$ cat server.erl
-module(server).
-compile(export_all).
  
start() ->
    start(1234).
  
start(Port) ->
    register(?MODULE, self()),
  
    spawn_link(fun ()-> S= listen(Port), accept(S) end),
  
    receive Any -> io:format("~p~n", [Any]) end.  %% to stop: test!stop.
  
listen(Port) ->
    Opts = [{active, false},
            binary,
            {backlog, 256},
            {packet, raw},
            {reuseaddr, true}],
    {ok, S} = gen_tcp:listen(Port, Opts),
    S.
  
accept(S) ->
    case gen_tcp:accept(S) of
        {ok, Socket} -> spawn_opt(?MODULE, loop, [Socket,0], []);
        Error    -> erlang:error(Error)
    end,   
    accept(S).
  
loop(S, N) ->
    case gen_tcp:recv(S, 1024) of
        {ok, _Data} ->
        io:format("~p got ~w, ~w~n",[S, size(_Data), N]),
        timer:sleep(100),
            loop(S, N+1);
  
        Error ->
            io:format("tcp ~p~n", [Error]),
            Error
    end.
$ erlc +debug_info server.erl
$ erl
Erlang R14B04 (erts-5.8.5) 1 [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
 
Eshell V5.8.5  (abort with ^G)
1> f(),{ok, {_, [{abstract_code, {_,Abs}}]}} =  beam_lib:chunks("server.beam", [abstract_code]),io:fwrite("~s~n", [erl_prettypr:format(erl_syntax:form_list(Abs))]).
-file("./server.erl", 1).
 
-module(server).
 
-compile(export_all).
 
start() -> start(1234).
 
start(Port) ->
    register(server, self()),
    spawn_link(fun () -> S = listen(Port), accept(S) end),
    receive Any -> io:format("~p~n", [Any]) end.
 
listen(Port) ->
    Opts = [{active, false}, binary, {backlog, 256},
            {packet, raw}, {reuseaddr, true}],
    {ok, S} = gen_tcp:listen(Port, Opts),
    S.
 
accept(S) ->
    case gen_tcp:accept(S) of
      {ok, Socket} ->
          spawn_opt(server, loop, [Socket, 0], []);
      Error -> erlang:error(Error)
    end,
    accept(S).
 
loop(S, N) ->
    case gen_tcp:recv(S, 1024) of
      {ok, _Data} ->
          io:format("~p got ~w, ~w~n", [S, size(_Data), N]),
          timer:sleep(100),
          loop(S, N + 1);
      Error -> io:format("tcp ~p~n", [Error]), Error
    end.
 
 
ok
2>

$ erl
Erlang R14B04 (erts-5.8.5) 1 [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
 
Eshell V5.8.5  (abort with ^G)
1> erts_debug:df(server).
ok
2>
 
$ cat server.dis
0117F108: i_func_info_IaaI 0 server start 0
0117F11C: i_move_call_only_fcr server:start/1 1234 x(0)
 
0117F128: i_func_info_IaaI 0 server start 1
0117F13C: allocate_zero_tt 1 1
0117F144: self_x x(1)
0117F14C: move_ry x(0) y(0)
0117F154: move_cr server x(0)
0117F15C: call_bif2_e erlang:register/2
0117F164: move_yr y(0) x(0)
0117F16C: i_make_fun_It 18102836 1
0117F178: init_y y(0)
0117F180: i_call_ext_e erlang:spawn_link/1
0117F188: i_loop_rec_fr f(0117F1B8) x(0)
0117F190: remove_message
0117F194: test_heap_It 2 1
0117F1A0: put_list_rnx x(0) [] x(1)
0117F1A8: i_move_call_ext_last_ePcr io:format/2 1 "~p~n" x(0)
0117F1B8: wait_locked_f f(0117F188)
 
0117F1C0: i_func_info_IaaI 0 server listen 1
0117F1D4: allocate_tt 0 1
0117F1DC: move_x1_c [{active,false},binary,{backlog,256},{packet,raw},{reuseaddr,true}]
0117F1E4: i_call_ext_e gen_tcp:listen/2
0117F1EC: is_tuple_of_arity_frA f(0117F218) x(0) 2
0117F1F8: extract_next_element2_x x(1)
0117F200: i_is_eq_exact_immed_fxc f(0117F218) x(1) ok
0117F210: move_deallocate_return_xrQ x(2) x(0) 0
0117F218: badmatch_r x(0)
 
0117F21C: i_func_info_IaaI 0 server accept 1
0117F230: allocate_tt 1 1
0117F238: move_ry x(0) y(0)
0117F240: i_call_ext_e gen_tcp:accept/1
0117F248: is_tuple_of_arity_frA f(0117F2AC) x(0) 2
0117F254: extract_next_element2_x x(1)
0117F25C: i_is_eq_exact_immed_fxc f(0117F2AC) x(1) ok
0117F26C: test_heap_It 2 3
0117F278: put_list_xcx x(2) [0] x(2)
0117F284: move_x1_c loop
0117F28C: move_nx [] x(3)
0117F294: i_move_call_ext_cre server x(0) erlang:spawn_opt/4
0117F2A0: move_call_last_yrfQ y(0) x(0) server:accept/1 1
0117F2AC: call_bif1_e erlang:error/1
 
0117F2B4: i_func_info_IaaI 0 server loop 2
0117F2C8: allocate_tt 2 2
0117F2D0: move_xy x(1) y(0)
0117F2D8: move_x1_c 1024
0117F2E0: move_ry x(0) y(1)
0117F2E8: i_call_ext_e gen_tcp:recv/2
0117F2F0: is_tuple_of_arity_frA f(0117F388) x(0) 2
0117F2FC: extract_next_element2_x x(1)
0117F304: i_is_eq_exact_immed_fxc f(0117F388) x(1) ok
0117F314: i_gc_bif1_jIsId j(00000000) 151104 x(2) 3 x(0)
0117F32C: test_heap_It 6 3
0117F338: put_list_ynx y(0) [] x(2)
0117F340: put_list_rxr x(0) x(2) x(0)
0117F348: put_list_yrx y(1) x(0) x(1)
0117F350: i_move_call_ext_cre "~p got ~w, ~w~n" x(0) io:format/2
0117F35C: i_move_call_ext_cre 100 x(0) timer:sleep/1
0117F368: i_increment_yIId y(0) 1 0 x(1)
0117F37C: move_call_last_yrfQ y(1) x(0) server:loop/2 2
0117F388: test_heap_It 2 1
0117F394: move_ry x(0) y(1)
0117F39C: put_list_ynx y(1) [] x(1)
0117F3A4: i_trim_I 1
0117F3AC: i_move_call_ext_cre "tcp ~p~n" x(0) io:format/2
0117F3B8: move_deallocate_return_yrQ y(0) x(0) 1
 
0117F3C0: i_func_info_IaaI 0 server module_info 0
0117F3D4: move_cr server x(0)
0117F3DC: allocate_tt 0 1
0117F3E4: call_bif1_e erlang:get_module_info/1
0117F3EC: deallocate_return_Q 0
 
0117F3F4: i_func_info_IaaI 0 server module_info 1
0117F408: move_rx x(0) x(1)
0117F410: move_cr server x(0)
0117F418: allocate_tt 0 2
0117F420: call_bif2_e erlang:get_module_info/2
0117F428: deallocate_return_Q 0
 
0117F430: i_func_info_IaaI 0 server '-start/1-fun-0-' 1
0117F444: allocate_tt 0 1
0117F44C: i_call_f server:listen/1
0117F454: i_call_last_fP server:accept/1 0