add close_notify as raw SSL_shutdown

this is needed for sending EOF, aka one-way shutdown.

src/lwt_ssl.ml

@@ -168,6 +168,13 @@ let ssl_shutdown (fd, s) =
 
 let shutdown (fd, _) cmd = Lwt_unix.shutdown fd cmd
 
+let close_notify = function
+  | (_, Plain) as s ->
+      shutdown s Unix.SHUTDOWN_SEND;
+      Lwt.return_true
+  | (fd, SSL s) ->
+      repeat_call fd (fun () -> Ssl.close_notify s)
+
 let close (fd, _) = Lwt_unix.close fd
 
 let abort (fd, _) = Lwt_unix.abort fd

src/lwt_ssl.mli

@@ -74,6 +74,7 @@ val close : socket -> unit Lwt.t
 val in_channel_of_descr : ?buffer:Lwt_bytes.t -> socket -> Lwt_io.input_channel
 val out_channel_of_descr : ?buffer:Lwt_bytes.t -> socket -> Lwt_io.output_channel
 
+val close_notify : socket -> bool Lwt.t
 val ssl_shutdown : socket -> unit Lwt.t
 
 val abort : socket -> exn -> unit