gistfile1.erl

-module(echo_server).

-export([handle_event/3, handle_sync_event/4, init/1,
    code_change/4, handle_info/3,
    terminate/3]).

-export([start/0, start_fsm/1, loop/2]).

-define(TCP_OPTIONS, [binary, {packet, 0}, {active, false}, {reuseaddr, true}]).

% echo_server specific code
start() ->
  {ok, Socket} = gen_tcp:listen(7000, ?TCP_OPTIONS),
  accept(Socket).

accept(LSocket) -> 
  {ok, Socket} = gen_tcp:accept(LSocket),
  io:format("New connection incoming, start new FSM ~p~n", [Socket]),
  proc_lib:spawn(?MODULE, start_fsm, [Socket]),
  accept(LSocket).

start_fsm(Socket) ->
  io:format("We gots connection: ~p~n", [Socket]),
  gen_fsm:enter_loop(?MODULE, [], loop, [Socket]).

loop(Event, Socket) ->
  io:format("In loop event ~p ~p~n", [Event, Socket]),
  case gen_tcp:recv(Socket, 0) of
    {ok, Data} ->
      gen_tcp:send(Socket, Data),
      {next_state, loop, Socket};
    {error, closed} ->
      {stop, connection_closed, Socket}
  end.

%%
%% Gen FSM Callbacks
%%
init(Socket) -> 
  io:format("Init! Socket is ~p~n", [Socket]),
  {ok, loop, Socket}.

handle_event(_Event, StateName, StateData) ->
  io:format("handle_event with ~p, ~p, ~p~n", [_Event, StateName, StateData]),
  {next_state, StateName, StateData}.

handle_sync_event(_Event, _From, StateName, StateData) ->
  io:format("handle_sync_event with ~p, ~p, ~p~n", [_Event, StateName, StateData]),
  {next_state, StateName, StateData}.

handle_info(_Info, StateName, StateData) ->
  io:format("handle_info with ~p, ~p, ~p~n", [_Info, StateName, StateData]),
  {next_state, StateName, StateData}.

terminate(Reason, StateName, VideoServer) ->
  io:format("terminate with ~p, ~p, ~p~n", [Reason, StateName, VideoServer]),
  {terminated, Reason}.

code_change(_OldVsn, StateName, StateData, _Extra) ->
  {ok, StateName, StateData}.


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

On run I get:

1> c(echo_server).
{ok,echo_server}
2> echo_server:start().
New connection incoming, start new FSM #Port<0.135>
We gots connection: #Port<0.135>

And that's it. Nothing about the loop 'state'