open Unix
let establish_server server_fun sockaddr =
let domain = domain_of_sockaddr in
let sock = Unix.socket domain Unix.SOCK_STREAM 0
in Unix.bind sock sockaddr ;
  Unix.listen sock 3;
  while true do
    let (s, caller) = Unix.accept sock
    in match Unix.fork() with
        0 -> if Unix.fork() <> 0 then exit 0 ;
          let inchan = Unix.in_channel_of_descr s
          and outchan = Unix.out_channel_of_descr s
          in server_fun inchan outchan ;
            close_in inchan ;
            close_out outchan ;
            exit 0
      | id -> Unix.close s; ignore(Unix.waitpid [] id)
  done
;;

let get_my_addr () =
   (Unix.gethostbyname(Unix.gethostname())).Unix.h_addr_list.(0) ;;

let main_server  serv_fun =
   if Array.length Sys.argv < 2 then Printf.eprintf "usage : serv_up port\n"
   else try
          let port =  int_of_string Sys.argv.(1) in
          let my_address = get_my_addr()
          in establish_server serv_fun  (Unix.ADDR_INET(my_address, port))
        with
          Failure("int_of_string") ->
            Printf.eprintf "serv_up : bad port number\n" ;;
let uppercase_service ic oc =
   try while true do
         let s = input_line ic in
         let r = String.uppercase s
         in output_string oc (r^"\n") ; flush oc
       done
   with _ -> Printf.printf "End of text\n" ; flush stdout ; exit 0 ;;

let go_uppercase_service () =
   Unix.handle_unix_error main_server uppercase_service ;;