aboutsummaryrefslogtreecommitdiffstats
path: root/lib/diameter/src/base/diameter_config.erl
blob: a790b946c1693fd5d71728a45af9a32b20ac62d7 (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
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2010-2017. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%%     http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%

%%
%% This module writes service/transport configuration to the table
%% diameter_config, so that the config will survive service process
%% death, and then turns it into calls towards diameter_service. It
%% also restarts services upon their death.
%%
%% The table diameter_config is only written here while
%% diameter_service reads. This is all somewhat after the fact. Once
%% upon a time the config was only stored in the service process,
%% causing much grief if these processes died (which they did with
%% some regularity) and one was forced to reconfigure. This module was
%% then inserted into the service start in order to keep a more
%% permanent record of the config. That said, service processes are
%% now much more robust than they once were and crashing is a thing of
%% the past.
%%

-module(diameter_config).
-behaviour(gen_server).

-export([start_service/2,
         stop_service/1,
         add_transport/2,
         remove_transport/2,
         have_transport/2,
         lookup/1,
         subscribe/2]).

%% server start
-export([start_link/0,
         start_link/1]).

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

%% callbacks
-export([sync/1]).    %% diameter_sync requests

%% debug
-export([state/0,
         uptime/0]).

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

%% Server state.
-record(state, {id = diameter_lib:now(),
                role :: server | transport}).

%% Registered name of the server.
-define(SERVER, ?MODULE).

%% Table config is written to.
-define(TABLE, ?MODULE).

%% Key on which a transport-specific child registers itself.
-define(TRANSPORT_KEY(Ref), {?MODULE, transport, Ref}).

%% Workaround for dialyzer's lack of understanding of match specs.
-type match(T)
   :: T | '_' | '$1' | '$2' | '$3' | '$4'.

%% Configuration records in ?TABLE.

-record(service,
        {name,
         rec     :: match(#diameter_service{}),
         options :: match(list())}).

-record(transport,
        {service, %% name
         ref = make_ref() :: match(reference()),
         type             :: match(connect | listen),
         options          :: match(list())}).

%% Monitor entry in ?TABLE.
-record(monitor, {mref = make_ref() :: reference(),
                  service}). %% name

%% The default sequence mask.
-define(NOMASK, {0,32}).

%% Time to lay low before restarting a dead service.
-define(RESTART_SLEEP, 2000).

%% Test for a valid timeout.
-define(IS_UINT32(N),
        is_integer(N) andalso 0 =< N andalso 0 == N bsr 32).

%% A minimal diameter_caps for checking for valid capabilities values.
-define(EXAMPLE_CAPS,
        #diameter_caps{origin_host = "TheHost",
                       origin_realm = "TheRealm",
                       host_ip_address = [{127,0,0,1}],
                       vendor_id = 42,
                       product_name = "TheProduct"}).

-define(VALUES(Rec), tl(tuple_to_list(Rec))).

%% The RFC 3588 common dictionary is used to validate capabilities
%% configuration. That a given transport may use the RFC 6733
%% dictionary is of no consequence.
-define(BASE, diameter_gen_base_rfc3588).

%%% The return values below assume the server diameter_config is started.
%%% The functions will exit if it isn't.

%% --------------------------------------------------------------------------
%% # start_service/2
%% --------------------------------------------------------------------------

-spec start_service(diameter:service_name(), [diameter:service_opt()])
   -> ok
    | {error, term()}.

start_service(SvcName, Opts)
  when is_list(Opts)  ->
    start_rc(sync(SvcName, {start_service, SvcName, Opts})).

start_rc({ok = T, _Pid}) ->
    T;
start_rc({error, _} = No) ->
    No;
start_rc(timeout) ->
    {error, application_not_started}.

%% --------------------------------------------------------------------------
%% # stop_service/1
%% --------------------------------------------------------------------------

-spec stop_service(diameter:service_name())
   -> ok.

stop_service(SvcName) ->
    sync(SvcName, {stop_service, SvcName}).

%% --------------------------------------------------------------------------
%% # add_transport/2
%% --------------------------------------------------------------------------

-spec add_transport(diameter:service_name(),
                    {connect|listen, [diameter:transport_opt()]})
   -> {ok, diameter:transport_ref()}
    | {error, term()}.

add_transport(SvcName, {T, Opts})
  when is_list(Opts), (T == connect orelse T == listen) ->
    sync(SvcName, {add, SvcName, T, Opts}).

%% --------------------------------------------------------------------------
%% # remove_transport(SvcName, Pred)
%%
%% Input:  Pred = arity 3 fun on transport ref, connect|listen and Opts,
%%                returning true if the transport is to be removed, false if
%%                not
%%              | arity 2 fun on Ref and Opts only
%%              | arity 1 fun on Opts only
%%              | Opts matching all transports that have all of the specified
%%                options
%%              | Ref matching only the transport with this reference.
%%              | {M,F,A} applied to Ref, connect|listen and Opts
%%              | boolean()
%%
%% Output: ok | {error, Reason}
%% --------------------------------------------------------------------------

-spec remove_transport(diameter:service_name(), diameter:transport_pred())
   -> ok
    | {error, term()}.

remove_transport(SvcName, Pred) ->
    try
        sync(SvcName, {remove, SvcName, pred(Pred)})
    catch
        ?FAILURE(Reason) ->
            {error, Reason}
    end.

pred(Pred)
  when is_function(Pred, 3) ->
    Pred;
pred(Pred)
  when is_function(Pred, 2) ->
    fun(R,_,O) -> Pred(R,O) end;
pred(Pred)
  when is_function(Pred, 1) ->
    fun(_,_,O) -> Pred(O) end;
pred(Opts)
  when is_list(Opts) ->
    fun(_,_,O) -> [] == Opts -- O end;
pred(Ref)
  when is_reference(Ref) ->
    fun(R,_,_) -> R == Ref end;
pred({M,F,A})
  when is_atom(M), is_atom(F), is_list(A) ->
    fun(R,T,O) -> apply(M,F,[R,T,O|A]) end;
pred({Type, Pred}) ->  %% backwards compatibility
    P = pred(Pred),
    fun(R,T,O) -> T == Type andalso P(R,T,O) end;
pred(B)
  when is_boolean(B) ->
    fun(_,_,_) -> B end;
pred(_) ->
    ?THROW(pred).

%% --------------------------------------------------------------------------
%% # subscribe/2
%% --------------------------------------------------------------------------

subscribe(Ref, T) ->
    diameter_reg:subscribe(?TRANSPORT_KEY(Ref), T).

%% --------------------------------------------------------------------------
%% # have_transport/2
%%
%% Output: true | false
%% --------------------------------------------------------------------------

have_transport(SvcName, Ref) ->
    member([{#transport{service = '$1',
                        ref = '$2',
                        _ = '_'},
             [{'andalso', {'=:=', '$1', {const, SvcName}},
                          {'=:=', '$2', {const, Ref}}}],
             [true]}]).

%% --------------------------------------------------------------------------
%% # lookup/1
%% --------------------------------------------------------------------------

lookup(SvcName) ->
    select([{#service{name = '$1', rec = '$2', options = '$3'},
             [{'=:=', '$1', {const, SvcName}}],
             [{{'$1', '$2', '$3'}}]},
            {#transport{service = '$1',
                        ref = '$2',
                        type = '$3',
                        options = '$4'},
             [{'=:=', '$1', {const, SvcName}}],
             [{{'$2', '$3', '$4'}}]}]).

%% ---------------------------------------------------------
%% EXPORTED INTERNAL FUNCTIONS
%% ---------------------------------------------------------

start_link() ->
    ServerName = {local, ?SERVER},
    Module     = ?MODULE,
    Args       = [],
    Options    = [{spawn_opt, diameter_lib:spawn_opts(server, [])}],
    gen_server:start_link(ServerName, Module, Args, Options).

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

state() ->
    call(state).

uptime() ->
    call(uptime).

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

%% ?SERVER start.
init([]) ->
    {ok, #state{role = server}};

%% Child start as a consequence of add_transport.
init({SvcName, Type, Opts}) ->
    Res = try
              add(SvcName, Type, Opts)
          catch
              ?FAILURE(Reason) -> {error, Reason}
          end,
    proc_lib:init_ack({ok, self(), Res}),
    loop(Res).

%% loop/1

loop({ok, _}) ->
    gen_server:enter_loop(?MODULE, [], #state{role = transport});

loop({error, _}) ->
    ok.  %% die

%%% ----------------------------------------------------------
%%% # handle_call/2
%%% ----------------------------------------------------------

handle_call(state, _, State) ->
    {reply, State, State};

handle_call(uptime, _, #state{id = Time} = S) ->
    {reply, diameter_lib:now_diff(Time), S};

handle_call(Req, From, State) ->
    ?UNEXPECTED([Req, From]),
    Reply = {error, {bad_request, Req}},
    {reply, Reply, State}.

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

handle_cast(Msg, State) ->
    ?UNEXPECTED([Msg]),
    {noreply, State}.

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

%% remove_transport is telling published child to die.
handle_info(stop, #state{role = transport} = S) ->
    {stop, normal, S};

%% A service process has died. This is most likely a consequence of
%% stop_service, in which case the restart will find no config for the
%% service and do nothing. The entry keyed on the monitor ref is only
%% removed as a result of the 'DOWN' notification however.
handle_info({'DOWN', MRef, process, _, Reason}, #state{role = server} = S) ->
    [#monitor{service = SvcName} = T] = select([{#monitor{mref = MRef,
                                                          _ = '_'},
                                                 [],
                                                 ['$_']}]),
    queue_restart(Reason, SvcName),
    delete_object(T),
    {noreply, S};

handle_info({monitor, SvcName, Pid}, #state{role = server} = S) ->
    insert_monitor(Pid, SvcName),
    {noreply, S};

handle_info({restart, SvcName}, #state{role = server} = S) ->
    restart(SvcName),
    {noreply, S};

handle_info(restart, #state{role = server} = S) ->
    restart(),
    {noreply, S};

handle_info(Info, State) ->
    ?UNEXPECTED([Info]),
    {noreply, State}.

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

terminate(_Reason, _State) ->
    ok.

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

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

%% ---------------------------------------------------------
%% INTERNAL FUNCTIONS
%% ---------------------------------------------------------

insert(T) ->
    ets:insert(?TABLE, T).

%% ?TABLE is a bag: check only for a service entry.
have_service(SvcName) ->
    member([{#service{name = '$1', _ = '_'},
             [{'=:=', '$1', {const, SvcName}}],
             [true]}]).

member(MatchSpec) ->
    '$end_of_table' =/= ets:select(?TABLE, MatchSpec, 1).

delete_object(T) ->
    ets:delete_object(?TABLE, T).

delete(Key) ->
    ets:delete(?TABLE, Key).

select(MatchSpec) ->
    ets:select(?TABLE, MatchSpec).

select_delete(MatchSpec) ->
    ets:select_delete(?TABLE, MatchSpec).

%% sync/2
%%
%% Interface functions used to be implemented as calls to ?SERVER but
%% now serialize things per service instead since stopping a service
%% can take time if the server doesn't answer DPR. A caller who wants
%% to stop multiple services can then improve performance by spawning
%% processes to stop them concurrently.

sync(SvcName, T) ->
    diameter_sync:call({?MODULE, SvcName},
		       {?MODULE, sync, [T]},
		       infinity,
		       infinity).

%% sync/1

sync({restart, SvcName}) ->
    have_service(SvcName) andalso start(SvcName);

sync({start_service, SvcName, Opts}) ->
    try
        start(have_service(SvcName), SvcName, Opts)
    catch
        ?FAILURE(Reason) -> {error, Reason}
    end;

sync({stop_service, SvcName}) ->
    stop(SvcName);

%% Start a child whose only purpose is to be alive for the lifetime of
%% the transport configuration and publish itself in diameter_reg.
%% This is to provide a way for processes to to be notified when the
%% configuration is removed (diameter_reg:subscribe/2).
sync({add, SvcName, Type, Opts}) ->
    {ok, _Pid, Res} = diameter_config_sup:start_child({SvcName, Type, Opts}),
    Res;

sync({remove, SvcName, Pred}) ->
    Recs = select([{#transport{service = '$1', _ = '_'},
                    [{'=:=', '$1', {const, SvcName}}],
                    ['$_']}]),
    F = fun(#transport{ref = R, type = T, options = O}) ->
                Pred(R,T,O)
        end,
    remove(SvcName, lists:filter(F, Recs)).

%% start/3

start(true, _, _) ->
    {error, already_started};
start(false, SvcName, Opts) ->
    insert(make_config(SvcName, Opts)),
    start(SvcName).

%% start/1

start(SvcName) ->
    RC = diameter_service:start(SvcName),
    startmon(SvcName, RC),
    RC.

startmon(SvcName, {ok, Pid}) ->
    ?SERVER ! {monitor, SvcName, Pid};
startmon(_, {error, _}) ->
    ok.

insert_monitor(Pid, SvcName) ->
    MRef = monitor(process, Pid),
    insert(#monitor{mref = MRef, service = SvcName}).

%% queue_restart/2

%% Service has gone down on monitor death. Note that all service-related
%% config is deleted.
queue_restart({shutdown, {monitor, _}}, SvcName) ->
    delete(SvcName);

%% Application shutdown: ignore.
queue_restart(shutdown, _) ->
    ok;

%% Or not.
queue_restart(_, SvcName) ->
    erlang:send_after(?RESTART_SLEEP, self(), {restart, SvcName}).

%% restart/1

restart(SvcName) ->
    sync(SvcName, {restart, SvcName}).

%% restart/0
%%
%% Start anything configured as required. Bang 'restart' to the server
%% to kick things into gear manually. (Not that it should be required
%% but it's been useful for test.)

restart() ->
    MatchSpec = [{#service{name = '$1', _ = '_'},
                  [],
                  ['$1']}],
    lists:foreach(fun restart/1, select(MatchSpec)).

%% stop/1

stop(SvcName) ->
    %% If the call to the service returns error for any reason other
    %% than the process not being alive then deleting the config from
    %% under it will surely bring it down.
    diameter_service:stop(SvcName),
    %% Delete only the service entry, not everything keyed on the name,
    select_delete([{#service{name = '$1', _ = '_'},
                    [{'=:=', '$1', {const, SvcName}}],
                    [true]}]),
    ok.
%% Note that a transport has to be removed for its statistics to be
%% deleted.

%% add/3

%% Can't check for a single common dictionary since a transport may
%% restrict applications so that that there's one while the service
%% has many.

add(SvcName, Type, Opts0) ->
    %% Ensure acceptable transport options. This won't catch all
    %% possible errors (faulty callbacks for example) but it catches
    %% many. diameter_service:merge_service/2 depends on usable
    %% capabilities for example.
    Opts = transport_opts(Opts0),

    Ref = make_ref(),
    true = diameter_reg:add_new(?TRANSPORT_KEY(Ref)),
    T = {Ref, Type, Opts},
    %% The call to the service returns error if the service isn't
    %% started yet, which is harmless. The transport will be started
    %% when the service is in that case.
    case start_transport(SvcName, T) of
        ok ->
            insert(#transport{service = SvcName,
                              ref = Ref,
                              type = Type,
                              options = Opts}),
            {ok, Ref};
        {error, _} = No ->
            No
    end.

transport_opts(Opts) ->
    lists:map(fun topt/1, Opts).

topt(T) ->
    case opt(T) of
        {value, X} ->
            X;
        true ->
            T;
        false ->
            ?THROW({invalid, T})
    end.

opt({transport_module, M}) ->
    is_atom(M);

opt({transport_config, _, Tmo}) ->
    ?IS_UINT32(Tmo) orelse Tmo == infinity;

opt({applications, As}) ->
    is_list(As);

opt({capabilities, Os}) ->
    is_list(Os) andalso ok == encode_CER(Os);

opt({K, Tmo})
  when K == capx_timeout;
       K == dpr_timeout;
       K == dpa_timeout ->
    ?IS_UINT32(Tmo);

opt({capx_strictness, B}) ->
    is_boolean(B);

opt({length_errors, T}) ->
    lists:member(T, [exit, handle, discard]);

opt({K, Tmo})
  when K == reconnect_timer;  %% deprecated
       K == connect_timer ->
    ?IS_UINT32(Tmo);

opt({watchdog_timer, {M,F,A}})
  when is_atom(M), is_atom(F), is_list(A) ->
    true;
opt({watchdog_timer, Tmo}) ->
    ?IS_UINT32(Tmo);

opt({watchdog_config, L}) ->
    is_list(L) andalso lists:all(fun wdopt/1, L);

opt({spawn_opt, {M,F,A}})
  when is_atom(M), is_atom(F), is_list(A) ->
    true;
opt({spawn_opt = K, Opts}) ->
    if is_list(Opts) ->
            {value, {K, spawn_opts(Opts)}};
       true ->
            false
    end;

opt({pool_size, N}) ->
    is_integer(N) andalso 0 < N;

%% Options that we can't validate.
opt({K, _})
  when K == transport_config;
       K == capabilities_cb;
       K == disconnect_cb;
       K == private ->
    true;

%% Anything else, which is ignored by us. This makes options sensitive
%% to spelling mistakes but arbitrary options are passed by some users
%% as a way to identify transports. (That is, can't just do away with
%% it.)
opt(_) ->
    true.

wdopt({K,N}) ->
    (K == okay orelse K == suspect) andalso is_integer(N) andalso 0 =< N;
wdopt(_) ->
    false.

%% start_transport/2

start_transport(SvcName, T) ->
    case diameter_service:start_transport(SvcName, T) of
        {ok, _Pid} ->
            ok;
        {error, no_service} ->
            ok;
        {error, _} = No ->
            No
    end.

%% remove/2

remove(_, []) ->
    ok;

remove(SvcName, L) ->
    Refs = lists:map(fun(#transport{ref = R}) -> R end, L),
    case stop_transport(SvcName, Refs) of
        ok ->
            lists:foreach(fun stop_child/1, Refs),
            diameter_stats:flush(Refs),
            lists:foreach(fun delete_object/1, L);
        {error, _} = No ->
            No
    end.

stop_child(Ref) ->
    case diameter_reg:match(?TRANSPORT_KEY(Ref)) of
        [{_, Pid}] ->  %% tell the transport-specific child to die
            Pid ! stop;
        [] ->          %% already removed/dead
            ok
    end.

stop_transport(SvcName, Refs) ->
    case diameter_service:stop_transport(SvcName, Refs) of
        ok ->
            ok;
        {error, no_service} ->
            ok;
        {error, _} = No ->
            No
    end.

%% make_config/2

make_config(SvcName, Opts) ->
    AppOpts = [T || {application, _} = T <- Opts],
    Apps = [init_app(T) || T <- AppOpts],

    [] == Apps andalso ?THROW(no_apps),

    %% Use the fact that diameter_caps has the same field names as CER.
    Fields = ?BASE:'#info-'(diameter_base_CER) -- ['AVP'],

    CapOpts = [T || {K,_} = T <- Opts, lists:member(K, Fields)],
    Caps = make_caps(#diameter_caps{}, CapOpts),

    ok = encode_CER(CapOpts),

    SvcOpts = make_opts((Opts -- AppOpts) -- CapOpts,
                        [{false, share_peers},
                         {false, use_shared_peers},
                         {false, monitor},
                         {?NOMASK, sequence},
                         {nodes, restrict_connections},
                         {16#FFFFFF, incoming_maxlen},
                         {true, strict_mbit},
                         {true, record_decode},
                         {true, string_decode},
                         {[], spawn_opt}]),

    D = proplists:get_value(string_decode, SvcOpts, true),

    #service{name = SvcName,
             rec = #diameter_service{applications = Apps,
                                     capabilities = binary_caps(Caps, D)},
             options = SvcOpts}.

binary_caps(Caps, true) ->
    Caps;
binary_caps(Caps, false) ->
    diameter_capx:binary_caps(Caps).

%% make_opts/2

make_opts(Opts, Defs) ->
    Known = [{K, get_opt(K, Opts, D)} || {D,K} <- Defs],
    Unknown = Opts -- Known,

    [] == Unknown orelse ?THROW({invalid, hd(Unknown)}),

    [{K, opt(K,V)} || {K,V} <- Known].

opt(incoming_maxlen, N)
  when 0 =< N, N < 1 bsl 24 ->
    N;

opt(spawn_opt, {M,F,A} = T)
  when is_atom(M), is_atom(F), is_list(A) ->
    T;

opt(spawn_opt, L)
  when is_list(L) ->
    spawn_opts(L);

opt(K, false = B)
  when K == share_peers;
       K == use_shared_peers;
       K == monitor;
       K == restrict_connections;
       K == strict_mbit;
       K == record_decode;
       K == string_decode ->
    B;

opt(K, true = B)
  when K == share_peers;
       K == use_shared_peers;
       K == strict_mbit;
       K == record_decode;
       K == string_decode ->
    B;

opt(record_decode, map = T) ->
    T;

opt(restrict_connections, T)
  when T == node;
       T == nodes ->
    T;

opt(K, T)
  when (K == share_peers
        orelse K == use_shared_peers
        orelse K == restrict_connections), ([] == T
                                            orelse is_atom(hd(T))) ->
    T;

opt(monitor, P)
  when is_pid(P) ->
    P;

opt(K, F)
  when K == restrict_connections;
       K == share_peers;
       K == use_shared_peers ->
    try diameter_lib:eval(F) of  %% but no guarantee that it won't fail later
        Nodes when is_list(Nodes) ->
            F;
        V ->
            ?THROW({value, {K,V}})
    catch
        E:R ->
            ?THROW({value, {K, E, R, ?STACK}})
    end;

opt(sequence, {_,_} = T) ->
    sequence(T);

opt(sequence = K, F) ->
    try diameter_lib:eval(F) of
        T -> sequence(T)
    catch
        E:R ->
            ?THROW({value, {K, E, R, ?STACK}})
    end;

opt(K, _) ->
    ?THROW({value, K}).

spawn_opts(L) ->
    [T || T <- L, T /= link, T /= monitor].

sequence({H,N} = T)
  when 0 =< N, N =< 32, 0 =< H, 0 == H bsr (32-N) ->
    T;

sequence(_) ->
    ?THROW({value, sequence}).

make_caps(Caps, Opts) ->
    case diameter_capx:make_caps(Caps, Opts) of
        {ok, T} ->
            T;
        {error, Reason} ->
            ?THROW(Reason)
    end.

%% Validate types by encoding a CER.
encode_CER(Opts) ->
    {ok, CER} = diameter_capx:build_CER(make_caps(?EXAMPLE_CAPS, Opts),
                                        ?BASE),

    Hdr = #diameter_header{version = ?DIAMETER_VERSION,
                           end_to_end_id = 0,
                           hop_by_hop_id = 0},

    try
        diameter_codec:encode(?BASE, #diameter_packet{header = Hdr,
                                                      msg = CER}),
        ok
    catch
        exit: Reason ->
            ?THROW(Reason)
    end.

init_app({application, Opts} = T) ->
    is_list(Opts) orelse ?THROW(T),

    [Dict, Mod] = get_opt([dictionary, module], Opts),
    Alias = get_opt(alias, Opts, Dict),
    ModS  = get_opt(state, Opts, Alias),
    M = get_opt(call_mutates_state, Opts, false, [true]),
    A = get_opt(answer_errors, Opts, discard, [callback, report]),
    P = get_opt(request_errors, Opts, answer_3xxx, [answer, callback]),
    #diameter_app{alias = Alias,
                  dictionary = Dict,
                  id = cb(Dict, id),
                  module = init_mod(Mod),
                  init_state = ModS,
                  mutable = M,
                  options = [{answer_errors, A},
                             {request_errors, P}]}.

init_mod(#diameter_callback{} = R) ->
    init_mod([diameter_callback, R]);
init_mod([diameter_callback, #diameter_callback{}] = L) ->
    L;
init_mod([diameter_callback = M | L])
  when is_list(L) ->
    [M, init_cb(L)];
init_mod(M)
  when is_atom(M) ->
    [M];
init_mod([M|_] = L)
  when is_atom(M) ->
    L;
init_mod(M) ->
    ?THROW({module, M}).

init_cb(List) ->
    Fields = record_info(fields, diameter_callback),
    Defaults = lists:zip(Fields, tl(tuple_to_list(#diameter_callback{}))),
    Values = [V || F <- Fields,
                   D <- [proplists:get_value(F, Defaults)],
                   V <- [proplists:get_value(F, List, D)]],
    #diameter_callback{} = list_to_tuple([diameter_callback | Values]).

%% Retrieve and validate.
get_opt(Key, List, Def, Other) ->
    init_opt(Key, get_opt(Key, List, Def), [Def|Other]).

init_opt(_, V, [V|_]) ->
    V;
init_opt(Name, V, [_|Vals]) ->
    init_opt(Name, V, Vals);
init_opt(Name, V, []) ->
    ?THROW({Name, V}).

%% Get a single value at the specified key.
get_opt(Keys, List)
  when is_list(Keys) ->
    [get_opt(K, List) || K <- Keys];
get_opt(Key, List) ->
    case [V || {K,V} <- List, K == Key] of
        [V] -> V;
        _   -> ?THROW({arity, Key})
    end.

%% Get an optional value at the specified key.
get_opt(Key, List, Def) ->
    case [V || {K,V} <- List, K == Key] of
        []  -> Def;
        [V] -> V;
        _   -> ?THROW({arity, Key})
    end.

cb(M,F) ->
    try M:F() of
        V -> V
    catch
        E: Reason ->
            ?THROW({callback, E, Reason, ?STACK})
    end.

%% call/1

call(Request) ->
    gen_server:call(?SERVER, Request, infinity).