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
//! `TcpStream` owned split support.
//!
//! A `TcpStream` can be split into an `OwnedReadHalf` and a `OwnedWriteHalf`
//! with the `TcpStream::into_split` method.  `OwnedReadHalf` implements
//! `AsyncRead` while `OwnedWriteHalf` implements `AsyncWrite`.
//!
//! Compared to the generic split of `AsyncRead + AsyncWrite`, this specialized
//! split has no associated overhead and enforces all invariants at the type
//! level.

use crate::future::poll_fn;
use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
use crate::net::TcpStream;

use std::error::Error;
use std::net::Shutdown;
use std::pin::Pin;
use std::sync::Arc;
use std::task::{Context, Poll};
use std::{fmt, io};

/// Owned read half of a [`TcpStream`], created by [`into_split`].
///
/// Reading from an `OwnedReadHalf` is usually done using the convenience methods found
/// on the [`AsyncReadExt`] trait. Examples import this trait through [the prelude].
///
/// [`TcpStream`]: TcpStream
/// [`into_split`]: TcpStream::into_split()
/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
/// [the prelude]: crate::prelude
#[derive(Debug)]
pub struct OwnedReadHalf {
    inner: Arc<TcpStream>,
}

/// Owned write half of a [`TcpStream`], created by [`into_split`].
///
/// Note that in the [`AsyncWrite`] implementation of this type, [`poll_shutdown`] will
/// shut down the TCP stream in the write direction.  Dropping the write half
/// will also shut down the write half of the TCP stream.
///
/// Writing to an `OwnedWriteHalf` is usually done using the convenience methods found
/// on the [`AsyncWriteExt`] trait. Examples import this trait through [the prelude].
///
/// [`TcpStream`]: TcpStream
/// [`into_split`]: TcpStream::into_split()
/// [`AsyncWrite`]: trait@crate::io::AsyncWrite
/// [`poll_shutdown`]: fn@crate::io::AsyncWrite::poll_shutdown
/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
/// [the prelude]: crate::prelude
#[derive(Debug)]
pub struct OwnedWriteHalf {
    inner: Arc<TcpStream>,
    shutdown_on_drop: bool,
}

pub(crate) fn split_owned(stream: TcpStream) -> (OwnedReadHalf, OwnedWriteHalf) {
    let arc = Arc::new(stream);
    let read = OwnedReadHalf {
        inner: Arc::clone(&arc),
    };
    let write = OwnedWriteHalf {
        inner: arc,
        shutdown_on_drop: true,
    };
    (read, write)
}

pub(crate) fn reunite(
    read: OwnedReadHalf,
    write: OwnedWriteHalf,
) -> Result<TcpStream, ReuniteError> {
    if Arc::ptr_eq(&read.inner, &write.inner) {
        write.forget();
        // This unwrap cannot fail as the api does not allow creating more than two Arcs,
        // and we just dropped the other half.
        Ok(Arc::try_unwrap(read.inner).expect("TcpStream: try_unwrap failed in reunite"))
    } else {
        Err(ReuniteError(read, write))
    }
}

/// Error indicating that two halves were not from the same socket, and thus could
/// not be reunited.
#[derive(Debug)]
pub struct ReuniteError(pub OwnedReadHalf, pub OwnedWriteHalf);

impl fmt::Display for ReuniteError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "tried to reunite halves that are not from the same socket"
        )
    }
}

impl Error for ReuniteError {}

impl OwnedReadHalf {
    /// Attempts to put the two halves of a `TcpStream` back together and
    /// recover the original socket. Succeeds only if the two halves
    /// originated from the same call to [`into_split`].
    ///
    /// [`into_split`]: TcpStream::into_split()
    pub fn reunite(self, other: OwnedWriteHalf) -> Result<TcpStream, ReuniteError> {
        reunite(self, other)
    }

    /// Attempt 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.
    ///
    /// See the [`TcpStream::poll_peek`] level documenation for more details.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::io;
    /// 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 read_half, _) = stream.into_split();
    ///     let mut buf = [0; 10];
    ///
    ///     poll_fn(|cx| {
    ///         read_half.poll_peek(cx, &mut buf)
    ///     }).await?;
    ///
    ///     Ok(())
    /// }
    /// ```
    ///
    /// [`TcpStream::poll_peek`]: TcpStream::poll_peek
    pub fn poll_peek(&mut self, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<io::Result<usize>> {
        self.inner.poll_peek(cx, buf)
    }

    /// 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.
    ///
    /// See the [`TcpStream::peek`] level documenation for more details.
    ///
    /// [`TcpStream::peek`]: TcpStream::peek
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use tokio::net::TcpStream;
    /// use tokio::prelude::*;
    /// use std::error::Error;
    ///
    /// #[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 read_half, _) = stream.into_split();
    ///
    ///     let mut b1 = [0; 10];
    ///     let mut b2 = [0; 10];
    ///
    ///     // Peek at the data
    ///     let n = read_half.peek(&mut b1).await?;
    ///
    ///     // Read the data
    ///     assert_eq!(n, read_half.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(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        poll_fn(|cx| self.poll_peek(cx, buf)).await
    }
}

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

impl OwnedWriteHalf {
    /// Attempts to put the two halves of a `TcpStream` back together and
    /// recover the original socket. Succeeds only if the two halves
    /// originated from the same call to [`into_split`].
    ///
    /// [`into_split`]: TcpStream::into_split()
    pub fn reunite(self, other: OwnedReadHalf) -> Result<TcpStream, ReuniteError> {
        reunite(other, self)
    }

    /// Destroy the write half, but don't close the write half of the stream
    /// until the read half is dropped. If the read half has already been
    /// dropped, this closes the stream.
    pub fn forget(mut self) {
        self.shutdown_on_drop = false;
        drop(self);
    }
}

impl Drop for OwnedWriteHalf {
    fn drop(&mut self) {
        if self.shutdown_on_drop {
            let _ = self.inner.shutdown(Shutdown::Write);
        }
    }
}

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

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

    fn is_write_vectored(&self) -> bool {
        self.inner.is_write_vectored()
    }

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

    // `poll_shutdown` on a write half shutdowns the stream in the "write" direction.
    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
        let res = self.inner.shutdown(Shutdown::Write);
        if res.is_ok() {
            Pin::into_inner(self).shutdown_on_drop = false;
        }
        res.into()
    }
}

impl AsRef<TcpStream> for OwnedReadHalf {
    fn as_ref(&self) -> &TcpStream {
        &*self.inner
    }
}

impl AsRef<TcpStream> for OwnedWriteHalf {
    fn as_ref(&self) -> &TcpStream {
        &*self.inner
    }
}