aboutsummaryrefslogtreecommitdiffstats
path: root/lib/diameter/src/base/diameter_watchdog.erl
blob: ac03ab12606e5a3af247f70eb5ada1e3f58a3a7b (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
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2010-2015. 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%
%%

%%
%% This module implements (as a process) the state machine documented
%% in Appendix A of RFC 3539.
%%

-module(diameter_watchdog).
-behaviour(gen_server).

%% towards diameter_service
-export([start/2]).

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

%% diameter_watchdog_sup callback
-export([start_link/1]).

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

-define(DEFAULT_TW_INIT, 30000). %% RFC 3539 ch 3.4.1
-define(NOMASK, {0,32}).  %% default sequence mask

-define(BASE, ?DIAMETER_DICT_COMMON).

-define(IS_NATURAL(N), (is_integer(N) andalso 0 =< N)).

-record(config,
        {suspect = 1 :: non_neg_integer(),    %% OKAY -> SUSPECT
         okay    = 3 :: non_neg_integer()}).  %% REOPEN -> OKAY

-record(watchdog,
        {%% PCB - Peer Control Block; see RFC 3539, Appendix A
         status = initial :: initial | okay | suspect | down | reopen,
         pending = false  :: boolean(),  %% DWA
         tw :: 6000..16#FFFFFFFF | {module(), atom(), list()},
                                %% {M,F,A} -> integer() >= 0
         num_dwa = 0 :: -1 | non_neg_integer(),
                     %% number of DWAs received in reopen,
                     %% or number of timeouts before okay -> suspect
         %% end PCB
         parent = self() :: pid(),              %% service process
         transport       :: pid() | undefined,  %% peer_fsm process
         tref :: reference()      %% reference for current watchdog timer
               | integer()        %% monotonic time
               | tuple()          %% now()
               | undefined,
         dictionary :: module(),  %% common dictionary
         receive_data :: term(),
                 %% term passed into diameter_service with incoming message
         sequence :: diameter:sequence(),     %% mask
         restrict :: {diameter:restriction(), boolean()},
         shutdown = false :: boolean(),
         config :: #config{}}).

%% ---------------------------------------------------------------------------
%% start/2
%%
%% Start a monitor before the watchdog is allowed to proceed to ensure
%% that a failed capabilities exchange produces the desired exit
%% reason.
%% ---------------------------------------------------------------------------

-spec start(Type, {RecvData, [Opt], SvcOpts, #diameter_service{}})
   -> {reference(), pid()}
 when Type :: {connect|accept, diameter:transport_ref()},
      RecvData :: term(),
      Opt :: diameter:transport_opt(),
      SvcOpts :: [diameter:service_opt()].

start({_,_} = Type, T) ->
    Ack = make_ref(),
    {ok, Pid} = diameter_watchdog_sup:start_child({Ack, Type, self(), T}),
    try
        {monitor(process, Pid), Pid}
    after
        send(Pid, Ack)
    end.

start_link(T) ->
    {ok, _} = proc_lib:start_link(?MODULE,
                                  init,
                                  [T],
                                  infinity,
                                  diameter_lib:spawn_opts(server, [])).

%% ===========================================================================
%% ===========================================================================

%% init/1

init(T) ->
    proc_lib:init_ack({ok, self()}),
    gen_server:enter_loop(?MODULE, [], i(T)).

i({Ack, T, Pid, {RecvData,
                 Opts,
                 SvcOpts,
                 #diameter_service{applications = Apps,
                                   capabilities = Caps}
                 = Svc}}) ->
    monitor(process, Pid),
    wait(Ack, Pid),
    {_, Seed} = diameter_lib:seed(),
    random:seed(Seed),
    putr(restart, {T, Opts, Svc, SvcOpts}),  %% save seeing it in trace
    putr(dwr, dwr(Caps)),                    %%
    {_,_} = Mask = proplists:get_value(sequence, SvcOpts),
    Restrict = proplists:get_value(restrict_connections, SvcOpts),
    Nodes = restrict_nodes(Restrict),
    Dict0 = common_dictionary(Apps),
    diameter_codec:setopts([{common_dictionary, Dict0},
                            {string_decode, false}]),
    #watchdog{parent = Pid,
              transport = start(T, Opts, SvcOpts, Nodes, Dict0, Svc),
              tw = proplists:get_value(watchdog_timer,
                                       Opts,
                                       ?DEFAULT_TW_INIT),
              receive_data = RecvData,
              dictionary = Dict0,
              sequence = Mask,
              restrict = {Restrict, lists:member(node(), Nodes)},
              config = config(Opts)}.

wait(Ref, Pid) ->
    receive
        Ref ->
            ok;
        {'DOWN', _, process, Pid, _} = D ->
            exit({shutdown, D})
    end.

%% config/1
%%
%% Could also configure counts for SUSPECT to DOWN and REOPEN to DOWN,
%% but don't.

config(Opts) ->
    Config = proplists:get_value(watchdog_config, Opts, []),
    lists:foldl(fun config/2, #config{}, Config).

config({suspect, N}, Rec)
  when ?IS_NATURAL(N) ->
    Rec#config{suspect = N};

config({okay, N}, Rec)
  when ?IS_NATURAL(N) ->
    Rec#config{okay = N}.

%% start/6

start(T, Opts, SvcOpts, Nodes, Dict0, Svc) ->
    {_MRef, Pid}
        = diameter_peer_fsm:start(T, Opts, {SvcOpts, Nodes, Dict0, Svc}),
    Pid.

%% common_dictionary/1
%%
%% Determine the dictionary of the Diameter common application with
%% Application Id 0. Fail on config errors.

common_dictionary(Apps) ->
    case
        orddict:fold(fun dict0/3,
                     false,
                     lists:foldl(fun(#diameter_app{dictionary = M}, D) ->
                                         orddict:append(M:id(), M, D)
                                 end,
                                 orddict:new(),
                                 Apps))
    of
        {value, Mod} ->
            Mod;
        false ->
            %% A transport should configure a common dictionary but
            %% don't require it. Not configuring a common dictionary
            %% means a user won't be able either send of receive
            %% messages in the common dictionary: incoming request
            %% will be answered with 3007 and outgoing requests cannot
            %% be sent. The dictionary returned here is only used for
            %% messages diameter sends and receives: CER/CEA, DPR/DPA
            %% and DWR/DWA.
            ?BASE
    end.

%% Each application should be represented by a single dictionary.
dict0(Id, [_,_|_] = Ms, _) ->
    config_error({multiple_dictionaries, Ms, {application_id, Id}});

%% An explicit common dictionary.
dict0(?APP_ID_COMMON, [Mod], _) ->
    {value, Mod};

%% A pure relay, in which case the common application is implicit.
%% This uses the fact that the common application will already have
%% been folded.
dict0(?APP_ID_RELAY, _, false) ->
    {value, ?BASE};

dict0(_, _, Acc) ->
    Acc.

config_error(T) ->
    exit({shutdown, {configuration_error, T}}).

%% handle_call/3

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

%% handle_cast/2

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

%% handle_info/2

handle_info(T, #watchdog{} = State) ->
    case transition(T, State) of
        ok ->
            {noreply, State};
        #watchdog{} = S ->
            close(T, State),     %% service expects 'close' message
            event(T, State, S),  %%   before 'watchdog'
            {noreply, S};
        stop ->
            ?LOG(stop, truncate(T)),
            event(T, State, State#watchdog{status = down}),
            {stop, {shutdown, T}, State}
    end.

truncate({'DOWN' = T, _, process, Pid, _}) ->
    {T, Pid};
truncate(T) ->
    T.

close({'DOWN', _, process, TPid, {shutdown, Reason}},
      #watchdog{transport = TPid,
                parent = Pid}) ->
    send(Pid, {close, self(), Reason});

close(_, _) ->
    ok.

event(_,
      #watchdog{status = From, transport = F},
      #watchdog{status = To, transport = T})
  when F == undefined, T == undefined;  %% transport not started
       From == initial, To == down;     %% never really left INITIAL
       From == To ->                    %% no state transition
    ok;
%% Note that there is no INITIAL -> DOWN transition in RFC 3539: ours
%% is just a consequence of stop.

event(Msg,
      #watchdog{status = From, transport = F, parent = Pid},
      #watchdog{status = To, transport = T}) ->
    TPid = tpid(F,T),
    E = {[TPid | data(Msg, TPid, From, To)], From, To},
    send(Pid, {watchdog, self(), E}),
    ?LOG(transition, {From, To}).

data(Msg, TPid, reopen, okay) ->
    {recv, TPid, 'DWA', _Pkt} = Msg,  %% assert
    {TPid, T} = eraser(open),
    [T];

data({open, TPid, _Hosts, T}, TPid, _From, To)
  when To == okay;
       To == reopen ->
    [T];

data(_, _, _, _) ->
    [].

tpid(_, Pid)
  when is_pid(Pid) ->
    Pid;

tpid(Pid, _) ->
    Pid.

send(Pid, T) ->
    Pid ! T.

%% terminate/2

terminate(_, _) ->
    ok.

%% code_change/3

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

%% ===========================================================================
%% ===========================================================================

%% transition/2
%%
%% The state transitions documented here are extracted from RFC 3539,
%% the commentary is ours.

%% Service is telling the watchdog of an accepting transport to die
%% following transport death in state INITIAL, or after connect_timer
%% expiry; or another watchdog is saying the same after reestablishing
%% a connection previously had by this one.
transition(close, #watchdog{}) ->
    {accept, _} = role(), %% assert
    stop;

%% Service is asking for the peer to be taken down gracefully.
transition({shutdown, Pid, _}, #watchdog{parent = Pid,
                                         transport = undefined}) ->
    stop;
transition({shutdown = T, Pid, Reason}, #watchdog{parent = Pid,
                                                  transport = TPid}
                                        = S) ->
    send(TPid, {T, self(), Reason}),
    S#watchdog{shutdown = true};

%% Transport is telling us that DPA has been sent in response to DPR,
%% or that DPR has been explicitly sent: transport death should lead
%% to ours.
transition({'DPR', TPid}, #watchdog{transport = TPid} = S) ->
    S#watchdog{shutdown = true};

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

%% Transport has accepted a connection.
transition({accepted = T, TPid}, #watchdog{transport = TPid,
                                           parent = Pid}) ->
    send(Pid, {T, self(), TPid}),
    ok;

%%   STATE         Event                Actions              New State
%%   =====         ------               -------              ----------
%%   INITIAL       Connection up        SetWatchdog()        OKAY

%% By construction, the watchdog timer isn't set until we move into
%% state okay as the result of the Peer State Machine reaching the
%% Open state.
%%
%% If we're accepting then we may be resuming a connection that went
%% down in another watchdog process, in which case this is the
%% transition below, from down to reopen. That is, it's not until we
%% know the identity of the peer (ie. now) that we know that we're in
%% state down rather than initial.

transition({open, TPid, Hosts, _} = Open,
           #watchdog{transport = TPid,
                     status = initial,
                     restrict = {_,R},
                     config = #config{suspect = OS}}
           = S) ->
    case okay(role(), Hosts, R) of
        okay ->
            set_watchdog(S#watchdog{status = okay,
                                    num_dwa = OS});
        reopen ->
            transition(Open, S#watchdog{status = down})
    end;

%%   DOWN          Connection up        NumDWA = 0
%%                                      SendWatchdog()
%%                                      SetWatchdog()
%%                                      Pending = TRUE       REOPEN

transition({open = Key, TPid, _Hosts, T},
           #watchdog{transport = TPid,
                     status = down,
                     config = #config{suspect = OS,
                                      okay = RO}}
           = S) ->
    case RO of
        0 ->  %% non-standard: skip REOPEN
            set_watchdog(S#watchdog{status = okay,
                                    num_dwa = OS});
        _ ->
            %% Store the info we need to notify the parent to reopen
            %% the connection after the requisite DWA's are received,
            %% at which time we eraser(open).
            putr(Key, {TPid, T}),
            set_watchdog(send_watchdog(S#watchdog{status = reopen,
                                                  num_dwa = 0}))
    end;

%%   OKAY          Connection down      CloseConnection()
%%                                      Failover()
%%                                      SetWatchdog()        DOWN
%%   SUSPECT       Connection down      CloseConnection()
%%                                      SetWatchdog()        DOWN
%%   REOPEN        Connection down      CloseConnection()
%%                                      SetWatchdog()        DOWN

%% Transport has died after DPA or service requested termination ...
transition({'DOWN', _, process, TPid, _Reason},
           #watchdog{transport = TPid,
                     shutdown = true}) ->
    stop;

%% ... or not.
transition({'DOWN', _, process, TPid, _Reason} = D,
           #watchdog{transport = TPid,
                     status = T,
                     restrict = {_,R}}
           = S0) ->
    S = S0#watchdog{pending = false,
                    transport = undefined},
    {M,_} = role(),

    %% Close an accepting watchdog immediately if there's no
    %% restriction on the number of connections to the same peer: the
    %% state machine never enters state REOPEN in this case.

    if T == initial;
       M == accept, not R ->
            close(D, S0),
            stop;
       true ->
            set_watchdog(S#watchdog{status = down})
    end;

%% Incoming message.
transition({recv, TPid, Name, Pkt}, #watchdog{transport = TPid} = S) ->
    recv(Name, Pkt, S);

%% Current watchdog has timed out.
transition({timeout, TRef, tw}, #watchdog{tref = TRef} = S) ->
    set_watchdog(0, timeout(S));

%% Message has arrived since the timer was started: subtract time
%% already elapsed from new timer.
transition({timeout, _, tw}, #watchdog{tref = T0} = S) ->
    set_watchdog(diameter_lib:micro_diff(T0) div 1000, S);

%% State query.
transition({state, Pid}, #watchdog{status = S}) ->
    send(Pid, {self(), S}),
    ok.

%% ===========================================================================

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

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

eraser(Key) ->
    erase({?MODULE, Key}).

%% encode/3

encode(dwr = M, Dict0, Mask) ->
    Msg = getr(M),
    Seq = diameter_session:sequence(Mask),
    Hdr = #diameter_header{version = ?DIAMETER_VERSION,
                           end_to_end_id = Seq,
                           hop_by_hop_id = Seq},
    Pkt = #diameter_packet{header = Hdr,
                           msg = Msg},
    diameter_codec:encode(Dict0, Pkt);

encode(dwa, Dict0, #diameter_packet{header = H, transport_data = TD}
                   = ReqPkt) ->
    AnsPkt = #diameter_packet{header
                              = H#diameter_header{is_request = false,
                                                  is_error = undefined,
                                                  is_retransmitted = false},
                              msg = dwa(ReqPkt),
                              transport_data = TD},

    diameter_codec:encode(Dict0, AnsPkt).

%% okay/3

okay({accept, Ref}, Hosts, Restrict) ->
    T = {?MODULE, connection, Ref, Hosts},
    diameter_reg:add(T),
    if Restrict ->
            okay(diameter_reg:match(T));
       true ->
            okay
    end;
%% Register before matching so that at least one of two registering
%% processes will match the other.

okay({connect, _}, _, _) ->
    okay.

%% okay/2

%% The peer hasn't been connected recently ...
okay([{_,P}]) ->
    P = self(),  %% assert
    okay;

%% ... or it has.
okay(C) ->
    [_|_] = [send(P, close) || {_,P} <- C, self() /= P],
    reopen.

%% role/0

role() ->
    element(1, getr(restart)).

%% set_watchdog/1

%% Timer not yet set.
set_watchdog(#watchdog{tref = undefined} = S) ->
    set_watchdog(0, S);

%% Timer already set: start at new one only at expiry.
set_watchdog(#watchdog{} = S) ->
    S#watchdog{tref = diameter_lib:now()};

set_watchdog(stop = No) ->
    No.

%% set_watchdog/2

set_watchdog(Ms, #watchdog{tw = TwInit} = S) ->
    S#watchdog{tref = erlang:start_timer(tw(TwInit, Ms), self(), tw)}.

%% A callback could return anything, so ensure the result isn't
%% negative. Don't prevent abuse, even though the smallest valid
%% timeout is 4000.
tw(TwInit, Ms) ->
    max(tw(TwInit) - Ms, 0).

tw(T)
  when is_integer(T), T >= 6000 ->
    T - 2000 + (random:uniform(4001) - 1); %% RFC3539 jitter of +/- 2 sec.
tw({M,F,A}) ->
    apply(M,F,A).

%% send_watchdog/1

send_watchdog(#watchdog{pending = false,
                        transport = TPid,
                        dictionary = Dict0,
                        sequence = Mask}
              = S) ->
    #diameter_packet{bin = Bin} = EPkt = encode(dwr, Dict0, Mask),
    diameter_traffic:incr(send, EPkt, TPid, Dict0),
    send(TPid, {send, Bin}),
    ?LOG(send, 'DWR'),
    S#watchdog{pending = true}.

%% Don't count encode errors since we don't expect any on DWR/DWA.

%% recv/3

recv(Name, Pkt, S) ->
    try rcv(Name, S) of
        #watchdog{} = NS ->
            rcv(Name, Pkt, S),
            NS
    catch
        {?MODULE, throwaway, #watchdog{} = NS} ->
            NS
    end.

%% rcv/3

rcv('DWR', Pkt, #watchdog{transport = TPid,
                          dictionary = Dict0}) ->
    ?LOG(recv, 'DWR'),
    DPkt = diameter_codec:decode(Dict0, Pkt),
    diameter_traffic:incr(recv, DPkt, TPid, Dict0),
    diameter_traffic:incr_error(recv, DPkt, TPid, Dict0),
    #diameter_packet{header = H,
                     transport_data = T,
                     bin = Bin}
        = EPkt
        = encode(dwa, Dict0, Pkt),
    diameter_traffic:incr(send, EPkt, TPid, Dict0),
    diameter_traffic:incr_rc(send, EPkt, TPid, Dict0),

    %% Strip potentially large message terms.
    send(TPid, {send, #diameter_packet{header = H,
                                       transport_data = T,
                                       bin = Bin}}),
    ?LOG(send, 'DWA');

rcv('DWA', Pkt, #watchdog{transport = TPid,
                          dictionary = Dict0}) ->
    ?LOG(recv, 'DWA'),
    diameter_traffic:incr(recv, Pkt, TPid, Dict0),
    diameter_traffic:incr_rc(recv,
                             diameter_codec:decode(Dict0, Pkt),
                             TPid,
                             Dict0);

rcv(N, _, _)
  when N == 'CER';
       N == 'CEA';
       N == 'DPR' ->
    false;
%% DPR can be sent explicitly with diameter:call/4. Only the
%% corresponding DPAs arrive here.

rcv(_, Pkt, #watchdog{transport = TPid,
                      dictionary = Dict0,
                      receive_data = T}) ->
    diameter_traffic:receive_message(TPid, Pkt, Dict0, T).

throwaway(S) ->
    throw({?MODULE, throwaway, S}).

%% rcv/2
%%
%% The lack of Hop-by-Hop and End-to-End Identifiers checks in a
%% received DWA is intentional. The purpose of the message is to
%% demonstrate life but a peer that consistently bungles it by sending
%% the wrong identifiers causes the connection to toggle between OPEN
%% and SUSPECT, with failover and failback as result, despite there
%% being no real problem with connectivity. Thus, relax and accept any
%% incoming DWA as being in response to an outgoing DWR.

%%   INITIAL       Receive DWA          Pending = FALSE
%%                                      Throwaway()          INITIAL
%%   INITIAL       Receive non-DWA      Throwaway()          INITIAL

rcv('DWA', #watchdog{status = initial} = S) ->
    throwaway(S#watchdog{pending = false});

rcv(_, #watchdog{status = initial} = S) ->
    throwaway(S);

%%   DOWN          Receive DWA          Pending = FALSE
%%                                      Throwaway()          DOWN
%%   DOWN          Receive non-DWA      Throwaway()          DOWN

rcv('DWA', #watchdog{status = down} = S) ->
    throwaway(S#watchdog{pending = false});

rcv(_, #watchdog{status = down} = S) ->
    throwaway(S);

%%   OKAY          Receive DWA          Pending = FALSE
%%                                      SetWatchdog()        OKAY
%%   OKAY          Receive non-DWA      SetWatchdog()        OKAY

rcv('DWA', #watchdog{status = okay} = S) ->
    set_watchdog(S#watchdog{pending = false});

rcv(_, #watchdog{status = okay} = S) ->
    set_watchdog(S);

%%   SUSPECT       Receive DWA          Pending = FALSE
%%                                      Failback()
%%                                      SetWatchdog()        OKAY
%%   SUSPECT       Receive non-DWA      Failback()
%%                                      SetWatchdog()        OKAY

rcv('DWA', #watchdog{status = suspect, config = #config{suspect = OS}} = S) ->
    set_watchdog(S#watchdog{status = okay,
                            num_dwa = OS,
                            pending = false});

rcv(_, #watchdog{status = suspect, config = #config{suspect = OS}} = S) ->
    set_watchdog(S#watchdog{status = okay,
                            num_dwa = OS});

%%   REOPEN        Receive DWA &        Pending = FALSE
%%                 NumDWA == 2          NumDWA++
%%                                      Failback()           OKAY

rcv('DWA', #watchdog{status = reopen,
                     num_dwa = N,
                     config = #config{suspect = OS,
                                      okay = RO}}
           = S)
  when N+1 == RO ->
    S#watchdog{status = okay,
               num_dwa = OS,
               pending = false};

%%   REOPEN        Receive DWA &        Pending = FALSE
%%                 NumDWA < 2           NumDWA++             REOPEN

rcv('DWA', #watchdog{status = reopen,
                     num_dwa = N}
           = S) ->
    S#watchdog{num_dwa = N+1,
               pending = false};

%%   REOPEN        Receive non-DWA      Throwaway()          REOPEN

rcv('DWR', #watchdog{status = reopen} = S) ->
    S;  %% ensure DWA: the RFC isn't explicit about answering

rcv(_, #watchdog{status = reopen} = S) ->
    throwaway(S).

%% timeout/1
%%
%% The caller sets the watchdog on the return value.

%%   OKAY          Timer expires &      SendWatchdog()
%%                 !Pending             SetWatchdog()
%%                                      Pending = TRUE       OKAY
%%   REOPEN        Timer expires &      SendWatchdog()
%%                 !Pending             SetWatchdog()
%%                                      Pending = TRUE       REOPEN

timeout(#watchdog{status = T,
                  pending = false}
        = S)
  when T == okay;
       T == reopen ->
    send_watchdog(S);

%%   OKAY          Timer expires &      Failover()
%%                 Pending              SetWatchdog()        SUSPECT

timeout(#watchdog{status = okay,
                  pending = true,
                  num_dwa = N}
        = S) ->
    case N of
        1 ->
            S#watchdog{status = suspect};
        0 ->  %% non-standard: never move to suspect
            S;
        N ->  %% non-standard: more timeouts before moving
            S#watchdog{num_dwa = N-1}
    end;

%%   SUSPECT       Timer expires        CloseConnection()
%%                                      SetWatchdog()        DOWN
%%   REOPEN        Timer expires &      CloseConnection()
%%                 Pending &            SetWatchdog()
%%                 NumDWA < 0                                DOWN

timeout(#watchdog{status = T,
                  pending = P,
                  num_dwa = N,
                  transport = TPid}
        = S)
  when T == suspect;
       T == reopen, P, N < 0 ->
    exit(TPid, {shutdown, watchdog_timeout}),
    S#watchdog{status = down};

%%   REOPEN        Timer expires &      NumDWA = -1
%%                 Pending &            SetWatchdog()
%%                 NumDWA >= 0                               REOPEN

timeout(#watchdog{status = reopen,
                  pending = true,
                  num_dwa = N}
        = S)
  when 0 =< N ->
    S#watchdog{num_dwa = -1};

%%   DOWN          Timer expires        AttemptOpen()
%%                                      SetWatchdog()        DOWN
%%   INITIAL       Timer expires        AttemptOpen()
%%                                      SetWatchdog()        INITIAL

%% RFC 3539, 3.4.1:
%%
%%   [5] While the connection is in the closed state, the AAA client MUST
%%       NOT attempt to send further watchdog messages on the connection.
%%       However, after the connection is closed, the AAA client continues
%%       to periodically attempt to reopen the connection.
%%
%%       The AAA client SHOULD wait for the transport layer to report
%%       connection failure before attempting again, but MAY choose to
%%       bound this wait time by the watchdog interval, Tw.

%% Don't bound, restarting the peer process only when the previous
%% process has died. We only need to handle state down since we start
%% the first watchdog when transitioning out of initial.

timeout(#watchdog{status = T} = S)
  when T == initial;
       T == down ->
    restart(S).

%% restart/1

restart(#watchdog{transport = undefined} = S) ->
    restart(getr(restart), S);
restart(S) ->  %% reconnect has won race with timeout
    S.

%% restart/2
%%
%% Only restart the transport in the connecting case. For an accepting
%% transport, there's no guarantee that an accepted connection in a
%% restarted transport if from the peer we've lost contact with so
%% have to be prepared for another watchdog to handle it. This is what
%% the diameter_reg registration in this module is for: the peer
%% connection is registered when leaving state initial and this is
%% used by a new accepting watchdog to realize that it's actually in
%% state down rather then initial when receiving notification of an
%% open connection.

restart({T, Opts, Svc}, S) ->  %% put in old code
    restart({T, Opts, Svc, []}, S);

restart({{connect, _} = T, Opts, Svc, SvcOpts},
        #watchdog{parent = Pid,
                  restrict = {R,_},
                  dictionary = Dict0}
        = S) ->
    send(Pid, {reconnect, self()}),
    Nodes = restrict_nodes(R),
    S#watchdog{transport = start(T, Opts, SvcOpts, Nodes, Dict0, Svc),
               restrict = {R, lists:member(node(), Nodes)}};

%% No restriction on the number of connections to the same peer: just
%% die. Note that a state machine never enters state REOPEN in this
%% case.
restart({{accept, _}, _, _, _}, #watchdog{restrict = {_, false}}) ->
    stop;  %% 'DOWN' was in old code: 'close' was not sent

%% Otherwise hang around until told to die, either by the service or
%% by another watchdog.
restart({{accept, _}, _, _, _}, S) ->
    S.

%% Don't currently use Opts/Svc in the accept case.

%% dwr/1

dwr(#diameter_caps{origin_host = OH,
                   origin_realm = OR,
                   origin_state_id = OSI}) ->
    ['DWR', {'Origin-Host', OH},
            {'Origin-Realm', OR},
            {'Origin-State-Id', OSI}].

%% dwa/1

dwa(#diameter_packet{header = H, errors = Es}) ->
    {RC, FailedAVP} = diameter_peer_fsm:result_code(H, Es),
    ['DWA', {'Result-Code', RC}
          | tl(getr(dwr)) ++ FailedAVP].

%% restrict_nodes/1

restrict_nodes(false) ->
    [];

restrict_nodes(nodes) ->
    [node() | nodes()];

restrict_nodes(node) ->
    [node()];

restrict_nodes(Nodes)
  when [] == Nodes;
       is_atom(hd(Nodes)) ->
    Nodes;

restrict_nodes(F) ->
    diameter_lib:eval(F).