-module(telnet_server).
-compile(export_all).
%% telnet control characters
-define(SE, 240).
-define(NOP, 241).
-define(DM, 242).
-define(BRK, 243).
-define(IP, 244).
-define(AO, 245).
-define(AYT, 246).
-define(EC, 247).
-define(EL, 248).
-define(GA, 249).
-define(SB, 250).
-define(WILL, 251).
-define(WONT, 252).
-define(DO, 253).
-define(DONT, 254).
-define(IAC, 255).
%% telnet options
-define(BINARY, 0).
-define(ECHO, 1).
-define(SUPPRESS_GO_AHEAD, 3).
-define(TERMINAL_TYPE, 24).
-record(state,
{listen,
client,
users,
authorized=false,
suppress_go_ahead=false,
buffer=[]}).
-type options() :: [{port,pos_integer()} | {users,users()}].
-type users() :: [{user(),password()}].
-type user() :: string().
-type password() :: string().
-spec start(Opts::options()) -> Pid::pid().
start(Opts) when is_list(Opts) ->
spawn_link(fun() -> init(Opts) end).
-spec stop(Pid::pid()) -> ok.
stop(Pid) ->
Ref = erlang:monitor(process,Pid),
Pid ! stop,
receive {'DOWN',Ref,_,_,_} -> ok end.
init(Opts) ->
Port = proplists:get_value(port,Opts),
Users = proplists:get_value(users,Opts,[]),
{ok, LSock} = gen_tcp:listen(Port, [list, {packet, 0},
{active, true}]),
State = #state{listen=LSock,users=Users},
accept(State),
ok = gen_tcp:close(LSock).
accept(#state{listen=LSock}=State) ->
Server = self(),
Acceptor = spawn_link(fun() -> do_accept(LSock,Server) end),
receive
{Acceptor,Sock} when is_port(Sock) ->
case init_client(State#state{client=Sock}) of
stopped ->
io:format("telnet_server stopped\n"),
ok;
R ->
io:format("connection to client closed with reason ~p~n",[R]),
accept(State)
end;
{Acceptor,closed} ->
io:format("listen socket closed unexpectedly, "
"terminating telnet_server\n"),
ok;
stop ->
io:format("telnet_server stopped\n"),
ok
end.
do_accept(LSock,Server) ->
case gen_tcp:accept(LSock) of
{ok, Sock} ->
ok = gen_tcp:controlling_process(Sock,Server),
Server ! {self(),Sock};
{error,closed} ->
%% This will happen when stop/1 is called, since listen
%% socket is closed. Then the server is probably already
%% dead by now, but to be 100% sure not to hang, we send a
%% message to say what happened.
Server ! {self(),closed}
end.
init_client(#state{client=Sock}=State) ->
R = case gen_tcp:send(Sock,"login: ") of
ok ->
loop(State);
Error ->
Error
end,
_ = gen_tcp:close(Sock),
R.
loop(State) ->
receive
{tcp,_,Data} ->
try handle_data(Data,State) of
{ok,State1} ->
loop(State1)
catch
throw:Error ->
Error
end;
{tcp_closed, _} ->
closed;
{tcp_error,_,Error} ->
{error,tcp,Error};
stop ->
stopped
end.
handle_data([?IAC|Cmd],State) ->
dbg("Server got cmd: ~p~n",[Cmd]),
handle_cmd(Cmd,State);
handle_data(Data,State) ->
dbg("Server got data: ~p~n",[Data]),
case get_line(Data,[]) of
{Line,Rest} ->
WholeLine = lists:flatten(lists:reverse(State#state.buffer,Line)),
{ok,State1} = do_handle_data(WholeLine,State),
case Rest of
[] -> {ok,State1};
_ -> handle_data(Rest,State1)
end;
false ->
{ok,State#state{buffer=[Data|State#state.buffer]}}
end.
%% Add function clause below to handle new telnet commands (sent with
%% ?IAC from client - this is not possible to do from ct_telnet API,
%% but ct_telnet sends DONT SUPPRESS_GO_AHEAD)
handle_cmd([?DO,?SUPPRESS_GO_AHEAD|T],State) ->
send([?IAC,?WILL,?SUPPRESS_GO_AHEAD],State),
handle_cmd(T,State#state{suppress_go_ahead=true});
handle_cmd([?DONT,?SUPPRESS_GO_AHEAD|T],State) ->
send([?IAC,?WONT,?SUPPRESS_GO_AHEAD],State),
handle_cmd(T,State#state{suppress_go_ahead=false});
handle_cmd([?IAC|T],State) ->
%% Multiple commands in one packet
handle_cmd(T,State);
handle_cmd([_H|T],State) ->
%% Not responding to this command
handle_cmd(T,State);
handle_cmd([],State) ->
{ok,State}.
%% Add function clause below to handle new text command (text entered
%% from the telnet prompt)
do_handle_data(Data,#state{authorized=false}=State) ->
check_user(Data,State);
do_handle_data(Data,#state{authorized={user,_}}=State) ->
check_pwd(Data,State);
do_handle_data("echo "++ Data,State) ->
send(Data++"\r\n> ",State),
{ok,State};
do_handle_data("repeat "++ Data,State) ->
send(Data++"\r\n"++Data++"\r\n> ",State),
{ok,State};
do_handle_data([],State) ->
send("> ",State),
{ok,State};
do_handle_data(_Data,State) ->
send("error: unknown command\r\n> ",State),
{ok,State}.
check_user(User,State) ->
case lists:keyfind(User,1,State#state.users) of
{User,Pwd} ->
dbg("user ok\n"),
send("Password: ",State),
{ok,State#state{authorized={user,Pwd}}};
false ->
throw({error,unknown_user})
end.
check_pwd(Pwd,#state{authorized={user,Pwd}}=State) ->
dbg("password ok\n"),
send("Welcome to the ultimate telnet server!\r\n> ",State),
{ok,State#state{authorized=true}};
check_pwd(_,_State) ->
throw({error,authentication}).
send(Data,State) ->
dbg("Server sending: ~p~n",[Data]),
case gen_tcp:send(State#state.client,Data) of
ok ->
ok;
{error,Error} ->
throw({error,send,Error})
end.
get_line([$\r,$\n|Rest],Acc) ->
{lists:reverse(Acc),Rest};
get_line([$\r,0|Rest],Acc) ->
{lists:reverse(Acc),Rest};
get_line([$\n|Rest],Acc) ->
{lists:reverse(Acc),Rest};
get_line([H|T],Acc) ->
get_line(T,[H|Acc]);
get_line([],_) ->
false.
dbg(_F) ->
io:format(_F).
dbg(_F,_A) ->
io:format(_F,_A).
