UDP server and client for factorial function.

udp_test.erl

%% udp test client and server, from joe armstrong's "programming erlang, second
%% edition"
-module(udp_test).
-export([start_server/0, client/1]).

start_server() ->
    spawn(fun() -> server(4000) end).

%% the server
server(port) ->
    {ok, socket} = gen_udp:open(port, [binary]),
    io:format("server opened socket: ~p~n", [socket]),
    loop(socket).

loop(socket) ->
    receive
       {udp, socket, host, port, bin} = msg ->
            io:format("server received: ~p~n", [msg]),
            n = binary_to_term(bin),
            fac = fac(n),
            gen_udp:send(socket, host, port, term_to_binary(fac)),
            loop(socket)
    end.

fac(0) ->
    1;
fac(n) ->
    n * fac(n - 1).

%% the client
client(n) ->
    {ok, socket} = gen_udp:open(0, [binary]),
    io:format("client opened socket = ~p~n", [socket]),
    ok = gen_udp:send(socket, "localhost", 4000,
                      term_to_binary(n)),
    value = receive
               {udp, socket, _, _, bin} = msg ->
                    io:format("client received: ~p~n", [msg]),
                    binary_to_term(bin)
            after 2000 ->
                    0
            end,
    gen_udp:close(socket),
    value.