tcp_echo_server.erl

% simple TCP secho server in Erlang
-module(tcp_echo_server).
-export([run/1]).
-define(TCPOPTS, [binary, {packet,0}, {active,false}, {reuseaddr,true}]).

% Call tcp_echo_server:run(Port) to start the service.
run(Port) ->
  run(Port, {127,0,0,1}).

run(Port, IpAddress) ->
  {ok, LSocket} = gen_tcp:listen(Port, ?TCPOPTS ++ [{ip, IpAddress}]),
  accept(LSocket).

% Wait for incoming connections and spawn the communicate loop
% when we get one.
accept(LSocket) ->
  {ok, Socket} = gen_tcp:accept(LSocket),
  spawn(fun() -> communicate(Socket) end),
  accept(LSocket).

% Echo back whatever data we receive on Socket.
communicate(Socket) ->
  case gen_tcp:recv(Socket, 0) of
    {ok, Data} ->
      gen_tcp:send(Socket, Data),
      communicate(Socket);
    {error, closed} ->
      ok
  end.