tcp_server.erl

-module(tcp_server).

-behaviour(gen_server).

%% API
-export([start_link/0]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
	 terminate/2, code_change/3]).

-define(SERVER, ?MODULE).

-record(state, {listen_socket}).

%%%===================================================================
%%% API
%%%===================================================================

start_link() ->
    gen_server:start_link({local, ?SERVER}, ?MODULE, [], []).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

init([]) ->
    {ok, Sock} = gen_tcp:listen(12345, [binary, {active, false}]),
    self() ! accept_connection,
    {ok, #state{listen_socket = Sock}}.

handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(accept_connection, #state{listen_socket = Sock} = State) ->
    {ok, _Pid} = tcp_socket:accept_connection(Sock),
    {noreply, State};

handle_info(accept_failed, State) ->
    %% If this process knows by some other means that this happened
    %% because the application is being shutdown, it can terminate
    %% with {stop, normal, State} which will suppress a crash report.
    {stop, accept_failed, State};

handle_info(_Info, State) ->
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

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

%%%===================================================================
%%% Internal functions
%%%===================================================================

tcp_socket.erl

-module(tcp_socket).

-behaviour(gen_server).

%% API
-export([accept_connection/1]).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
	 terminate/2, code_change/3]).

-define(SERVER, ?MODULE).

-record(state, {listener_pid, listen_socket, socket}).

%%%===================================================================
%%% API
%%%===================================================================

accept_connection(Listen_socket) ->
    Listener_pid = self(),
    gen_server:start_link(?MODULE, [Listener_pid, Listen_socket], []).

%%%===================================================================
%%% gen_server callbacks
%%%===================================================================

init([Listener_pid, Listen_socket]) ->
    self() ! do_accept,
    {ok, #state{listener_pid = Listener_pid, listen_socket = Listen_socket}}.

handle_call(_Request, _From, State) ->
    Reply = ok,
    {reply, Reply, State}.

handle_cast(_Msg, State) ->
    {noreply, State}.

handle_info(do_accept, #state{listener_pid = Listener_pid,
			      listen_socket = Listen_socket} = State) ->
    case gen_tcp:accept(Listen_socket) of
	{ok, Socket} ->
	    Listener_pid ! accept_connection,
	    inet:setopts(Socket, [{active, once}]),
	    {noreply, State#state{socket = Socket}};
	_Err ->
	    Listener_pid ! accept_failed,
	    {stop, normal, State}
    end;

handle_info(_Info, State) ->
    {noreply, State}.

terminate(_Reason, _State) ->
    ok.

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

%%%===================================================================
%%% Internal functions
%%%===================================================================