summaryrefslogtreecommitdiff
path: root/src/sys/socket/mod.rs
blob: 2725e57c43809a3d0da8b9987b36873849707f81 (plain)
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
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
//! Socket interface functions
//!
//! [Further reading](http://man7.org/linux/man-pages/man7/socket.7.html)
use cfg_if::cfg_if;
use crate::{Error, Result, errno::Errno};
use libc::{self, c_void, c_int, iovec, socklen_t, size_t,
        CMSG_FIRSTHDR, CMSG_NXTHDR, CMSG_DATA, CMSG_LEN};
use std::{mem, ptr, slice};
use std::os::unix::io::RawFd;
use crate::sys::time::TimeVal;
use crate::sys::uio::IoVec;

mod addr;
pub mod sockopt;

/*
 *
 * ===== Re-exports =====
 *
 */

#[cfg(not(any(target_os = "illumos", target_os = "solaris")))]
pub use self::addr::{
    AddressFamily,
    SockAddr,
    InetAddr,
    UnixAddr,
    IpAddr,
    Ipv4Addr,
    Ipv6Addr,
    LinkAddr,
};
#[cfg(any(target_os = "illumos", target_os = "solaris"))]
pub use self::addr::{
    AddressFamily,
    SockAddr,
    InetAddr,
    UnixAddr,
    IpAddr,
    Ipv4Addr,
    Ipv6Addr,
};

#[cfg(any(target_os = "android", target_os = "linux"))]
pub use crate::sys::socket::addr::netlink::NetlinkAddr;
#[cfg(any(target_os = "android", target_os = "linux"))]
pub use crate::sys::socket::addr::alg::AlgAddr;
#[cfg(any(target_os = "android", target_os = "linux"))]
pub use crate::sys::socket::addr::vsock::VsockAddr;

pub use libc::{
    cmsghdr,
    msghdr,
    sa_family_t,
    sockaddr,
    sockaddr_in,
    sockaddr_in6,
    sockaddr_storage,
    sockaddr_un,
};

// Needed by the cmsg_space macro
#[doc(hidden)]
pub use libc::{c_uint, CMSG_SPACE};

/// These constants are used to specify the communication semantics
/// when creating a socket with [`socket()`](fn.socket.html)
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
#[repr(i32)]
pub enum SockType {
    /// Provides sequenced, reliable, two-way, connection-
    /// based byte streams.  An out-of-band data transmission
    /// mechanism may be supported.
    Stream = libc::SOCK_STREAM,
    /// Supports datagrams (connectionless, unreliable
    /// messages of a fixed maximum length).
    Datagram = libc::SOCK_DGRAM,
    /// Provides a sequenced, reliable, two-way connection-
    /// based data transmission path for datagrams of fixed
    /// maximum length; a consumer is required to read an
    /// entire packet with each input system call.
    SeqPacket = libc::SOCK_SEQPACKET,
    /// Provides raw network protocol access.
    Raw = libc::SOCK_RAW,
    /// Provides a reliable datagram layer that does not
    /// guarantee ordering.
    Rdm = libc::SOCK_RDM,
}

/// Constants used in [`socket`](fn.socket.html) and [`socketpair`](fn.socketpair.html)
/// to specify the protocol to use.
#[repr(i32)]
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum SockProtocol {
    /// TCP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
    Tcp = libc::IPPROTO_TCP,
    /// UDP protocol ([ip(7)](http://man7.org/linux/man-pages/man7/ip.7.html))
    Udp = libc::IPPROTO_UDP,
    /// Allows applications and other KEXTs to be notified when certain kernel events occur
    /// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
    #[cfg(any(target_os = "ios", target_os = "macos"))]
    KextEvent = libc::SYSPROTO_EVENT,
    /// Allows applications to configure and control a KEXT
    /// ([ref](https://developer.apple.com/library/content/documentation/Darwin/Conceptual/NKEConceptual/control/control.html))
    #[cfg(any(target_os = "ios", target_os = "macos"))]
    KextControl = libc::SYSPROTO_CONTROL,
    /// Receives routing and link updates and may be used to modify the routing tables (both IPv4 and IPv6), IP addresses, link
    // parameters, neighbor setups, queueing disciplines, traffic classes and packet classifiers
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkRoute = libc::NETLINK_ROUTE,
    /// Reserved for user-mode socket protocols
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkUserSock = libc::NETLINK_USERSOCK,
    /// Query information about sockets of various protocol families from the kernel
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkSockDiag = libc::NETLINK_SOCK_DIAG,
    /// SELinux event notifications.
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkSELinux = libc::NETLINK_SELINUX,
    /// Open-iSCSI
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkISCSI = libc::NETLINK_ISCSI,
    /// Auditing
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkAudit = libc::NETLINK_AUDIT,
    /// Access to FIB lookup from user space
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkFIBLookup = libc::NETLINK_FIB_LOOKUP,
    /// Netfilter subsystem
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkNetFilter = libc::NETLINK_NETFILTER,
    /// SCSI Transports
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkSCSITransport = libc::NETLINK_SCSITRANSPORT,
    /// Infiniband RDMA
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkRDMA = libc::NETLINK_RDMA,
    /// Transport IPv6 packets from netfilter to user space.  Used by ip6_queue kernel module.
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkIPv6Firewall = libc::NETLINK_IP6_FW,
    /// DECnet routing messages
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkDECNetRoutingMessage = libc::NETLINK_DNRTMSG,
    /// Kernel messages to user space
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkKObjectUEvent = libc::NETLINK_KOBJECT_UEVENT,
    /// Netlink interface to request information about ciphers registered with the kernel crypto API as well as allow
    /// configuration of the kernel crypto API.
    /// ([ref](https://www.man7.org/linux/man-pages/man7/netlink.7.html))
    #[cfg(any(target_os = "android", target_os = "linux"))]
    NetlinkCrypto = libc::NETLINK_CRYPTO,
}

libc_bitflags!{
    /// Additional socket options
    pub struct SockFlag: c_int {
        /// Set non-blocking mode on the new socket
        #[cfg(any(target_os = "android",
                  target_os = "dragonfly",
                  target_os = "freebsd",
                  target_os = "illumos",
                  target_os = "linux",
                  target_os = "netbsd",
                  target_os = "openbsd"))]
        SOCK_NONBLOCK;
        /// Set close-on-exec on the new descriptor
        #[cfg(any(target_os = "android",
                  target_os = "dragonfly",
                  target_os = "freebsd",
                  target_os = "illumos",
                  target_os = "linux",
                  target_os = "netbsd",
                  target_os = "openbsd"))]
        SOCK_CLOEXEC;
        /// Return `EPIPE` instead of raising `SIGPIPE`
        #[cfg(target_os = "netbsd")]
        SOCK_NOSIGPIPE;
        /// For domains `AF_INET(6)`, only allow `connect(2)`, `sendto(2)`, or `sendmsg(2)`
        /// to the DNS port (typically 53)
        #[cfg(target_os = "openbsd")]
        SOCK_DNS;
    }
}

libc_bitflags!{
    /// Flags for send/recv and their relatives
    pub struct MsgFlags: c_int {
        /// Sends or requests out-of-band data on sockets that support this notion
        /// (e.g., of type [`Stream`](enum.SockType.html)); the underlying protocol must also
        /// support out-of-band data.
        MSG_OOB;
        /// Peeks at an incoming message. The data is treated as unread and the next
        /// [`recv()`](fn.recv.html)
        /// or similar function shall still return this data.
        MSG_PEEK;
        /// Receive operation blocks until the full amount of data can be
        /// returned. The function may return smaller amount of data if a signal
        /// is caught, an error or disconnect occurs.
        MSG_WAITALL;
        /// Enables nonblocking operation; if the operation would block,
        /// `EAGAIN` or `EWOULDBLOCK` is returned.  This provides similar
        /// behavior to setting the `O_NONBLOCK` flag
        /// (via the [`fcntl`](../../fcntl/fn.fcntl.html)
        /// `F_SETFL` operation), but differs in that `MSG_DONTWAIT` is a per-
        /// call option, whereas `O_NONBLOCK` is a setting on the open file
        /// description (see [open(2)](http://man7.org/linux/man-pages/man2/open.2.html)),
        /// which will affect all threads in
        /// the calling process and as well as other processes that hold
        /// file descriptors referring to the same open file description.
        MSG_DONTWAIT;
        /// Receive flags: Control Data was discarded (buffer too small)
        MSG_CTRUNC;
        /// For raw ([`Packet`](addr/enum.AddressFamily.html)), Internet datagram
        /// (since Linux 2.4.27/2.6.8),
        /// netlink (since Linux 2.6.22) and UNIX datagram (since Linux 3.4)
        /// sockets: return the real length of the packet or datagram, even
        /// when it was longer than the passed buffer. Not implemented for UNIX
        /// domain ([unix(7)](https://linux.die.net/man/7/unix)) sockets.
        ///
        /// For use with Internet stream sockets, see [tcp(7)](https://linux.die.net/man/7/tcp).
        MSG_TRUNC;
        /// Terminates a record (when this notion is supported, as for
        /// sockets of type [`SeqPacket`](enum.SockType.html)).
        MSG_EOR;
        /// This flag specifies that queued errors should be received from
        /// the socket error queue. (For more details, see
        /// [recvfrom(2)](https://linux.die.net/man/2/recvfrom))
        #[cfg(any(target_os = "android", target_os = "linux"))]
        MSG_ERRQUEUE;
        /// Set the `close-on-exec` flag for the file descriptor received via a UNIX domain
        /// file descriptor using the `SCM_RIGHTS` operation (described in
        /// [unix(7)](https://linux.die.net/man/7/unix)).
        /// This flag is useful for the same reasons as the `O_CLOEXEC` flag of
        /// [open(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html).
        ///
        /// Only used in [`recvmsg`](fn.recvmsg.html) function.
        #[cfg(any(target_os = "android",
                  target_os = "dragonfly",
                  target_os = "freebsd",
                  target_os = "linux",
                  target_os = "netbsd",
                  target_os = "openbsd"))]
        MSG_CMSG_CLOEXEC;
    }
}

cfg_if! {
    if #[cfg(any(target_os = "android", target_os = "linux"))] {
        /// Unix credentials of the sending process.
        ///
        /// This struct is used with the `SO_PEERCRED` ancillary message
        /// and the `SCM_CREDENTIALS` control message for UNIX sockets.
        #[repr(transparent)]
        #[derive(Clone, Copy, Debug, Eq, PartialEq)]
        pub struct UnixCredentials(libc::ucred);

        impl UnixCredentials {
            /// Creates a new instance with the credentials of the current process
            pub fn new() -> Self {
                UnixCredentials(libc::ucred {
                    pid: crate::unistd::getpid().as_raw(),
                    uid: crate::unistd::getuid().as_raw(),
                    gid: crate::unistd::getgid().as_raw(),
                })
            }

            /// Returns the process identifier
            pub fn pid(&self) -> libc::pid_t {
                self.0.pid
            }

            /// Returns the user identifier
            pub fn uid(&self) -> libc::uid_t {
                self.0.uid
            }

            /// Returns the group identifier
            pub fn gid(&self) -> libc::gid_t {
                self.0.gid
            }
        }

        impl Default for UnixCredentials {
            fn default() -> Self {
                Self::new()
            }
        }

        impl From<libc::ucred> for UnixCredentials {
            fn from(cred: libc::ucred) -> Self {
                UnixCredentials(cred)
            }
        }

        impl Into<libc::ucred> for UnixCredentials {
            fn into(self) -> libc::ucred {
                self.0
            }
        }
    } else if #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))] {
        /// Unix credentials of the sending process.
        ///
        /// This struct is used with the `SCM_CREDS` ancillary message for UNIX sockets.
        #[repr(transparent)]
        #[derive(Clone, Copy, Debug, Eq, PartialEq)]
        pub struct UnixCredentials(libc::cmsgcred);

        impl UnixCredentials {
            /// Returns the process identifier
            pub fn pid(&self) -> libc::pid_t {
                self.0.cmcred_pid
            }

            /// Returns the real user identifier
            pub fn uid(&self) -> libc::uid_t {
                self.0.cmcred_uid
            }

            /// Returns the effective user identifier
            pub fn euid(&self) -> libc::uid_t {
                self.0.cmcred_euid
            }

            /// Returns the real group identifier
            pub fn gid(&self) -> libc::gid_t {
                self.0.cmcred_gid
            }

            /// Returns a list group identifiers (the first one being the effective GID)
            pub fn groups(&self) -> &[libc::gid_t] {
                unsafe { slice::from_raw_parts(self.0.cmcred_groups.as_ptr() as *const libc::gid_t, self.0.cmcred_ngroups as _) }
            }
        }

        impl From<libc::cmsgcred> for UnixCredentials {
            fn from(cred: libc::cmsgcred) -> Self {
                UnixCredentials(cred)
            }
        }
    }
}

/// Request for multicast socket operations
///
/// This is a wrapper type around `ip_mreq`.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct IpMembershipRequest(libc::ip_mreq);

impl IpMembershipRequest {
    /// Instantiate a new `IpMembershipRequest`
    ///
    /// If `interface` is `None`, then `Ipv4Addr::any()` will be used for the interface.
    pub fn new(group: Ipv4Addr, interface: Option<Ipv4Addr>) -> Self {
        IpMembershipRequest(libc::ip_mreq {
            imr_multiaddr: group.0,
            imr_interface: interface.unwrap_or_else(Ipv4Addr::any).0,
        })
    }
}

/// Request for ipv6 multicast socket operations
///
/// This is a wrapper type around `ipv6_mreq`.
#[repr(transparent)]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct Ipv6MembershipRequest(libc::ipv6_mreq);

impl Ipv6MembershipRequest {
    /// Instantiate a new `Ipv6MembershipRequest`
    pub fn new(group: Ipv6Addr) -> Self {
        Ipv6MembershipRequest(libc::ipv6_mreq {
            ipv6mr_multiaddr: group.0,
            ipv6mr_interface: 0,
        })
    }
}

/// Create a buffer large enough for storing some control messages as returned
/// by [`recvmsg`](fn.recvmsg.html).
///
/// # Examples
///
/// ```
/// # #[macro_use] extern crate nix;
/// # use nix::sys::time::TimeVal;
/// # use std::os::unix::io::RawFd;
/// # fn main() {
/// // Create a buffer for a `ControlMessageOwned::ScmTimestamp` message
/// let _ = cmsg_space!(TimeVal);
/// // Create a buffer big enough for a `ControlMessageOwned::ScmRights` message
/// // with two file descriptors
/// let _ = cmsg_space!([RawFd; 2]);
/// // Create a buffer big enough for a `ControlMessageOwned::ScmRights` message
/// // and a `ControlMessageOwned::ScmTimestamp` message
/// let _ = cmsg_space!(RawFd, TimeVal);
/// # }
/// ```
// Unfortunately, CMSG_SPACE isn't a const_fn, or else we could return a
// stack-allocated array.
#[macro_export]
macro_rules! cmsg_space {
    ( $( $x:ty ),* ) => {
        {
            let mut space = 0;
            $(
                // CMSG_SPACE is always safe
                space += unsafe {
                    $crate::sys::socket::CMSG_SPACE(::std::mem::size_of::<$x>() as $crate::sys::socket::c_uint)
                } as usize;
            )*
            Vec::<u8>::with_capacity(space)
        }
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct RecvMsg<'a> {
    pub bytes: usize,
    cmsghdr: Option<&'a cmsghdr>,
    pub address: Option<SockAddr>,
    pub flags: MsgFlags,
    mhdr: msghdr,
}

impl<'a> RecvMsg<'a> {
    /// Iterate over the valid control messages pointed to by this
    /// msghdr.
    pub fn cmsgs(&self) -> CmsgIterator {
        CmsgIterator {
            cmsghdr: self.cmsghdr,
            mhdr: &self.mhdr
        }
    }
}

#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct CmsgIterator<'a> {
    /// Control message buffer to decode from. Must adhere to cmsg alignment.
    cmsghdr: Option<&'a cmsghdr>,
    mhdr: &'a msghdr
}

impl<'a> Iterator for CmsgIterator<'a> {
    type Item = ControlMessageOwned;

    fn next(&mut self) -> Option<ControlMessageOwned> {
        match self.cmsghdr {
            None => None,   // No more messages
            Some(hdr) => {
                // Get the data.
                // Safe if cmsghdr points to valid data returned by recvmsg(2)
                let cm = unsafe { Some(ControlMessageOwned::decode_from(hdr))};
                // Advance the internal pointer.  Safe if mhdr and cmsghdr point
                // to valid data returned by recvmsg(2)
                self.cmsghdr = unsafe {
                    let p = CMSG_NXTHDR(self.mhdr as *const _, hdr as *const _);
                    p.as_ref()
                };
                cm
            }
        }
    }
}

/// A type-safe wrapper around a single control message, as used with
/// [`recvmsg`](#fn.recvmsg).
///
/// [Further reading](http://man7.org/linux/man-pages/man3/cmsg.3.html)
//  Nix version 0.13.0 and earlier used ControlMessage for both recvmsg and
//  sendmsg.  However, on some platforms the messages returned by recvmsg may be
//  unaligned.  ControlMessageOwned takes those messages by copy, obviating any
//  alignment issues.
//
//  See https://github.com/nix-rust/nix/issues/999
#[derive(Clone, Debug, Eq, PartialEq)]
pub enum ControlMessageOwned {
    /// Received version of
    /// [`ControlMessage::ScmRights`][#enum.ControlMessage.html#variant.ScmRights]
    ScmRights(Vec<RawFd>),
    /// Received version of
    /// [`ControlMessage::ScmCredentials`][#enum.ControlMessage.html#variant.ScmCredentials]
    #[cfg(any(target_os = "android", target_os = "linux"))]
    ScmCredentials(UnixCredentials),
    /// Received version of
    /// [`ControlMessage::ScmCreds`][#enum.ControlMessage.html#variant.ScmCreds]
    #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
    ScmCreds(UnixCredentials),
    /// A message of type `SCM_TIMESTAMP`, containing the time the
    /// packet was received by the kernel.
    ///
    /// See the kernel's explanation in "SO_TIMESTAMP" of
    /// [networking/timestamping](https://www.kernel.org/doc/Documentation/networking/timestamping.txt).
    ///
    /// # Examples
    ///
    /// # #[macro_use] extern crate nix;
    /// # use nix::sys::socket::*;
    /// # use nix::sys::uio::IoVec;
    /// # use nix::sys::time::*;
    /// # use std::time::*;
    /// # fn main() {
    /// // Set up
    /// let message = "Ohayō!".as_bytes();
    /// let in_socket = socket(
    ///     AddressFamily::Inet,
    ///     SockType::Datagram,
    ///     SockFlag::empty(),
    ///     None).unwrap();
    /// setsockopt(in_socket, sockopt::ReceiveTimestamp, &true).unwrap();
    /// let localhost = InetAddr::new(IpAddr::new_v4(127, 0, 0, 1), 0);
    /// bind(in_socket, &SockAddr::new_inet(localhost)).unwrap();
    /// let address = getsockname(in_socket).unwrap();
    /// // Get initial time
    /// let time0 = SystemTime::now();
    /// // Send the message
    /// let iov = [IoVec::from_slice(message)];
    /// let flags = MsgFlags::empty();
    /// let l = sendmsg(in_socket, &iov, &[], flags, Some(&address)).unwrap();
    /// assert_eq!(message.len(), l);
    /// // Receive the message
    /// let mut buffer = vec![0u8; message.len()];
    /// let mut cmsgspace = cmsg_space!(TimeVal);
    /// let iov = [IoVec::from_mut_slice(&mut buffer)];
    /// let r = recvmsg(in_socket, &iov, Some(&mut cmsgspace), flags).unwrap();
    /// let rtime = match r.cmsgs().next() {
    ///     Some(ControlMessageOwned::ScmTimestamp(rtime)) => rtime,
    ///     Some(_) => panic!("Unexpected control message"),
    ///     None => panic!("No control message")
    /// };
    /// // Check the final time
    /// let time1 = SystemTime::now();
    /// // the packet's received timestamp should lie in-between the two system
    /// // times, unless the system clock was adjusted in the meantime.
    /// let rduration = Duration::new(rtime.tv_sec() as u64,
    ///                               rtime.tv_usec() as u32 * 1000);
    /// assert!(time0.duration_since(UNIX_EPOCH).unwrap() <= rduration);
    /// assert!(rduration <= time1.duration_since(UNIX_EPOCH).unwrap());
    /// // Close socket
    /// nix::unistd::close(in_socket).unwrap();
    /// # }
    /// ```
    ScmTimestamp(TimeVal),
    #[cfg(any(
        target_os = "android",
        target_os = "ios",
        target_os = "linux",
        target_os = "macos",
        target_os = "netbsd",
    ))]
    Ipv4PacketInfo(libc::in_pktinfo),
    #[cfg(any(
        target_os = "android",
        target_os = "dragonfly",
        target_os = "freebsd",
        target_os = "ios",
        target_os = "linux",
        target_os = "macos",
        target_os = "openbsd",
        target_os = "netbsd",
    ))]
    Ipv6PacketInfo(libc::in6_pktinfo),
    #[cfg(any(
        target_os = "freebsd",
        target_os = "ios",
        target_os = "macos",
        target_os = "netbsd",
        target_os = "openbsd",
    ))]
    Ipv4RecvIf(libc::sockaddr_dl),
    #[cfg(any(
        target_os = "freebsd",
        target_os = "ios",
        target_os = "macos",
        target_os = "netbsd",
        target_os = "openbsd",
    ))]
    Ipv4RecvDstAddr(libc::in_addr),

    /// UDP Generic Receive Offload (GRO) allows receiving multiple UDP
    /// packets from a single sender.
    /// Fixed-size payloads are following one by one in a receive buffer.
    /// This Control Message indicates the size of all smaller packets,
    /// except, maybe, the last one.
    ///
    /// `UdpGroSegment` socket option should be enabled on a socket
    /// to allow receiving GRO packets.
    #[cfg(target_os = "linux")]
    UdpGroSegments(u16),

    /// Catch-all variant for unimplemented cmsg types.
    #[doc(hidden)]
    Unknown(UnknownCmsg),
}

impl ControlMessageOwned {
    /// Decodes a `ControlMessageOwned` from raw bytes.
    ///
    /// This is only safe to call if the data is correct for the message type
    /// specified in the header. Normally, the kernel ensures that this is the
    /// case. "Correct" in this case includes correct length, alignment and
    /// actual content.
    // Clippy complains about the pointer alignment of `p`, not understanding
    // that it's being fed to a function that can handle that.
    #[allow(clippy::cast_ptr_alignment)]
    unsafe fn decode_from(header: &cmsghdr) -> ControlMessageOwned
    {
        let p = CMSG_DATA(header);
        let len = header as *const _ as usize + header.cmsg_len as usize
            - p as usize;
        match (header.cmsg_level, header.cmsg_type) {
            (libc::SOL_SOCKET, libc::SCM_RIGHTS) => {
                let n = len / mem::size_of::<RawFd>();
                let mut fds = Vec::with_capacity(n);
                for i in 0..n {
                    let fdp = (p as *const RawFd).add(i);
                    fds.push(ptr::read_unaligned(fdp));
                }
                ControlMessageOwned::ScmRights(fds)
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            (libc::SOL_SOCKET, libc::SCM_CREDENTIALS) => {
                let cred: libc::ucred = ptr::read_unaligned(p as *const _);
                ControlMessageOwned::ScmCredentials(cred.into())
            }
            #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
            (libc::SOL_SOCKET, libc::SCM_CREDS) => {
                let cred: libc::cmsgcred = ptr::read_unaligned(p as *const _);
                ControlMessageOwned::ScmCreds(cred.into())
            }
            (libc::SOL_SOCKET, libc::SCM_TIMESTAMP) => {
                let tv: libc::timeval = ptr::read_unaligned(p as *const _);
                ControlMessageOwned::ScmTimestamp(TimeVal::from(tv))
            },
            #[cfg(any(
                target_os = "android",
                target_os = "freebsd",
                target_os = "ios",
                target_os = "linux",
                target_os = "macos"
            ))]
            (libc::IPPROTO_IPV6, libc::IPV6_PKTINFO) => {
                let info = ptr::read_unaligned(p as *const libc::in6_pktinfo);
                ControlMessageOwned::Ipv6PacketInfo(info)
            }
            #[cfg(any(
                target_os = "android",
                target_os = "ios",
                target_os = "linux",
                target_os = "macos",
                target_os = "netbsd",
            ))]
            (libc::IPPROTO_IP, libc::IP_PKTINFO) => {
                let info = ptr::read_unaligned(p as *const libc::in_pktinfo);
                ControlMessageOwned::Ipv4PacketInfo(info)
            }
            #[cfg(any(
                target_os = "freebsd",
                target_os = "ios",
                target_os = "macos",
                target_os = "netbsd",
                target_os = "openbsd",
            ))]
            (libc::IPPROTO_IP, libc::IP_RECVIF) => {
                let dl = ptr::read_unaligned(p as *const libc::sockaddr_dl);
                ControlMessageOwned::Ipv4RecvIf(dl)
            },
            #[cfg(any(
                target_os = "freebsd",
                target_os = "ios",
                target_os = "macos",
                target_os = "netbsd",
                target_os = "openbsd",
            ))]
            (libc::IPPROTO_IP, libc::IP_RECVDSTADDR) => {
                let dl = ptr::read_unaligned(p as *const libc::in_addr);
                ControlMessageOwned::Ipv4RecvDstAddr(dl)
            },
            #[cfg(target_os = "linux")]
            (libc::SOL_UDP, libc::UDP_GRO) => {
                let gso_size: u16 = ptr::read_unaligned(p as *const _);
                ControlMessageOwned::UdpGroSegments(gso_size)
            },
            (_, _) => {
                let sl = slice::from_raw_parts(p, len);
                let ucmsg = UnknownCmsg(*header, Vec::<u8>::from(&sl[..]));
                ControlMessageOwned::Unknown(ucmsg)
            }
        }
    }
}

/// A type-safe zero-copy wrapper around a single control message, as used wih
/// [`sendmsg`](#fn.sendmsg).  More types may be added to this enum; do not
/// exhaustively pattern-match it.
///
/// [Further reading](http://man7.org/linux/man-pages/man3/cmsg.3.html)
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum ControlMessage<'a> {
    /// A message of type `SCM_RIGHTS`, containing an array of file
    /// descriptors passed between processes.
    ///
    /// See the description in the "Ancillary messages" section of the
    /// [unix(7) man page](http://man7.org/linux/man-pages/man7/unix.7.html).
    ///
    /// Using multiple `ScmRights` messages for a single `sendmsg` call isn't
    /// recommended since it causes platform-dependent behaviour: It might
    /// swallow all but the first `ScmRights` message or fail with `EINVAL`.
    /// Instead, you can put all fds to be passed into a single `ScmRights`
    /// message.
    ScmRights(&'a [RawFd]),
    /// A message of type `SCM_CREDENTIALS`, containing the pid, uid and gid of
    /// a process connected to the socket.
    ///
    /// This is similar to the socket option `SO_PEERCRED`, but requires a
    /// process to explicitly send its credentials. A process running as root is
    /// allowed to specify any credentials, while credentials sent by other
    /// processes are verified by the kernel.
    ///
    /// For further information, please refer to the
    /// [`unix(7)`](http://man7.org/linux/man-pages/man7/unix.7.html) man page.
    #[cfg(any(target_os = "android", target_os = "linux"))]
    ScmCredentials(&'a UnixCredentials),
    /// A message of type `SCM_CREDS`, containing the pid, uid, euid, gid and groups of
    /// a process connected to the socket.
    ///
    /// This is similar to the socket options `LOCAL_CREDS` and `LOCAL_PEERCRED`, but
    /// requires a process to explicitly send its credentials.
    ///
    /// Credentials are always overwritten by the kernel, so this variant does have
    /// any data, unlike the receive-side
    /// [`ControlMessageOwned::ScmCreds`][#enum.ControlMessageOwned.html#variant.ScmCreds].
    ///
    /// For further information, please refer to the
    /// [`unix(4)`](https://www.freebsd.org/cgi/man.cgi?query=unix) man page.
    #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
    ScmCreds,

    /// Set IV for `AF_ALG` crypto API.
    ///
    /// For further information, please refer to the
    /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
    #[cfg(any(
        target_os = "android",
        target_os = "linux",
    ))]
    AlgSetIv(&'a [u8]),
    /// Set crypto operation for `AF_ALG` crypto API. It may be one of
    /// `ALG_OP_ENCRYPT` or `ALG_OP_DECRYPT`
    ///
    /// For further information, please refer to the
    /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
    #[cfg(any(
        target_os = "android",
        target_os = "linux",
    ))]
    AlgSetOp(&'a libc::c_int),
    /// Set the length of associated authentication data (AAD) (applicable only to AEAD algorithms)
    /// for `AF_ALG` crypto API.
    ///
    /// For further information, please refer to the
    /// [`documentation`](https://kernel.readthedocs.io/en/sphinx-samples/crypto-API.html)
    #[cfg(any(
        target_os = "android",
        target_os = "linux",
    ))]
    AlgSetAeadAssoclen(&'a u32),

    /// UDP GSO makes it possible for applications to generate network packets
    /// for a virtual MTU much greater than the real one.
    /// The length of the send data no longer matches the expected length on
    /// the wire.
    /// The size of the datagram payload as it should appear on the wire may be
    /// passed through this control message.
    /// Send buffer should consist of multiple fixed-size wire payloads
    /// following one by one, and the last, possibly smaller one.
    #[cfg(target_os = "linux")]
    UdpGsoSegments(&'a u16),

    /// Configure the sending addressing and interface for v4
    ///
    /// For further information, please refer to the
    /// [`ip(7)`](http://man7.org/linux/man-pages/man7/ip.7.html) man page.
    #[cfg(any(target_os = "linux",
              target_os = "macos",
              target_os = "netbsd",
              target_os = "android",
              target_os = "ios",))]
    Ipv4PacketInfo(&'a libc::in_pktinfo),

    /// Configure the sending addressing and interface for v6
    ///
    /// For further information, please refer to the
    /// [`ipv6(7)`](http://man7.org/linux/man-pages/man7/ipv6.7.html) man page.
    #[cfg(any(target_os = "linux",
              target_os = "macos",
              target_os = "netbsd",
              target_os = "freebsd",
              target_os = "android",
              target_os = "ios",))]
    Ipv6PacketInfo(&'a libc::in6_pktinfo),
}

// An opaque structure used to prevent cmsghdr from being a public type
#[doc(hidden)]
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct UnknownCmsg(cmsghdr, Vec<u8>);

impl<'a> ControlMessage<'a> {
    /// The value of CMSG_SPACE on this message.
    /// Safe because CMSG_SPACE is always safe
    fn space(&self) -> usize {
        unsafe{CMSG_SPACE(self.len() as libc::c_uint) as usize}
    }

    /// The value of CMSG_LEN on this message.
    /// Safe because CMSG_LEN is always safe
    #[cfg(any(target_os = "android",
              all(target_os = "linux", not(target_env = "musl"))))]
    fn cmsg_len(&self) -> usize {
        unsafe{CMSG_LEN(self.len() as libc::c_uint) as usize}
    }

    #[cfg(not(any(target_os = "android",
                  all(target_os = "linux", not(target_env = "musl")))))]
    fn cmsg_len(&self) -> libc::c_uint {
        unsafe{CMSG_LEN(self.len() as libc::c_uint)}
    }

    /// Return a reference to the payload data as a byte pointer
    fn copy_to_cmsg_data(&self, cmsg_data: *mut u8) {
        let data_ptr = match *self {
            ControlMessage::ScmRights(fds) => {
                fds as *const _ as *const u8
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::ScmCredentials(creds) => {
                &creds.0 as *const libc::ucred as *const u8
            }
            #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
            ControlMessage::ScmCreds => {
                // The kernel overwrites the data, we just zero it
                // to make sure it's not uninitialized memory
                unsafe { ptr::write_bytes(cmsg_data, 0, self.len()) };
                return
            }
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetIv(iv) => {
                #[allow(deprecated)] // https://github.com/rust-lang/libc/issues/1501
                let af_alg_iv = libc::af_alg_iv {
                    ivlen: iv.len() as u32,
                    iv: [0u8; 0],
                };

                let size = mem::size_of_val(&af_alg_iv);

                unsafe {
                    ptr::copy_nonoverlapping(
                        &af_alg_iv as *const _ as *const u8,
                        cmsg_data,
                        size,
                    );
                    ptr::copy_nonoverlapping(
                        iv.as_ptr(),
                        cmsg_data.add(size),
                        iv.len()
                    );
                };

                return
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetOp(op) => {
                op as *const _ as *const u8
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetAeadAssoclen(len) => {
                len as *const _ as *const u8
            },
            #[cfg(target_os = "linux")]
            ControlMessage::UdpGsoSegments(gso_size) => {
                gso_size as *const _ as *const u8
            },
            #[cfg(any(target_os = "linux", target_os = "macos",
                      target_os = "netbsd", target_os = "android",
                      target_os = "ios",))]
            ControlMessage::Ipv4PacketInfo(info) => info as *const _ as *const u8,
            #[cfg(any(target_os = "linux", target_os = "macos",
                      target_os = "netbsd", target_os = "freebsd",
                      target_os = "android", target_os = "ios",))]
            ControlMessage::Ipv6PacketInfo(info) => info as *const _ as *const u8,
        };
        unsafe {
            ptr::copy_nonoverlapping(
                data_ptr,
                cmsg_data,
                self.len()
            )
        };
    }

    /// The size of the payload, excluding its cmsghdr
    fn len(&self) -> usize {
        match *self {
            ControlMessage::ScmRights(fds) => {
                mem::size_of_val(fds)
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::ScmCredentials(creds) => {
                mem::size_of_val(creds)
            }
            #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
            ControlMessage::ScmCreds => {
                mem::size_of::<libc::cmsgcred>()
            }
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetIv(iv) => {
                mem::size_of_val(&iv) + iv.len()
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetOp(op) => {
                mem::size_of_val(op)
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetAeadAssoclen(len) => {
                mem::size_of_val(len)
            },
            #[cfg(target_os = "linux")]
            ControlMessage::UdpGsoSegments(gso_size) => {
                mem::size_of_val(gso_size)
            },
            #[cfg(any(target_os = "linux", target_os = "macos",
              target_os = "netbsd", target_os = "android",
              target_os = "ios",))]
            ControlMessage::Ipv4PacketInfo(info) => mem::size_of_val(info),
            #[cfg(any(target_os = "linux", target_os = "macos",
              target_os = "netbsd", target_os = "freebsd",
              target_os = "android", target_os = "ios",))]
            ControlMessage::Ipv6PacketInfo(info) => mem::size_of_val(info),
        }
    }

    /// Returns the value to put into the `cmsg_level` field of the header.
    fn cmsg_level(&self) -> libc::c_int {
        match *self {
            ControlMessage::ScmRights(_) => libc::SOL_SOCKET,
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::ScmCredentials(_) => libc::SOL_SOCKET,
            #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
            ControlMessage::ScmCreds => libc::SOL_SOCKET,
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetIv(_) | ControlMessage::AlgSetOp(_) |
                ControlMessage::AlgSetAeadAssoclen(_) => libc::SOL_ALG,
            #[cfg(target_os = "linux")]
            ControlMessage::UdpGsoSegments(_) => libc::SOL_UDP,
            #[cfg(any(target_os = "linux", target_os = "macos",
                      target_os = "netbsd", target_os = "android",
                      target_os = "ios",))]
            ControlMessage::Ipv4PacketInfo(_) => libc::IPPROTO_IP,
            #[cfg(any(target_os = "linux", target_os = "macos",
              target_os = "netbsd", target_os = "freebsd",
              target_os = "android", target_os = "ios",))]
            ControlMessage::Ipv6PacketInfo(_) => libc::IPPROTO_IPV6,
        }
    }

    /// Returns the value to put into the `cmsg_type` field of the header.
    fn cmsg_type(&self) -> libc::c_int {
        match *self {
            ControlMessage::ScmRights(_) => libc::SCM_RIGHTS,
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::ScmCredentials(_) => libc::SCM_CREDENTIALS,
            #[cfg(any(target_os = "freebsd", target_os = "dragonfly"))]
            ControlMessage::ScmCreds => libc::SCM_CREDS,
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetIv(_) => {
                libc::ALG_SET_IV
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetOp(_) => {
                libc::ALG_SET_OP
            },
            #[cfg(any(target_os = "android", target_os = "linux"))]
            ControlMessage::AlgSetAeadAssoclen(_) => {
                libc::ALG_SET_AEAD_ASSOCLEN
            },
            #[cfg(target_os = "linux")]
            ControlMessage::UdpGsoSegments(_) => {
                libc::UDP_SEGMENT
            },
            #[cfg(any(target_os = "linux", target_os = "macos",
                      target_os = "netbsd", target_os = "android",
                      target_os = "ios",))]
            ControlMessage::Ipv4PacketInfo(_) => libc::IP_PKTINFO,
            #[cfg(any(target_os = "linux", target_os = "macos",
                      target_os = "netbsd", target_os = "freebsd",
                      target_os = "android", target_os = "ios",))]
            ControlMessage::Ipv6PacketInfo(_) => libc::IPV6_PKTINFO,
        }
    }

    // Unsafe: cmsg must point to a valid cmsghdr with enough space to
    // encode self.
    unsafe fn encode_into(&self, cmsg: *mut cmsghdr) {
        (*cmsg).cmsg_level = self.cmsg_level();
        (*cmsg).cmsg_type = self.cmsg_type();
        (*cmsg).cmsg_len = self.cmsg_len();
        self.copy_to_cmsg_data(CMSG_DATA(cmsg));
    }
}


/// Send data in scatter-gather vectors to a socket, possibly accompanied
/// by ancillary data. Optionally direct the message at the given address,
/// as with sendto.
///
/// Allocates if cmsgs is nonempty.
pub fn sendmsg(fd: RawFd, iov: &[IoVec<&[u8]>], cmsgs: &[ControlMessage],
               flags: MsgFlags, addr: Option<&SockAddr>) -> Result<usize>
{
    let capacity = cmsgs.iter().map(|c| c.space()).sum();

    // First size the buffer needed to hold the cmsgs.  It must be zeroed,
    // because subsequent code will not clear the padding bytes.
    let mut cmsg_buffer = vec![0u8; capacity];

    let mhdr = pack_mhdr_to_send(&mut cmsg_buffer[..], &iov, &cmsgs, addr);

    let ret = unsafe { libc::sendmsg(fd, &mhdr, flags.bits()) };

    Errno::result(ret).map(|r| r as usize)
}

#[cfg(any(
    target_os = "linux",
    target_os = "android",
    target_os = "freebsd",
    target_os = "netbsd",
))]
#[derive(Debug)]
pub struct SendMmsgData<'a, I, C>
    where
        I: AsRef<[IoVec<&'a [u8]>]>,
        C: AsRef<[ControlMessage<'a>]>
{
    pub iov: I,
    pub cmsgs: C,
    pub addr: Option<SockAddr>,
    pub _lt: std::marker::PhantomData<&'a I>,
}

/// An extension of `sendmsg` that allows the caller to transmit multiple
/// messages on a socket using a single system call. This has performance
/// benefits for some applications.
///
/// Allocations are performed for cmsgs and to build `msghdr` buffer
///
/// # Arguments
///
/// * `fd`:             Socket file descriptor
/// * `data`:           Struct that implements `IntoIterator` with `SendMmsgData` items
/// * `flags`:          Optional flags passed directly to the operating system.
///
/// # Returns
/// `Vec` with numbers of sent bytes on each sent message.
///
/// # References
/// [`sendmsg`](fn.sendmsg.html)
#[cfg(any(
    target_os = "linux",
    target_os = "android",
    target_os = "freebsd",
    target_os = "netbsd",
))]
pub fn sendmmsg<'a, I, C>(
    fd: RawFd,
    data: impl std::iter::IntoIterator<Item=&'a SendMmsgData<'a, I, C>>,
    flags: MsgFlags
) -> Result<Vec<usize>>
    where
        I: AsRef<[IoVec<&'a [u8]>]> + 'a,
        C: AsRef<[ControlMessage<'a>]> + 'a,
{
    let iter = data.into_iter();

    let size_hint = iter.size_hint();
    let reserve_items = size_hint.1.unwrap_or(size_hint.0);

    let mut output = Vec::<libc::mmsghdr>::with_capacity(reserve_items);

    let mut cmsgs_buffer = vec![0u8; 0];

    for d in iter {
        let cmsgs_start = cmsgs_buffer.len();
        let cmsgs_required_capacity: usize = d.cmsgs.as_ref().iter().map(|c| c.space()).sum();
        let cmsgs_buffer_need_capacity = cmsgs_start + cmsgs_required_capacity;
        cmsgs_buffer.resize(cmsgs_buffer_need_capacity, 0);

        output.push(libc::mmsghdr {
            msg_hdr: pack_mhdr_to_send(
                &mut cmsgs_buffer[cmsgs_start..],
                &d.iov,
                &d.cmsgs,
                d.addr.as_ref()
            ),
            msg_len: 0,
        });
    };

    let ret = unsafe { libc::sendmmsg(fd, output.as_mut_ptr(), output.len() as _, flags.bits() as _) };

    let sent_messages = Errno::result(ret)? as usize;
    let mut sent_bytes = Vec::with_capacity(sent_messages);

    for item in &output {
        sent_bytes.push(item.msg_len as usize);
    }

    Ok(sent_bytes)
}


#[cfg(any(
    target_os = "linux",
    target_os = "android",
    target_os = "freebsd",
    target_os = "netbsd",
))]
#[derive(Debug)]
pub struct RecvMmsgData<'a, I>
    where
        I: AsRef<[IoVec<&'a mut [u8]>]> + 'a,
{
    pub iov: I,
    pub cmsg_buffer: Option<&'a mut Vec<u8>>,
}

/// An extension of `recvmsg` that allows the caller to receive multiple
/// messages from a socket using a single system call. This has
/// performance benefits for some applications.
///
/// `iov` and `cmsg_buffer` should be constructed similarly to `recvmsg`
///
/// Multiple allocations are performed
///
/// # Arguments
///
/// * `fd`:             Socket file descriptor
/// * `data`:           Struct that implements `IntoIterator` with `RecvMmsgData` items
/// * `flags`:          Optional flags passed directly to the operating system.
///
/// # RecvMmsgData
///
/// * `iov`:            Scatter-gather list of buffers to receive the message
/// * `cmsg_buffer`:    Space to receive ancillary data.  Should be created by
///                     [`cmsg_space!`](macro.cmsg_space.html)
///
/// # Returns
/// A `Vec` with multiple `RecvMsg`, one per received message
///
/// # References
/// - [`recvmsg`](fn.recvmsg.html)
/// - [`RecvMsg`](struct.RecvMsg.html)
#[cfg(any(
    target_os = "linux",
    target_os = "android",
    target_os = "freebsd",
    target_os = "netbsd",
))]
pub fn recvmmsg<'a, I>(
    fd: RawFd,
    data: impl std::iter::IntoIterator<Item=&'a mut RecvMmsgData<'a, I>,
        IntoIter=impl ExactSizeIterator + Iterator<Item=&'a mut RecvMmsgData<'a, I>>>,
    flags: MsgFlags,
    timeout: Option<crate::sys::time::TimeSpec>
) -> Result<Vec<RecvMsg<'a>>>
    where
        I: AsRef<[IoVec<&'a mut [u8]>]> + 'a,
{
    let iter = data.into_iter();

    let num_messages = iter.len();

    let mut output: Vec<libc::mmsghdr> = Vec::with_capacity(num_messages);

    // Addresses should be pre-allocated.  pack_mhdr_to_receive will store them
    // as raw pointers, so we may not move them.  Turn the vec into a boxed
    // slice so we won't inadvertently reallocate the vec.
    let mut addresses = vec![mem::MaybeUninit::uninit(); num_messages]
        .into_boxed_slice();

    let results: Vec<_> = iter.enumerate().map(|(i, d)| {
        let (msg_controllen, mhdr) = unsafe {
            pack_mhdr_to_receive(
                d.iov.as_ref(),
                &mut d.cmsg_buffer,
                addresses[i].as_mut_ptr(),
            )
        };

        output.push(
            libc::mmsghdr {
                msg_hdr: mhdr,
                msg_len: 0,
            }
        );

        (msg_controllen as usize, &mut d.cmsg_buffer)
    }).collect();

    let timeout = if let Some(mut t) = timeout {
        t.as_mut() as *mut libc::timespec
    } else {
        ptr::null_mut()
    };

    let ret = unsafe { libc::recvmmsg(fd, output.as_mut_ptr(), output.len() as _, flags.bits() as _, timeout) };

    let _ = Errno::result(ret)?;

    Ok(output
        .into_iter()
        .take(ret as usize)
        .zip(addresses.iter().map(|addr| unsafe{addr.assume_init()}))
        .zip(results.into_iter())
        .map(|((mmsghdr, address), (msg_controllen, cmsg_buffer))| {
            unsafe {
                read_mhdr(
                    mmsghdr.msg_hdr,
                    mmsghdr.msg_len as isize,
                    msg_controllen,
                    address,
                    cmsg_buffer
                )
            }
        })
        .collect())
}

unsafe fn read_mhdr<'a, 'b>(
    mhdr: msghdr,
    r: isize,
    msg_controllen: usize,
    address: sockaddr_storage,
    cmsg_buffer: &'a mut Option<&'b mut Vec<u8>>
) -> RecvMsg<'b> {
    let cmsghdr = {
        if mhdr.msg_controllen > 0 {
            // got control message(s)
            cmsg_buffer
                .as_mut()
                .unwrap()
                .set_len(mhdr.msg_controllen as usize);
            debug_assert!(!mhdr.msg_control.is_null());
            debug_assert!(msg_controllen >= mhdr.msg_controllen as usize);
            CMSG_FIRSTHDR(&mhdr as *const msghdr)
        } else {
            ptr::null()
        }.as_ref()
    };

    let address = sockaddr_storage_to_addr(
        &address ,
         mhdr.msg_namelen as usize
    ).ok();

    RecvMsg {
        bytes: r as usize,
        cmsghdr,
        address,
        flags: MsgFlags::from_bits_truncate(mhdr.msg_flags),
        mhdr,
    }
}

unsafe fn pack_mhdr_to_receive<'a, I>(
    iov: I,
    cmsg_buffer: &mut Option<&mut Vec<u8>>,
    address: *mut sockaddr_storage,
) -> (usize, msghdr)
    where
        I: AsRef<[IoVec<&'a mut [u8]>]> + 'a,
{
    let (msg_control, msg_controllen) = cmsg_buffer.as_mut()
        .map(|v| (v.as_mut_ptr(), v.capacity()))
        .unwrap_or((ptr::null_mut(), 0));

    let mhdr = {
        // Musl's msghdr has private fields, so this is the only way to
        // initialize it.
        let mut mhdr = mem::MaybeUninit::<msghdr>::zeroed();
        let p = mhdr.as_mut_ptr();
        (*p).msg_name = address as *mut c_void;
        (*p).msg_namelen = mem::size_of::<sockaddr_storage>() as socklen_t;
        (*p).msg_iov = iov.as_ref().as_ptr() as *mut iovec;
        (*p).msg_iovlen = iov.as_ref().len() as _;
        (*p).msg_control = msg_control as *mut c_void;
        (*p).msg_controllen = msg_controllen as _;
        (*p).msg_flags = 0;
        mhdr.assume_init()
    };

    (msg_controllen, mhdr)
}

fn pack_mhdr_to_send<'a, I, C>(
    cmsg_buffer: &mut [u8],
    iov: I,
    cmsgs: C,
    addr: Option<&SockAddr>
) -> msghdr
    where
        I: AsRef<[IoVec<&'a [u8]>]>,
        C: AsRef<[ControlMessage<'a>]>
{
    let capacity = cmsg_buffer.len();

    // Next encode the sending address, if provided
    let (name, namelen) = match addr {
        Some(addr) => {
            let (x, y) = addr.as_ffi_pair();
            (x as *const _, y)
        },
        None => (ptr::null(), 0),
    };

    // The message header must be initialized before the individual cmsgs.
    let cmsg_ptr = if capacity > 0 {
        cmsg_buffer.as_ptr() as *mut c_void
    } else {
        ptr::null_mut()
    };

    let mhdr = unsafe {
        // Musl's msghdr has private fields, so this is the only way to
        // initialize it.
        let mut mhdr = mem::MaybeUninit::<msghdr>::zeroed();
        let p = mhdr.as_mut_ptr();
        (*p).msg_name = name as *mut _;
        (*p).msg_namelen = namelen;
        // transmute iov into a mutable pointer.  sendmsg doesn't really mutate
        // the buffer, but the standard says that it takes a mutable pointer
        (*p).msg_iov = iov.as_ref().as_ptr() as *mut _;
        (*p).msg_iovlen = iov.as_ref().len() as _;
        (*p).msg_control = cmsg_ptr;
        (*p).msg_controllen = capacity as _;
        (*p).msg_flags = 0;
        mhdr.assume_init()
    };

    // Encode each cmsg.  This must happen after initializing the header because
    // CMSG_NEXT_HDR and friends read the msg_control and msg_controllen fields.
    // CMSG_FIRSTHDR is always safe
    let mut pmhdr: *mut cmsghdr = unsafe { CMSG_FIRSTHDR(&mhdr as *const msghdr) };
    for cmsg in cmsgs.as_ref() {
        assert_ne!(pmhdr, ptr::null_mut());
        // Safe because we know that pmhdr is valid, and we initialized it with
        // sufficient space
        unsafe { cmsg.encode_into(pmhdr) };
        // Safe because mhdr is valid
        pmhdr = unsafe { CMSG_NXTHDR(&mhdr as *const msghdr, pmhdr) };
    }

    mhdr
}

/// Receive message in scatter-gather vectors from a socket, and
/// optionally receive ancillary data into the provided buffer.
/// If no ancillary data is desired, use () as the type parameter.
///
/// # Arguments
///
/// * `fd`:             Socket file descriptor
/// * `iov`:            Scatter-gather list of buffers to receive the message
/// * `cmsg_buffer`:    Space to receive ancillary data.  Should be created by
///                     [`cmsg_space!`](macro.cmsg_space.html)
/// * `flags`:          Optional flags passed directly to the operating system.
///
/// # References
/// [recvmsg(2)](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recvmsg.html)
pub fn recvmsg<'a>(fd: RawFd, iov: &[IoVec<&mut [u8]>],
                   mut cmsg_buffer: Option<&'a mut Vec<u8>>,
                   flags: MsgFlags) -> Result<RecvMsg<'a>>
{
    let mut address = mem::MaybeUninit::uninit();

    let (msg_controllen, mut mhdr) = unsafe {
        pack_mhdr_to_receive(&iov, &mut cmsg_buffer, address.as_mut_ptr())
    };

    let ret = unsafe { libc::recvmsg(fd, &mut mhdr, flags.bits()) };

    let r = Errno::result(ret)?;

    Ok(unsafe { read_mhdr(mhdr, r, msg_controllen, address.assume_init(), &mut cmsg_buffer) })
}


/// Create an endpoint for communication
///
/// The `protocol` specifies a particular protocol to be used with the
/// socket.  Normally only a single protocol exists to support a
/// particular socket type within a given protocol family, in which case
/// protocol can be specified as `None`.  However, it is possible that many
/// protocols may exist, in which case a particular protocol must be
/// specified in this manner.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socket.html)
pub fn socket<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, flags: SockFlag, protocol: T) -> Result<RawFd> {
    let protocol = match protocol.into() {
        None => 0,
        Some(p) => p as c_int,
    };

    // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
    // little easier to understand by separating it out. So we have to merge these bitfields
    // here.
    let mut ty = ty as c_int;
    ty |= flags.bits();

    let res = unsafe { libc::socket(domain as c_int, ty, protocol) };

    Errno::result(res)
}

/// Create a pair of connected sockets
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/socketpair.html)
pub fn socketpair<T: Into<Option<SockProtocol>>>(domain: AddressFamily, ty: SockType, protocol: T,
                  flags: SockFlag) -> Result<(RawFd, RawFd)> {
    let protocol = match protocol.into() {
        None => 0,
        Some(p) => p as c_int,
    };

    // SockFlags are usually embedded into `ty`, but we don't do that in `nix` because it's a
    // little easier to understand by separating it out. So we have to merge these bitfields
    // here.
    let mut ty = ty as c_int;
    ty |= flags.bits();

    let mut fds = [-1, -1];

    let res = unsafe { libc::socketpair(domain as c_int, ty, protocol, fds.as_mut_ptr()) };
    Errno::result(res)?;

    Ok((fds[0], fds[1]))
}

/// Listen for connections on a socket
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/listen.html)
pub fn listen(sockfd: RawFd, backlog: usize) -> Result<()> {
    let res = unsafe { libc::listen(sockfd, backlog as c_int) };

    Errno::result(res).map(drop)
}

/// Bind a name to a socket
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/bind.html)
pub fn bind(fd: RawFd, addr: &SockAddr) -> Result<()> {
    let res = unsafe {
        let (ptr, len) = addr.as_ffi_pair();
        libc::bind(fd, ptr, len)
    };

    Errno::result(res).map(drop)
}

/// Accept a connection on a socket
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/accept.html)
pub fn accept(sockfd: RawFd) -> Result<RawFd> {
    let res = unsafe { libc::accept(sockfd, ptr::null_mut(), ptr::null_mut()) };

    Errno::result(res)
}

/// Accept a connection on a socket
///
/// [Further reading](http://man7.org/linux/man-pages/man2/accept.2.html)
#[cfg(any(all(
            target_os = "android",
            any(
                target_arch = "aarch64",
                target_arch = "x86",
                target_arch = "x86_64"
            )
          ),
          target_os = "freebsd",
          target_os = "linux",
          target_os = "openbsd"))]
pub fn accept4(sockfd: RawFd, flags: SockFlag) -> Result<RawFd> {
    let res = unsafe { libc::accept4(sockfd, ptr::null_mut(), ptr::null_mut(), flags.bits()) };

    Errno::result(res)
}

/// Initiate a connection on a socket
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/connect.html)
pub fn connect(fd: RawFd, addr: &SockAddr) -> Result<()> {
    let res = unsafe {
        let (ptr, len) = addr.as_ffi_pair();
        libc::connect(fd, ptr, len)
    };

    Errno::result(res).map(drop)
}

/// Receive data from a connection-oriented socket. Returns the number of
/// bytes read
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recv.html)
pub fn recv(sockfd: RawFd, buf: &mut [u8], flags: MsgFlags) -> Result<usize> {
    unsafe {
        let ret = libc::recv(
            sockfd,
            buf.as_ptr() as *mut c_void,
            buf.len() as size_t,
            flags.bits());

        Errno::result(ret).map(|r| r as usize)
    }
}

/// Receive data from a connectionless or connection-oriented socket. Returns
/// the number of bytes read and, for connectionless sockets,  the socket
/// address of the sender.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/recvfrom.html)
pub fn recvfrom(sockfd: RawFd, buf: &mut [u8])
    -> Result<(usize, Option<SockAddr>)>
{
    unsafe {
        let mut addr: sockaddr_storage = mem::zeroed();
        let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

        let ret = Errno::result(libc::recvfrom(
            sockfd,
            buf.as_ptr() as *mut c_void,
            buf.len() as size_t,
            0,
            &mut addr as *mut libc::sockaddr_storage as *mut libc::sockaddr,
            &mut len as *mut socklen_t))? as usize;

        match sockaddr_storage_to_addr(&addr, len as usize) {
            Err(Error::Sys(Errno::ENOTCONN)) => Ok((ret, None)),
            Ok(addr) => Ok((ret, Some(addr))),
            Err(e) => Err(e)
        }
    }
}

/// Send a message to a socket
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/sendto.html)
pub fn sendto(fd: RawFd, buf: &[u8], addr: &SockAddr, flags: MsgFlags) -> Result<usize> {
    let ret = unsafe {
        let (ptr, len) = addr.as_ffi_pair();
        libc::sendto(fd, buf.as_ptr() as *const c_void, buf.len() as size_t, flags.bits(), ptr, len)
    };

    Errno::result(ret).map(|r| r as usize)
}

/// Send data to a connection-oriented socket. Returns the number of bytes read
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/send.html)
pub fn send(fd: RawFd, buf: &[u8], flags: MsgFlags) -> Result<usize> {
    let ret = unsafe {
        libc::send(fd, buf.as_ptr() as *const c_void, buf.len() as size_t, flags.bits())
    };

    Errno::result(ret).map(|r| r as usize)
}

/*
 *
 * ===== Socket Options =====
 *
 */

/// Represents a socket option that can be accessed or set. Used as an argument
/// to `getsockopt`
pub trait GetSockOpt : Copy {
    type Val;

    #[doc(hidden)]
    fn get(&self, fd: RawFd) -> Result<Self::Val>;
}

/// Represents a socket option that can be accessed or set. Used as an argument
/// to `setsockopt`
pub trait SetSockOpt : Clone {
    type Val;

    #[doc(hidden)]
    fn set(&self, fd: RawFd, val: &Self::Val) -> Result<()>;
}

/// Get the current value for the requested socket option
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockopt.html)
pub fn getsockopt<O: GetSockOpt>(fd: RawFd, opt: O) -> Result<O::Val> {
    opt.get(fd)
}

/// Sets the value for the requested socket option
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/setsockopt.html)
///
/// # Examples
///
/// ```
/// use nix::sys::socket::setsockopt;
/// use nix::sys::socket::sockopt::KeepAlive;
/// use std::net::TcpListener;
/// use std::os::unix::io::AsRawFd;
///
/// let listener = TcpListener::bind("0.0.0.0:0").unwrap();
/// let fd = listener.as_raw_fd();
/// let res = setsockopt(fd, KeepAlive, &true);
/// assert!(res.is_ok());
/// ```
pub fn setsockopt<O: SetSockOpt>(fd: RawFd, opt: O, val: &O::Val) -> Result<()> {
    opt.set(fd, val)
}

/// Get the address of the peer connected to the socket `fd`.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getpeername.html)
pub fn getpeername(fd: RawFd) -> Result<SockAddr> {
    unsafe {
        let mut addr = mem::MaybeUninit::uninit();
        let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

        let ret = libc::getpeername(
            fd,
            addr.as_mut_ptr() as *mut libc::sockaddr,
            &mut len
        );

        Errno::result(ret)?;

        sockaddr_storage_to_addr(&addr.assume_init(), len as usize)
    }
}

/// Get the current address to which the socket `fd` is bound.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/getsockname.html)
pub fn getsockname(fd: RawFd) -> Result<SockAddr> {
    unsafe {
        let mut addr = mem::MaybeUninit::uninit();
        let mut len = mem::size_of::<sockaddr_storage>() as socklen_t;

        let ret = libc::getsockname(
            fd,
            addr.as_mut_ptr() as *mut libc::sockaddr,
            &mut len
        );

        Errno::result(ret)?;

        sockaddr_storage_to_addr(&addr.assume_init(), len as usize)
    }
}

/// Return the appropriate `SockAddr` type from a `sockaddr_storage` of a
/// certain size.
///
/// In C this would usually be done by casting.  The `len` argument
/// should be the number of bytes in the `sockaddr_storage` that are actually
/// allocated and valid.  It must be at least as large as all the useful parts
/// of the structure.  Note that in the case of a `sockaddr_un`, `len` need not
/// include the terminating null.
pub fn sockaddr_storage_to_addr(
    addr: &sockaddr_storage,
    len: usize) -> Result<SockAddr> {

    assert!(len <= mem::size_of::<sockaddr_un>());
    if len < mem::size_of_val(&addr.ss_family) {
        return Err(Error::Sys(Errno::ENOTCONN));
    }

    match c_int::from(addr.ss_family) {
        libc::AF_INET => {
            assert_eq!(len as usize, mem::size_of::<sockaddr_in>());
            let sin = unsafe {
                *(addr as *const sockaddr_storage as *const sockaddr_in)
            };
            Ok(SockAddr::Inet(InetAddr::V4(sin)))
        }
        libc::AF_INET6 => {
            assert_eq!(len as usize, mem::size_of::<sockaddr_in6>());
            let sin6 = unsafe {
                *(addr as *const _ as *const sockaddr_in6)
            };
            Ok(SockAddr::Inet(InetAddr::V6(sin6)))
        }
        libc::AF_UNIX => {
            let pathlen = len - offset_of!(sockaddr_un, sun_path);
            let sun = unsafe {
                *(addr as *const _ as *const sockaddr_un)
            };
            Ok(SockAddr::Unix(UnixAddr(sun, pathlen)))
        }
        #[cfg(any(target_os = "android", target_os = "linux"))]
        libc::AF_PACKET => {
            use libc::sockaddr_ll;
            // Apparently the Linux kernel can return smaller sizes when
            // the value in the last element of sockaddr_ll (`sll_addr`) is
            // smaller than the declared size of that field
            assert!(len as usize <= mem::size_of::<sockaddr_ll>());
            let sll = unsafe {
                *(addr as *const _ as *const sockaddr_ll)
            };
            Ok(SockAddr::Link(LinkAddr(sll)))
        }
        #[cfg(any(target_os = "android", target_os = "linux"))]
        libc::AF_NETLINK => {
            use libc::sockaddr_nl;
            let snl = unsafe {
                *(addr as *const _ as *const sockaddr_nl)
            };
            Ok(SockAddr::Netlink(NetlinkAddr(snl)))
        }
        #[cfg(any(target_os = "android", target_os = "linux"))]
        libc::AF_ALG => {
            use libc::sockaddr_alg;
            let salg = unsafe {
                *(addr as *const _ as *const sockaddr_alg)
            };
            Ok(SockAddr::Alg(AlgAddr(salg)))
        }
        #[cfg(any(target_os = "android", target_os = "linux"))]
        libc::AF_VSOCK => {
            use libc::sockaddr_vm;
            let svm = unsafe {
                *(addr as *const _ as *const sockaddr_vm)
            };
            Ok(SockAddr::Vsock(VsockAddr(svm)))
        }
        af => panic!("unexpected address family {}", af),
    }
}


#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum Shutdown {
    /// Further receptions will be disallowed.
    Read,
    /// Further  transmissions will be disallowed.
    Write,
    /// Further receptions and transmissions will be disallowed.
    Both,
}

/// Shut down part of a full-duplex connection.
///
/// [Further reading](http://pubs.opengroup.org/onlinepubs/9699919799/functions/shutdown.html)
pub fn shutdown(df: RawFd, how: Shutdown) -> Result<()> {
    unsafe {
        use libc::shutdown;

        let how = match how {
            Shutdown::Read  => libc::SHUT_RD,
            Shutdown::Write => libc::SHUT_WR,
            Shutdown::Both  => libc::SHUT_RDWR,
        };

        Errno::result(shutdown(df, how)).map(drop)
    }
}

#[cfg(test)]
mod tests {
    #[test]
    fn can_use_cmsg_space() {
        let _ = cmsg_space!(u8);
    }
}