Question

我正在尝试更好地编写一个小型Lwt（和电池）端口扫描仪了解Lwt然而，每当我尝试扫描时，我都会遇到一个奇怪的异常 scan_ports_range一次有太多端口。我怀疑我的机制保持最大连接数打开不起作用...

Exception: Unix.Unix_error (Batteries.Unix.EMFILE, "socket",""). Fatal error: exception Sys_error("/home/(censored)/.opam/4.00.1/lib/utop: Too many open files") （这也崩溃utop btw）

代码如下。要触发错误评估： scan_ports_range ~host:"127.0.0.1" (1000,2000)

对我的lwt风格的任何批评/建议也是受欢迎的，因为我已经才开始学习它。

open Lwt

let addr_parts addr = 
  let (host, port) = String.split addr ":" in (host, int_of_string port)

let addr ~host ~port = 
  lwt entry = Lwt_unix.gethostbyname host in
  if Array.length entry.Unix.h_addr_list = 0 then begin
    failwith (Printf.sprintf "no address found for host %S\n" host)
  end;
  return (Unix.ADDR_INET (entry.Unix.h_addr_list.(0), port))

let test_connection ?(timeout=1.0) addr = 
  let fd = Lwt_unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
  let connect_close = 
    (Lwt_unix.connect fd addr) >>= (fun () -> Lwt_unix.close fd)  in
  try_lwt
    (pick [connect_close ; Lwt_unix.timeout timeout])
    >>= (fun () -> return true)
  with _ -> return false

let scan_ports ~host ~ports =
  ports |> Lwt_list.map_p (fun port ->
        lwt adr = addr ~host ~port in
        test_connection adr >>= (fun res -> return (res,port)) )
    >>= (fun l -> return ( l |> List.filter_map ( function
      | false, _ -> None | true, port -> Some(port) ) ) )

let scan_ports_range ?(max_open=20) ~host (a, b) =
  let rec loop acc enum = 
    match Enum.peek enum with
    | None -> acc |> List.concat |> List.rev |> return
    | Some _ -> 
        let ports = enum |> Enum.take max_open |> List.of_enum in
        let open_ports = scan_ports ~host ~ports in
        open_ports >>= (fun l -> loop (l::acc) enum )
  in loop [] (a--b)

Answer 1

作为一个疯狂的猜测，我认为你需要在超时的情况下强制关闭套接字，因此剔除可能是：

pick [connect_close ; Lwt_unix.timeout timeout]

Answer 2

根据Thomas的说法，这是更正后的代码。

let test_connection ?(timeout=1.0) addr = 
  let fd = Lwt_unix.socket Unix.PF_INET Unix.SOCK_STREAM 0 in
  let connect_close = 
    (Lwt_unix.connect fd addr) >>= (fun () -> Lwt_unix.close fd)  in
  try_lwt
    (pick [connect_close ; Lwt_unix.timeout timeout])
    >>= (fun () -> return true)
  with _ -> (Lwt_unix.close fd) >>= (fun () -> return false)

小Lwt端口扫描仪不工作

2 个答案: