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
use crate::io::{Interest, PollEvented, ReadBuf, Ready};
use crate::net::unix::SocketAddr;

use std::fmt;
use std::io;
use std::net::Shutdown;
#[cfg(not(tokio_no_as_fd))]
use std::os::unix::io::{AsFd, BorrowedFd};
use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
use std::os::unix::net;
use std::path::Path;
use std::task::{Context, Poll};

cfg_io_util! {
    use bytes::BufMut;
}

cfg_net_unix! {
    /// An I/O object representing a Unix datagram socket.
    ///
    /// A socket can be either named (associated with a filesystem path) or
    /// unnamed.
    ///
    /// This type does not provide a `split` method, because this functionality
    /// can be achieved by wrapping the socket in an [`Arc`]. Note that you do
    /// not need a `Mutex` to share the `UnixDatagram` — an `Arc<UnixDatagram>`
    /// is enough. This is because all of the methods take `&self` instead of
    /// `&mut self`.
    ///
    /// **Note:** named sockets are persisted even after the object is dropped
    /// and the program has exited, and cannot be reconnected. It is advised
    /// that you either check for and unlink the existing socket if it exists,
    /// or use a temporary file that is guaranteed to not already exist.
    ///
    /// [`Arc`]: std::sync::Arc
    ///
    /// # Examples
    /// Using named sockets, associated with a filesystem path:
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind each socket to a filesystem path
    /// let tx_path = tmp.path().join("tx");
    /// let tx = UnixDatagram::bind(&tx_path)?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// let bytes = b"hello world";
    /// tx.send_to(bytes, &rx_path).await?;
    ///
    /// let mut buf = vec![0u8; 24];
    /// let (size, addr) = rx.recv_from(&mut buf).await?;
    ///
    /// let dgram = &buf[..size];
    /// assert_eq!(dgram, bytes);
    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
    ///
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Using unnamed sockets, created as a pair
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create the pair of sockets
    /// let (sock1, sock2) = UnixDatagram::pair()?;
    ///
    /// // Since the sockets are paired, the paired send/recv
    /// // functions can be used
    /// let bytes = b"hello world";
    /// sock1.send(bytes).await?;
    ///
    /// let mut buff = vec![0u8; 24];
    /// let size = sock2.recv(&mut buff).await?;
    ///
    /// let dgram = &buff[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub struct UnixDatagram {
        io: PollEvented<mio::net::UnixDatagram>,
    }
}

impl UnixDatagram {
    /// Waits for any of the requested ready states.
    ///
    /// This function is usually paired with `try_recv()` or `try_send()`. It
    /// can be used to concurrently recv / send to the same socket on a single
    /// task without splitting the socket.
    ///
    /// The function may complete without the socket being ready. This is a
    /// false-positive and attempting an operation will return with
    /// `io::ErrorKind::WouldBlock`. The function can also return with an empty
    /// [`Ready`] set, so you should always check the returned value and possibly
    /// wait again if the requested states are not set.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. Once a readiness event occurs, the method
    /// will continue to return immediately until the readiness event is
    /// consumed by an attempt to read or write that fails with `WouldBlock` or
    /// `Poll::Pending`.
    ///
    /// # Examples
    ///
    /// Concurrently receive from and send to the socket on the same task
    /// without splitting.
    ///
    /// ```no_run
    /// use tokio::io::Interest;
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///     socket.connect(&server_path)?;
    ///
    ///     loop {
    ///         let ready = socket.ready(Interest::READABLE | Interest::WRITABLE).await?;
    ///
    ///         if ready.is_readable() {
    ///             let mut data = [0; 1024];
    ///             match socket.try_recv(&mut data[..]) {
    ///                 Ok(n) => {
    ///                     println!("received {:?}", &data[..n]);
    ///                 }
    ///                 // False-positive, continue
    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
    ///                 Err(e) => {
    ///                     return Err(e);
    ///                 }
    ///             }
    ///         }
    ///
    ///         if ready.is_writable() {
    ///             // Write some data
    ///             match socket.try_send(b"hello world") {
    ///                 Ok(n) => {
    ///                     println!("sent {} bytes", n);
    ///                 }
    ///                 // False-positive, continue
    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
    ///                 Err(e) => {
    ///                     return Err(e);
    ///                 }
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
        let event = self.io.registration().readiness(interest).await?;
        Ok(event.ready)
    }

    /// Waits for the socket to become writable.
    ///
    /// This function is equivalent to `ready(Interest::WRITABLE)` and is
    /// usually paired with `try_send()` or `try_send_to()`.
    ///
    /// The function may complete without the socket being writable. This is a
    /// false-positive and attempting a `try_send()` will return with
    /// `io::ErrorKind::WouldBlock`.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. Once a readiness event occurs, the method
    /// will continue to return immediately until the readiness event is
    /// consumed by an attempt to write that fails with `WouldBlock` or
    /// `Poll::Pending`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///     socket.connect(&server_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         socket.writable().await?;
    ///
    ///         // Try to send data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_send(b"hello world") {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn writable(&self) -> io::Result<()> {
        self.ready(Interest::WRITABLE).await?;
        Ok(())
    }

    /// Polls for write/send readiness.
    ///
    /// If the socket is not currently ready for sending, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the socket
    /// becomes ready for sending, `Waker::wake` will be called on the
    /// waker.
    ///
    /// Note that on multiple calls to `poll_send_ready` or `poll_send`, only
    /// the `Waker` from the `Context` passed to the most recent call is
    /// scheduled to receive a wakeup. (However, `poll_recv_ready` retains a
    /// second, independent waker.)
    ///
    /// This function is intended for cases where creating and pinning a future
    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
    /// preferred, as this supports polling from multiple tasks at once.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not ready for writing.
    /// * `Poll::Ready(Ok(()))` if the socket is ready for writing.
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    ///
    /// [`writable`]: method@Self::writable
    pub fn poll_send_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
    }

    /// Waits for the socket to become readable.
    ///
    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
    /// paired with `try_recv()`.
    ///
    /// The function may complete without the socket being readable. This is a
    /// false-positive and attempting a `try_recv()` will return with
    /// `io::ErrorKind::WouldBlock`.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. Once a readiness event occurs, the method
    /// will continue to return immediately until the readiness event is
    /// consumed by an attempt to read that fails with `WouldBlock` or
    /// `Poll::Pending`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///     socket.connect(&server_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         socket.readable().await?;
    ///
    ///         // The buffer is **not** included in the async task and will
    ///         // only exist on the stack.
    ///         let mut buf = [0; 1024];
    ///
    ///         // Try to recv data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_recv(&mut buf) {
    ///             Ok(n) => {
    ///                 println!("GOT {:?}", &buf[..n]);
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn readable(&self) -> io::Result<()> {
        self.ready(Interest::READABLE).await?;
        Ok(())
    }

    /// Polls for read/receive readiness.
    ///
    /// If the socket is not currently ready for receiving, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the
    /// socket becomes ready for reading, `Waker::wake` will be called on the
    /// waker.
    ///
    /// Note that on multiple calls to `poll_recv_ready`, `poll_recv` or
    /// `poll_peek`, only the `Waker` from the `Context` passed to the most
    /// recent call is scheduled to receive a wakeup. (However,
    /// `poll_send_ready` retains a second, independent waker.)
    ///
    /// This function is intended for cases where creating and pinning a future
    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
    /// preferred, as this supports polling from multiple tasks at once.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not ready for reading.
    /// * `Poll::Ready(Ok(()))` if the socket is ready for reading.
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    ///
    /// [`readable`]: method@Self::readable
    pub fn poll_recv_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
    }

    /// Creates a new `UnixDatagram` bound to the specified path.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind the socket to a filesystem path
    /// let socket_path = tmp.path().join("socket");
    /// let socket = UnixDatagram::bind(&socket_path)?;
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn bind<P>(path: P) -> io::Result<UnixDatagram>
    where
        P: AsRef<Path>,
    {
        let socket = mio::net::UnixDatagram::bind(path)?;
        UnixDatagram::new(socket)
    }

    /// Creates an unnamed pair of connected sockets.
    ///
    /// This function will create a pair of interconnected Unix sockets for
    /// communicating back and forth between one another.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create the pair of sockets
    /// let (sock1, sock2) = UnixDatagram::pair()?;
    ///
    /// // Since the sockets are paired, the paired send/recv
    /// // functions can be used
    /// let bytes = b"hail eris";
    /// sock1.send(bytes).await?;
    ///
    /// let mut buff = vec![0u8; 24];
    /// let size = sock2.recv(&mut buff).await?;
    ///
    /// let dgram = &buff[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn pair() -> io::Result<(UnixDatagram, UnixDatagram)> {
        let (a, b) = mio::net::UnixDatagram::pair()?;
        let a = UnixDatagram::new(a)?;
        let b = UnixDatagram::new(b)?;

        Ok((a, b))
    }

    /// Creates new `UnixDatagram` from a `std::os::unix::net::UnixDatagram`.
    ///
    /// This function is intended to be used to wrap a UnixDatagram from the
    /// standard library in the Tokio equivalent.
    ///
    /// # Notes
    ///
    /// The caller is responsible for ensuring that the socker is in
    /// non-blocking mode. Otherwise all I/O operations on the socket
    /// will block the thread, which will cause unexpected behavior.
    /// Non-blocking mode can be set using [`set_nonblocking`].
    ///
    /// [`set_nonblocking`]: std::os::unix::net::UnixDatagram::set_nonblocking
    ///
    /// # Panics
    ///
    /// This function panics if it is not called from within a runtime with
    /// IO enabled.
    ///
    /// The runtime is usually set implicitly when this function is called
    /// from a future driven by a Tokio runtime, otherwise runtime can be set
    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use std::os::unix::net::UnixDatagram as StdUDS;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind the socket to a filesystem path
    /// let socket_path = tmp.path().join("socket");
    /// let std_socket = StdUDS::bind(&socket_path)?;
    /// std_socket.set_nonblocking(true)?;
    /// let tokio_socket = UnixDatagram::from_std(std_socket)?;
    ///
    /// # Ok(())
    /// # }
    /// ```
    #[track_caller]
    pub fn from_std(datagram: net::UnixDatagram) -> io::Result<UnixDatagram> {
        let socket = mio::net::UnixDatagram::from_std(datagram);
        let io = PollEvented::new(socket)?;
        Ok(UnixDatagram { io })
    }

    /// Turns a [`tokio::net::UnixDatagram`] into a [`std::os::unix::net::UnixDatagram`].
    ///
    /// The returned [`std::os::unix::net::UnixDatagram`] will have nonblocking
    /// mode set as `true`. Use [`set_nonblocking`] to change the blocking mode
    /// if needed.
    ///
    /// # Examples
    ///
    /// ```rust,no_run
    /// # use std::error::Error;
    /// # async fn dox() -> Result<(), Box<dyn Error>> {
    /// let tokio_socket = tokio::net::UnixDatagram::bind("/path/to/the/socket")?;
    /// let std_socket = tokio_socket.into_std()?;
    /// std_socket.set_nonblocking(false)?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// [`tokio::net::UnixDatagram`]: UnixDatagram
    /// [`std::os::unix::net::UnixDatagram`]: std::os::unix::net::UnixDatagram
    /// [`set_nonblocking`]: fn@std::os::unix::net::UnixDatagram::set_nonblocking
    pub fn into_std(self) -> io::Result<std::os::unix::net::UnixDatagram> {
        self.io
            .into_inner()
            .map(|io| io.into_raw_fd())
            .map(|raw_fd| unsafe { std::os::unix::net::UnixDatagram::from_raw_fd(raw_fd) })
    }

    fn new(socket: mio::net::UnixDatagram) -> io::Result<UnixDatagram> {
        let io = PollEvented::new(socket)?;
        Ok(UnixDatagram { io })
    }

    /// Creates a new `UnixDatagram` which is not bound to any address.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // Create an unbound socket
    /// let tx = UnixDatagram::unbound()?;
    ///
    /// // Create another, bound socket
    /// let tmp = tempdir()?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// // Send to the bound socket
    /// let bytes = b"hello world";
    /// tx.send_to(bytes, &rx_path).await?;
    ///
    /// let mut buf = vec![0u8; 24];
    /// let (size, addr) = rx.recv_from(&mut buf).await?;
    ///
    /// let dgram = &buf[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn unbound() -> io::Result<UnixDatagram> {
        let socket = mio::net::UnixDatagram::unbound()?;
        UnixDatagram::new(socket)
    }

    /// Connects the socket to the specified address.
    ///
    /// The `send` method may be used to send data to the specified address.
    /// `recv` and `recv_from` will only receive data from that address.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // Create an unbound socket
    /// let tx = UnixDatagram::unbound()?;
    ///
    /// // Create another, bound socket
    /// let tmp = tempdir()?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// // Connect to the bound socket
    /// tx.connect(&rx_path)?;
    ///
    /// // Send to the bound socket
    /// let bytes = b"hello world";
    /// tx.send(bytes).await?;
    ///
    /// let mut buf = vec![0u8; 24];
    /// let (size, addr) = rx.recv_from(&mut buf).await?;
    ///
    /// let dgram = &buf[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn connect<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
        self.io.connect(path)
    }

    /// Sends data on the socket to the socket's peer.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. If `send` is used as the event in a
    /// [`tokio::select!`](crate::select) statement and some other branch
    /// completes first, then it is guaranteed that the message was not sent.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create the pair of sockets
    /// let (sock1, sock2) = UnixDatagram::pair()?;
    ///
    /// // Since the sockets are paired, the paired send/recv
    /// // functions can be used
    /// let bytes = b"hello world";
    /// sock1.send(bytes).await?;
    ///
    /// let mut buff = vec![0u8; 24];
    /// let size = sock2.recv(&mut buff).await?;
    ///
    /// let dgram = &buff[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::WRITABLE, || self.io.send(buf))
            .await
    }

    /// Tries to send a datagram to the peer without waiting.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///     socket.connect(&server_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         socket.writable().await?;
    ///
    ///         // Try to send data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_send(b"hello world") {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_send(&self, buf: &[u8]) -> io::Result<usize> {
        self.io
            .registration()
            .try_io(Interest::WRITABLE, || self.io.send(buf))
    }

    /// Tries to send a datagram to the peer without waiting.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         socket.writable().await?;
    ///
    ///         // Try to send data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_send_to(b"hello world", &server_path) {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_send_to<P>(&self, buf: &[u8], target: P) -> io::Result<usize>
    where
        P: AsRef<Path>,
    {
        self.io
            .registration()
            .try_io(Interest::WRITABLE, || self.io.send_to(buf, target))
    }

    /// Receives data from the socket.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. If `recv` is used as the event in a
    /// [`tokio::select!`](crate::select) statement and some other branch
    /// completes first, it is guaranteed that no messages were received on this
    /// socket.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create the pair of sockets
    /// let (sock1, sock2) = UnixDatagram::pair()?;
    ///
    /// // Since the sockets are paired, the paired send/recv
    /// // functions can be used
    /// let bytes = b"hello world";
    /// sock1.send(bytes).await?;
    ///
    /// let mut buff = vec![0u8; 24];
    /// let size = sock2.recv(&mut buff).await?;
    ///
    /// let dgram = &buff[..size];
    /// assert_eq!(dgram, bytes);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::READABLE, || self.io.recv(buf))
            .await
    }

    /// Tries to receive a datagram from the peer without waiting.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///     socket.connect(&server_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         socket.readable().await?;
    ///
    ///         // The buffer is **not** included in the async task and will
    ///         // only exist on the stack.
    ///         let mut buf = [0; 1024];
    ///
    ///         // Try to recv data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_recv(&mut buf) {
    ///             Ok(n) => {
    ///                 println!("GOT {:?}", &buf[..n]);
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_recv(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.io
            .registration()
            .try_io(Interest::READABLE, || self.io.recv(buf))
    }

    cfg_io_util! {
        /// Tries to receive data from the socket without waiting.
        ///
        /// This method can be used even if `buf` is uninitialized.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::net::UnixDatagram;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     // Connect to a peer
        ///     let dir = tempfile::tempdir().unwrap();
        ///     let client_path = dir.path().join("client.sock");
        ///     let server_path = dir.path().join("server.sock");
        ///     let socket = UnixDatagram::bind(&client_path)?;
        ///
        ///     loop {
        ///         // Wait for the socket to be readable
        ///         socket.readable().await?;
        ///
        ///         let mut buf = Vec::with_capacity(1024);
        ///
        ///         // Try to recv data, this may still fail with `WouldBlock`
        ///         // if the readiness event is a false positive.
        ///         match socket.try_recv_buf_from(&mut buf) {
        ///             Ok((n, _addr)) => {
        ///                 println!("GOT {:?}", &buf[..n]);
        ///                 break;
        ///             }
        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
        ///                 continue;
        ///             }
        ///             Err(e) => {
        ///                 return Err(e);
        ///             }
        ///         }
        ///     }
        ///
        ///     Ok(())
        /// }
        /// ```
        pub fn try_recv_buf_from<B: BufMut>(&self, buf: &mut B) -> io::Result<(usize, SocketAddr)> {
            let (n, addr) = self.io.registration().try_io(Interest::READABLE, || {
                let dst = buf.chunk_mut();
                let dst =
                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };

                // Safety: We trust `UnixDatagram::recv_from` to have filled up `n` bytes in the
                // buffer.
                let (n, addr) = (*self.io).recv_from(dst)?;

                unsafe {
                    buf.advance_mut(n);
                }

                Ok((n, addr))
            })?;

            Ok((n, SocketAddr(addr)))
        }

        /// Receives from the socket, advances the
        /// buffer's internal cursor and returns how many bytes were read and the origin.
        ///
        /// This method can be used even if `buf` is uninitialized.
        ///
        /// # Examples
        /// ```
        /// # use std::error::Error;
        /// # #[tokio::main]
        /// # async fn main() -> Result<(), Box<dyn Error>> {
        /// use tokio::net::UnixDatagram;
        /// use tempfile::tempdir;
        ///
        /// // We use a temporary directory so that the socket
        /// // files left by the bound sockets will get cleaned up.
        /// let tmp = tempdir()?;
        ///
        /// // Bind each socket to a filesystem path
        /// let tx_path = tmp.path().join("tx");
        /// let tx = UnixDatagram::bind(&tx_path)?;
        /// let rx_path = tmp.path().join("rx");
        /// let rx = UnixDatagram::bind(&rx_path)?;
        ///
        /// let bytes = b"hello world";
        /// tx.send_to(bytes, &rx_path).await?;
        ///
        /// let mut buf = Vec::with_capacity(24);
        /// let (size, addr) = rx.recv_buf_from(&mut buf).await?;
        ///
        /// let dgram = &buf[..size];
        /// assert_eq!(dgram, bytes);
        /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
        ///
        /// # Ok(())
        /// # }
        /// ```
        pub async fn recv_buf_from<B: BufMut>(&self, buf: &mut B) -> io::Result<(usize, SocketAddr)> {
            self.io.registration().async_io(Interest::READABLE, || {
                let dst = buf.chunk_mut();
                let dst =
                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };

                // Safety: We trust `UnixDatagram::recv_from` to have filled up `n` bytes in the
                // buffer.
                let (n, addr) = (*self.io).recv_from(dst)?;

                unsafe {
                    buf.advance_mut(n);
                }
                Ok((n,SocketAddr(addr)))
            }).await
        }

        /// Tries to read data from the stream into the provided buffer, advancing the
        /// buffer's internal cursor, returning how many bytes were read.
        ///
        /// This method can be used even if `buf` is uninitialized.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::net::UnixDatagram;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     // Connect to a peer
        ///     let dir = tempfile::tempdir().unwrap();
        ///     let client_path = dir.path().join("client.sock");
        ///     let server_path = dir.path().join("server.sock");
        ///     let socket = UnixDatagram::bind(&client_path)?;
        ///     socket.connect(&server_path)?;
        ///
        ///     loop {
        ///         // Wait for the socket to be readable
        ///         socket.readable().await?;
        ///
        ///         let mut buf = Vec::with_capacity(1024);
        ///
        ///         // Try to recv data, this may still fail with `WouldBlock`
        ///         // if the readiness event is a false positive.
        ///         match socket.try_recv_buf(&mut buf) {
        ///             Ok(n) => {
        ///                 println!("GOT {:?}", &buf[..n]);
        ///                 break;
        ///             }
        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
        ///                 continue;
        ///             }
        ///             Err(e) => {
        ///                 return Err(e);
        ///             }
        ///         }
        ///     }
        ///
        ///     Ok(())
        /// }
        /// ```
        pub fn try_recv_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
            self.io.registration().try_io(Interest::READABLE, || {
                let dst = buf.chunk_mut();
                let dst =
                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };

                // Safety: We trust `UnixDatagram::recv` to have filled up `n` bytes in the
                // buffer.
                let n = (*self.io).recv(dst)?;

                unsafe {
                    buf.advance_mut(n);
                }

                Ok(n)
            })
        }

        /// Receives data from the socket from the address to which it is connected,
        /// advancing the buffer's internal cursor, returning how many bytes were read.
        ///
        /// This method can be used even if `buf` is uninitialized.
        ///
        /// # Examples
        /// ```
        /// # use std::error::Error;
        /// # #[tokio::main]
        /// # async fn main() -> Result<(), Box<dyn Error>> {
        /// use tokio::net::UnixDatagram;
        ///
        /// // Create the pair of sockets
        /// let (sock1, sock2) = UnixDatagram::pair()?;
        ///
        /// // Since the sockets are paired, the paired send/recv
        /// // functions can be used
        /// let bytes = b"hello world";
        /// sock1.send(bytes).await?;
        ///
        /// let mut buff = Vec::with_capacity(24);
        /// let size = sock2.recv_buf(&mut buff).await?;
        ///
        /// let dgram = &buff[..size];
        /// assert_eq!(dgram, bytes);
        ///
        /// # Ok(())
        /// # }
        /// ```
        pub async fn recv_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
            self.io.registration().async_io(Interest::READABLE, || {
                let dst = buf.chunk_mut();
                let dst =
                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };

                // Safety: We trust `UnixDatagram::recv_from` to have filled up `n` bytes in the
                // buffer.
                let n = (*self.io).recv(dst)?;

                unsafe {
                    buf.advance_mut(n);
                }
                Ok(n)
            }).await
        }
    }

    /// Sends data on the socket to the specified address.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. If `send_to` is used as the event in a
    /// [`tokio::select!`](crate::select) statement and some other branch
    /// completes first, then it is guaranteed that the message was not sent.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind each socket to a filesystem path
    /// let tx_path = tmp.path().join("tx");
    /// let tx = UnixDatagram::bind(&tx_path)?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// let bytes = b"hello world";
    /// tx.send_to(bytes, &rx_path).await?;
    ///
    /// let mut buf = vec![0u8; 24];
    /// let (size, addr) = rx.recv_from(&mut buf).await?;
    ///
    /// let dgram = &buf[..size];
    /// assert_eq!(dgram, bytes);
    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub async fn send_to<P>(&self, buf: &[u8], target: P) -> io::Result<usize>
    where
        P: AsRef<Path>,
    {
        self.io
            .registration()
            .async_io(Interest::WRITABLE, || self.io.send_to(buf, target.as_ref()))
            .await
    }

    /// Receives data from the socket.
    ///
    /// # Cancel safety
    ///
    /// This method is cancel safe. If `recv_from` is used as the event in a
    /// [`tokio::select!`](crate::select) statement and some other branch
    /// completes first, it is guaranteed that no messages were received on this
    /// socket.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind each socket to a filesystem path
    /// let tx_path = tmp.path().join("tx");
    /// let tx = UnixDatagram::bind(&tx_path)?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// let bytes = b"hello world";
    /// tx.send_to(bytes, &rx_path).await?;
    ///
    /// let mut buf = vec![0u8; 24];
    /// let (size, addr) = rx.recv_from(&mut buf).await?;
    ///
    /// let dgram = &buf[..size];
    /// assert_eq!(dgram, bytes);
    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
        let (n, addr) = self
            .io
            .registration()
            .async_io(Interest::READABLE, || self.io.recv_from(buf))
            .await?;

        Ok((n, SocketAddr(addr)))
    }

    /// Attempts to receive a single datagram on the specified address.
    ///
    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
    /// receive a wakeup.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not ready to read
    /// * `Poll::Ready(Ok(addr))` reads data from `addr` into `ReadBuf` if the socket is ready
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    pub fn poll_recv_from(
        &self,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<SocketAddr>> {
        let (n, addr) = ready!(self.io.registration().poll_read_io(cx, || {
            // Safety: will not read the maybe uninitialized bytes.
            let b = unsafe {
                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
            };

            self.io.recv_from(b)
        }))?;

        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
        unsafe {
            buf.assume_init(n);
        }
        buf.advance(n);
        Poll::Ready(Ok(SocketAddr(addr)))
    }

    /// Attempts to send data to the specified address.
    ///
    /// Note that on multiple calls to a `poll_*` method in the send direction, only the
    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
    /// receive a wakeup.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not ready to write
    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent.
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    pub fn poll_send_to<P>(
        &self,
        cx: &mut Context<'_>,
        buf: &[u8],
        target: P,
    ) -> Poll<io::Result<usize>>
    where
        P: AsRef<Path>,
    {
        self.io
            .registration()
            .poll_write_io(cx, || self.io.send_to(buf, target.as_ref()))
    }

    /// Attempts to send data on the socket to the remote address to which it
    /// was previously `connect`ed.
    ///
    /// The [`connect`] method will connect this socket to a remote address.
    /// This method will fail if the socket is not connected.
    ///
    /// Note that on multiple calls to a `poll_*` method in the send direction,
    /// only the `Waker` from the `Context` passed to the most recent call will
    /// be scheduled to receive a wakeup.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not available to write
    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    ///
    /// [`connect`]: method@Self::connect
    pub fn poll_send(&self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>> {
        self.io
            .registration()
            .poll_write_io(cx, || self.io.send(buf))
    }

    /// Attempts to receive a single datagram message on the socket from the remote
    /// address to which it is `connect`ed.
    ///
    /// The [`connect`] method will connect this socket to a remote address. This method
    /// resolves to an error if the socket is not connected.
    ///
    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
    /// receive a wakeup.
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if the socket is not ready to read
    /// * `Poll::Ready(Ok(()))` reads data `ReadBuf` if the socket is ready
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    ///
    /// [`connect`]: method@Self::connect
    pub fn poll_recv(&self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<io::Result<()>> {
        let n = ready!(self.io.registration().poll_read_io(cx, || {
            // Safety: will not read the maybe uninitialized bytes.
            let b = unsafe {
                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
            };

            self.io.recv(b)
        }))?;

        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
        unsafe {
            buf.assume_init(n);
        }
        buf.advance(n);
        Poll::Ready(Ok(()))
    }

    /// Tries to receive data from the socket without waiting.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UnixDatagram;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let dir = tempfile::tempdir().unwrap();
    ///     let client_path = dir.path().join("client.sock");
    ///     let server_path = dir.path().join("server.sock");
    ///     let socket = UnixDatagram::bind(&client_path)?;
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         socket.readable().await?;
    ///
    ///         // The buffer is **not** included in the async task and will
    ///         // only exist on the stack.
    ///         let mut buf = [0; 1024];
    ///
    ///         // Try to recv data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match socket.try_recv_from(&mut buf) {
    ///             Ok((n, _addr)) => {
    ///                 println!("GOT {:?}", &buf[..n]);
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e);
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
        let (n, addr) = self
            .io
            .registration()
            .try_io(Interest::READABLE, || self.io.recv_from(buf))?;

        Ok((n, SocketAddr(addr)))
    }

    /// Tries to read or write from the socket using a user-provided IO operation.
    ///
    /// If the socket is ready, the provided closure is called. The closure
    /// should attempt to perform IO operation on the socket by manually
    /// calling the appropriate syscall. If the operation fails because the
    /// socket is not actually ready, then the closure should return a
    /// `WouldBlock` error and the readiness flag is cleared. The return value
    /// of the closure is then returned by `try_io`.
    ///
    /// If the socket is not ready, then the closure is not called
    /// and a `WouldBlock` error is returned.
    ///
    /// The closure should only return a `WouldBlock` error if it has performed
    /// an IO operation on the socket that failed due to the socket not being
    /// ready. Returning a `WouldBlock` error in any other situation will
    /// incorrectly clear the readiness flag, which can cause the socket to
    /// behave incorrectly.
    ///
    /// The closure should not perform the IO operation using any of the methods
    /// defined on the Tokio `UnixDatagram` type, as this will mess with the
    /// readiness flag and can cause the socket to behave incorrectly.
    ///
    /// This method is not intended to be used with combined interests.
    /// The closure should perform only one type of IO operation, so it should not
    /// require more than one ready state. This method may panic or sleep forever
    /// if it is called with a combined interest.
    ///
    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
    ///
    /// [`readable()`]: UnixDatagram::readable()
    /// [`writable()`]: UnixDatagram::writable()
    /// [`ready()`]: UnixDatagram::ready()
    pub fn try_io<R>(
        &self,
        interest: Interest,
        f: impl FnOnce() -> io::Result<R>,
    ) -> io::Result<R> {
        self.io
            .registration()
            .try_io(interest, || self.io.try_io(f))
    }

    /// Reads or writes from the socket using a user-provided IO operation.
    ///
    /// The readiness of the socket is awaited and when the socket is ready,
    /// the provided closure is called. The closure should attempt to perform
    /// IO operation on the socket by manually calling the appropriate syscall.
    /// If the operation fails because the socket is not actually ready,
    /// then the closure should return a `WouldBlock` error. In such case the
    /// readiness flag is cleared and the socket readiness is awaited again.
    /// This loop is repeated until the closure returns an `Ok` or an error
    /// other than `WouldBlock`.
    ///
    /// The closure should only return a `WouldBlock` error if it has performed
    /// an IO operation on the socket that failed due to the socket not being
    /// ready. Returning a `WouldBlock` error in any other situation will
    /// incorrectly clear the readiness flag, which can cause the socket to
    /// behave incorrectly.
    ///
    /// The closure should not perform the IO operation using any of the methods
    /// defined on the Tokio `UnixDatagram` type, as this will mess with the
    /// readiness flag and can cause the socket to behave incorrectly.
    ///
    /// This method is not intended to be used with combined interests.
    /// The closure should perform only one type of IO operation, so it should not
    /// require more than one ready state. This method may panic or sleep forever
    /// if it is called with a combined interest.
    pub async fn async_io<R>(
        &self,
        interest: Interest,
        mut f: impl FnMut() -> io::Result<R>,
    ) -> io::Result<R> {
        self.io
            .registration()
            .async_io(interest, || self.io.try_io(&mut f))
            .await
    }

    /// Returns the local address that this socket is bound to.
    ///
    /// # Examples
    /// For a socket bound to a local path
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // We use a temporary directory so that the socket
    /// // files left by the bound sockets will get cleaned up.
    /// let tmp = tempdir()?;
    ///
    /// // Bind socket to a filesystem path
    /// let socket_path = tmp.path().join("socket");
    /// let socket = UnixDatagram::bind(&socket_path)?;
    ///
    /// assert_eq!(socket.local_addr()?.as_pathname().unwrap(), &socket_path);
    ///
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// For an unbound socket
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create an unbound socket
    /// let socket = UnixDatagram::unbound()?;
    ///
    /// assert!(socket.local_addr()?.is_unnamed());
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn local_addr(&self) -> io::Result<SocketAddr> {
        self.io.local_addr().map(SocketAddr)
    }

    /// Returns the address of this socket's peer.
    ///
    /// The `connect` method will connect the socket to a peer.
    ///
    /// # Examples
    /// For a peer with a local path
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use tempfile::tempdir;
    ///
    /// // Create an unbound socket
    /// let tx = UnixDatagram::unbound()?;
    ///
    /// // Create another, bound socket
    /// let tmp = tempdir()?;
    /// let rx_path = tmp.path().join("rx");
    /// let rx = UnixDatagram::bind(&rx_path)?;
    ///
    /// // Connect to the bound socket
    /// tx.connect(&rx_path)?;
    ///
    /// assert_eq!(tx.peer_addr()?.as_pathname().unwrap(), &rx_path);
    ///
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// For an unbound peer
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create the pair of sockets
    /// let (sock1, sock2) = UnixDatagram::pair()?;
    ///
    /// assert!(sock1.peer_addr()?.is_unnamed());
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
        self.io.peer_addr().map(SocketAddr)
    }

    /// Returns the value of the `SO_ERROR` option.
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    ///
    /// // Create an unbound socket
    /// let socket = UnixDatagram::unbound()?;
    ///
    /// if let Ok(Some(err)) = socket.take_error() {
    ///     println!("Got error: {:?}", err);
    /// }
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
        self.io.take_error()
    }

    /// Shuts down the read, write, or both halves of this connection.
    ///
    /// This function will cause all pending and future I/O calls on the
    /// specified portions to immediately return with an appropriate value
    /// (see the documentation of `Shutdown`).
    ///
    /// # Examples
    /// ```
    /// # use std::error::Error;
    /// # #[tokio::main]
    /// # async fn main() -> Result<(), Box<dyn Error>> {
    /// use tokio::net::UnixDatagram;
    /// use std::net::Shutdown;
    ///
    /// // Create an unbound socket
    /// let (socket, other) = UnixDatagram::pair()?;
    ///
    /// socket.shutdown(Shutdown::Both)?;
    ///
    /// // NOTE: the following commented out code does NOT work as expected.
    /// // Due to an underlying issue, the recv call will block indefinitely.
    /// // See: https://github.com/tokio-rs/tokio/issues/1679
    /// //let mut buff = vec![0u8; 24];
    /// //let size = socket.recv(&mut buff).await?;
    /// //assert_eq!(size, 0);
    ///
    /// let send_result = socket.send(b"hello world").await;
    /// assert!(send_result.is_err());
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
        self.io.shutdown(how)
    }
}

impl TryFrom<std::os::unix::net::UnixDatagram> for UnixDatagram {
    type Error = io::Error;

    /// Consumes stream, returning the Tokio I/O object.
    ///
    /// This is equivalent to
    /// [`UnixDatagram::from_std(stream)`](UnixDatagram::from_std).
    fn try_from(stream: std::os::unix::net::UnixDatagram) -> Result<Self, Self::Error> {
        Self::from_std(stream)
    }
}

impl fmt::Debug for UnixDatagram {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.io.fmt(f)
    }
}

impl AsRawFd for UnixDatagram {
    fn as_raw_fd(&self) -> RawFd {
        self.io.as_raw_fd()
    }
}

#[cfg(not(tokio_no_as_fd))]
impl AsFd for UnixDatagram {
    fn as_fd(&self) -> BorrowedFd<'_> {
        unsafe { BorrowedFd::borrow_raw(self.as_raw_fd()) }
    }
}