(*  Title:      scgi_echo.ML

     Author:     Timothy Bourke, NICTA

 Simple SCGI server.

 *)

 signature SCGI_SERVER =

 sig

   val max_threads : int Unsynchronized.ref

   type handler = ScgiReq.t * Word8Vector.vector * (string -> unit) -> unit

   val register : (string * Mime.t option * handler) -> unit

   val server : string -> int -> unit

   val server' : int -> string -> int -> unit (* keeps trying for port *)

 end;

 structure ScgiServer : SCGI_SERVER =

 struct

 val max_threads = Unsynchronized.ref 5;

 type handler = ScgiReq.t * Word8Vector.vector * (string -> unit) -> unit;

 local

 val servers = Unsynchronized.ref (Symtab.empty : (Mime.t option * handler) Symtab.table);

 in

 fun register (name, mime, f) =

   Unsynchronized.change servers (Symtab.update_new (name, (mime, f)));

 fun lookup name = Symtab.lookup (!servers) name;

 fun dump_handlers () = (

     tracing("  with handlers:");

     app (fn (x, _) => tracing ("    - " ^ x)) (Symtab.dest (!servers)))

 end;

 fun server server_prefix port =

   let

     val passive_sock = SocketUtil.init_server_socket (SOME "localhost") port;

     val thread_wait = ConditionVar.conditionVar ();

     val thread_wait_mutex = Mutex.mutex ();

     local

     val threads = Unsynchronized.ref ([] : Thread.thread list);

     fun purge () = Unsynchronized.change threads (filter Thread.isActive);

     in

     fun add_thread th = Unsynchronized.change threads (cons th);

     fun launch_thread threadf =

       (purge ();

        if length (!threads) < (!max_threads) then ()

        else (tracing ("Waiting for a free thread...");

              ConditionVar.wait (thread_wait, thread_wait_mutex));

        add_thread

          (Thread.fork

             (fn () => exception_trace threadf,

              [Thread.EnableBroadcastInterrupt true,

               Thread.InterruptState

               Thread.InterruptAsynchOnce])))

     end;

     fun loop () =

       let

         val (sock, _)= Socket.accept passive_sock;

         val (sin, sout) = SocketUtil.make_streams sock;

         fun send msg = BinIO.output (sout, Byte.stringToBytes msg);

         fun send_log msg = (tracing msg; send msg);

         fun get_content (st, 0) = Word8Vector.fromList []

           | get_content x = BinIO.inputN x;

         fun do_req () =

           let

             val (req as ScgiReq.Req {path_info, request_method, ...},

                  content_is) =

               ScgiReq.parse sin

               handle ScgiReq.InvalidReq s =>

                 (send

                    (HttpUtil.reply_header (HttpStatus.bad_request, NONE, []));

                  raise Fail ("Invalid request: " ^ s));

             val () = tracing ("request: " ^ path_info);

           in

             (case lookup (unprefix server_prefix path_info) of

                NONE => send (HttpUtil.reply_header (HttpStatus.not_found, NONE, []))

              | SOME (NONE, f) => f (req, get_content content_is, send)

              | SOME (t, f) =>

                 (send (HttpUtil.reply_header (HttpStatus.ok, t, []));

                  if request_method = ScgiReq.Head then ()

                  else f (req, get_content content_is, send)))

           end;

         fun thread_req () =

           (do_req () handle e => (warning (exnMessage e));

            BinIO.closeOut sout handle e => warning (exnMessage e);

            BinIO.closeIn sin handle e => warning (exnMessage e);

            Socket.close sock handle e => warning (exnMessage e);

            tracing ("request done.");

            ConditionVar.signal thread_wait);

       in

         launch_thread thread_req;

         loop ()

       end;

   in

     tracing ("SCGI server started.");

     dump_handlers ();

     loop ();

     Socket.close passive_sock

   end;

 local

 val delay = 5;

 in

 fun server' 0 server_prefix port = (warning "Giving up."; exit 1)

   | server' countdown server_prefix port =

       server server_prefix port

         handle OS.SysErr ("bind failed", _) =>

           (warning ("Could not acquire port "

                     ^ Int.toString port ^ ". Trying again in "

                     ^ Int.toString delay ^ " seconds...");

            OS.Process.sleep (Time.fromSeconds delay);

            server' (countdown - 1) server_prefix port);

 end;

 end;