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
use crate::io::{Interest, PollEvented, ReadBuf, Ready};
use crate::net::{to_socket_addrs, ToSocketAddrs};

use std::convert::TryFrom;
use std::fmt;
use std::io;
use std::net::{self, Ipv4Addr, Ipv6Addr, SocketAddr};
use std::task::{Context, Poll};

cfg_io_util! {
    use bytes::BufMut;
}

cfg_net! {
    /// A UDP socket.
    ///
    /// UDP is "connectionless", unlike TCP. Meaning, regardless of what address you've bound to, a `UdpSocket`
    /// is free to communicate with many different remotes. In tokio there are basically two main ways to use `UdpSocket`:
    ///
    /// * one to many: [`bind`](`UdpSocket::bind`) and use [`send_to`](`UdpSocket::send_to`)
    ///   and [`recv_from`](`UdpSocket::recv_from`) to communicate with many different addresses
    /// * one to one: [`connect`](`UdpSocket::connect`) and associate with a single address, using [`send`](`UdpSocket::send`)
    ///   and [`recv`](`UdpSocket::recv`) to communicate only with that remote address
    ///
    /// This type does not provide a `split` method, because this functionality
    /// can be achieved by instead wrapping the socket in an [`Arc`]. Note that
    /// you do not need a `Mutex` to share the `UdpSocket` — an `Arc<UdpSocket>`
    /// is enough. This is because all of the methods take `&self` instead of
    /// `&mut self`. Once you have wrapped it in an `Arc`, you can call
    /// `.clone()` on the `Arc<UdpSocket>` to get multiple shared handles to the
    /// same socket. An example of such usage can be found further down.
    ///
    /// [`Arc`]: std::sync::Arc
    ///
    /// # Streams
    ///
    /// If you need to listen over UDP and produce a [`Stream`], you can look
    /// at [`UdpFramed`].
    ///
    /// [`UdpFramed`]: https://docs.rs/tokio-util/latest/tokio_util/udp/struct.UdpFramed.html
    /// [`Stream`]: https://docs.rs/futures/0.3/futures/stream/trait.Stream.html
    ///
    /// # Example: one to many (bind)
    ///
    /// Using `bind` we can create a simple echo server that sends and recv's with many different clients:
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
    ///     let mut buf = [0; 1024];
    ///     loop {
    ///         let (len, addr) = sock.recv_from(&mut buf).await?;
    ///         println!("{:?} bytes received from {:?}", len, addr);
    ///
    ///         let len = sock.send_to(&buf[..len], addr).await?;
    ///         println!("{:?} bytes sent", len);
    ///     }
    /// }
    /// ```
    ///
    /// # Example: one to one (connect)
    ///
    /// Or using `connect` we can echo with a single remote address using `send` and `recv`:
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
    ///
    ///     let remote_addr = "127.0.0.1:59611";
    ///     sock.connect(remote_addr).await?;
    ///     let mut buf = [0; 1024];
    ///     loop {
    ///         let len = sock.recv(&mut buf).await?;
    ///         println!("{:?} bytes received from {:?}", len, remote_addr);
    ///
    ///         let len = sock.send(&buf[..len]).await?;
    ///         println!("{:?} bytes sent", len);
    ///     }
    /// }
    /// ```
    ///
    /// # Example: Splitting with `Arc`
    ///
    /// Because `send_to` and `recv_from` take `&self`. It's perfectly alright
    /// to use an `Arc<UdpSocket>` and share the references to multiple tasks.
    /// Here is a similar "echo" example that supports concurrent
    /// sending/receiving:
    ///
    /// ```no_run
    /// use tokio::{net::UdpSocket, sync::mpsc};
    /// use std::{io, net::SocketAddr, sync::Arc};
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
    ///     let r = Arc::new(sock);
    ///     let s = r.clone();
    ///     let (tx, mut rx) = mpsc::channel::<(Vec<u8>, SocketAddr)>(1_000);
    ///
    ///     tokio::spawn(async move {
    ///         while let Some((bytes, addr)) = rx.recv().await {
    ///             let len = s.send_to(&bytes, &addr).await.unwrap();
    ///             println!("{:?} bytes sent", len);
    ///         }
    ///     });
    ///
    ///     let mut buf = [0; 1024];
    ///     loop {
    ///         let (len, addr) = r.recv_from(&mut buf).await?;
    ///         println!("{:?} bytes received from {:?}", len, addr);
    ///         tx.send((buf[..len].to_vec(), addr)).await.unwrap();
    ///     }
    /// }
    /// ```
    ///
    pub struct UdpSocket {
        io: PollEvented<mio::net::UdpSocket>,
    }
}

impl UdpSocket {
    /// This function will create a new UDP socket and attempt to bind it to
    /// the `addr` provided.
    ///
    /// Binding with a port number of 0 will request that the OS assigns a port
    /// to this listener. The port allocated can be queried via the `local_addr`
    /// method.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
    ///     // use `sock`
    /// #   let _ = sock;
    ///     Ok(())
    /// }
    /// ```
    pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<UdpSocket> {
        let addrs = to_socket_addrs(addr).await?;
        let mut last_err = None;

        for addr in addrs {
            match UdpSocket::bind_addr(addr) {
                Ok(socket) => return Ok(socket),
                Err(e) => last_err = Some(e),
            }
        }

        Err(last_err.unwrap_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidInput,
                "could not resolve to any address",
            )
        }))
    }

    fn bind_addr(addr: SocketAddr) -> io::Result<UdpSocket> {
        let sys = mio::net::UdpSocket::bind(addr)?;
        UdpSocket::new(sys)
    }

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

    /// Creates new `UdpSocket` from a previously bound `std::net::UdpSocket`.
    ///
    /// This function is intended to be used to wrap a UDP socket from the
    /// standard library in the Tokio equivalent. The conversion assumes nothing
    /// about the underlying socket; it is left up to the user to set it in
    /// non-blocking mode.
    ///
    /// This can be used in conjunction with socket2's `Socket` interface to
    /// configure a socket before it's handed off, such as setting options like
    /// `reuse_address` or binding to multiple addresses.
    ///
    /// # Panics
    ///
    /// This function panics if thread-local runtime is not set.
    ///
    /// 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.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// # use std::{io, net::SocketAddr};
    ///
    /// # #[tokio::main]
    /// # async fn main() -> io::Result<()> {
    /// let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
    /// let std_sock = std::net::UdpSocket::bind(addr)?;
    /// std_sock.set_nonblocking(true)?;
    /// let sock = UdpSocket::from_std(std_sock)?;
    /// // use `sock`
    /// # Ok(())
    /// # }
    /// ```
    pub fn from_std(socket: net::UdpSocket) -> io::Result<UdpSocket> {
        let io = mio::net::UdpSocket::from_std(socket);
        UdpSocket::new(io)
    }

    /// Turns a [`tokio::net::UdpSocket`] into a [`std::net::UdpSocket`].
    ///
    /// The returned [`std::net::UdpSocket`] 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;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let tokio_socket = tokio::net::UdpSocket::bind("127.0.0.1:0").await?;
    ///     let std_socket = tokio_socket.into_std()?;
    ///     std_socket.set_nonblocking(false)?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// [`tokio::net::UdpSocket`]: UdpSocket
    /// [`std::net::UdpSocket`]: std::net::UdpSocket
    /// [`set_nonblocking`]: fn@std::net::UdpSocket::set_nonblocking
    pub fn into_std(self) -> io::Result<std::net::UdpSocket> {
        #[cfg(unix)]
        {
            use std::os::unix::io::{FromRawFd, IntoRawFd};
            self.io
                .into_inner()
                .map(|io| io.into_raw_fd())
                .map(|raw_fd| unsafe { std::net::UdpSocket::from_raw_fd(raw_fd) })
        }

        #[cfg(windows)]
        {
            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
            self.io
                .into_inner()
                .map(|io| io.into_raw_socket())
                .map(|raw_socket| unsafe { std::net::UdpSocket::from_raw_socket(raw_socket) })
        }
    }

    /// Returns the local address that this socket is bound to.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// # use std::{io, net::SocketAddr};
    ///
    /// # #[tokio::main]
    /// # async fn main() -> io::Result<()> {
    /// let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
    /// let sock = UdpSocket::bind(addr).await?;
    /// // the address the socket is bound to
    /// let local_addr = sock.local_addr()?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn local_addr(&self) -> io::Result<SocketAddr> {
        self.io.local_addr()
    }

    /// Connects the UDP socket setting the default destination for send() and
    /// limiting packets that are read via recv from the address specified in
    /// `addr`.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// # use std::{io, net::SocketAddr};
    ///
    /// # #[tokio::main]
    /// # async fn main() -> io::Result<()> {
    /// let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
    ///
    /// let remote_addr = "127.0.0.1:59600".parse::<SocketAddr>().unwrap();
    /// sock.connect(remote_addr).await?;
    /// let mut buf = [0u8; 32];
    /// // recv from remote_addr
    /// let len = sock.recv(&mut buf).await?;
    /// // send to remote_addr
    /// let _len = sock.send(&buf[..len]).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn connect<A: ToSocketAddrs>(&self, addr: A) -> io::Result<()> {
        let addrs = to_socket_addrs(addr).await?;
        let mut last_err = None;

        for addr in addrs {
            match self.io.connect(addr) {
                Ok(_) => return Ok(()),
                Err(e) => last_err = Some(e),
            }
        }

        Err(last_err.unwrap_or_else(|| {
            io::Error::new(
                io::ErrorKind::InvalidInput,
                "could not resolve to any address",
            )
        }))
    }

    /// 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`.
    ///
    /// # 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::{self, Interest};
    /// use tokio::net::UdpSocket;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     loop {
    ///         let ready = socket.ready(Interest::READABLE | Interest::WRITABLE).await?;
    ///
    ///         if ready.is_readable() {
    ///             // The buffer is **not** included in the async task and will only exist
    ///             // on the stack.
    ///             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::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Bind socket
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     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 udp stream is not currently ready for sending, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the udp
    /// stream 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 udp stream is not ready for writing.
    /// * `Poll::Ready(Ok(()))` if the udp stream 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(|_| ())
    }

    /// Sends data on the socket to the remote address that the socket is
    /// connected to.
    ///
    /// The [`connect`] method will connect this socket to a remote address.
    /// This method will fail if the socket is not connected.
    ///
    /// [`connect`]: method@Self::connect
    ///
    /// # Return
    ///
    /// On success, the number of bytes sent is returned, otherwise, the
    /// encountered error is returned.
    ///
    /// # 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
    ///
    /// ```no_run
    /// use tokio::io;
    /// use tokio::net::UdpSocket;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Bind socket
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     // Send a message
    ///     socket.send(b"hello world").await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::WRITABLE, || self.io.send(buf))
            .await
    }

    /// 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))
    }

    /// Tries to send data on the socket to the remote address to which it is
    /// connected.
    ///
    /// When the socket buffer is full, `Err(io::ErrorKind::WouldBlock)` is
    /// returned. This function is usually paired with `writable()`.
    ///
    /// # Returns
    ///
    /// If successful, `Ok(n)` is returned, where `n` is the number of bytes
    /// sent. If the socket is not ready to send data,
    /// `Err(ErrorKind::WouldBlock)` is returned.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Bind a UDP socket
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    ///     // Connect to a peer
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     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))
    }

    /// 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::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     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 udp stream is not currently ready for receiving, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the udp
    /// 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 udp stream is not ready for reading.
    /// * `Poll::Ready(Ok(()))` if the udp stream 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(|_| ())
    }

    /// Receives a single datagram message on the socket from the remote address
    /// to which it is connected. On success, returns the number of bytes read.
    ///
    /// The function must be called with valid byte array `buf` of sufficient
    /// size to hold the message bytes. If a message is too long to fit in the
    /// supplied buffer, excess bytes may be discarded.
    ///
    /// The [`connect`] method will connect this socket to a remote address.
    /// This method will fail if the socket is not connected.
    ///
    /// # 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.
    ///
    /// [`connect`]: method@Self::connect
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Bind socket
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     let mut buf = vec![0; 10];
    ///     let n = socket.recv(&mut buf).await?;
    ///
    ///     println!("received {} bytes {:?}", n, &buf[..n]);
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::READABLE, || self.io.recv(buf))
            .await
    }

    /// 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 a single datagram message on the socket from the remote
    /// address to which it is connected. On success, returns the number of
    /// bytes read.
    ///
    /// The function must be called with valid byte array buf of sufficient size
    /// to hold the message bytes. If a message is too long to fit in the
    /// supplied buffer, excess bytes may be discarded.
    ///
    /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
    /// returned. This function is usually paired with `readable()`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     socket.connect("127.0.0.1:8081").await?;
    ///
    ///     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 stream into the provided buffer, advancing the
        /// buffer's internal cursor, returning how many bytes were read.
        ///
        /// The function must be called with valid byte array buf of sufficient size
        /// to hold the message bytes. If a message is too long to fit in the
        /// supplied buffer, excess bytes may be discarded.
        ///
        /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
        /// returned. This function is usually paired with `readable()`.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::net::UdpSocket;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     // Connect to a peer
        ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
        ///     socket.connect("127.0.0.1:8081").await?;
        ///
        ///     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 `UdpSocket::recv` to have filled up `n` bytes in the
                // buffer.
                let n = (&*self.io).recv(dst)?;

                unsafe {
                    buf.advance_mut(n);
                }

                Ok(n)
            })
        }

        /// Tries to receive a single datagram message on the socket. On success,
        /// returns the number of bytes read and the origin.
        ///
        /// The function must be called with valid byte array buf of sufficient size
        /// to hold the message bytes. If a message is too long to fit in the
        /// supplied buffer, excess bytes may be discarded.
        ///
        /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
        /// returned. This function is usually paired with `readable()`.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::net::UdpSocket;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> io::Result<()> {
        ///     // Connect to a peer
        ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
        ///
        ///     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)> {
            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 `UdpSocket::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))
            })
        }
    }

    /// Sends data on the socket to the given address. On success, returns the
    /// number of bytes written.
    ///
    /// Address type can be any implementor of [`ToSocketAddrs`] trait. See its
    /// documentation for concrete examples.
    ///
    /// It is possible for `addr` to yield multiple addresses, but `send_to`
    /// will only send data to the first address yielded by `addr`.
    ///
    /// This will return an error when the IP version of the local socket does
    /// not match that returned from [`ToSocketAddrs`].
    ///
    /// [`ToSocketAddrs`]: crate::net::ToSocketAddrs
    ///
    /// # 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.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///     let len = socket.send_to(b"hello world", "127.0.0.1:8081").await?;
    ///
    ///     println!("Sent {} bytes", len);
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn send_to<A: ToSocketAddrs>(&self, buf: &[u8], target: A) -> io::Result<usize> {
        let mut addrs = to_socket_addrs(target).await?;

        match addrs.next() {
            Some(target) => self.send_to_addr(buf, target).await,
            None => Err(io::Error::new(
                io::ErrorKind::InvalidInput,
                "no addresses to send data to",
            )),
        }
    }

    /// Attempts to send data on the socket to a given 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(
        &self,
        cx: &mut Context<'_>,
        buf: &[u8],
        target: SocketAddr,
    ) -> Poll<io::Result<usize>> {
        self.io
            .registration()
            .poll_write_io(cx, || self.io.send_to(buf, target))
    }

    /// Tries to send data on the socket to the given address, but if the send is
    /// blocked this will return right away.
    ///
    /// This function is usually paired with `writable()`.
    ///
    /// # Returns
    ///
    /// If successful, returns the number of bytes sent
    ///
    /// Users should ensure that when the remote cannot receive, the
    /// [`ErrorKind::WouldBlock`] is properly handled. An error can also occur
    /// if the IP version of the socket does not match that of `target`.
    ///
    /// [`ErrorKind::WouldBlock`]: std::io::ErrorKind::WouldBlock
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    ///     let dst = "127.0.0.1:8081".parse()?;
    ///
    ///     loop {
    ///         socket.writable().await?;
    ///
    ///         match socket.try_send_to(&b"hello world"[..], dst) {
    ///             Ok(sent) => {
    ///                 println!("sent {} bytes", sent);
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 // Writable false positive.
    ///                 continue;
    ///             }
    ///             Err(e) => return Err(e.into()),
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_send_to(&self, buf: &[u8], target: SocketAddr) -> io::Result<usize> {
        self.io
            .registration()
            .try_io(Interest::WRITABLE, || self.io.send_to(buf, target))
    }

    async fn send_to_addr(&self, buf: &[u8], target: SocketAddr) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::WRITABLE, || self.io.send_to(buf, target))
            .await
    }

    /// Receives a single datagram message on the socket. On success, returns
    /// the number of bytes read and the origin.
    ///
    /// The function must be called with valid byte array `buf` of sufficient
    /// size to hold the message bytes. If a message is too long to fit in the
    /// supplied buffer, excess bytes may be discarded.
    ///
    /// # 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.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    ///     let mut buf = vec![0u8; 32];
    ///     let (len, addr) = socket.recv_from(&mut buf).await?;
    ///
    ///     println!("received {:?} bytes from {:?}", len, addr);
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
        self.io
            .registration()
            .async_io(Interest::READABLE, || self.io.recv_from(buf))
            .await
    }

    /// Attempts to receive a single datagram on the socket.
    ///
    /// 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(addr))
    }

    /// Tries to receive a single datagram message on the socket. On success,
    /// returns the number of bytes read and the origin.
    ///
    /// The function must be called with valid byte array buf of sufficient size
    /// to hold the message bytes. If a message is too long to fit in the
    /// supplied buffer, excess bytes may be discarded.
    ///
    /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
    /// returned. This function is usually paired with `readable()`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Connect to a peer
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    ///     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)> {
        self.io
            .registration()
            .try_io(Interest::READABLE, || self.io.recv_from(buf))
    }

    /// 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 from 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 `UdpSocket` type, as this will mess with the
    /// readiness flag and can cause the socket to behave incorrectly.
    ///
    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
    ///
    /// [`readable()`]: UdpSocket::readable()
    /// [`writable()`]: UdpSocket::writable()
    /// [`ready()`]: UdpSocket::ready()
    pub fn try_io<R>(
        &self,
        interest: Interest,
        f: impl FnOnce() -> io::Result<R>,
    ) -> io::Result<R> {
        self.io.registration().try_io(interest, f)
    }

    /// Receives data from the socket, without removing it from the input queue.
    /// On success, returns the number of bytes read and the address from whence
    /// the data came.
    ///
    /// # Notes
    ///
    /// On Windows, if the data is larger than the buffer specified, the buffer
    /// is filled with the first part of the data, and peek_from returns the error
    /// WSAEMSGSIZE(10040). The excess data is lost.
    /// Make sure to always use a sufficiently large buffer to hold the
    /// maximum UDP packet size, which can be up to 65536 bytes in size.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    ///     let mut buf = vec![0u8; 32];
    ///     let (len, addr) = socket.peek_from(&mut buf).await?;
    ///
    ///     println!("peeked {:?} bytes from {:?}", len, addr);
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
        self.io
            .registration()
            .async_io(Interest::READABLE, || self.io.peek_from(buf))
            .await
    }

    /// Receives data from the socket, without removing it from the input queue.
    /// On success, returns the number of bytes read.
    ///
    /// # Notes
    ///
    /// 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
    ///
    /// On Windows, if the data is larger than the buffer specified, the buffer
    /// is filled with the first part of the data, and peek returns the error
    /// WSAEMSGSIZE(10040). The excess data is lost.
    /// Make sure to always use a sufficiently large buffer to hold the
    /// maximum UDP packet size, which can be up to 65536 bytes in size.
    ///
    /// # 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_peek_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.peek_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(addr))
    }

    /// Gets the value of the `SO_BROADCAST` option for this socket.
    ///
    /// For more information about this option, see [`set_broadcast`].
    ///
    /// [`set_broadcast`]: method@Self::set_broadcast
    pub fn broadcast(&self) -> io::Result<bool> {
        self.io.broadcast()
    }

    /// Sets the value of the `SO_BROADCAST` option for this socket.
    ///
    /// When enabled, this socket is allowed to send packets to a broadcast
    /// address.
    pub fn set_broadcast(&self, on: bool) -> io::Result<()> {
        self.io.set_broadcast(on)
    }

    /// Gets the value of the `IP_MULTICAST_LOOP` option for this socket.
    ///
    /// For more information about this option, see [`set_multicast_loop_v4`].
    ///
    /// [`set_multicast_loop_v4`]: method@Self::set_multicast_loop_v4
    pub fn multicast_loop_v4(&self) -> io::Result<bool> {
        self.io.multicast_loop_v4()
    }

    /// Sets the value of the `IP_MULTICAST_LOOP` option for this socket.
    ///
    /// If enabled, multicast packets will be looped back to the local socket.
    ///
    /// # Note
    ///
    /// This may not have any affect on IPv6 sockets.
    pub fn set_multicast_loop_v4(&self, on: bool) -> io::Result<()> {
        self.io.set_multicast_loop_v4(on)
    }

    /// Gets the value of the `IP_MULTICAST_TTL` option for this socket.
    ///
    /// For more information about this option, see [`set_multicast_ttl_v4`].
    ///
    /// [`set_multicast_ttl_v4`]: method@Self::set_multicast_ttl_v4
    pub fn multicast_ttl_v4(&self) -> io::Result<u32> {
        self.io.multicast_ttl_v4()
    }

    /// Sets the value of the `IP_MULTICAST_TTL` option for this socket.
    ///
    /// Indicates the time-to-live value of outgoing multicast packets for
    /// this socket. The default value is 1 which means that multicast packets
    /// don't leave the local network unless explicitly requested.
    ///
    /// # Note
    ///
    /// This may not have any affect on IPv6 sockets.
    pub fn set_multicast_ttl_v4(&self, ttl: u32) -> io::Result<()> {
        self.io.set_multicast_ttl_v4(ttl)
    }

    /// Gets the value of the `IPV6_MULTICAST_LOOP` option for this socket.
    ///
    /// For more information about this option, see [`set_multicast_loop_v6`].
    ///
    /// [`set_multicast_loop_v6`]: method@Self::set_multicast_loop_v6
    pub fn multicast_loop_v6(&self) -> io::Result<bool> {
        self.io.multicast_loop_v6()
    }

    /// Sets the value of the `IPV6_MULTICAST_LOOP` option for this socket.
    ///
    /// Controls whether this socket sees the multicast packets it sends itself.
    ///
    /// # Note
    ///
    /// This may not have any affect on IPv4 sockets.
    pub fn set_multicast_loop_v6(&self, on: bool) -> io::Result<()> {
        self.io.set_multicast_loop_v6(on)
    }

    /// Gets the value of the `IP_TTL` option for this socket.
    ///
    /// For more information about this option, see [`set_ttl`].
    ///
    /// [`set_ttl`]: method@Self::set_ttl
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// # use std::io;
    ///
    /// # async fn dox() -> io::Result<()> {
    /// let sock = UdpSocket::bind("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", sock.ttl()?);
    /// # Ok(())
    /// # }
    /// ```
    pub fn ttl(&self) -> io::Result<u32> {
        self.io.ttl()
    }

    /// Sets the value for the `IP_TTL` option on this socket.
    ///
    /// This value sets the time-to-live field that is used in every packet sent
    /// from this socket.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::UdpSocket;
    /// # use std::io;
    ///
    /// # async fn dox() -> io::Result<()> {
    /// let sock = UdpSocket::bind("127.0.0.1:8080").await?;
    /// sock.set_ttl(60)?;
    ///
    /// # Ok(())
    /// # }
    /// ```
    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
        self.io.set_ttl(ttl)
    }

    /// Executes an operation of the `IP_ADD_MEMBERSHIP` type.
    ///
    /// This function specifies a new multicast group for this socket to join.
    /// The address must be a valid multicast address, and `interface` is the
    /// address of the local interface with which the system should join the
    /// multicast group. If it's equal to `INADDR_ANY` then an appropriate
    /// interface is chosen by the system.
    pub fn join_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
        self.io.join_multicast_v4(&multiaddr, &interface)
    }

    /// Executes an operation of the `IPV6_ADD_MEMBERSHIP` type.
    ///
    /// This function specifies a new multicast group for this socket to join.
    /// The address must be a valid multicast address, and `interface` is the
    /// index of the interface to join/leave (or 0 to indicate any interface).
    pub fn join_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
        self.io.join_multicast_v6(multiaddr, interface)
    }

    /// Executes an operation of the `IP_DROP_MEMBERSHIP` type.
    ///
    /// For more information about this option, see [`join_multicast_v4`].
    ///
    /// [`join_multicast_v4`]: method@Self::join_multicast_v4
    pub fn leave_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
        self.io.leave_multicast_v4(&multiaddr, &interface)
    }

    /// Executes an operation of the `IPV6_DROP_MEMBERSHIP` type.
    ///
    /// For more information about this option, see [`join_multicast_v6`].
    ///
    /// [`join_multicast_v6`]: method@Self::join_multicast_v6
    pub fn leave_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
        self.io.leave_multicast_v6(multiaddr, interface)
    }

    /// Returns the value of the `SO_ERROR` option.
    ///
    /// # Examples
    /// ```
    /// use tokio::net::UdpSocket;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     // Create a socket
    ///     let socket = UdpSocket::bind("0.0.0.0:8080").await?;
    ///
    ///     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()
    }
}

impl TryFrom<std::net::UdpSocket> for UdpSocket {
    type Error = io::Error;

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

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

#[cfg(all(unix))]
mod sys {
    use super::UdpSocket;
    use std::os::unix::prelude::*;

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

#[cfg(windows)]
mod sys {
    use super::UdpSocket;
    use std::os::windows::prelude::*;

    impl AsRawSocket for UdpSocket {
        fn as_raw_socket(&self) -> RawSocket {
            self.io.as_raw_socket()
        }
    }
}