aboutsummaryrefslogblamecommitdiffstats
path: root/lib/kernel/doc/src/gen_sctp.xml
blob: de41178a17e73c72eb5a0419909588f755160ecc (plain) (tree)
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
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075


















































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































































                                                                                                                                                                             
<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2007</year><year>2009</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      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.
    
    </legalnotice>

    <title>gen_sctp</title>
    <prepared>[email protected]</prepared>
    <responsible></responsible>
    <docno>1</docno>
    <approved></approved>
    <checked></checked>
    <date>2007-03-21</date>
    <rev>A</rev>
    <file>gen_sctp.sgml</file>
  </header>
  <module>gen_sctp</module>
  <modulesummary>The gen_sctp module provides functions for communicating with sockets using the SCTP protocol.</modulesummary>
  <description>
    <p>The <c>gen_sctp</c> module provides functions for communicating with
      sockets using the SCTP protocol. The implementation assumes that
      the OS kernel supports SCTP
      <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">(RFC2960)</url> through the user-level
      <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions.</url>
      During development this implementation was tested on 
      Linux Fedora Core 5.0 (kernel 2.6.15-2054 or later is needed),
      and on Solaris 10, 11. During OTP adaptation it was tested on
      SUSE Linux Enterprise Server 10 (x86_64) kernel 2.6.16.27-0.6-smp,
      with lksctp-tools-1.0.6, briefly on Solaris 10, and later on
      SUSE Linux Enterprise Server 10 Service Pack 1 (x86_64)
      kernel 2.6.16.54-0.2.3-smp with lksctp-tools-1.0.7.</p>
    <p>Record definitions for the <c>gen_sctp</c> module can be found using:</p>
    <pre>
  -include_lib("kernel/include/inet_sctp.hrl").    </pre>
    <p>These record definitions use the "new" spelling 'adaptation',
      not the deprecated 'adaption', regardless of which
      spelling the underlying C API uses.</p>
  </description>

  <section>
    <marker id="contents"></marker>
    <title>CONTENTS</title>
    <list type="bulleted">
      <item><seealso marker="#types">DATA TYPES</seealso></item>
      <item><seealso marker="#exports">EXPORTS</seealso></item>
      <item><seealso marker="#options">SCTP SOCKET OPTIONS</seealso></item>
      <item><seealso marker="#examples">SCTP EXAMPLES</seealso></item>
      <item><seealso marker="#seealso">SEE ALSO</seealso></item>
      <item><seealso marker="#authors">AUTHORS</seealso></item>
    </list>
  </section>

  <section>
    <marker id="types"></marker>
    <title>DATA TYPES</title>
    <marker id="type-assoc_id"></marker>
    <taglist>
      <tag><c>assoc_id()</c></tag>
      <item>
        <p>An opaque term returned in for example #sctp_paddr_change{}
          that identifies an association for an SCTP socket. The term
          is opaque except for the special value <c>0</c> that has a
          meaning such as "the whole endpoint" or "all future associations".</p>
        <marker id="type-charlist"></marker>
      </item>
      <tag><c>charlist() = [char()]</c></tag>
      <item>      <marker id="type-iolist"></marker>
</item>
      <tag><c>iolist() = [char() | binary()]</c></tag>
      <item>      <marker id="type-ip_address"></marker>
</item>
      <tag><c>ip_address()</c></tag>
      <item>
        <p>Represents an address of an SCTP socket. 
          It is a tuple as explained in
          <seealso marker="inet">inet(3)</seealso>.</p>
        <marker id="type-port_number"></marker>
      </item>
      <tag><c>port_number() = 0 .. 65535</c></tag>
      <item>      <marker id="type-posix"></marker>
</item>
      <tag><c>posix()</c></tag>
      <item>
        <p>See 
          <seealso marker="inet#error_codes">inet(3); POSIX Error Codes.</seealso></p>
        <marker id="type-sctp_option"></marker>
      </item>
      <tag><c>sctp_option()</c></tag>
      <item>
        <p>One of the 
          <seealso marker="#options">SCTP Socket Options.</seealso></p>
        <marker id="type-sctp_socket"></marker>
      </item>
      <tag><c>sctp_socket()</c></tag>
      <item>
        <p>Socket identifier returned from <c>open/*</c>.</p>
        <marker id="type-timeout"></marker>
      </item>
      <tag><c>timeout() = int() | infinity</c></tag>
      <item>
        <p>Timeout used in SCTP connect and receive calls.</p>
      </item>
    </taglist>
    <marker id="exports"></marker>
  </section>
  <funcs>
    <func>
      <name>abort(sctp_socket(), Assoc) -&gt; ok | {error, posix()}</name>
      <fsummary>Abnormally terminate the association given by Assoc, without flushing of unsent data</fsummary>
      <type>
        <v>Assoc = #sctp_assoc_change{}</v>
      </type>
      <desc>
        <p>Abnormally terminates the association given by <c>Assoc</c>, without
          flushing of unsent data. The socket itself remains open. Other
          associations opened on this socket are still valid, and it can be
          used in new associations.</p>
      </desc>
    </func>
    <func>
      <name>close(sctp_socket()) -&gt; ok | {error, posix()}</name>
      <fsummary>Completely close the socket and all associations on it</fsummary>
      <desc>
        <p>Completely closes the socket and all associations on it. The unsent
          data is flushed as in <c>eof/2</c>. The <c>close/1</c> call 
          is blocking or otherwise depending of the value of
          the <seealso marker="#option-linger">linger</seealso> socket
          <seealso marker="#options">option</seealso>.
          If <c>close</c> does not linger or linger timeout expires,
          the call returns and the data is flushed in the background.</p>
      </desc>
    </func>
    <func>
      <name>connect(Socket, Addr, Port, Opts) -&gt; {ok,Assoc} | {error, posix()}</name>
      <fsummary>Same as <c>connect(Socket, Addr, Port, Opts, infinity)</c>.</fsummary>
      <desc>
        <p>Same as <c>connect(Socket, Addr, Port, Opts, infinity)</c>.</p>
      </desc>
    </func>
    <func>
      <name>connect(Socket, Addr, Port, [Opt], Timeout) -&gt; {ok, Assoc} | {error, posix()}</name>
      <fsummary>Establish a new association for the socket <c>Socket</c>, with a peer (SCTP server socket)</fsummary>
      <type>
        <v>Socket  = sctp_socket()</v>
        <v>Addr    = ip_address() | Host</v>
        <v>Port    = port_number()</v>
        <v>Opt     = sctp_option()</v>
        <v>Timeout = timeout()</v>
        <v>Host    = atom() | string()</v>
        <v>Assoc   = #sctp_assoc_change{}</v>
      </type>
      <desc>
        <p>Establishes a new association for the socket <c>Socket</c>,
          with the peer (SCTP server socket) given by
          <c>Addr</c> and <c>Port</c>. The <c>Timeout</c>,
          is expressed in milliseconds.</p>
        <p>A socket can be associated with multiple peers.
                    <marker id="record-sctp_assoc_change"></marker>

          The result of <c>connect/*</c> is an <c>#sctp_assoc_change{}</c>
          event which contains, in particular, the new 
          <seealso marker="#type-assoc_id">Association ID:</seealso></p>
        <pre>
  #sctp_assoc_change{
        state             = atom(),
        error             = atom(),
        outbound_streams  = int(),
        inbound_streams   = int(),
        assoc_id          = assoc_id()
  }        </pre>
        <p>The number of outbound and inbound streams can be set by
          giving an <c>sctp_initmsg</c> option to <c>connect</c>
          as in:</p>
        <pre>
  connect(Socket, Ip, Port,
        [{sctp_initmsg,#sctp_initmsg{num_ostreams=OutStreams,
                                     max_instreams=MaxInStreams}}])        </pre>
        <p>All options <c>Opt</c> are set on the socket before the 
          association is attempted. If an option record has got undefined
          field values, the options record is first read from the socket
          for those values. In effect, <c>Opt</c> option records only 
          define field values to change before connecting.</p>
        <p>The returned <c>outbound_streams</c> and <c>inbound_streams</c>
          are the actual stream numbers on the socket, which may be different
          from the requested values (<c>OutStreams</c> and <c>MaxInStreams</c>
          respectively) if the peer requires lower values.</p>
        <p>The following values of <c>state</c> are possible:</p>
        <list type="bulleted">
          <item>
            <p><c>comm_up</c>: association successfully established. This
              indicates a successful completion of <c>connect</c>.</p>
          </item>
          <item>
            <p><c>cant_assoc</c>: association cannot be established
              (<c>connect/*</c> failure).</p>
          </item>
        </list>
        <p>All other states do not normally occur in the output from
          <c>connect/*</c>. Rather, they may occur in
          <c>#sctp_assoc_change{}</c> events received instead of data in
          <seealso marker="#recv/1">recv/*</seealso> calls.
          All of them indicate losing the association due to various
          error conditions, and are listed here for the sake of completeness.
          The <c>error</c> field may provide more detailed diagnostics.</p>
        <list type="bulleted">
          <item>
            <p><c>comm_lost</c>;</p>
          </item>
          <item>
            <p><c>restart</c>;</p>
          </item>
          <item>
            <p><c>shutdown_comp</c>.</p>
          </item>
        </list>
      </desc>
    </func>
    <func>
      <name>controlling_process(sctp_socket(), pid()) -&gt; ok</name>
      <fsummary>Assign a new controlling process pid to the socket</fsummary>
      <desc>
        <p>Assigns a new controlling process Pid to Socket. Same implementation
          as <c>gen_udp:controlling_process/2</c>.</p>
      </desc>
    </func>
    <func>
      <name>eof(Socket, Assoc) -&gt; ok | {error, Reason}</name>
      <fsummary>Gracefully terminate the association given by Assoc, with flushing of all unsent data</fsummary>
      <type>
        <v>Socket = sctp_socket()</v>
        <v>Assoc  = #sctp_assoc_change{}</v>
      </type>
      <desc>
        <p>Gracefully terminates the association given by <c>Assoc</c>, with
          flushing of all unsent data. The socket itself remains open. Other
          associations opened on this socket are still valid, and it can be
          used in new associations.</p>
      </desc>
    </func>
    <func>
      <name>listen(Socket, IsServer) -&gt; ok | {error, Reason}</name>
      <fsummary>Set up a socket to listen.</fsummary>
      <type>
        <v>Socket   = sctp_socket()</v>
        <v>IsServer = bool()</v>
      </type>
      <desc>
        <p>Sets up a socket to listen on the IP address and port number
          it is bound to. IsServer must be 'true' or 'false'.
          In the contrast to TCP, in SCTP there is no listening queue length.
          If IsServer is 'true' the socket accepts new associations, i.e.
          it will become an SCTP server socket.</p>
      </desc>
    </func>
    <func>
      <name>open() -&gt; {ok, Socket} | {error, posix()}</name>
      <name>open(Port) -&gt; {ok, Socket} | {error, posix()}</name>
      <name>open([Opt]) -&gt; {ok, Socket} | {error, posix()}</name>
      <name>open(Port, [Opt]) -&gt; {ok, Socket} | {error, posix()}</name>
      <fsummary>Create an SCTP socket and bind it to local addresses</fsummary>
      <type>
        <v>Opt  = {ip,IP} | {ifaddr,IP} | {port,Port} | sctp_option()</v>
        <v>IP   = ip_address() | any | loopback</v>
        <v>Port = port_number()</v>
      </type>
      <desc>
        <p>Creates an SCTP socket and binds it to the local addresses 
          specified by all <c>{ip,IP}</c> (or synonymously <c>{ifaddr,IP}</c>)
          options (this feature is called SCTP multi-homing).
          The default <c>IP</c> and <c>Port</c> are <c>any</c> 
          and <c>0</c>, meaning bind to all local addresses on any
          one free port.</p>
        <p>A default set of socket <seealso marker="#options">options</seealso>
          is used. In particular, the socket is opened in 
          <seealso marker="#option-binary">binary</seealso> and
          <seealso marker="#option-active">passive</seealso> mode,
          and with reasonably large
          <seealso marker="#option-sndbuf">kernel</seealso> and driver
          <seealso marker="#option-buffer">buffers.</seealso></p>
      </desc>
    </func>
    <func>
      <name>recv(sctp_socket()) -&gt; {ok, {FromIP, FromPort, AncData, BinMsg}} | {error, Reason}</name>
      <name>recv(sctp_socket(), timeout()) -&gt; {ok, {FromIP, FromPort, AncData, Data}} | {error, Reason}</name>
      <fsummary>Receive a message from a socket</fsummary>
      <type>
        <v>FromIP   = ip_address()</v>
        <v>FromPort = port_number()</v>
        <v>AncData  = [#sctp_sndrcvinfo{}]</v>
        <v>Data     = binary() | charlist() | #sctp_sndrcvinfo{} |
                      #sctp_assoc_change{} | #sctp_paddr_change{} |
                      #sctp_adaptation_event{} </v>
        <v>Reason   = posix() | #sctp_send_failed{} | #scpt_paddr_change{} |
                      #sctp_pdapi_event{} | #sctp_remote_error{} |
                      #sctp_shutdown_event{}</v>
      </type>
      <desc>
        <p>Receives the <c>Data</c> message from any association of the socket.
          If the receive times out <c>{error,timeout</c> is returned.
          The default timeout is <c>infinity</c>.
          <c>FromIP</c> and <c>FromPort</c> indicate the sender's address.</p>
        <p><c>AncData</c> is a list of Ancillary Data items which
          may be received along with the main <c>Data</c>.
          This list can be empty, or contain a single
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso>
          record, if receiving of such ancillary data is enabled
          (see option 
          <seealso marker="#option-sctp_events">sctp_events</seealso>).
          It is enabled by default, since such ancillary data
          provide an easy way of determining the association and stream
          over which the message has been received.
          (An alternative way would be to get the Association ID from the
          <c>FromIP</c> and <c>FromPort</c> using the
          <seealso marker="#option-sctp_get_peer_addr_info">sctp_get_peer_addr_info</seealso> socket option,
          but this would still not produce the Stream number).</p>
        <p>The actual <c>Data</c> received may be a <c>binary()</c>,
          or <c>list()</c> of bytes (integers in the range 0 through 255)
          depending on the socket mode, or an SCTP Event.
                    <marker id="sctp_events"></marker>

          The following SCTP Events are possible:</p>
        <list type="bulleted">
          <item>
            <p><seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso></p>
          </item>
          <item>
            <p><seealso marker="#record-sctp_assoc_change">#sctp_assoc_change{}</seealso>;</p>
          </item>
          <item>
            <pre>
  #sctp_paddr_change{
        addr      = {ip_address(),port()},
        state     = atom(),
        error     = int(),
        assoc_id  = assoc_id()
  }            </pre>
            <p>Indicates change of the status of the peer's IP address given by
              <c>addr</c> within the association <c>assoc_id</c>.
              Possible values of <c>state</c> (mostly self-explanatory) include:</p>
            <list type="bulleted">
              <item>
                <p><c>addr_unreachable</c>;</p>
              </item>
              <item>
                <p><c>addr_available</c>;</p>
              </item>
              <item>
                <p><c>addr_removed</c>;</p>
              </item>
              <item>
                <p><c>addr_added</c>;</p>
              </item>
              <item>
                <p><c>addr_made_prim</c>.</p>
              </item>
              <item>
                <p><c>addr_confirmed</c>.</p>
              </item>
            </list>
            <p>In case of an error (e.g. <c>addr_unreachable</c>), the
              <c>error</c> field provides additional diagnostics. In such cases,
              the <c>#sctp_paddr_change{}</c> Event is automatically 
              converted into an <c>error</c> term returned by 
              <c>gen_sctp:recv</c>. The <c>error</c> field value can be
              converted into a string using <c>error_string/1</c>.</p>
          </item>
          <item>
            <pre>
  #sctp_send_failed{
        flags     = true | false,
        error     = int(),
        info      = #sctp_sndrcvinfo{},
        assoc_id  = assoc_id()
        data      = binary()
  }            </pre>
            <p>The sender may receive this event if a send operation fails.
              The <c>flags</c> is a Boolean specifying whether the data have
              actually been transmitted over the wire; <c>error</c> provides
              extended diagnostics, use <c>error_string/1</c>;
              <c>info</c> is the original
              <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso> record used in the failed
              <seealso marker="#send/3">send/*,</seealso> and <c>data</c> 
              is the whole original data chunk attempted to be sent.</p>
            <p>In the current implementation of the Erlang/SCTP binding,
              this Event is internally converted into an <c>error</c> term 
              returned by <c>recv/*</c>.</p>
          </item>
          <item>
            <pre>
  #sctp_adaptation_event{
        adaptation_ind = int(),
        assoc_id       = assoc_id()
  }            </pre>
            <p>Delivered when a peer sends an Adaptation Layer Indication
              parameter (configured through the option
              <seealso marker="#option-sctp_adaptation_layer">sctp_adaptation_layer</seealso>).
              Note that with the current implementation of
              the Erlang/SCTP binding, this event is disabled by default.</p>
          </item>
          <item>
            <pre>
  #sctp_pdapi_event{
        indication = sctp_partial_delivery_aborted,
        assoc_id   = assoc_id()
  }            </pre>
            <p>A partial delivery failure. In the current implementation of
              the Erlang/SCTP binding, this Event is internally converted
              into an <c>error</c> term returned by <c>recv/*</c>.</p>
          </item>
        </list>
      </desc>
    </func>
    <func>
      <name>send(Socket, SndRcvInfo, Data) -&gt; ok | {error, Reason}</name>
      <fsummary>Send a message using an <c>#sctp_sndrcvinfo{}</c>record</fsummary>
      <type>
        <v>Socket     = sctp_socket()</v>
        <v>SndRcvInfo = #sctp_sndrcvinfo{}</v>
        <v>Data       = binary() | iolist()</v>
      </type>
      <desc>
        <p>Sends the <c>Data</c> message with all sending parameters from a
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso> record.
          This way, the user can specify the PPID (passed to the remote end)
          and Context (passed to the local SCTP layer) which can be used
          for example for error identification.
          However, such a fine level of user control is rarely required.
          The send/4 function is sufficient for most applications.</p>
      </desc>
    </func>
    <func>
      <name>send(Socket, Assoc, Stream, Data) -&gt; ok | {error, Reason}</name>
      <fsummary>Send a message over an existing association and given stream</fsummary>
      <type>
        <v>Socket = sctp_socket()</v>
        <v>Assoc  = #sctp_assoc_change{} | assoc_id()</v>
        <v>Stream = integer()</v>
        <v>Data   = binary() | iolist()</v>
      </type>
      <desc>
        <p>Sends <c>Data</c> message over an existing association and given
          stream.</p>
      </desc>
    </func>
    <func>
      <name>error_string(integer()) -> ok | string() | undefined</name>
      <fsummary>Translate an SCTP error number into a string</fsummary>
      <desc>
        <p>Translates an SCTP error number from for example 
          <c>#sctp_remote_error{}</c> or <c>#sctp_send_failed{}</c> into
          an explanatory string, or one of the atoms <c>ok</c> for no
          error and <c>undefined</c> for an unrecognized error.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="options"></marker>
    <title>SCTP SOCKET OPTIONS</title>
    <p>The set of admissible SCTP socket options is by construction
      orthogonal to the sets of TCP, UDP and generic INET options:
      only those options which are explicitly listed below are allowed
      for SCTP sockets. Options can be set on the socket using
      <c>gen_sctp:open/1,2</c> or <c>inet:setopts/2</c>,
      retrieved using <c>inet:getopts/2</c>, and when calling
      <c>gen_sctp:connect/4,5</c> options can be changed.</p>
    <marker id="option-binary"></marker>
    <marker id="option-list"></marker>
    <taglist>
      <tag><c>{mode, list|binary}</c>or just <c>list</c> or <c>binary</c>.</tag>
      <item>
        <p>Determines the type of data returned from <c>gen_sctp:recv/1,2</c>.</p>
        <marker id="option-active"></marker>
      </item>
      <tag><c>{active, true|false|once}</c></tag>
      <item>
        <list type="bulleted">
          <item>
            <p>If <c>false</c> (passive mode, the default),
              the caller needs to do an explicit <c>gen_sctp:recv</c> call
              in order to retrieve the available data from the socket.</p>
          </item>
          <item>
            <p>If <c>true</c> (full active mode), the pending data or events are
              sent to the owning process.</p>
            <p><em>NB:</em> This can cause the message queue to overflow,
              as there is no way to throttle the sender in this case
              (no flow control!).</p>
          </item>
          <item>
            <p>If <c>once</c>, only one message is automatically placed
              in the message queue, after that the mode is automatically
              re-set to passive. This provides flow control as well as
              the possibility for the receiver to listen for its incoming
              SCTP data interleaved with other inter-process messages.</p>
          </item>
        </list>
        <marker id="option-buffer"></marker>
      </item>
      <tag><c>{buffer, int()}</c></tag>
      <item>
        <p>Determines the size of the user-level software buffer used by
          the SCTP driver. Not to be confused with <c>sndbuf</c>
          and <c>recbuf</c> options which correspond to
          the kernel socket buffers. It is recommended
          to have <c>val(buffer) &gt;= max(val(sndbuf),val(recbuf))</c>.
          In fact, the <c>val(buffer)</c> is automatically set to
          the above maximum when <c>sndbuf</c> or <c>recbuf</c> values are set.</p>
      </item>
      <tag><c>{tos, int()}</c></tag>
      <item>
        <p>Sets the Type-Of-Service field on the IP datagrams being sent,
          to the given value, which effectively determines a prioritization
          policy for the outbound packets. The acceptable values
          are system-dependent. TODO: we do not provide
          symbolic names for these values yet.</p>
      </item>
      <tag><c>{priority, int()}</c></tag>
      <item>
        <p>A protocol-independent equivalent of <c>tos</c> above. Setting
          priority implies setting tos as well.</p>
      </item>
      <tag><c>{dontroute, true|false}</c></tag>
      <item>
        <p>By default <c>false</c>. If <c>true</c>, the kernel does not
          send packets via any gateway, only sends them to directly
          connected hosts.</p>
      </item>
      <tag><c>{reuseaddr, true|false}</c></tag>
      <item>
        <p>By default <c>false</c>. If true, the local binding address
          <c>{IP,Port}</c> of the socket can be re-used immediately:
          no waiting in the CLOSE_WAIT state is performed (may be
          required for high-throughput servers).</p>
        <marker id="option-linger"></marker>
      </item>
      <tag><c>{linger, {true|false, int()}</c></tag>
      <item>
        <p>Determines the timeout in seconds for flushing unsent data in the
          <c>gen_sctp:close/1</c> socket call. If the 1st component of the value
          tuple is <c>false</c>, the 2nd one is ignored, which means that
          <c>gen_sctp:close/1</c> returns immediately not waiting
          for data to be flushed. Otherwise, the 2nd component is
          the flushing time-out in seconds.</p>
        <marker id="option-sndbuf"></marker>
      </item>
      <tag><c>{sndbuf, int()}</c></tag>
      <item>
        <p>The size, in bytes, of the *kernel* send buffer for this socket.
          Sending errors would occur for datagrams larger than
          <c>val(sndbuf)</c>. Setting this option also adjusts
          the size of the driver buffer (see <c>buffer</c> above).</p>
      </item>
      <tag><c>{recbuf, int()}</c></tag>
      <item>
        <p>The size, in bytes, of the *kernel* recv buffer for this socket.
          Sending errors would occur for datagrams larger than
          <c>val(sndbuf)</c>. Setting this option also adjusts
          the size of the driver buffer (see <c>buffer</c> above).</p>
      </item>
      <tag><c>{sctp_rtoinfo, #sctp_rtoinfo{}}</c></tag>
      <item>
        <pre>
  #sctp_rtoinfo{
        assoc_id = assoc_id(),
        initial  = int(),
        max      = int(),
        min      = int()
  }        </pre>
        <p>Determines re-transmission time-out parameters, in milliseconds,
          for the association(s) given by <c>assoc_id</c>. 
          If <c>assoc_id = 0</c> (default) indicates the whole endpoint. See
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the exact semantics of the fields values.</p>
      </item>
      <tag><c>{sctp_associnfo, #sctp_assocparams{}}</c></tag>
      <item>
        <pre>
  #sctp_assocparams{
        assoc_id                 = assoc_id(),
        asocmaxrxt               = int(),
        number_peer_destinations = int(),
        peer_rwnd                = int(),
        local_rwnd               = int(),
        cookie_life              = int()
  }        </pre>
        <p>Determines association parameters for the association(s) given by
          <c>assoc_id</c>. <c>assoc_id = 0</c> (default) indicates
          the whole endpoint. See 
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the discussion of their semantics. Rarely used.</p>
      </item>
      <tag><c>{sctp_initmsg, #sctp_initmsg{}}</c></tag>
      <item>
        <pre>
  #sctp_initmsg{
       num_ostreams   = int(),
       max_instreams  = int(),
       max_attempts   = int(),
       max_init_timeo = int()
  }        </pre>
        <p>Determines the default parameters which this socket attempts
          to negotiate with its peer while establishing an association with it.
          Should be set after <c>open/*</c> but before the first
          <c>connect/*</c>. <c>#sctp_initmsg{}</c> can also be used
          as ancillary data with the first call of <c>send/*</c> to
          a new peer (when a new association is created).</p>
        <list type="bulleted">
          <item>
            <p><c>num_ostreams</c>: number of outbound streams;</p>
          </item>
          <item>
            <p><c>max_instreams</c>: max number of in-bound streams;</p>
          </item>
          <item>
            <p><c>max_attempts</c>: max re-transmissions while
              establishing an association;</p>
          </item>
          <item>
            <p><c>max_init_timeo</c>: time-out in milliseconds
              for establishing an association.</p>
          </item>
        </list>
        <p></p>
      </item>
      <tag><c>{sctp_autoclose, int()|infinity}</c></tag>
      <item>
        <p>Determines the time (in seconds) after which an idle association is
          automatically closed.</p>
      </item>
      <tag><c>{sctp_nodelay, true|false}</c></tag>
      <item>
        <p>Turns on|off the Nagle algorithm for merging small packets
          into larger ones (which improves throughput at the expense
          of latency).</p>
      </item>
      <tag><c>{sctp_disable_fragments, true|false}</c></tag>
      <item>
        <p>If <c>true</c>, induces an error on an attempt to send
          a message which is larger than the current PMTU size
          (which would require fragmentation/re-assembling).
          Note that message fragmentation does not affect
          the logical atomicity of its delivery; this option
          is provided for performance reasons only.</p>
      </item>
      <tag><c>{sctp_i_want_mapped_v4_addr, true|false}</c></tag>
      <item>
        <p>Turns on|off automatic mapping of IPv4 addresses into IPv6 ones
          (if the socket address family is AF_INET6).</p>
      </item>
      <tag><c>{sctp_maxseg, int()}</c></tag>
      <item>
        <p>Determines the maximum chunk size if message fragmentation is used.
          If <c>0</c>, the chunk size is limited by the Path MTU only.</p>
      </item>
      <tag><c>{sctp_primary_addr, #sctp_prim{}}</c></tag>
      <item>
        <pre>
  #sctp_prim{
        assoc_id = assoc_id(),
        addr     = {IP, Port}
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>For the association given by <c>assoc_id</c>,
          <c>{IP,Port}</c> must be one of the peer's addresses.
          This option determines that the given address is
          treated by the local SCTP stack as the peer's primary address.</p>
      </item>
      <tag><c>{sctp_set_peer_primary_addr, #sctp_setpeerprim{}}</c></tag>
      <item>
        <pre>
  #sctp_setpeerprim{
        assoc_id = assoc_id(),
        addr     = {IP, Port}
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>When set, informs the peer that it should use <c>{IP, Port}</c>
          as the primary address of the local endpoint for the association
          given by <c>assoc_id</c>.</p>
        <marker id="option-sctp_adaptation_layer"></marker>
      </item>
      <tag><c>{sctp_adaptation_layer, #sctp_setadaptation{}}</c></tag>
      <item>
        <marker id="record-sctp_setadaptation"></marker>
        <pre>
  #sctp_setadaptation{
        adaptation_ind = int()
  }        </pre>
        <p>When set, requests that the local endpoint uses the value given by
          <c>adaptation_ind</c> as the Adaptation Indication parameter for
          establishing new associations. See
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extenstions for SCTP</url> for more details.</p>
      </item>
      <tag><c>{sctp_peer_addr_params, #sctp_paddrparams{}}</c></tag>
      <item>
        <pre>
  #sctp_paddrparams{
        assoc_id   = assoc_id(),
        address    = {IP, Port},
        hbinterval = int(),
        pathmaxrxt = int(),
        pathmtu    = int(),
        sackdelay  = int(),
        flags      = list()
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>This option determines various per-address parameters for
          the association given by <c>assoc_id</c> and the peer address
          <c>address</c> (the SCTP protocol supports multi-homing,
          so more than 1 address can correspond to a given association).</p>
        <list type="bulleted">
          <item>
            <p><c>hbinterval</c>: heartbeat interval, in milliseconds;</p>
          </item>
          <item>
            <p><c>pathmaxrxt</c>: max number of retransmissions
              before this address is considered unreachable (and an
              alternative address is selected);</p>
          </item>
          <item>
            <p><c>pathmtu</c>: fixed Path MTU, if automatic discovery is
              disabled (see <c>flags</c> below);</p>
          </item>
          <item>
            <p><c>sackdelay</c>: delay in milliseconds for SAC messages
              (if the delay is enabled, see <c>flags</c> below);</p>
          </item>
          <item>
            <p><c>flags</c>: the following flags are available:</p>
            <list type="bulleted">
              <item>
                <p><c>hb_enable</c>:  enable heartbeat; </p>
              </item>
              <item>
                <p><c>hb_disable</c>: disable heartbeat;</p>
              </item>
              <item>
                <p><c>hb_demand</c>: initiate heartbeat immediately;</p>
              </item>
              <item>
                <p><c>pmtud_enable</c>: enable automatic Path MTU discovery;</p>
              </item>
              <item>
                <p><c>pmtud_disable</c>: disable automatic Path MTU discovery;</p>
              </item>
              <item>
                <p><c>sackdelay_enable</c>: enable SAC delay;</p>
              </item>
              <item>
                <p><c>sackdelay_disable</c>: disable SAC delay.</p>
              </item>
            </list>
            <p></p>
          </item>
        </list>
        <p></p>
      </item>
      <tag><c>{sctp_default_send_param, #sctp_sndrcvinfo{}}</c></tag>
      <item>
        <marker id="record-sctp_sndrcvinfo"></marker>
        <pre>
  #sctp_sndrcvinfo{
        stream     = int(),
        ssn        = int(),
        flags      = list(),
        ppid       = int(),
        context    = int(),
        timetolive = int(),
        tsn        = int(),
        cumtsn     = int(),
        assoc_id   = assoc_id()
  }        </pre>
        <p><c>#sctp_sndrcvinfo{}</c> is used both in this socket option, and as
          ancillary data while sending or receiving SCTP messages. When
          set as an option, it provides a default values for subsequent
          <c>gen_sctp:send</c>calls on the association given by
          <c>assoc_id</c>. <c>assoc_id = 0</c> (default) indicates
          the whole endpoint. The following fields typically need
          to be specified by the sender:</p>
        <list type="bulleted">
          <item>
            <p><c>sinfo_stream</c>: stream number (0-base) within the association
              to send the messages through;</p>
          </item>
          <item>
            <p><c>sinfo_flags</c>: the following flags are recognised:</p>
            <list type="bulleted">
              <item>
                <p><c>unordered</c>: the message is to be sent unordered;</p>
              </item>
              <item>
                <p><c>addr_over</c>: the address specified in
                  <c>gen_sctp:send</c> overwrites the primary peer address;</p>
              </item>
              <item>
                <p><c>abort</c>: abort the current association without
                  flushing any unsent data;</p>
              </item>
              <item>
                <p><c>eof</c>: gracefully shut down the current
                  association, with flushing of unsent data.</p>
              </item>
            </list>
            <p></p>
            <p>Other fields are rarely used. See 
              <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and 
              <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for full information.</p>
          </item>
        </list>
        <p></p>
        <marker id="option-sctp_events"></marker>
      </item>
      <tag><c>{sctp_events, #sctp_event_subscribe{}}</c></tag>
      <item>
        <marker id="record-sctp_event_subscribe"></marker>
        <pre>
  #sctp_event_subscribe{
          data_io_event          = true | false,
          association_event      = true | false,
          address_event          = true | false,
          send_failure_event     = true | false,
          peer_error_event       = true | false,
          shutdown_event         = true | false,
          partial_delivery_event = true | false,
          adaptation_layer_event = true | false
    }        </pre>
        <p>This option determines which
          <seealso marker="#sctp_events">SCTP Events</seealso> are to be
          received (via <seealso marker="#recv/1">recv/*</seealso>)
          along with the data. The only
          exception is <c>data_io_event</c> which enables or disables
          receiving of 
          <seealso marker="#record-sctp_sndrcvinfo">#sctp_sndrcvinfo{}</seealso>
          ancillary data, not events.
          By default, all flags except <c>adaptation_layer_event</c> are
          enabled, although <c>sctp_data_io_event</c> and
          <c>association_event</c> are used by the driver itself and not
          exported to the user level.</p>
      </item>
      <tag><c>{sctp_delayed_ack_time, #sctp_assoc_value{}}</c></tag>
      <item>
        <pre>
  #sctp_assoc_value{
        assoc_id    = assoc_id(),
        assoc_value = int()
  }        </pre>
        <p>Rarely used. Determines the ACK time
          (given by <c>assoc_value</c> in milliseconds) for
          the given association or the whole endpoint
          if <c>assoc_value = 0</c> (default).</p>
      </item>
      <tag><c>{sctp_status, #sctp_status{}}</c></tag>
      <item>
        <pre>
  #sctp_status{
        assoc_id            = assoc_id(),
        state               = atom(),
        rwnd                = int(),
        unackdata           = int(),
        penddata            = int(),
        instrms             = int(),
        outstrms            = int(),
        fragmentation_point = int(),
        primary             = #sctp_paddrinfo{}
  }        </pre>
        <p>This option is read-only. It determines the status of
          the SCTP association given by <c>assoc_id</c>. Possible values of
          <c>state</c> follows. The state designations are mostly
          self-explanatory. <c>state_empty</c> is the default which means
          that no other state is active:</p>
        <list type="bulleted">
          <item>
            <p><c>sctp_state_empty</c></p>
          </item>
          <item>
            <p><c>sctp_state_closed</c></p>
          </item>
          <item>
            <p><c>sctp_state_cookie_wait</c></p>
          </item>
          <item>
            <p><c>sctp_state_cookie_echoed</c></p>
          </item>
          <item>
            <p><c>sctp_state_established</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_pending</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_sent</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_received</c></p>
          </item>
          <item>
            <p><c>sctp_state_shutdown_ack_sent</c></p>
          </item>
        </list>
        <p>The semantics of other fields is the following:</p>
        <list type="bulleted">
          <item>
            <p><c>sstat_rwnd</c>: the association peer's current receiver
              window size;</p>
          </item>
          <item>
            <p><c>sstat_unackdata</c>: number of unacked data chunks;</p>
          </item>
          <item>
            <p><c>sstat_penddata</c>: number of data chunks pending receipt;</p>
          </item>
          <item>
            <p><c>sstat_instrms</c>: number of inbound streams;</p>
          </item>
          <item>
            <p><c>sstat_outstrms</c>: number of outbound streams;</p>
          </item>
          <item>
            <p><c>sstat_fragmentation_point</c>: message size at which SCTP
              fragmentation will occur;</p>
          </item>
          <item>
            <p><c>sstat_primary</c>: information on the current primary peer
              address (see below for the format of <c>#sctp_paddrinfo{}</c>).</p>
          </item>
        </list>
        <p></p>
        <marker id="option-sctp_get_peer_addr_info"></marker>
      </item>
      <tag><c>{sctp_get_peer_addr_info, #sctp_paddrinfo{}}</c></tag>
      <item>
        <marker id="record-sctp_paddrinfo"></marker>
        <pre>
  #sctp_paddrinfo{
        assoc_id  = assoc_id(),
        address   = {IP, Port},
        state     = inactive | active,
        cwnd      = int(),
        srtt      = int(),
        rto       = int(),
        mtu       = int()
  }
  IP = ip_address()
  Port = port_number()        </pre>
        <p>This option is read-only. It determines the parameters specific to
          the peer's address given by <c>address</c> within the association
          given by <c>assoc_id</c>. The <c>address</c> field must be set by the
          caller; all other fields are filled in on return.
          If <c>assoc_id = 0</c> (default), the <c>address</c>
          is automatically translated into the corresponding
          association ID. This option is rarely used; see
          <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> and
          <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP</url> for the semantics of all fields.</p>
      </item>
    </taglist>
  </section>

  <section>
    <marker id="examples"></marker>
    <title>SCTP EXAMPLES</title>
    <list type="bulleted">
      <item>
        <p>Example of an Erlang SCTP Server which receives SCTP messages and
          prints them on the standard output:</p>
        <pre>
  -module(sctp_server).
  
  -export([server/0,server/1,server/2]).
  -include_lib("kernel/include/inet.hrl").
  -include_lib("kernel/include/inet_sctp.hrl").
  
  server() -&gt;
      server(any, 2006).
  
  server([Host,Port]) when is_list(Host), is_list(Port) -&gt;
      {ok, #hostent{h_addr_list = [IP|_]}} = inet:gethostbyname(Host),
      io:format("~w -&gt; ~w~n", [Host, IP]),
      server([IP, list_to_integer(Port)]).
  
  server(IP, Port) when is_tuple(IP) orelse IP == any orelse IP == loopback,
                        is_integer(Port) -&gt;
      {ok,S} = gen_sctp:open([{ip,IP},{port,Port}],[{recbuf,65536}]),
      io:format("Listening on ~w:~w. ~w~n", [IP,Port,S]),
      ok     = gen_sctp:listen(S, true),
      server_loop(S).
  
  server_loop(S) -&gt;
      case gen_sctp:recv(S) of
      {error, Error} -&gt;
          io:format("SCTP RECV ERROR: ~p~n", [Error]);
      Data -&gt;
          io:format("Received: ~p~n", [Data])
      end,
      server_loop(S).        </pre>
        <p></p>
      </item>
      <item>
        <p>Example of an Erlang SCTP Client which interacts with the above Server.
          Note that in this example, the Client creates an association with
          the Server with 5 outbound streams. For this reason, sending of
          "Test 0" over Stream 0 succeeds, but sending of "Test 5"
          over Stream 5 fails. The client then <c>abort</c>s the association,
          which results in the corresponding Event being received on
          the Server side.</p>
        <pre>
  -module(sctp_client).
  
  -export([client/0, client/1, client/2]).
  -include_lib("kernel/include/inet.hrl").
  -include_lib("kernel/include/inet_sctp.hrl").
 
  client() -&gt;
      client([localhost]).
  
  client([Host]) -&gt;
      client(Host, 2006);
  
  client([Host, Port]) when is_list(Host), is_list(Port) -&gt;
      client(Host,list_to_integer(Port)),
      init:stop().
  
  client(Host, Port) when is_integer(Port) -&gt;
      {ok,S}     = gen_sctp:open(),
      {ok,Assoc} = gen_sctp:connect
          (S, Host, Port, [{sctp_initmsg,#sctp_initmsg{num_ostreams=5}}]),
      io:format("Connection Successful, Assoc=~p~n", [Assoc]),
      
      io:write(gen_sctp:send(S, Assoc, 0, &lt;&lt;"Test 0"&gt;&gt;)),
      io:nl(),
      timer:sleep(10000),
      io:write(gen_sctp:send(S, Assoc, 5, &lt;&lt;"Test 5"&gt;&gt;)),
      io:nl(),
      timer:sleep(10000),
      io:write(gen_sctp:abort(S, Assoc)),
      io:nl(),
      
      timer:sleep(1000),
      gen_sctp:close(S).        </pre>
        <p></p>
      </item>
    </list>
  </section>

  <section>
    <marker id="seealso"></marker>
    <title>SEE ALSO</title>
    <p><seealso marker="inet">inet(3)</seealso>,
      <seealso marker="gen_tcp">gen_tcp(3)</seealso>,
      <seealso marker="gen_udp">gen_upd(3)</seealso>,
      <url href="http://www.rfc-archive.org/getrfc.php?rfc=2960">RFC2960</url> (Stream Control Transmission Protocol),
      <url href="http://tools.ietf.org/html/draft-ietf-tsvwg-sctpsocket-13">Sockets API Extensions for SCTP.</url></p>
    <marker id="authors"></marker>
  </section>
</erlref>