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
use crate::future::poll_fn;
use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf, Ready};
use crate::net::tcp::split::{split, ReadHalf, WriteHalf};
use crate::net::tcp::split_owned::{split_owned, OwnedReadHalf, OwnedWriteHalf};
use crate::net::{to_socket_addrs, ToSocketAddrs};

use std::convert::TryFrom;
use std::fmt;
use std::io;
use std::net::{Shutdown, SocketAddr};
use std::pin::Pin;
use std::task::{Context, Poll};
use std::time::Duration;

cfg_io_util! {
    use bytes::BufMut;
}

cfg_net! {
    /// A TCP stream between a local and a remote socket.
    ///
    /// A TCP stream can either be created by connecting to an endpoint, via the
    /// [`connect`] method, or by [accepting] a connection from a [listener]. A
    /// TCP stream can also be created via the [`TcpSocket`] type.
    ///
    /// Reading and writing to a `TcpStream` is usually done using the
    /// convenience methods found on the [`AsyncReadExt`] and [`AsyncWriteExt`]
    /// traits.
    ///
    /// [`connect`]: method@TcpStream::connect
    /// [accepting]: method@crate::net::TcpListener::accept
    /// [listener]: struct@crate::net::TcpListener
    /// [`TcpSocket`]: struct@crate::net::TcpSocket
    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use tokio::io::AsyncWriteExt;
    /// use std::error::Error;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     // Write some data.
    ///     stream.write_all(b"hello world!").await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    ///
    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
    ///
    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
    ///
    /// To shut down the stream in the write direction, you can call the
    /// [`shutdown()`] method. This will cause the other peer to receive a read of
    /// length 0, indicating that no more data will be sent. This only closes
    /// the stream in one direction.
    ///
    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
    pub struct TcpStream {
        io: PollEvented<mio::net::TcpStream>,
    }
}

impl TcpStream {
    /// Opens a TCP connection to a remote host.
    ///
    /// `addr` is an address of the remote host. Anything which implements the
    /// [`ToSocketAddrs`] trait can be supplied as the address.  If `addr`
    /// yields multiple addresses, connect will be attempted with each of the
    /// addresses until a connection is successful. If none of the addresses
    /// result in a successful connection, the error returned from the last
    /// connection attempt (the last address) is returned.
    ///
    /// To configure the socket before connecting, you can use the [`TcpSocket`]
    /// type.
    ///
    /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
    /// [`TcpSocket`]: struct@crate::net::TcpSocket
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use tokio::io::AsyncWriteExt;
    /// use std::error::Error;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     // Write some data.
    ///     stream.write_all(b"hello world!").await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    ///
    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
    ///
    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
    pub async fn connect<A: ToSocketAddrs>(addr: A) -> io::Result<TcpStream> {
        let addrs = to_socket_addrs(addr).await?;

        let mut last_err = None;

        for addr in addrs {
            match TcpStream::connect_addr(addr).await {
                Ok(stream) => return Ok(stream),
                Err(e) => last_err = Some(e),
            }
        }

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

    /// Establishes a connection to the specified `addr`.
    async fn connect_addr(addr: SocketAddr) -> io::Result<TcpStream> {
        let sys = mio::net::TcpStream::connect(addr)?;
        TcpStream::connect_mio(sys).await
    }

    pub(crate) async fn connect_mio(sys: mio::net::TcpStream) -> io::Result<TcpStream> {
        let stream = TcpStream::new(sys)?;

        // Once we've connected, wait for the stream to be writable as
        // that's when the actual connection has been initiated. Once we're
        // writable we check for `take_socket_error` to see if the connect
        // actually hit an error or not.
        //
        // If all that succeeded then we ship everything on up.
        poll_fn(|cx| stream.io.registration().poll_write_ready(cx)).await?;

        if let Some(e) = stream.io.take_error()? {
            return Err(e);
        }

        Ok(stream)
    }

    pub(crate) fn new(connected: mio::net::TcpStream) -> io::Result<TcpStream> {
        let io = PollEvented::new(connected)?;
        Ok(TcpStream { io })
    }

    /// Creates new `TcpStream` from a `std::net::TcpStream`.
    ///
    /// This function is intended to be used to wrap a TCP stream from the
    /// standard library in the Tokio equivalent. The conversion assumes nothing
    /// about the underlying stream; it is left up to the user to set it in
    /// non-blocking mode.
    ///
    /// # Examples
    ///
    /// ```rust,no_run
    /// use std::error::Error;
    /// use tokio::net::TcpStream;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let std_stream = std::net::TcpStream::connect("127.0.0.1:34254")?;
    ///     std_stream.set_nonblocking(true)?;
    ///     let stream = TcpStream::from_std(std_stream)?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// # 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.
    pub fn from_std(stream: std::net::TcpStream) -> io::Result<TcpStream> {
        let io = mio::net::TcpStream::from_std(stream);
        let io = PollEvented::new(io)?;
        Ok(TcpStream { io })
    }

    /// Turns a [`tokio::net::TcpStream`] into a [`std::net::TcpStream`].
    ///
    /// The returned [`std::net::TcpStream`] will have nonblocking mode set as `true`.
    /// Use [`set_nonblocking`] to change the blocking mode if needed.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::error::Error;
    /// use std::io::Read;
    /// use tokio::net::TcpListener;
    /// # use tokio::net::TcpStream;
    /// # use tokio::io::AsyncWriteExt;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let mut data = [0u8; 12];
    ///     let listener = TcpListener::bind("127.0.0.1:34254").await?;
    /// #   let handle = tokio::spawn(async {
    /// #       let mut stream: TcpStream = TcpStream::connect("127.0.0.1:34254").await.unwrap();
    /// #       stream.write(b"Hello world!").await.unwrap();
    /// #   });
    ///     let (tokio_tcp_stream, _) = listener.accept().await?;
    ///     let mut std_tcp_stream = tokio_tcp_stream.into_std()?;
    /// #   handle.await.expect("The task being joined has panicked");
    ///     std_tcp_stream.set_nonblocking(false)?;
    ///     std_tcp_stream.read_exact(&mut data)?;
    /// #   assert_eq!(b"Hello world!", &data);
    ///     Ok(())
    /// }
    /// ```
    /// [`tokio::net::TcpStream`]: TcpStream
    /// [`std::net::TcpStream`]: std::net::TcpStream
    /// [`set_nonblocking`]: fn@std::net::TcpStream::set_nonblocking
    pub fn into_std(self) -> io::Result<std::net::TcpStream> {
        #[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::TcpStream::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::TcpStream::from_raw_socket(raw_socket) })
        }
    }

    /// Returns the local address that this stream is bound to.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", stream.local_addr()?);
    /// # Ok(())
    /// # }
    /// ```
    pub fn local_addr(&self) -> io::Result<SocketAddr> {
        self.io.local_addr()
    }

    /// Returns the remote address that this stream is connected to.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", stream.peer_addr()?);
    /// # Ok(())
    /// # }
    /// ```
    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
        self.io.peer_addr()
    }

    /// Attempts to receive data on the socket, without removing that data from
    /// the queue, registering the current task for wakeup if data is not yet
    /// available.
    ///
    /// Note that on multiple calls to `poll_peek`, `poll_read` or
    /// `poll_read_ready`, only the `Waker` from the `Context` passed to the
    /// most recent call is scheduled to receive a wakeup. (However,
    /// `poll_write` retains a second, independent waker.)
    ///
    /// # Return value
    ///
    /// The function returns:
    ///
    /// * `Poll::Pending` if data is not yet available.
    /// * `Poll::Ready(Ok(n))` if data is available. `n` is the number of bytes peeked.
    /// * `Poll::Ready(Err(e))` if an error is encountered.
    ///
    /// # Errors
    ///
    /// This function may encounter any standard I/O error except `WouldBlock`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::io::{self, ReadBuf};
    /// use tokio::net::TcpStream;
    ///
    /// use futures::future::poll_fn;
    ///
    /// #[tokio::main]
    /// async fn main() -> io::Result<()> {
    ///     let stream = TcpStream::connect("127.0.0.1:8000").await?;
    ///     let mut buf = [0; 10];
    ///     let mut buf = ReadBuf::new(&mut buf);
    ///
    ///     poll_fn(|cx| {
    ///         stream.poll_peek(cx, &mut buf)
    ///     }).await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn poll_peek(
        &self,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<usize>> {
        loop {
            let ev = ready!(self.io.registration().poll_read_ready(cx))?;

            let b = unsafe {
                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
            };

            match self.io.peek(b) {
                Ok(ret) => {
                    unsafe { buf.assume_init(ret) };
                    buf.advance(ret);
                    return Poll::Ready(Ok(ret));
                }
                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
                    self.io.registration().clear_readiness(ev);
                }
                Err(e) => return Poll::Ready(Err(e)),
            }
        }
    }

    /// Waits for any of the requested ready states.
    ///
    /// This function is usually paired with `try_read()` or `try_write()`. It
    /// can be used to concurrently read / write to the same socket on a single
    /// task without splitting the socket.
    ///
    /// # 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 read and write to the stream on the same task without
    /// splitting.
    ///
    /// ```no_run
    /// use tokio::io::Interest;
    /// use tokio::net::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     loop {
    ///         let ready = stream.ready(Interest::READABLE | Interest::WRITABLE).await?;
    ///
    ///         if ready.is_readable() {
    ///             let mut data = vec![0; 1024];
    ///             // Try to read data, this may still fail with `WouldBlock`
    ///             // if the readiness event is a false positive.
    ///             match stream.try_read(&mut data) {
    ///                 Ok(n) => {
    ///                     println!("read {} bytes", n);
    ///                 }
    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                     continue;
    ///                 }
    ///                 Err(e) => {
    ///                     return Err(e.into());
    ///                 }
    ///             }
    ///
    ///         }
    ///
    ///         if ready.is_writable() {
    ///             // Try to write data, this may still fail with `WouldBlock`
    ///             // if the readiness event is a false positive.
    ///             match stream.try_write(b"hello world") {
    ///                 Ok(n) => {
    ///                     println!("write {} bytes", n);
    ///                 }
    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                     continue
    ///                 }
    ///                 Err(e) => {
    ///                     return Err(e.into());
    ///                 }
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    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 readable.
    ///
    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
    /// paired with `try_read()`.
    ///
    /// # 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::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     let mut msg = vec![0; 1024];
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         stream.readable().await?;
    ///
    ///         // Try to read data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_read(&mut msg) {
    ///             Ok(n) => {
    ///                 msg.truncate(n);
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     println!("GOT = {:?}", msg);
    ///     Ok(())
    /// }
    /// ```
    pub async fn readable(&self) -> io::Result<()> {
        self.ready(Interest::READABLE).await?;
        Ok(())
    }

    /// Polls for read readiness.
    ///
    /// If the tcp stream is not currently ready for reading, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the tcp
    /// stream becomes ready for reading, `Waker::wake` will be called on the
    /// waker.
    ///
    /// Note that on multiple calls to `poll_read_ready`, `poll_read` or
    /// `poll_peek`, only the `Waker` from the `Context` passed to the most
    /// recent call is scheduled to receive a wakeup. (However,
    /// `poll_write_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 tcp stream is not ready for reading.
    /// * `Poll::Ready(Ok(()))` if the tcp 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_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
    }

    /// Tries to read data from the stream into the provided buffer, returning how
    /// many bytes were read.
    ///
    /// Receives any pending data from the socket but does not wait for new data
    /// to arrive. On success, returns the number of bytes read. Because
    /// `try_read()` is non-blocking, the buffer does not have to be stored by
    /// the async task and can exist entirely on the stack.
    ///
    /// Usually, [`readable()`] or [`ready()`] is used with this function.
    ///
    /// [`readable()`]: TcpStream::readable()
    /// [`ready()`]: TcpStream::ready()
    ///
    /// # Return
    ///
    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
    /// and will no longer yield data. If the stream is not ready to read data
    /// `Err(io::ErrorKind::WouldBlock)` is returned.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         stream.readable().await?;
    ///
    ///         // Creating the buffer **after** the `await` prevents it from
    ///         // being stored in the async task.
    ///         let mut buf = [0; 4096];
    ///
    ///         // Try to read data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_read(&mut buf) {
    ///             Ok(0) => break,
    ///             Ok(n) => {
    ///                 println!("read {} bytes", n);
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
        use std::io::Read;

        self.io
            .registration()
            .try_io(Interest::READABLE, || (&*self.io).read(buf))
    }

    /// Tries to read data from the stream into the provided buffers, returning
    /// how many bytes were read.
    ///
    /// Data is copied to fill each buffer in order, with the final buffer
    /// written to possibly being only partially filled. This method behaves
    /// equivalently to a single call to [`try_read()`] with concatenated
    /// buffers.
    ///
    /// Receives any pending data from the socket but does not wait for new data
    /// to arrive. On success, returns the number of bytes read. Because
    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
    /// stored by the async task and can exist entirely on the stack.
    ///
    /// Usually, [`readable()`] or [`ready()`] is used with this function.
    ///
    /// [`try_read()`]: TcpStream::try_read()
    /// [`readable()`]: TcpStream::readable()
    /// [`ready()`]: TcpStream::ready()
    ///
    /// # Return
    ///
    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
    /// and will no longer yield data. If the stream is not ready to read data
    /// `Err(io::ErrorKind::WouldBlock)` is returned.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use std::error::Error;
    /// use std::io::{self, IoSliceMut};
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     loop {
    ///         // Wait for the socket to be readable
    ///         stream.readable().await?;
    ///
    ///         // Creating the buffer **after** the `await` prevents it from
    ///         // being stored in the async task.
    ///         let mut buf_a = [0; 512];
    ///         let mut buf_b = [0; 1024];
    ///         let mut bufs = [
    ///             IoSliceMut::new(&mut buf_a),
    ///             IoSliceMut::new(&mut buf_b),
    ///         ];
    ///
    ///         // Try to read data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_read_vectored(&mut bufs) {
    ///             Ok(0) => break,
    ///             Ok(n) => {
    ///                 println!("read {} bytes", n);
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
        use std::io::Read;

        self.io
            .registration()
            .try_io(Interest::READABLE, || (&*self.io).read_vectored(bufs))
    }

    cfg_io_util! {
        /// Tries to read data from the stream into the provided buffer, advancing the
        /// buffer's internal cursor, returning how many bytes were read.
        ///
        /// Receives any pending data from the socket but does not wait for new data
        /// to arrive. On success, returns the number of bytes read. Because
        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
        /// the async task and can exist entirely on the stack.
        ///
        /// Usually, [`readable()`] or [`ready()`] is used with this function.
        ///
        /// [`readable()`]: TcpStream::readable()
        /// [`ready()`]: TcpStream::ready()
        ///
        /// # Return
        ///
        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
        /// and will no longer yield data. If the stream is not ready to read data
        /// `Err(io::ErrorKind::WouldBlock)` is returned.
        ///
        /// # Examples
        ///
        /// ```no_run
        /// use tokio::net::TcpStream;
        /// use std::error::Error;
        /// use std::io;
        ///
        /// #[tokio::main]
        /// async fn main() -> Result<(), Box<dyn Error>> {
        ///     // Connect to a peer
        ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
        ///
        ///     loop {
        ///         // Wait for the socket to be readable
        ///         stream.readable().await?;
        ///
        ///         let mut buf = Vec::with_capacity(4096);
        ///
        ///         // Try to read data, this may still fail with `WouldBlock`
        ///         // if the readiness event is a false positive.
        ///         match stream.try_read_buf(&mut buf) {
        ///             Ok(0) => break,
        ///             Ok(n) => {
        ///                 println!("read {} bytes", n);
        ///             }
        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
        ///                 continue;
        ///             }
        ///             Err(e) => {
        ///                 return Err(e.into());
        ///             }
        ///         }
        ///     }
        ///
        ///     Ok(())
        /// }
        /// ```
        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
            self.io.registration().try_io(Interest::READABLE, || {
                use std::io::Read;

                let dst = buf.chunk_mut();
                let dst =
                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };

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

                unsafe {
                    buf.advance_mut(n);
                }

                Ok(n)
            })
        }
    }

    /// Waits for the socket to become writable.
    ///
    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
    /// paired with `try_write()`.
    ///
    /// # 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::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         stream.writable().await?;
    ///
    ///         // Try to write data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_write(b"hello world") {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub async fn writable(&self) -> io::Result<()> {
        self.ready(Interest::WRITABLE).await?;
        Ok(())
    }

    /// Polls for write readiness.
    ///
    /// If the tcp stream is not currently ready for writing, this method will
    /// store a clone of the `Waker` from the provided `Context`. When the tcp
    /// stream becomes ready for writing, `Waker::wake` will be called on the
    /// waker.
    ///
    /// Note that on multiple calls to `poll_write_ready` or `poll_write`, only
    /// the `Waker` from the `Context` passed to the most recent call is
    /// scheduled to receive a wakeup. (However, `poll_read_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 tcp stream is not ready for writing.
    /// * `Poll::Ready(Ok(()))` if the tcp 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_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
    }

    /// Try to write a buffer to the stream, returning how many bytes were
    /// written.
    ///
    /// The function will attempt to write the entire contents of `buf`, but
    /// only part of the buffer may be written.
    ///
    /// This function is usually paired with `writable()`.
    ///
    /// # Return
    ///
    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
    /// number of bytes written. If the stream is not ready to write data,
    /// `Err(io::ErrorKind::WouldBlock)` is returned.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         stream.writable().await?;
    ///
    ///         // Try to write data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_write(b"hello world") {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
        use std::io::Write;

        self.io
            .registration()
            .try_io(Interest::WRITABLE, || (&*self.io).write(buf))
    }

    /// Tries to write several buffers to the stream, returning how many bytes
    /// were written.
    ///
    /// Data is written from each buffer in order, with the final buffer read
    /// from possible being only partially consumed. This method behaves
    /// equivalently to a single call to [`try_write()`] with concatenated
    /// buffers.
    ///
    /// This function is usually paired with `writable()`.
    ///
    /// [`try_write()`]: TcpStream::try_write()
    ///
    /// # Return
    ///
    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
    /// number of bytes written. If the stream is not ready to write data,
    /// `Err(io::ErrorKind::WouldBlock)` is returned.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use std::error::Error;
    /// use std::io;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];
    ///
    ///     loop {
    ///         // Wait for the socket to be writable
    ///         stream.writable().await?;
    ///
    ///         // Try to write data, this may still fail with `WouldBlock`
    ///         // if the readiness event is a false positive.
    ///         match stream.try_write_vectored(&bufs) {
    ///             Ok(n) => {
    ///                 break;
    ///             }
    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
    ///                 continue;
    ///             }
    ///             Err(e) => {
    ///                 return Err(e.into());
    ///             }
    ///         }
    ///     }
    ///
    ///     Ok(())
    /// }
    /// ```
    pub fn try_write_vectored(&self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
        use std::io::Write;

        self.io
            .registration()
            .try_io(Interest::WRITABLE, || (&*self.io).write_vectored(bufs))
    }

    /// 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 `TcpStream` 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()`]: TcpStream::readable()
    /// [`writable()`]: TcpStream::writable()
    /// [`ready()`]: TcpStream::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 on the socket from the remote address to which it is
    /// connected, without removing that data from the queue. On success,
    /// returns the number of bytes peeked.
    ///
    /// Successive calls return the same data. This is accomplished by passing
    /// `MSG_PEEK` as a flag to the underlying recv system call.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use tokio::io::AsyncReadExt;
    /// use std::error::Error;
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<(), Box<dyn Error>> {
    ///     // Connect to a peer
    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    ///     let mut b1 = [0; 10];
    ///     let mut b2 = [0; 10];
    ///
    ///     // Peek at the data
    ///     let n = stream.peek(&mut b1).await?;
    ///
    ///     // Read the data
    ///     assert_eq!(n, stream.read(&mut b2[..n]).await?);
    ///     assert_eq!(&b1[..n], &b2[..n]);
    ///
    ///     Ok(())
    /// }
    /// ```
    ///
    /// The [`read`] method is defined on the [`AsyncReadExt`] trait.
    ///
    /// [`read`]: fn@crate::io::AsyncReadExt::read
    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
    pub async fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
        self.io
            .registration()
            .async_io(Interest::READABLE, || self.io.peek(buf))
            .await
    }

    /// Shuts down the read, write, or both halves of this connection.
    ///
    /// This function will cause all pending and future I/O on the specified
    /// portions to return immediately with an appropriate value (see the
    /// documentation of `Shutdown`).
    pub(super) fn shutdown_std(&self, how: Shutdown) -> io::Result<()> {
        self.io.shutdown(how)
    }

    /// Gets the value of the `TCP_NODELAY` option on this socket.
    ///
    /// For more information about this option, see [`set_nodelay`].
    ///
    /// [`set_nodelay`]: TcpStream::set_nodelay
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", stream.nodelay()?);
    /// # Ok(())
    /// # }
    /// ```
    pub fn nodelay(&self) -> io::Result<bool> {
        self.io.nodelay()
    }

    /// Sets the value of the `TCP_NODELAY` option on this socket.
    ///
    /// If set, this option disables the Nagle algorithm. This means that
    /// segments are always sent as soon as possible, even if there is only a
    /// small amount of data. When not set, data is buffered until there is a
    /// sufficient amount to send out, thereby avoiding the frequent sending of
    /// small packets.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// stream.set_nodelay(true)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn set_nodelay(&self, nodelay: bool) -> io::Result<()> {
        self.io.set_nodelay(nodelay)
    }

    /// Reads the linger duration for this socket by getting the `SO_LINGER`
    /// option.
    ///
    /// For more information about this option, see [`set_linger`].
    ///
    /// [`set_linger`]: TcpStream::set_linger
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", stream.linger()?);
    /// # Ok(())
    /// # }
    /// ```
    pub fn linger(&self) -> io::Result<Option<Duration>> {
        socket2::SockRef::from(self).linger()
    }

    /// Sets the linger duration of this socket by setting the SO_LINGER option.
    ///
    /// This option controls the action taken when a stream has unsent messages and the stream is
    /// closed. If SO_LINGER is set, the system shall block the process until it can transmit the
    /// data or until the time expires.
    ///
    /// If SO_LINGER is not specified, and the stream is closed, the system handles the call in a
    /// way that allows the process to continue as quickly as possible.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// stream.set_linger(None)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn set_linger(&self, dur: Option<Duration>) -> io::Result<()> {
        socket2::SockRef::from(self).set_linger(dur)
    }

    /// Gets the value of the `IP_TTL` option for this socket.
    ///
    /// For more information about this option, see [`set_ttl`].
    ///
    /// [`set_ttl`]: TcpStream::set_ttl
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// println!("{:?}", stream.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::TcpStream;
    ///
    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
    ///
    /// stream.set_ttl(123)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
        self.io.set_ttl(ttl)
    }

    // These lifetime markers also appear in the generated documentation, and make
    // it more clear that this is a *borrowed* split.
    #[allow(clippy::needless_lifetimes)]
    /// Splits a `TcpStream` into a read half and a write half, which can be used
    /// to read and write the stream concurrently.
    ///
    /// This method is more efficient than [`into_split`], but the halves cannot be
    /// moved into independently spawned tasks.
    ///
    /// [`into_split`]: TcpStream::into_split()
    pub fn split<'a>(&'a mut self) -> (ReadHalf<'a>, WriteHalf<'a>) {
        split(self)
    }

    /// Splits a `TcpStream` into a read half and a write half, which can be used
    /// to read and write the stream concurrently.
    ///
    /// Unlike [`split`], the owned halves can be moved to separate tasks, however
    /// this comes at the cost of a heap allocation.
    ///
    /// **Note:** Dropping the write half will shut down the write half of the TCP
    /// stream. This is equivalent to calling [`shutdown()`] on the `TcpStream`.
    ///
    /// [`split`]: TcpStream::split()
    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
    pub fn into_split(self) -> (OwnedReadHalf, OwnedWriteHalf) {
        split_owned(self)
    }

    // == Poll IO functions that takes `&self` ==
    //
    // To read or write without mutable access to the `UnixStream`, combine the
    // `poll_read_ready` or `poll_write_ready` methods with the `try_read` or
    // `try_write` methods.

    pub(crate) fn poll_read_priv(
        &self,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        // Safety: `TcpStream::read` correctly handles reads into uninitialized memory
        unsafe { self.io.poll_read(cx, buf) }
    }

    pub(super) fn poll_write_priv(
        &self,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write(cx, buf)
    }

    pub(super) fn poll_write_vectored_priv(
        &self,
        cx: &mut Context<'_>,
        bufs: &[io::IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        self.io.poll_write_vectored(cx, bufs)
    }
}

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

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

// ===== impl Read / Write =====

impl AsyncRead for TcpStream {
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>,
    ) -> Poll<io::Result<()>> {
        self.poll_read_priv(cx, buf)
    }
}

impl AsyncWrite for TcpStream {
    fn poll_write(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &[u8],
    ) -> Poll<io::Result<usize>> {
        self.poll_write_priv(cx, buf)
    }

    fn poll_write_vectored(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        bufs: &[io::IoSlice<'_>],
    ) -> Poll<io::Result<usize>> {
        self.poll_write_vectored_priv(cx, bufs)
    }

    fn is_write_vectored(&self) -> bool {
        true
    }

    #[inline]
    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
        // tcp flush is a no-op
        Poll::Ready(Ok(()))
    }

    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
        self.shutdown_std(std::net::Shutdown::Write)?;
        Poll::Ready(Ok(()))
    }
}

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

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

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

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

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