aboutsummaryrefslogtreecommitdiffstats
path: root/lib/diameter/src/transport/diameter_tcp.erl
blob: b68a16b5215bc91f23c1a4880c859c7fff123acd (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2010-2016. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%

-module(diameter_tcp).

-behaviour(gen_server).

%% interface
-export([start/3]).

%% child start from supervisor
-export([start_link/1]).

%% child start from here
-export([init/1]).

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

-export([listener/1,%% diameter_sync callback
         info/1]).  %% service_info callback

-export([ports/0,
         ports/1]).

-export_type([connect_option/0,
              listen_option/0]).

-include_lib("diameter/include/diameter.hrl").

%% Keys into process dictionary.
-define(INFO_KEY, info).
-define(REF_KEY,  ref).

-define(ERROR(T), erlang:error({T, ?MODULE, ?LINE})).

-define(DEFAULT_PORT, 3868).  %% RFC 3588, ch 2.1
-define(LISTENER_TIMEOUT, 30000).
-define(DEFAULT_FRAGMENT_TIMEOUT, 1000).

-define(IS_UINT32(N), (is_integer(N) andalso 0 =< N andalso 0 == N bsr 32)).
-define(IS_TIMEOUT(N), (infinity == N orelse ?IS_UINT32(N))).

%% cb_info passed to ssl.
-define(TCP_CB(Mod), {Mod, tcp, tcp_closed, tcp_error}).

%% The same gen_server implementation supports three different kinds
%% of processes: an actual transport process, one that will club it to
%% death should the parent die before a connection is established, and
%% a process owning the listening port.

%% Listener process state.
-record(listener, {socket    :: inet:socket(),
                   count = 1 :: non_neg_integer(),
                   tref      :: reference()}).

%% Monitor process state.
-record(monitor,
        {parent             :: pid(),
         transport = self() :: pid()}).

-type length() :: 0..16#FFFFFF. %% message length from Diameter header
-type size()   :: non_neg_integer().  %% accumulated binary size
-type frag()   :: {length(), size(), binary(), list(binary())}
                | binary().

-type connect_option() :: {raddr, inet:ip_address()}
                        | {rport, pos_integer()}
                        | {ssl_options, true | [ssl:connect_option()]}
                        | option()
                        | ssl:connect_option()
                        | gen_tcp:connect_option().

-type match() :: inet:ip_address()
               | string()
               | [match()].

-type listen_option() :: {accept, match()}
                       | {ssl_options, true | [ssl:listen_option()]}
                       | ssl:listen_option()
                       | gen_tcp:listen_option().

-type option() :: {port, non_neg_integer()}
                | {fragment_timer, 0..16#FFFFFFFF}
                | {throttle_cb, diameter:evaluable()}.

%% Accepting/connecting transport process state.
-record(transport,
        {socket  :: inet:socket() | ssl:sslsocket(), %% accept/connect socket
         parent  :: pid(),          %% of process that started us
         module  :: module(),       %% gen_tcp-like module
         frag = <<>> :: frag(),     %% message fragment
         ssl     :: boolean() | [term()],       %% ssl options
         timeout :: infinity | 0..16#FFFFFFFF,  %% fragment timeout
         tref = false  :: false | reference(),  %% fragment timer reference
         flush = false :: boolean(),            %% flush fragment at timeout?
         throttle_cb :: false | diameter:evaluable(), %% ask to receive
         throttled :: boolean() | binary()}).   %% stopped receiving?

%% The usual transport using gen_tcp can be replaced by anything
%% sufficiently gen_tcp-like by passing a 'module' option as the first
%% (for simplicity) transport option. The transport_module diameter_etcp
%% uses this to set itself as the module to call, its start/3 just
%% calling start/3 here with the option set.

%% ---------------------------------------------------------------------------
%% # start/3
%% ---------------------------------------------------------------------------

-spec start({accept, Ref}, #diameter_service{}, [listen_option()])
   -> {ok, pid(), [inet:ip_address()]}
 when Ref :: diameter:transport_ref();
           ({connect, Ref}, #diameter_service{}, [connect_option()])
   -> {ok, pid(), [inet:ip_address()]}
    | {ok, pid()}
 when Ref :: diameter:transport_ref().

start({T, Ref}, #diameter_service{capabilities = Caps}, Opts) ->
    diameter_tcp_sup:start(),  %% start tcp supervisors on demand
    {Mod, Rest} = split(Opts),
    Addrs = Caps#diameter_caps.host_ip_address,
    Arg = {T, Ref, Mod, self(), Rest, Addrs},
    diameter_tcp_sup:start_child(Arg).

split([{module, M} | Opts]) ->
    {M, Opts};
split(Opts) ->
    {gen_tcp, Opts}.

%% start_link/1

start_link(T) ->
    proc_lib:start_link(?MODULE,
                        init,
                        [T],
                        infinity,
                        diameter_lib:spawn_opts(server, [])).

%% ---------------------------------------------------------------------------
%% # info/1
%% ---------------------------------------------------------------------------

info({Mod, Sock}) ->
    lists:flatmap(fun(K) -> info(Mod, K, Sock) end,
                  [{socket, fun sockname/2},
                   {peer, fun peername/2},
                   {statistics, fun getstat/2}
                   | ssl_info(Mod, Sock)]).

info(Mod, {K,F}, Sock) ->
    case F(Mod, Sock) of
        {ok, V} ->
            [{K,V}];
        _ ->
            []
    end.

ssl_info(ssl = M, Sock) ->
    [{M, ssl_info(Sock)}];
ssl_info(_, _) ->
    [].

ssl_info(Sock) ->
    [{peercert, C} || {ok, C} <- [ssl:peercert(Sock)]].

%% ---------------------------------------------------------------------------
%% # init/1
%% ---------------------------------------------------------------------------

init(T) ->
    gen_server:enter_loop(?MODULE, [], i(T)).

%% i/1

%% A transport process.
i({T, Ref, Mod, Pid, Opts, Addrs})
  when T == accept;
       T == connect ->
    monitor(process, Pid),
    %% Since accept/connect might block indefinitely, spawn a process
    %% that does nothing but kill us with the parent until call
    %% returns.
    {ok, MPid} = diameter_tcp_sup:start_child(#monitor{parent = Pid}),
    {[SO|TO], Rest} = proplists:split(Opts, [ssl_options,
                                             fragment_timer,
                                             throttle_cb]),
    SslOpts = ssl_opts(SO),
    OwnOpts = lists:append(TO),
    Tmo = proplists:get_value(fragment_timer,
                              OwnOpts,
                              ?DEFAULT_FRAGMENT_TIMEOUT),
    ?IS_TIMEOUT(Tmo) orelse ?ERROR({fragment_timer, Tmo}),
    Throttle = proplists:get_value(throttle_cb, OwnOpts, false),
    Sock = init(T, Ref, Mod, Pid, SslOpts, Rest, Addrs),
    MPid ! {stop, self()},  %% tell the monitor to die
    M = if SslOpts -> ssl; true -> Mod end,
    putr(?REF_KEY, Ref),
    throttle(#transport{parent = Pid,
                        module = M,
                        socket = Sock,
                        ssl = SslOpts,
                        timeout = Tmo,
                        throttle_cb = Throttle,
                        throttled = false /= Throttle});
%% Put the reference in the process dictionary since we now use it
%% advertise the ssl socket after TLS upgrade.

%% A monitor process to kill the transport if the parent dies.
i(#monitor{parent = Pid, transport = TPid} = S) ->
    proc_lib:init_ack({ok, self()}),
    monitor(process, Pid),
    monitor(process, TPid),
    S;
%% In principle a link between the transport and killer processes
%% could do the same thing: have the accepting/connecting process be
%% killed when the killer process dies as a consequence of parent
%% death. However, a link can be unlinked and this is exactly what
%% gen_tcp seems to so. Links should be left to supervisors.

i({listen, LRef, APid, {Mod, Opts, Addrs}}) ->
    {[LA, LP], Rest} = proplists:split(Opts, [ip, port]),
    LAddrOpt = get_addr(LA, Addrs),
    LPort = get_port(LP),
    {ok, LSock} = Mod:listen(LPort, gen_opts(LAddrOpt, Rest)),
    LAddr = laddr(LAddrOpt, Mod, LSock),
    true = diameter_reg:add_new({?MODULE, listener, {LRef, {LAddr, LSock}}}),
    proc_lib:init_ack({ok, self(), {LAddr, LSock}}),
    monitor(process, APid),
    start_timer(#listener{socket = LSock}).

laddr([], Mod, Sock) ->
    {ok, {Addr, _Port}} = sockname(Mod, Sock),
    Addr;
laddr([{ip, Addr}], _, _) ->
    Addr.

ssl_opts([]) ->
    false;
ssl_opts([{ssl_options, true}]) ->
    true;
ssl_opts([{ssl_options, Opts}])
  when is_list(Opts) ->
    Opts;
ssl_opts(T) ->
    ?ERROR({ssl_options, T}).

%% init/7

%% Establish a TLS connection before capabilities exchange ...
init(Type, Ref, Mod, Pid, true, Opts, Addrs) ->
    init(Type, Ref, ssl, Pid, [{cb_info, ?TCP_CB(Mod)} | Opts], Addrs);

%% ... or not.
init(Type, Ref, Mod, Pid, _, Opts, Addrs) ->
    init(Type, Ref, Mod, Pid, Opts, Addrs).

%% init/6

init(accept = T, Ref, Mod, Pid, Opts, Addrs) ->
    {[Matches], Rest} = proplists:split(Opts, [accept]),
    {LAddr, LSock} = listener(Ref, {Mod, Rest, Addrs}),
    proc_lib:init_ack({ok, self(), [LAddr]}),
    Sock = ok(accept(Mod, LSock)),
    ok = accept_peer(Mod, Sock, accept(Matches)),
    publish(Mod, T, Ref, Sock),
    diameter_peer:up(Pid),
    Sock;

init(connect = T, Ref, Mod, Pid, Opts, Addrs) ->
    {[LA, RA, RP], Rest} = proplists:split(Opts, [ip, raddr, rport]),
    LAddrOpt = get_addr(LA, Addrs),
    RAddr = get_addr(RA),
    RPort = get_port(RP),
    proc_lib:init_ack(init_rc(LAddrOpt)),
    Sock = ok(connect(Mod, RAddr, RPort, gen_opts(LAddrOpt, Rest))),
    publish(Mod, T, Ref, Sock),
    up(Pid, {RAddr, RPort}, LAddrOpt, Mod, Sock),
    Sock.

init_rc([{ip, Addr}]) ->
    {ok, self(), [Addr]};
init_rc([]) ->
    {ok, self()}.

up(Pid, Remote, [{ip, _Addr}], _, _) ->
    diameter_peer:up(Pid, Remote);
up(Pid, Remote, [], Mod, Sock) ->
    {Addr, _Port} = ok(sockname(Mod, Sock)),
    diameter_peer:up(Pid, Remote, [Addr]).

publish(Mod, T, Ref, Sock) ->
    true = diameter_reg:add_new({?MODULE, T, {Ref, Sock}}),
    putr(?INFO_KEY, {Mod, Sock}).  %% for info/1

ok({ok, T}) ->
    T;
ok(No) ->
    x(No).

x(Reason) ->
    exit({shutdown, Reason}).

%% accept_peer/3

accept_peer(_Mod, _Sock, []) ->
    ok;

accept_peer(Mod, Sock, Matches) ->
    {RAddr, _} = ok(peername(Mod, Sock)),
    diameter_peer:match([RAddr], Matches)
        orelse x({accept, RAddr, Matches}),
    ok.

%% accept/1

accept(Opts) ->
    [[M] || {accept, M} <- Opts].

%% listener/2

%% Accepting processes can be started concurrently: ensure only one
%% listener is started.
listener(LRef, T) ->
    diameter_sync:call({?MODULE, listener, LRef},
                       {?MODULE, listener, [{LRef, T, self()}]},
                       infinity,
                       infinity).

listener({LRef, T, TPid}) ->
    l(diameter_reg:match({?MODULE, listener, {LRef, '_'}}), LRef, T, TPid).

%% Existing listening process ...
l([{{?MODULE, listener, {_, AS}}, LPid}], _, _, TPid) ->
    LPid ! {accept, TPid},
    AS;

%% ... or not.
l([], LRef, T, TPid) ->
    {ok, _, AS} = diameter_tcp_sup:start_child({listen, LRef, TPid, T}),
    AS.

%% get_addr/1

get_addr(As) ->
    diameter_lib:ipaddr(addr(As, [])).

%% get_addr/2

get_addr([], []) ->
    [];
get_addr(As, Def) ->
    [{ip, diameter_lib:ipaddr(addr(As, Def))}].

%% Take the first address from the service if several are unspecified.
addr([], [Addr | _]) ->
    Addr;
addr([{_, Addr}], _) ->
    Addr;
addr(As, Addrs) ->
    ?ERROR({invalid_addrs, As, Addrs}).

%% get_port/1

get_port([{_, Port}]) ->
    Port;
get_port([]) ->
    ?DEFAULT_PORT;
get_port(Ps) ->
    ?ERROR({invalid_ports, Ps}).

%% gen_opts/2

gen_opts(LAddrOpt, Opts) ->
    {L,_} = proplists:split(Opts, [binary, packet, active]),
    [[],[],[]] == L orelse ?ERROR({reserved_options, Opts}),
    [binary, {packet, 0}, {active, false}] ++ LAddrOpt ++ Opts.

%% ---------------------------------------------------------------------------
%% # ports/1
%% ---------------------------------------------------------------------------

ports() ->
    Ts = diameter_reg:match({?MODULE, '_', '_'}),
    [{type(T), resolve(T,S), Pid} || {{?MODULE, T, {_,S}}, Pid} <- Ts].

ports(Ref) ->
    Ts = diameter_reg:match({?MODULE, '_', {Ref, '_'}}),
    [{type(T), resolve(T,S), Pid} || {{?MODULE, T, {R,S}}, Pid} <- Ts,
                                     R == Ref].

type(listener) ->
    listen;
type(T) ->
    T.

sock(listener, {_LAddr, Sock}) ->
    Sock;
sock(_, Sock) ->
    Sock.

resolve(Type, S) ->
    Sock = sock(Type, S),
    try
        ok(portnr(Sock))
    catch
        _:_ -> Sock
    end.

portnr(Sock)
  when is_port(Sock) ->
    portnr(gen_tcp, Sock);
portnr(Sock) ->
    portnr(ssl, Sock).

%% ---------------------------------------------------------------------------
%% # handle_call/3
%% ---------------------------------------------------------------------------

handle_call(_, _, State) ->
    {reply, nok, State}.

%% ---------------------------------------------------------------------------
%% # handle_cast/2
%% ---------------------------------------------------------------------------

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

%% ---------------------------------------------------------------------------
%% # handle_info/2
%% ---------------------------------------------------------------------------

handle_info(T, #transport{} = S) ->
    {noreply, #transport{} = t(T,S)};

handle_info(T, #listener{} = S) ->
    {noreply, #listener{} = l(T,S)};

handle_info(T, #monitor{} = S) ->
    m(T,S),
    x(T).

%% ---------------------------------------------------------------------------
%% # code_change/3
%% ---------------------------------------------------------------------------

code_change(_, State, _) ->
    {ok, State}.

%% ---------------------------------------------------------------------------
%% # terminate/2
%% ---------------------------------------------------------------------------

terminate(_, _) ->
    ok.

%% ---------------------------------------------------------------------------

putr(Key, Val) ->
    put({?MODULE, Key}, Val).

getr(Key) ->
    get({?MODULE, Key}).

%% start_timer/1

start_timer(#listener{count = 0} = S) ->
    S#listener{tref = erlang:start_timer(?LISTENER_TIMEOUT, self(), close)};
start_timer(S) ->
    S.

%% m/2
%%
%% Transition monitor state.

%% Transport is telling us to die.
m({stop, TPid}, #monitor{transport = TPid}) ->
    ok;

%% Transport has died.
m({'DOWN', _, process, TPid, _}, #monitor{transport = TPid}) ->
    ok;

%% Transport parent has died.
m({'DOWN', _, process, Pid, _}, #monitor{parent = Pid,
                                         transport = TPid}) ->
    exit(TPid, {shutdown, parent}).

%% l/2
%%
%% Transition listener state.

%% Another accept transport is attaching.
l({accept, TPid}, #listener{count = N} = S) ->
    monitor(process, TPid),
    S#listener{count = N+1};

%% Accepting process has died.
l({'DOWN', _, process, _, _}, #listener{count = N} = S) ->
    start_timer(S#listener{count = N-1});

%% Timeout after the last accepting process has died.
l({timeout, TRef, close = T}, #listener{tref = TRef,
                                        count = 0}) ->
    x(T);
l({timeout, _, close}, #listener{} = S) ->
    S.

%% t/2
%%
%% Transition transport state.

t(T,S) ->
    case transition(T,S) of
        ok ->
            S;
        #transport{} = NS ->
            NS;
        {stop, Reason} ->
            x(Reason);
        stop ->
            x(T)
    end.

%% transition/2

%% Initial incoming message when we might need to upgrade to TLS:
%% don't receive another message until we know.
transition({tcp, Sock, Bin}, #transport{socket = Sock,
                                        parent = Pid,
                                        frag = Head,
                                        ssl = Opts}
                             = S)
  when is_list(Opts) ->
    case rcv(Head, Bin) of
        {Msg, B} ->
            diameter_peer:recv(Pid, Msg),
            S#transport{frag = B};
        Frag ->
            setopts(S),
            start_fragment_timer(S#transport{frag = Frag})
    end;

%% Incoming message.
transition({P, Sock, Bin}, #transport{socket = Sock,
                                      ssl = B,
                                      throttled = T}
                           = S)
  when P == tcp, not B;
       P == ssl, B ->
    false = T,  %% assert
    recv(Bin, S);

%% Make a new throttling callback after a timeout.
transition(throttle, #transport{throttled = B} = S) ->
    true = false /= B,  %% assert
    throttle(S);

%% Capabilties exchange has decided on whether or not to run over TLS.
transition({diameter, {tls, Ref, Type, B}}, #transport{parent = Pid}
                                            = S) ->
    #transport{}
        = NS
        = tls_handshake(Type, B, S),
    Pid ! {diameter, {tls, Ref}},
    throttle(NS#transport{ssl = B});

transition({C, Sock}, #transport{socket = Sock,
                                 ssl = B})
  when C == tcp_closed, not B;
       C == ssl_closed, B ->
    stop;

transition({E, Sock, _Reason} = T, #transport{socket = Sock,
                                              ssl = B}
                                   = S)
  when E == tcp_error, not B;
       E == ssl_error, B ->
    ?ERROR({T,S});

%% Outgoing message.
transition({diameter, {send, Bin}}, #transport{socket = Sock,
                                               module = M}) ->
    case send(M, Sock, Bin) of
        ok ->
            ok;
        {error, Reason} ->
            {stop, {send, Reason}}
    end;

%% Request to close the transport connection.
transition({diameter, {close, Pid}}, #transport{parent = Pid,
                                                socket = Sock,
                                                module = M}) ->
    M:close(Sock),
    stop;

%% Timeout for reception of outstanding packets.
transition({timeout, TRef, flush}, #transport{tref = TRef} = S) ->
    flush(S#transport{tref = false});

%% Request for the local port number.
transition({resolve_port, Pid}, #transport{socket = Sock,
                                           module = M})
  when is_pid(Pid) ->
    Pid ! portnr(M, Sock),
    ok;

%% Parent process has died.
transition({'DOWN', _, process, Pid, _}, #transport{parent = Pid}) ->
    stop.

%% Crash on anything unexpected.

%% tls_handshake/3
%%
%% In the case that no tls message is received (eg. the service hasn't
%% been configured to advertise TLS support) we will simply never ask
%% for another TCP message, which will force the watchdog to
%% eventually take us down.

%% TLS has already been established with the connection.
tls_handshake(_, _, #transport{ssl = true} = S) ->
    S;

%% Capabilities exchange negotiated TLS but transport was not
%% configured with an options list.
tls_handshake(_, true, #transport{ssl = false}) ->
    ?ERROR(no_ssl_options);

%% Capabilities exchange negotiated TLS: upgrade the connection.
tls_handshake(Type, true, #transport{socket = Sock,
                                     module = M,
                                     ssl = Opts}
                          = S) ->
    {ok, SSock} = tls(Type, Sock, [{cb_info, ?TCP_CB(M)} | Opts]),
    Ref = getr(?REF_KEY),
    true = diameter_reg:add_new({?MODULE, Type, {Ref, SSock}}),
    S#transport{socket = SSock,
                module = ssl};

%% Capabilities exchange has not negotiated TLS.
tls_handshake(_, false, S) ->
    S.

tls(connect, Sock, Opts) ->
    ssl:connect(Sock, Opts);
tls(accept, Sock, Opts) ->
    ssl:ssl_accept(Sock, Opts).

%% recv/2
%%
%% Reassemble fragmented messages and extract multiple message sent
%% using Nagle.

%% Receive packets until a full message is received, then check
%% whether to keep receiving.
recv(Bin, #transport{frag = Head, throttled = false} = S) ->
    case rcv(Head, Bin) of
        {Msg, B} ->
            throttle(S#transport{frag = B, throttled = Msg});
        Frag ->
            setopts(S),
            start_fragment_timer(S#transport{frag = Frag,
                                             flush = false})
    end.

%% recv/1

recv(S) ->
    recv(<<>>, S).

%% rcv/2

%% No previous fragment.
rcv(<<>>, Bin) ->
    rcv(Bin);

%% Not even the first four bytes of the header.
rcv(Head, Bin)
  when is_binary(Head) ->
    rcv(<<Head/binary, Bin/binary>>);

%% Or enough to know how many bytes to extract.
rcv({Len, N, Head, Acc}, Bin) ->
    rcv(Len, N + size(Bin), Head, [Bin | Acc]).

%% rcv/4

%% Extract a message for which we have all bytes.
rcv(Len, N, Head, Acc)
  when Len =< N ->
    recv1(Len, bin(Head, Acc));

%% Wait for more packets.
rcv(Len, N, Head, Acc) ->
    {Len, N, Head, Acc}.

%% rcv/1

%% Nothing left.
rcv(<<>> = Bin) ->
    Bin;

%% The Message Length isn't even sufficient for a header. Chances are
%% things will go south from here but if we're lucky then the bytes we
%% have extend to an intended message boundary and we can recover by
%% simply receiving them. Make it so.
rcv(<<_:1/binary, Len:24, _/binary>> = Bin)
  when Len < 20 ->
    {Bin, <<>>};

%% Enough bytes to extract a message.
rcv(<<_:1/binary, Len:24, _/binary>> = Bin)
  when Len =< size(Bin) ->
    recv1(Len, Bin);

%% Or not: wait for more packets.
rcv(<<_:1/binary, Len:24, _/binary>> = Head) ->
    {Len, size(Head), Head, []};

%% Not even 4 bytes yet.
rcv(Head) ->
    Head.

%% recv1/2

recv1(Len, Bin) ->
    <<Msg:Len/binary, Rest/binary>> = Bin,
    {Msg, Rest}.

%% bin/1-2

bin(Head, Acc) ->
    list_to_binary([Head | lists:reverse(Acc)]).

bin({_, _, Head, Acc}) ->
    bin(Head, Acc);
bin(Bin)
  when is_binary(Bin) ->
    Bin.

%% flush/1

%% An erroneously large message length may leave us with a fragment
%% that lingers if the peer doesn't have anything more to send. Start
%% a timer to force reception if an incoming message doesn't arrive
%% first. This won't stop a peer from sending a large bogus value and
%% following it up however but such a state of affairs can only go on
%% for so long since an unanswered DWR will eventually be the result.
%%
%% An erroneously small message length causes problems as well but
%% since all messages with length problems are discarded this should
%% also eventually lead to watchdog failover.

%% No fragment to flush or not receiving messages.
flush(#transport{frag = Frag, throttled = B} = S)
  when Frag == <<>>;
       B /= false ->
    S;

%% Messages have been received since last timer expiry.
flush(#transport{flush = false} = S) ->
    start_fragment_timer(S#transport{flush = true});

%% No messages since last expiry.
flush(#transport{frag = Frag, parent = Pid} = S) ->
    diameter_peer:recv(Pid, bin(Frag)),
    S#transport{frag = <<>>}.

%% start_fragment_timer/1
%%
%% Start a timer only if there's none running and a message to flush.

start_fragment_timer(#transport{frag = B, tref = TRef} = S)
  when B == <<>>;
       TRef /= false ->
    S;

start_fragment_timer(#transport{timeout = Tmo} = S) ->
    S#transport{tref = erlang:start_timer(Tmo, self(), flush)}.

%% accept/2

accept(ssl, LSock) ->
    case ssl:transport_accept(LSock) of
        {ok, Sock} ->
            {ssl:ssl_accept(Sock), Sock};
        {error, _} = No ->
            No
    end;
accept(Mod, LSock) ->
    Mod:accept(LSock).

%% connect/4

connect(Mod, Host, Port, Opts) ->
    Mod:connect(Host, Port, Opts).

%% send/3

send(gen_tcp, Sock, Bin) ->
    gen_tcp:send(Sock, Bin);
send(ssl, Sock, Bin) ->
    ssl:send(Sock, Bin);
send(M, Sock, Bin) ->
    M:send(Sock, Bin).

%% setopts/3

setopts(gen_tcp, Sock, Opts) ->
    inet:setopts(Sock, Opts);
setopts(ssl, Sock, Opts) ->
    ssl:setopts(Sock, Opts);
setopts(M, Sock, Opts) ->
    M:setopts(Sock, Opts).

%% setopts/1

setopts(#transport{socket = Sock, module = M}) ->
    setopts(M, Sock).

%% setopts/2

setopts(M, Sock) ->
    case setopts(M, Sock, [{active, once}]) of
        ok -> ok;
        X  -> x({setopts, M, Sock, X})  %% possibly on peer disconnect
    end.

%% throttle/1

throttle(#transport{throttled = false} = S) ->
    recv(S);

throttle(#transport{throttle_cb = F, throttled = B} = S) ->
    throttle(cb(F, B), S).

%% cb/2

cb(false, _) ->
    ok;

cb(F, B) ->
    diameter_lib:eval([F, true /= B andalso B]).

%% throttle/2

%% Callback says to receive another message.
throttle(ok, #transport{throttled = true} = S) ->
    recv(S#transport{throttled = false});

%% Callback says to accept a received message.
throttle(ok, #transport{parent = Pid, throttled = Msg} = S) ->
    diameter_peer:recv(Pid, Msg),
    throttle(S#transport{throttled = true});

throttle({ok = T, F}, S) ->
    throttle(T, S#transport{throttle_cb = F});

%% Callback says to accept a received message and acknowledged the
%% returned pid with a {request, Pid} message if a request pid is
%% spawned, a discard message otherwise. The latter does not mean that
%% the message was necessarily discarded: it could have been an
%% answer.
throttle(NPid, #transport{parent = Pid, throttled = Msg} = S)
  when is_pid(NPid), is_binary(Msg) ->
    diameter_peer:recv(Pid, {Msg, NPid}),
    throttle(S#transport{throttled = true});

throttle({NPid, F}, #transport{throttled = Msg} = S)
  when is_pid(NPid), is_binary(Msg) ->
    throttle(NPid, S#transport{throttle_cb = F});

%% Callback to accept a received message says to discard it.
throttle(discard, #transport{throttled = Msg} = S)
  when is_binary(Msg) ->
    throttle(S#transport{throttled = true});

throttle({discard = T, F}, #transport{throttled = Msg} = S)
  when is_binary(Msg) ->
    throttle(T, S#transport{throttle_cb = F});

%% Callback says to ask again in the specified number of milliseconds.
throttle({timeout, Tmo}, #transport{} = S) ->
    erlang:send_after(Tmo, self(), throttle),
    S;

throttle({timeout = T, Tmo, F}, S) ->
    throttle({T, Tmo}, S#transport{throttle_cb = F});

throttle(T, #transport{throttle_cb = F}) ->
    ?ERROR({invalid_return, T, F}).

%% portnr/2

portnr(gen_tcp, Sock) ->
    inet:port(Sock);
portnr(M, Sock) ->
    case M:sockname(Sock) of
        {ok, {_Addr, PortNr}} ->
            {ok, PortNr};
        {error, _} = No ->
            No
    end.

%% sockname/2

sockname(gen_tcp, Sock) ->
    inet:sockname(Sock);
sockname(M, Sock) ->
    M:sockname(Sock).

%% peername/2

peername(gen_tcp, Sock) ->
    inet:peername(Sock);
peername(M, Sock) ->
    M:peername(Sock).

%% getstat/2

getstat(gen_tcp, Sock) ->
    inet:getstat(Sock);
getstat(M, Sock) ->
    M:getstat(Sock).
%% Note that ssl:getstat/1 doesn't yet exist in R15B01.