aboutsummaryrefslogtreecommitdiffstats
path: root/lib/kernel/doc/src/inet.xml
blob: bf6c4cfb1ab0d7f8ba950b2751d248dfd7fddd9a (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
<?xml version="1.0" encoding="latin1" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1997</year><year>2012</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>inet</title>
    <prepared>[email protected]</prepared>
    <docno></docno>
    <date>1998-02-04</date>
    <rev>A</rev>
  </header>
  <module>inet</module>
  <modulesummary>Access to TCP/IP Protocols</modulesummary>
  <description>
    <p>Provides access to TCP/IP protocols.</p>
    <p>See also <em>ERTS User's Guide, Inet configuration</em> for more
      information on how to configure an Erlang runtime system for IP
      communication.</p>
    <p>Two Kernel configuration parameters affect the behaviour of all
      sockets opened on an Erlang node:
      <c>inet_default_connect_options</c> can contain a list of default
      options used for all sockets returned when doing <c>connect</c>,
      and <c>inet_default_listen_options</c> can contain a list of
      default options used when issuing a <c>listen</c> call. When
      <c>accept</c> is issued, the values of the listensocket options
      are inherited, why no such application variable is needed for
      <c>accept</c>.</p>
    <p>Using the Kernel configuration parameters mentioned above, one
      can set default options for all TCP sockets on a node. This should
      be used with care, but options like <c>{delay_send,true}</c>
      might be specified in this way. An example of starting an Erlang
      node with all sockets using delayed send could look like this:</p>
    <pre>
$ <input>erl -sname test -kernel \</input>
<input>inet_default_connect_options '[{delay_send,true}]' \</input>
<input>inet_default_listen_options '[{delay_send,true}]'</input></pre>
    <p>Note that the default option <c>{active, true}</c> currently
      cannot be changed, for internal reasons.</p>
    <p>Addresses as inputs to functions can be either a string or a
      tuple. For instance, the IP address 150.236.20.73 can be passed to
      <c>gethostbyaddr/1</c> either as the string "150.236.20.73"
      or as the tuple <c>{150, 236, 20, 73}</c>.</p>
    <p>IPv4 address examples:</p>
    <code type="none">
Address          ip_address()
-------          ------------
127.0.0.1        {127,0,0,1}
192.168.42.2     {192,168,42,2}</code>
    <p>IPv6 address examples:</p>
    <code type="none">
Address          ip_address()
-------          ------------
::1             {0,0,0,0,0,0,0,1}
::192.168.42.2  {0,0,0,0,0,0,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
FFFF::192.168.42.2
                {16#FFFF,0,0,0,0,0,(192 bsl 8) bor 168,(42 bsl 8) bor 2}
3ffe:b80:1f8d:2:204:acff:fe17:bf38
                {16#3ffe,16#b80,16#1f8d,16#2,16#204,16#acff,16#fe17,16#bf38}
fe80::204:acff:fe17:bf38
                {16#fe80,0,0,0,0,16#204,16#acff,16#fe17,16#bf38}</code>
    <p>A function that may be useful is <c>inet_parse:address/1</c>:</p>
    <pre>
1> <input>inet_parse:address("192.168.42.2").</input>
{ok,{192,168,42,2}}
2> <input>inet_parse:address("FFFF::192.168.42.2").</input>
{ok,{65535,0,0,0,0,0,49320,10754}}</pre>
  </description>

  <datatypes>
    <datatype>
      <name name="hostent"/>
      <desc>
        <p>The record is defined in the Kernel include file "inet.hrl".
          Add the following directive to the module:</p>
<code>-include_lib("kernel/include/inet.hrl").</code></desc>
    </datatype>
    <datatype>
      <name name="hostname"/>
    </datatype>
    <datatype>
      <name name="ip_address"/>
    </datatype>
    <datatype>
      <name name="ip4_address"/>
    </datatype>
    <datatype>
      <name name="ip6_address"/>
    </datatype>
    <datatype>
      <name name="port_number"/>
    </datatype>
    <datatype>
      <name name="posix"/>
      <desc><p>An atom which is named from the Posix error codes
         used in Unix, and in the runtime libraries of most
          C compilers. See
          <seealso marker="#error_codes">POSIX Error Codes</seealso>.</p>
      </desc>
    </datatype>
    <datatype>
      <name><marker id="type-socket">socket()</marker></name>
      <desc><p>See <seealso marker="gen_tcp#type-socket">gen_tcp(3)</seealso>
         and <seealso marker="gen_udp#type-socket">gen_udp(3)</seealso>.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="address_family"/>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="close" arity="1"/>
      <fsummary>Close a socket of any type</fsummary>
      <desc>
        <p>Closes a socket of any type.</p>
      </desc>
    </func>
    <func>
      <name name="get_rc" arity="0"/>
      <fsummary>Return a list of IP configuration parameters</fsummary>
      <desc>
        <p>Returns the state of the Inet configuration database in 
          form of a list of recorded configuration parameters. (See the
          ERTS User's Guide, Inet configuration, for more information).
          Only parameters with other than default values are returned.</p>
      </desc>
    </func>
    <func>
      <name name="format_error" arity="1"/>
      <fsummary>Return a descriptive string for an error reason</fsummary>
      <desc>
        <p>Returns a diagnostic error string. See the section below
          for possible Posix values and the corresponding
          strings.</p>
      </desc>
    </func>
    <func>
      <name name="getaddr" arity="2"/>
      <fsummary>Return the IP-address for a host</fsummary>
      <desc>
        <p>Returns the IP-address for <c><anno>Host</anno></c> as a tuple of
          integers. <c><anno>Host</anno></c> can be an IP-address, a single hostname
          or a fully qualified hostname.</p>
      </desc>
    </func>
    <func>
      <name name="getaddrs" arity="2"/>
      <fsummary>Return the IP-addresses for a host</fsummary>
      <desc>
        <p>Returns a list of all IP-addresses for <c><anno>Host</anno></c>.
          <c><anno>Host</anno></c> can be an IP-address, a single hostname or a fully
          qualified hostname.</p>
      </desc>
    </func>
    <func>
      <name name="gethostbyaddr" arity="1"/>
      <fsummary>Return a hostent record for the host with the given address</fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record given an address.</p>
      </desc>
    </func>
    <func>
      <name name="gethostbyname" arity="1"/>
      <fsummary>Return a hostent record for the host with the given name</fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record given a hostname.</p>
      </desc>
    </func>
    <func>
      <name name="gethostbyname" arity="2"/>
      <fsummary>Return a hostent record for the host with the given name</fsummary>
      <desc>
        <p>Returns a <c>hostent</c> record given a hostname, restricted
          to the given address family.</p>
      </desc>
    </func>
    <func>
      <name name="gethostname" arity="0"/>
      <fsummary>Return the local hostname</fsummary>
      <desc>
        <p>Returns the local hostname. Will never fail.</p>
      </desc>
    </func>

    <func>
      <name name="getifaddrs" arity="0"/>
      <fsummary>Return a list of interfaces and their addresses</fsummary>
    <desc>
      <p>
	Returns a list of 2-tuples containing interface names and the
	interface's addresses. <c><anno>Ifname</anno></c> is a Unicode string.
	<c><anno>Hwaddr</anno></c> is hardware dependent, e.g on Ethernet interfaces
	it is the 6-byte Ethernet address (MAC address (EUI-48 address)).
      </p>
      <p>
	The <c>{addr,<anno>Addr</anno>}</c>, <c>{netmask,_}</c> and <c>{broadaddr,_}</c>
	tuples are repeated in the result list iff the interface has multiple
	addresses. If you come across an interface that has
	multiple <c>{flag,_}</c> or <c>{hwaddr,_}</c> tuples you have
	a really strange interface or possibly a bug in this function.
	The <c>{flag,_}</c> tuple is mandatory, all other optional.
      </p>
      <p>
	Do not rely too much on the order of <c><anno>Flag</anno></c> atoms or
	<c><anno>Ifopt</anno></c> tuples. There are some rules, though:
	<list>
	  <item>
	    Immediately after <c>{addr,_}</c> follows <c>{netmask,_}</c>
	  </item>
	  <item>
	    Immediately thereafter follows <c>{broadaddr,_}</c> if
	    the <c>broadcast</c> flag is <em>not</em> set and the
	    <c>pointtopoint</c> flag <em>is</em> set.
	  </item>
	  <item>
	    Any <c>{netmask,_}</c>, <c>{broadaddr,_}</c> or
	    <c>{dstaddr,_}</c> tuples that follow an <c>{addr,_}</c>
	    tuple concerns that address.
	  </item>
	</list>
      </p>
      <p>
	The <c>{hwaddr,_}</c> tuple is not returned on Solaris since the
	hardware address historically belongs to the link layer and only
	the superuser can read such addresses.
      </p>
      <p>
	On Windows, the data is fetched from quite different OS API
	functions, so the <c><anno>Netmask</anno></c> and <c><anno>Broadaddr</anno></c>
	values may be calculated, just as some <c><anno>Flag</anno></c> values.
	You have been warned. Report flagrant bugs.
      </p>
    </desc>
    </func>

    <func>
      <name name="getopts" arity="2"/>
      <fsummary>Get one or more options for a socket</fsummary>
      <type name="socket_getopt"/>
      <type name="socket_setopt"/>
      <desc>
        <p>Gets one or more options for a socket. 
          See <seealso marker="#setopts/2">setopts/2</seealso> 
          for a list of available options.</p>
        <p>The number of elements in the returned <c><anno>OptionValues</anno></c>
          list does not necessarily correspond to the number of options
          asked for. If the operating system fails to support an option,
          it is simply left out in the returned list. An error tuple is only
          returned when getting options for the socket is impossible
          (i.e. the socket is closed or the buffer size in a raw request
          is too large). This behavior is kept for backward
          compatibility reasons.</p>
        <p>A raw option request <c>RawOptReq = {raw, Protocol, OptionNum, ValueSpec}</c> can be used to get information about
          socket options not (explicitly) supported by the emulator. The
          use of raw socket options makes the code non portable, but
          allows the Erlang programmer to take advantage of unusual features
          present on the current platform.</p>
        <p>The <c>RawOptReq</c> consists of the tag <c>raw</c> followed
          by the protocol level, the option number and either a binary
          or the size, in bytes, of the
          buffer in which the option value is to be stored. A binary
          should be used when the underlying <c>getsockopt</c> requires 
          <em>input</em>
          in the argument field, in which case the size of the binary
          should correspond to the required buffer
          size of the return value. The supplied values in a <c>RawOptReq</c>
          correspond to the second, third and fourth/fifth parameters to the
          <c>getsockopt</c> call in the C socket API. The value stored
          in the buffer is returned as a binary <c>ValueBin</c> 
          where all values are coded in the native endianess.</p>
        <p>Asking for and inspecting raw socket options require low
          level information about the current operating system and TCP
          stack.</p>
        <p>As an example, consider a Linux machine where the
          <c>TCP_INFO</c> option could be used to collect TCP statistics
          for a socket. Lets say we're interested in the
          <c>tcpi_sacked</c> field of the <c>struct tcp_info</c>
          filled in when asking for <c>TCP_INFO</c>. To
          be able to access this information, we need to know both the
          numeric value of the protocol level <c>IPPROTO_TCP</c>, the
          numeric value of the option <c>TCP_INFO</c>, the size of the
          <c>struct tcp_info</c> and the size and offset of
          the specific field. By inspecting the headers or writing a small C
          program, we found <c>IPPROTO_TCP</c> to be 6,
          <c>TCP_INFO</c> to be 11, the structure size to be 92 (bytes),
          the offset of <c>tcpi_sacked</c> to be 28 bytes and the actual
          value to be a 32 bit integer. We could use the following
          code to retrieve the value:</p>
        <code type="none"><![CDATA[
        get_tcpi_sacked(Sock) -> 
            {ok,[{raw,_,_,Info}]} = inet:getopts(Sock,[{raw,6,11,92}]),
            <<_:28/binary,TcpiSacked:32/native,_/binary>> = Info,
            TcpiSacked.]]></code>
        <p>Preferably, you would check the machine type, the OS
          and the kernel version prior to executing anything similar to the
          code above.</p>
      </desc>
    </func>

    <func>
      <name name="getstat" arity="1"/>
      <name name="getstat" arity="2"/>
      <fsummary>Get one or more statistic options for a socket</fsummary>
      <type name="stat_option"/>
      <desc>
        <p>Gets one or more statistic options for a socket.</p>
	<p><c>getstat(<anno>Socket</anno>)</c> is equivalent to
	<c>getstat(<anno>Socket</anno>,&nbsp;[recv_avg,&nbsp;recv_cnt,&nbsp;recv_dvi,&nbsp;recv_max,&nbsp;recv_oct,&nbsp;send_avg,&nbsp;send_cnt,&nbsp;send_dvi,&nbsp;send_max,&nbsp;send_oct])</c></p>
	  <p>The following options are available:</p>
        <taglist>
	  <tag><c>recv_avg</c></tag>
	  <item>
            <p>Average size of packets in bytes received to the socket.</p>
	  </item>
	  <tag><c>recv_cnt</c></tag>
	  <item>
            <p>Number of packets received to the socket.</p>
	  </item>
	  <tag><c>recv_dvi</c></tag>
	  <item>
            <p>Average packet size deviation in bytes received to the socket.</p>
	  </item>
	  <tag><c>recv_max</c></tag>
	  <item>
            <p>The size of the largest packet in bytes received to the socket.</p>
	  </item>
	  <tag><c>recv_oct</c></tag>
	  <item>
            <p>Number of bytes received to the socket.</p>
	  </item>

	  <tag><c>send_avg</c></tag>
	  <item>
            <p>Average size of packets in bytes sent from the socket.</p>
	  </item>
	  <tag><c>send_cnt</c></tag>
	  <item>
            <p>Number of packets sent from the socket.</p>
	  </item>
	  <tag><c>send_dvi</c></tag>
	  <item>
            <p>Average packet size deviation in bytes received sent from the socket.</p>
	  </item>
	  <tag><c>send_max</c></tag>
	  <item>
            <p>The size of the largest packet in bytes sent from the socket.</p>
	  </item>
	  <tag><c>send_oct</c></tag>
	  <item>
            <p>Number of bytes sent from the socket.</p>
	  </item>
        </taglist>
      </desc>
    </func>

    <func>
      <name name="peername" arity="1"/>
      <fsummary>Return the address and port for the other end of a connection</fsummary>
      <desc>
        <p>Returns the address and port for the other end of a
          connection.</p>
      </desc>
    </func>
    <func>
      <name name="port" arity="1"/>
      <fsummary>Return the local port number for a socket</fsummary>
      <desc>
        <p>Returns the local port number for a socket.</p>
      </desc>
    </func>
    <func>
      <name name="sockname" arity="1"/>
      <fsummary>Return the local address and port number for a socket</fsummary>
      <desc>
        <p>Returns the local address and port number for a socket.</p>
      </desc>
    </func>
    <func>
      <name name="setopts" arity="2"/>
      <fsummary>Set one or more options for a socket</fsummary>
      <type name="socket_setopt"/>
      <desc>
        <p>Sets one or more options for a socket. The following options
          are available:</p>
        <taglist>
          <tag><c>{active, true | false | once}</c></tag>
          <item>
            <p>If the value is <c>true</c>, which is the default,
              everything received from the socket will be sent as
              messages to the receiving process. If the value is
              <c>false</c> (passive mode), the process must explicitly
              receive incoming data by calling <c>gen_tcp:recv/2,3</c>
              or <c>gen_udp:recv/2,3</c> (depending on the type of
              socket).</p>
            <p>If the value is <c>once</c> (<c>{active, once}</c>),
              <em>one</em> data message from the socket will be sent
              to the process.  To receive one more message,
              <c>setopts/2</c> must be called again with the
              <c>{active, once}</c> option.</p>
            <p>When using <c>{active, once}</c>, the socket changes
              behaviour automatically when data is received. This can
              sometimes be confusing in combination with connection
              oriented sockets (i.e. <c>gen_tcp</c>) as a socket with
              <c>{active, false}</c> behaviour reports closing
              differently than a socket with <c>{active, true}</c>
              behaviour. To make programming easier, a socket where
              the peer closed and this was detected while in
              <c>{active, false}</c> mode, will still generate the
              message
              <c>{tcp_closed,Socket}</c> when set to <c>{active, once}</c> or <c>{active, true}</c> mode. It is therefore
              safe to assume that the message
              <c>{tcp_closed,Socket}</c>, possibly followed by socket
              port termination (depending on the <c>exit_on_close</c>
              option) will eventually appear when a socket changes
              back and forth between <c>{active, true}</c> and
              <c>{active, false}</c> mode. However, 
              <em>when</em> peer closing is detected is all up to the
              underlying TCP/IP stack and protocol.</p>
            <p>Note that <c>{active,true}</c> mode provides no flow
              control; a fast sender could easily overflow the
              receiver with incoming messages. Use active mode only if
              your high-level protocol provides its own flow control
              (for instance, acknowledging received messages) or the
              amount of data exchanged is small. <c>{active,false}</c>
              mode or use of the <c>{active, once}</c> mode provides
              flow control; the other side will not be able send
              faster than the receiver can read.</p>
          </item>
          <tag><c>{broadcast, Boolean}</c>(UDP sockets)</tag>
          <item>
            <p>Enable/disable permission to send broadcasts.</p>
          </item>
          <tag><c>{delay_send, Boolean}</c></tag>
          <item>
            <p>Normally, when an Erlang process sends to a socket,
              the driver will try to immediately send the data. If that
              fails, the driver will use any means available to queue
              up the message to be sent whenever the operating system
              says it can handle it. Setting <c>{delay_send, true}</c>
              will make <em>all</em> messages queue up. This makes
              the messages actually sent onto the network be larger but
              fewer. The option actually affects the scheduling of send
              requests versus Erlang processes instead of changing any
              real property of the socket. Needless to say it is an
              implementation specific option. Default is <c>false</c>.</p>
          </item>
          <tag><c>{dontroute, Boolean}</c></tag>
          <item>
            <p>Enable/disable routing bypass for outgoing messages.</p>
          </item>
          <tag><c>{exit_on_close, Boolean}</c></tag>
          <item>
            <p>By default this option is set to <c>true</c>.</p>
            <p>The only reason to set it to <c>false</c> is if you want
              to continue sending data to the socket after a close has
              been detected, for instance if the peer has used
              <seealso marker="gen_tcp#shutdown/2">gen_tcp:shutdown/2</seealso>
              to shutdown the write side.</p>
          </item>
          <tag><c>{header, Size}</c></tag>
          <item>
            <p>This option is only meaningful if the <c>binary</c>
              option was specified when the socket was created. If
              the <c>header</c> option is specified, the first
              <c>Size</c> number bytes of data received from the socket
              will be elements of a list, and the rest of the data will
              be a binary given as the tail of the same list. If for
              example <c>Size == 2</c>, the data received will match
              <c>[Byte1,Byte2|Binary]</c>.</p>
          </item>
          <tag><c>{keepalive, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Enables/disables periodic transmission on a connected
              socket, when no other data is being exchanged. If
              the other end does not respond, the connection is
              considered broken and an error message will be sent to
              the controlling process. Default disabled.</p>
          </item>
          <tag><c>{nodelay, Boolean}</c>(TCP/IP sockets)</tag>
          <item>
            <p>If <c>Boolean == true</c>, the <c>TCP_NODELAY</c> option
              is turned on for the socket, which means that even small
              amounts of data will be sent immediately.</p>
          </item>
          <tag><c>{packet, PacketType}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Defines the type of packets to use for a socket.
              The following values are valid:</p>
            <taglist>
              <tag><c>raw | 0</c></tag>
              <item>
                <p>No packaging is done.</p>
              </item>
              <tag><c>1 | 2 | 4</c></tag>
              <item>
                <p>Packets consist of a header specifying the number of
                  bytes in the packet, followed by that number of bytes.
                  The length of header can be one, two, or four bytes;
                  containing an unsigned integer in big-endian byte order.
                  Each send operation will generate the header, and the header
                  will be stripped off on each receive operation.</p>
                <p>In current implementation the 4-byte header is limited to 2Gb.</p>
              </item>
              <tag><c>asn1 | cdr | sunrm | fcgi | tpkt | line</c></tag>
              <item>
                <p>These packet types only have effect on receiving.
                  When sending a packet, it is the responsibility of
                  the application to supply a correct header. On
                  receiving, however, there will be one message sent to
                  the controlling process for each complete packet
                  received, and, similarly, each call to
                  <c>gen_tcp:recv/2,3</c> returns one complete packet.
                  The header is <em>not</em> stripped off.</p>
                <p>The meanings of the packet types are as follows:
                                    <br></br>
<c>asn1</c> - ASN.1 BER,
                                    <br></br>
<c>sunrm</c> - Sun's RPC encoding,
                                    <br></br>
<c>cdr</c> - CORBA (GIOP 1.1),
                                    <br></br>
<c>fcgi</c> - Fast CGI,
                                    <br></br>
<c>tpkt</c> - TPKT format [RFC1006],
                                    <br></br>
<c>line</c> - Line mode, a packet is a line
                  terminated with newline, lines longer than
                  the receive buffer are truncated.</p>
              </item>
              <tag><c>http | http_bin</c></tag>
              <item>
                <p>The Hypertext Transfer Protocol. The packets
                 are returned with the format according to <c>HttpPacket</c>
                 described in <seealso marker="erts:erlang#decode_packet/3">
                 erlang:decode_packet/3</seealso>. A socket in passive
                 mode will return <c>{ok, HttpPacket}</c> from <c>gen_tcp:recv</c>
                 while an active socket will send messages like <c>{http,
                 Socket, HttpPacket}</c>.</p>
              </item>
              <tag><c>httph | httph_bin</c></tag>
              <item>
                <p>These two types are often not needed as the socket will
		automatically switch from <c>http</c>/<c>http_bin</c> to
		<c>httph</c>/<c>httph_bin</c> internally after the first line
		has been read. There might be occasions however when they are
		useful, such as parsing trailers from chunked encoding.</p>
              </item>
            </taglist>
          </item>
          <tag><c>{packet_size, Integer}</c>(TCP/IP sockets)</tag>
          <item>
            <p>Sets the max allowed length of the packet body. If
              the packet header indicates that the length of the packet
              is longer than the max allowed length, the packet is
              considered invalid. The same happens if the packet header
              is too big for the socket receive buffer.</p>
	    <p>For line oriented protocols (<c>line</c>,<c>http*</c>),
	    option <c>packet_size</c> also guarantees that lines up to the
	    indicated length are accepted and not considered invalid due
	    to internal buffer limitations.</p>
          </item>
          <tag><c>{read_packets, Integer}</c>(UDP sockets)</tag>
          <item>
            <p>Sets the max number of UDP packets to read without
              intervention from the socket when data is available.
              When this many packets have been read and delivered
              to the destination process, new packets are not read
              until a new notification of available data has arrived.
              The default is 5, and if this parameter is set too
              high the system can become unresponsive due to
              UDP packet flooding.</p>
          </item>
          <tag><c>{recbuf, Integer}</c></tag>
          <item>
            <p>Gives the size of the receive buffer to use for
              the socket.</p>
          </item>
          <tag><c>{reuseaddr, Boolean}</c></tag>
          <item>
            <p>Allows or disallows local reuse of port numbers. By
              default, reuse is disallowed.</p>
          </item>
          <tag><c>{send_timeout, Integer}</c></tag>
          <item>
            <p>Only allowed for connection oriented sockets.</p>
            <p>Specifies a longest time to wait for a send operation to
              be accepted by the underlying TCP stack. When the limit is
              exceeded, the send operation will return
              <c>{error,timeout}</c>. How much of a packet that actually
              got sent is unknown, why the socket should be closed
              whenever a timeout has occurred (see <c>send_timeout_close</c>).
              Default is <c>infinity</c>.</p>
          </item>
          <tag><c>{send_timeout_close, Boolean}</c></tag>
          <item>
            <p>Only allowed for connection oriented sockets.</p>
            <p>Used together with <c>send_timeout</c> to specify whether
              the socket will be automatically closed when the send operation
              returns <c>{error,timeout}</c>. The recommended setting is
              <c>true</c> which will automatically close the socket.
              Default is <c>false</c> due to backward compatibility.</p>
          </item>

          <tag><c>{sndbuf, Integer}</c></tag>
          <item>
            <p>Gives the size of the send buffer to use for the socket.</p>
          </item>
          <tag><c>{priority, Integer}</c></tag>
          <item>
            <p>Sets the SO_PRIORITY socket level option on platforms where 
              this is implemented. The behaviour and allowed range varies on 
              different systems. The option is ignored on platforms where the 
              option is not implemented. Use with caution.</p>
          </item>
          <tag><c>{tos, Integer}</c></tag>
          <item>
            <p>Sets IP_TOS IP level options on platforms where this is 
              implemented. The behaviour and allowed range varies on different 
              systems. The option is ignored on platforms where the option is 
              not implemented. Use with caution.</p>
          </item>
        </taglist>
        <p>In addition to the options mentioned above, <em>raw</em>
          option specifications can be used. The raw options are
          specified as a tuple of arity four, beginning with the tag
          <c>raw</c>, followed by the protocol level, the option number
          and the actual option value specified as a binary. This
          corresponds to the second, third and fourth argument to the
          <c>setsockopt</c> call in the C socket API. The option value
          needs to be coded in the native endianess of the platform and,
          if a structure is required, needs to follow the struct
          alignment conventions on the specific platform.</p>
        <p>Using raw socket options require detailed knowledge about
          the current operating system and TCP stack.</p>
        <p>As an example of the usage of raw options, consider a Linux
          system where you want to set the <c>TCP_LINGER2</c> option on
          the <c>IPPROTO_TCP</c> protocol level in the stack. You know
          that on this particular system it defaults to 60 (seconds),
          but you would like to lower it to 30 for a particular
          socket. The <c>TCP_LINGER2</c> option is not explicitly
          supported by inet, but you know that the protocol level
          translates to the number 6, the option number to the number 8
          and the value is to be given as a 32 bit integer. You can use
          this line of code to set the option for the socket named
          <c>Sock</c>:</p>
        <code type="none"><![CDATA[
        inet:setopts(Sock,[{raw,6,8,<<30:32/native>>}]),]]></code>
        <p>As many options are silently discarded by the stack if they
          are given out of range, it could be a good idea to check that
          a raw option really got accepted. This code places the value
          in the variable TcpLinger2:</p>
        <code type="none"><![CDATA[
        {ok,[{raw,6,8,<<TcpLinger2:32/native>>}]}=inet:getopts(Sock,[{raw,6,8,4}]),]]></code>
        <p>Code such as the examples above is inherently non portable,
          even different versions of the same  OS on the same platform
          may respond differently to this kind of option
          manipulation. Use with care.</p>
        <p>Note that the default options for TCP/IP sockets can be
          changed with the Kernel configuration parameters mentioned in
          the beginning of this document.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <marker id="error_codes"></marker>
    <title>POSIX Error Codes</title>
    <list type="bulleted">
      <item><c>e2big</c> - argument list too long</item>
      <item><c>eacces</c> - permission denied</item>
      <item><c>eaddrinuse</c> - address already in use</item>
      <item><c>eaddrnotavail</c> - cannot assign requested address</item>
      <item><c>eadv</c> - advertise error</item>
      <item><c>eafnosupport</c> - address family not supported by
       protocol family</item>
      <item><c>eagain</c> - resource temporarily unavailable</item>
      <item><c>ealign</c> - EALIGN</item>
      <item><c>ealready</c> - operation already in progress</item>
      <item><c>ebade</c> - bad exchange descriptor</item>
      <item><c>ebadf</c> - bad file number</item>
      <item><c>ebadfd</c> - file descriptor in bad state</item>
      <item><c>ebadmsg</c> - not a data message</item>
      <item><c>ebadr</c> - bad request descriptor</item>
      <item><c>ebadrpc</c> - RPC structure is bad</item>
      <item><c>ebadrqc</c> - bad request code</item>
      <item><c>ebadslt</c> - invalid slot</item>
      <item><c>ebfont</c> - bad font file format</item>
      <item><c>ebusy</c> - file busy</item>
      <item><c>echild</c> - no children</item>
      <item><c>echrng</c> - channel number out of range</item>
      <item><c>ecomm</c> - communication error on send</item>
      <item><c>econnaborted</c> - software caused connection abort</item>
      <item><c>econnrefused</c> - connection refused</item>
      <item><c>econnreset</c> - connection reset by peer</item>
      <item><c>edeadlk</c> - resource deadlock avoided</item>
      <item><c>edeadlock</c> - resource deadlock avoided</item>
      <item><c>edestaddrreq</c> - destination address required</item>
      <item><c>edirty</c> - mounting a dirty fs w/o force</item>
      <item><c>edom</c> - math argument out of range</item>
      <item><c>edotdot</c> - cross mount point</item>
      <item><c>edquot</c> - disk quota exceeded</item>
      <item><c>eduppkg</c> - duplicate package name</item>
      <item><c>eexist</c> - file already exists</item>
      <item><c>efault</c> - bad address in system call argument</item>
      <item><c>efbig</c> - file too large</item>
      <item><c>ehostdown</c> - host is down</item>
      <item><c>ehostunreach</c> - host is unreachable</item>
      <item><c>eidrm</c> - identifier removed</item>
      <item><c>einit</c> - initialization error</item>
      <item><c>einprogress</c> - operation now in progress</item>
      <item><c>eintr</c> - interrupted system call</item>
      <item><c>einval</c> - invalid argument</item>
      <item><c>eio</c> - I/O error</item>
      <item><c>eisconn</c> - socket is already connected</item>
      <item><c>eisdir</c> - illegal operation on a directory</item>
      <item><c>eisnam</c> - is a named file</item>
      <item><c>el2hlt</c> - level 2 halted</item>
      <item><c>el2nsync</c> - level 2 not synchronized</item>
      <item><c>el3hlt</c> - level 3 halted</item>
      <item><c>el3rst</c> - level 3 reset</item>
      <item><c>elbin</c> - ELBIN</item>
      <item><c>elibacc</c> - cannot access a needed shared library</item>
      <item><c>elibbad</c> - accessing a corrupted shared library</item>
      <item><c>elibexec</c> - cannot exec a shared library directly</item>
      <item><c>elibmax</c> - attempting to link in more shared
       libraries than system limit</item>
      <item><c>elibscn</c> - .lib section in a.out corrupted</item>
      <item><c>elnrng</c> - link number out of range</item>
      <item><c>eloop</c> - too many levels of symbolic links</item>
      <item><c>emfile</c> - too many open files</item>
      <item><c>emlink</c> - too many links</item>
      <item><c>emsgsize</c> - message too long</item>
      <item><c>emultihop</c> - multihop attempted</item>
      <item><c>enametoolong</c> - file name too long</item>
      <item><c>enavail</c> - not available</item>
      <item><c>enet</c> - ENET</item>
      <item><c>enetdown</c> - network is down</item>
      <item><c>enetreset</c> - network dropped connection on reset</item>
      <item><c>enetunreach</c> - network is unreachable</item>
      <item><c>enfile</c> - file table overflow</item>
      <item><c>enoano</c> - anode table overflow</item>
      <item><c>enobufs</c> - no buffer space available</item>
      <item><c>enocsi</c> - no CSI structure available</item>
      <item><c>enodata</c> - no data available</item>
      <item><c>enodev</c> - no such device</item>
      <item><c>enoent</c> - no such file or directory</item>
      <item><c>enoexec</c> - exec format error</item>
      <item><c>enolck</c> - no locks available</item>
      <item><c>enolink</c> - link has be severed</item>
      <item><c>enomem</c> - not enough memory</item>
      <item><c>enomsg</c> - no message of desired type</item>
      <item><c>enonet</c> - machine is not on the network</item>
      <item><c>enopkg</c> - package not installed</item>
      <item><c>enoprotoopt</c> - bad protocol option</item>
      <item><c>enospc</c> - no space left on device</item>
      <item><c>enosr</c> - out of stream resources or not a stream
       device</item>
      <item><c>enosym</c> - unresolved symbol name</item>
      <item><c>enosys</c> - function not implemented</item>
      <item><c>enotblk</c> - block device required</item>
      <item><c>enotconn</c> - socket is not connected</item>
      <item><c>enotdir</c> - not a directory</item>
      <item><c>enotempty</c> - directory not empty</item>
      <item><c>enotnam</c> - not a named file</item>
      <item><c>enotsock</c> - socket operation on non-socket</item>
      <item><c>enotsup</c> - operation not supported</item>
      <item><c>enotty</c> - inappropriate device for ioctl</item>
      <item><c>enotuniq</c> - name not unique on network</item>
      <item><c>enxio</c> - no such device or address</item>
      <item><c>eopnotsupp</c> - operation not supported on socket</item>
      <item><c>eperm</c> - not owner</item>
      <item><c>epfnosupport</c> - protocol family not supported</item>
      <item><c>epipe</c> - broken pipe</item>
      <item><c>eproclim</c> - too many processes</item>
      <item><c>eprocunavail</c> - bad procedure for program</item>
      <item><c>eprogmismatch</c> - program version wrong</item>
      <item><c>eprogunavail</c> - RPC program not available</item>
      <item><c>eproto</c> - protocol error</item>
      <item><c>eprotonosupport</c> - protocol not supported</item>
      <item><c>eprototype</c> - protocol wrong type for socket</item>
      <item><c>erange</c> - math result unrepresentable</item>
      <item><c>erefused</c> - EREFUSED</item>
      <item><c>eremchg</c> - remote address changed</item>
      <item><c>eremdev</c> - remote device</item>
      <item><c>eremote</c> - pathname hit remote file system</item>
      <item><c>eremoteio</c> - remote i/o error</item>
      <item><c>eremoterelease</c> - EREMOTERELEASE</item>
      <item><c>erofs</c> - read-only file system</item>
      <item><c>erpcmismatch</c> - RPC version is wrong</item>
      <item><c>erremote</c> - object is remote</item>
      <item><c>eshutdown</c> - cannot send after socket shutdown</item>
      <item><c>esocktnosupport</c> - socket type not supported</item>
      <item><c>espipe</c> - invalid seek</item>
      <item><c>esrch</c> - no such process</item>
      <item><c>esrmnt</c> - srmount error</item>
      <item><c>estale</c> - stale remote file handle</item>
      <item><c>esuccess</c> - Error 0</item>
      <item><c>etime</c> - timer expired</item>
      <item><c>etimedout</c> - connection timed out</item>
      <item><c>etoomanyrefs</c> - too many references</item>
      <item><c>etxtbsy</c> - text file or pseudo-device busy</item>
      <item><c>euclean</c> - structure needs cleaning</item>
      <item><c>eunatch</c> - protocol driver not attached</item>
      <item><c>eusers</c> - too many users</item>
      <item><c>eversion</c> - version mismatch</item>
      <item><c>ewouldblock</c> - operation would block</item>
      <item><c>exdev</c> - cross-domain link</item>
      <item><c>exfull</c> - message tables full</item>
      <item><c>nxdomain</c> - the hostname or domain name could not be
       found</item>
    </list>
  </section>
</erlref>