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set_tcp_nodelay absorbs EOPNOTSUPP when not explicitely set #1092

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Merged
raphael-proust merged 1 commit into from
Jan 1, 2026
Merged

set_tcp_nodelay absorbs EOPNOTSUPP when not explicitely set #1092

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19 changes: 15 additions & 4 deletions src/unix/lwt_io.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -1553,7 +1553,18 @@ let close_socket fd =
(fun () ->
Lwt_unix.close fd)

let open_connection ?fd ?(set_tcp_nodelay=true) ?(prepare_fd=ignore) ?in_buffer ?out_buffer sockaddr =
let optionally_set_tcp_nodelay set_tcp_nodelay fd =
match set_tcp_nodelay with
| Some false -> ()
| Some true -> Lwt_unix.setsockopt fd Unix.TCP_NODELAY true
| None ->
(* if not explicitly requested, we attempt to set nodelay but we don't fail in case of error *)
try
Lwt_unix.setsockopt fd Unix.TCP_NODELAY true
with
Unix.Unix_error (Unix.EOPNOTSUPP, _, _) -> ()

let open_connection ?fd ?set_tcp_nodelay ?(prepare_fd=ignore) ?in_buffer ?out_buffer sockaddr =
let fd =
match fd with
| None ->
Expand All @@ -1562,7 +1573,7 @@ let open_connection ?fd ?(set_tcp_nodelay=true) ?(prepare_fd=ignore) ?in_buffer
fd
in

if set_tcp_nodelay then Lwt_unix.setsockopt fd Unix.TCP_NODELAY true;
optionally_set_tcp_nodelay set_tcp_nodelay fd;
prepare_fd fd;

let close = lazy (close_socket fd) in
Expand Down Expand Up @@ -1609,7 +1620,7 @@ let shutdown_server_deprecated server =
let establish_server_generic
bind_function
?fd:preexisting_socket_for_listening
?(set_tcp_nodelay=true)
?set_tcp_nodelay
?(prepare_listening_fd=ignore)
?(prepare_client_fd=ignore)
?(backlog = Lwt_unix.somaxconn () [@ocaml.warning "-3"])
Expand Down Expand Up @@ -1658,7 +1669,7 @@ let establish_server_generic
with Invalid_argument _ -> ()
end;

if set_tcp_nodelay then Lwt_unix.setsockopt client_socket Unix.TCP_NODELAY true;
optionally_set_tcp_nodelay set_tcp_nodelay client_socket;
prepare_client_fd client_socket;
connection_handler_callback client_address client_socket;

Expand Down
5 changes: 4 additions & 1 deletion src/unix/lwt_io.mli
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Expand Up @@ -577,7 +577,7 @@ val open_connection :
Nagle's algorithm (https://en.wikipedia.org/wiki/Nagle%27s_algorithm).
See for example https://brooker.co.za/blog/2024/05/09/nagle.html for why.

The default value is [true].
The default value is to attempt to set [TCP_NODELAY] but ignore [EOPNOTSUPP].

@param prepare_fd is a custom callback that can be used to modify the socket FD
before it is turned into high level channels.
Expand Down Expand Up @@ -695,6 +695,9 @@ val establish_server_with_client_address :
The channels are closed automatically when the promise returned by [f]
resolves. To avoid this behavior, pass [~no_close:true].

See {!open_connection} for more details about [set_tcp_nodelay]
and [prepare_*_fd].

@since 3.1.0 *)

val shutdown_server : server -> unit Lwt.t
Expand Down
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