Mirage test that sends one byte to TCP endpoint (10.0.0.1/7001), with tracing on

config.ml

open Mirage

let main = foreign "Unikernel.Main" (stackv4 @-> job)

let stack console =
  match get_mode () with
  | `Xen -> direct_stackv4_with_default_ipv4 console tap0
  | `Unix -> assert false

let tracing = mprof_trace ~size:1000000 ()

let () =
  register "bench" ~tracing [
    main $ stack default_console;
  ]

unikernel.ml

open Lwt

let laptop_ip = Ipaddr.V4.of_string_exn "10.0.0.1"

let () =
  let open Tcp in
  [Pcb.info; Pcb.debug; State.debug] |> List.iter (fun log ->
    Log.enable log;
    Log.set_stats log false
  )

let () =
  Lwt.async_exception_hook := fun ex -> Printf.eprintf "Uncaught exception: %s\n%!" (Printexc.to_string ex)

module Main (S: V1_LWT.STACKV4) = struct
  let buffer = Io_page.get 1 |> Io_page.to_cstruct

  let start s =
    let t = S.tcpv4 s in

    match_lwt S.TCPV4.create_connection t (laptop_ip, 7001) with
    | `Error _err -> failwith "TCP error 7001"
    | `Ok flow ->
    
    let payload = Cstruct.sub buffer 0 1 in
    Cstruct.set_char payload 0 '!';

    match_lwt S.TCPV4.write flow payload with
    | `Error _ | `Eof -> assert false
    | `Ok () ->

    S.TCPV4.close flow >>= fun () ->
    OS.Time.sleep 10.0
end

Perfect, thanks; I was just recreating something from the snippet you put in the issue but I'll grab this and give it a try instead.