echo.erl

-module(echo).
-export([listen/1, accept/1]).
-define(TCP_OPTIONS, [binary, {active, false}]).

listen(Port) ->
    {ok, Socket} = gen_tcp:listen(Port, ?TCP_OPTIONS),
    accept(Socket).

accept(LSocket) ->
    {ok, Socket} = gen_tcp:accept(LSocket),
    spawn(?MODULE, accept, [LSocket]),
    loop(Socket, []).

loop(Socket, BList) ->
    case gen_tcp:recv(Socket, 0) of
        {ok, Data} ->
            loop(Socket, [Data|BList]);
	{error, closed} ->
	    gen_tcp:send(Socket, lists:reverse(BList)),
            ok
    end.