not (Queue.is_empty queue) then
     let (elt_size, elt) = Queue.pop queue in

src/utils/lwt_pipe.mli

@@ -45,6 +45,10 @@ val push_now_exn : 'a t -> 'a -> unit
 (** [push_now q v] adds [v] at the ends of [q] immediately or
     raise [Full] if [q] is currently full. *)
 
+val safe_push_now : 'a t -> 'a -> unit
+(** [safe_push_now q v] may adds [v] at the ends of [q]. It does
+    nothing if the queue is fulled or closed. *)
+
 val pop_now : 'a t -> 'a option
 (** [pop_now q] maybe removes and returns the first element in [q] if
     [q] contains at least one element. *)