(* Compilieren mit:
   ocamlc unix.cma echoserver.ml
   oder
   ocamlopt unix.cmxa echoserver.ml
*)

open Unix
open Printf

let err_mlecho_syntax = "ERROR bad syntax for MLECHO\n"
let err_unknown_cmd = "ERROR unknown command\n"

(* Diese Exception werden nur ausgelöst, wenn weniger geschrieben
   wurde, als beabsichtigt. *)
exception WriteFailure

let readline sd =
  let c = " " in
  let rec loop res =
    if (read sd c 0 1) = 1 then
      if c = "\n"
      then res^c
      else loop (res^c)
    else raise End_of_file
  in
    loop ""

let write_safe sd s =
  let len = String.length s in
    if (write sd s 0 len) < len
    then raise WriteFailure

let strncmp s1 s2 n =
  let s1' = String.sub s1 0 (min n (String.length s1))
  and s2' = String.sub s2 0 (min n (String.length s2)) in
    s1' = s2'

let isdigit c =
  let i = int_of_char c in
    (48 <= i) && (i <= 57)

let atoi c =
  (int_of_char c) - 48

let get_ip sock_addr =
  match sock_addr with
      ADDR_INET (inet_addr, port) ->
        string_of_inet_addr inet_addr
    | _ -> failwith "get_ip"

let main () =
  let sd = socket PF_INET SOCK_STREAM 0 in
    bind sd (ADDR_INET(inet_addr_any, 9000));
    listen sd 5;
    let rec server_loop () =
      let (csd, client_addr) = accept sd in
      let rec client_loop () =
	let cmd = readline csd in
	  if strncmp "ECHO " cmd 5
	  then begin
	    write_safe csd
	      ("REPLY "^(String.sub cmd 5 ((String.length cmd)-5)));
	    client_loop ()
	  end
	  else if strncmp "INFO" cmd 4
	  then begin
	    write_safe csd ("YOURIP "^(get_ip client_addr)^"\n");
	    client_loop ()
	  end
	  else if strncmp "MLECHO " cmd 7
	  then begin
	    if ((String.length cmd) = 10) && isdigit(cmd.[7])
	    then begin
	      let nlines = atoi cmd.[7] in
	      let rec loop n =
		if n = 0
		then []
		else (readline csd)::(loop (n - 1))
	      in
	      let lines = loop nlines in
		write_safe csd (sprintf "MLREPLY %d\n" nlines);
		List.iter (write_safe csd) lines
	    end
	    else write_safe csd err_mlecho_syntax;
	    client_loop ()
	  end
	  else if strncmp "QUIT" cmd 4
	  then begin
	    close csd;
	    server_loop ()
	  end else begin
	    write_safe csd err_unknown_cmd;
	    client_loop ()
	  end
      in
	client_loop ()
    in
      handle_unix_error
	server_loop ()