Reads by forcing non-blocking on the fd and doesn't explicitly retry on the errors

resource_unavailable.ml

open Lwt
open Lwt_unix

let read fd =
  let maxlen = 1024 in
  let buf = Bytes.create maxlen in
  Lwt.catch
    (fun _ ->
      Lwt_log.info "reading" >>= fun () -> 
      let len = Unix.read (Lwt_unix.unix_file_descr fd) buf 0 maxlen in
      if len = 0 then
        Lwt_log.info "len = 0"
      else
        Lwt_log.info "got some bytes")
    (fun err ->
      match err with
      | Unix.Unix_error (EAGAIN,_,_) ->
         Lwt_log.info (Printf.sprintf "error = EAGAIN")
      | _ ->
         Lwt_log.info (Printf.sprintf "error = _"))

let connect fd =
  ignore(Lwt_unix.connect fd @@ ADDR_INET(Unix.inet_addr_of_string "172.217.195.113", 80));
  read fd >>= fun _ ->
  Lwt.return 0

let () =
  Lwt_log.default :=
    Lwt_log.channel
      ~template:"$(date).$(milliseconds) [$(level)] $(message)"
      ~close_mode:`Keep
      ~channel:Lwt_io.stdout
      ();

  Lwt_log.add_rule "*" Lwt_log.Info;

  Lwt_main.run begin
    let fd = Lwt_unix.socket PF_INET SOCK_STREAM 0 in
    Pervasives.exit (Lwt_main.run (connect fd))
  end