Very Simple Echo Sever in Erlang

echo_server.erl

-module(echo_server).

-export([start/0,stop/1]).

-define(PORT, 12321).

start() ->
    Options = [binary, {packet, raw}, {active, true}, {reuseaddr, true}],
    case gen_tcp:listen(?PORT, Options) of
        {ok, Listen} -> spawn(fun() -> acceptor_loop(Listen) end),
                        {ok, Listen};
        {error, _} ->
            stop
    end.

stop(Listen) ->
    gen_tcp:close(Listen),
    ok.

acceptor_loop(Listen) ->
    case gen_tcp:accept(Listen) of
        {ok, Client} ->
            Pid = spawn(fun() -> server_loop(Client) end),
            gen_tcp:controlling_process(Client, Pid),
            acceptor_loop(Listen);
        {error, closed} ->
            stop;
        {error, timeout} ->
            io:format("accept failed: timeout~n"),
            stop;
        {error, Reason} ->
            io:format("accept failed: ~p~n", [Reason]),
            stop
    end.

server_loop(Client) ->
    receive
        {tcp, Client, Data} ->
            gen_tcp:send(Client, Data),
            inet:setopts(Client, [{active, once}]),
            server_loop(Client);
        {tcp_closed, _} ->
            ok;
        _ ->
            error
    end.