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

use super::copy::CopyBuffer;

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

use std::io;
use std::pin::Pin;
use std::task::{ready, Context, Poll};

enum TransferState {
    Running(CopyBuffer),
    ShuttingDown(u64),
    Done(u64),
}

fn transfer_one_direction<A, B>(
    cx: &mut Context<'_>,
    state: &mut TransferState,
    r: &mut A,
    w: &mut B,
) -> Poll<io::Result<u64>>
where
    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
{
    let mut r = Pin::new(r);
    let mut w = Pin::new(w);

    loop {
        match state {
            TransferState::Running(buf) => {
                let count = ready!(buf.poll_copy(cx, r.as_mut(), w.as_mut()))?;
                *state = TransferState::ShuttingDown(count);
            }
            TransferState::ShuttingDown(count) => {
                ready!(w.as_mut().poll_shutdown(cx))?;

                *state = TransferState::Done(*count);
            }
            TransferState::Done(count) => return Poll::Ready(Ok(*count)),
        }
    }
}
/// Copies data in both directions between `a` and `b`.
///
/// This function returns a future that will read from both streams,
/// writing any data read to the opposing stream.
/// This happens in both directions concurrently.
///
/// If an EOF is observed on one stream, [`shutdown()`] will be invoked on
/// the other, and reading from that stream will stop. Copying of data in
/// the other direction will continue.
///
/// The future will complete successfully once both directions of communication has been shut down.
/// A direction is shut down when the reader reports EOF,
/// at which point [`shutdown()`] is called on the corresponding writer. When finished,
/// it will return a tuple of the number of bytes copied from a to b
/// and the number of bytes copied from b to a, in that order.
///
/// It uses two 8 KB buffers for transferring bytes between `a` and `b` by default.
/// To set your own buffers sizes use [`copy_bidirectional_with_sizes()`].
///
/// [`shutdown()`]: crate::io::AsyncWriteExt::shutdown
///
/// # Errors
///
/// The future will immediately return an error if any IO operation on `a`
/// or `b` returns an error. Some data read from either stream may be lost (not
/// written to the other stream) in this case.
///
/// # Return value
///
/// Returns a tuple of bytes copied `a` to `b` and bytes copied `b` to `a`.
#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
pub async fn copy_bidirectional<A, B>(a: &mut A, b: &mut B) -> io::Result<(u64, u64)>
where
    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
{
    copy_bidirectional_impl(
        a,
        b,
        CopyBuffer::new(super::DEFAULT_BUF_SIZE),
        CopyBuffer::new(super::DEFAULT_BUF_SIZE),
    )
    .await
}

/// Copies data in both directions between `a` and `b` using buffers of the specified size.
///
/// This method is the same as the [`copy_bidirectional()`], except that it allows you to set the
/// size of the internal buffers used when copying data.
#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
pub async fn copy_bidirectional_with_sizes<A, B>(
    a: &mut A,
    b: &mut B,
    a_to_b_buf_size: usize,
    b_to_a_buf_size: usize,
) -> io::Result<(u64, u64)>
where
    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
{
    copy_bidirectional_impl(
        a,
        b,
        CopyBuffer::new(a_to_b_buf_size),
        CopyBuffer::new(b_to_a_buf_size),
    )
    .await
}

async fn copy_bidirectional_impl<A, B>(
    a: &mut A,
    b: &mut B,
    a_to_b_buffer: CopyBuffer,
    b_to_a_buffer: CopyBuffer,
) -> io::Result<(u64, u64)>
where
    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
{
    let mut a_to_b = TransferState::Running(a_to_b_buffer);
    let mut b_to_a = TransferState::Running(b_to_a_buffer);
    poll_fn(|cx| {
        let a_to_b = transfer_one_direction(cx, &mut a_to_b, a, b)?;
        let b_to_a = transfer_one_direction(cx, &mut b_to_a, b, a)?;

        // It is not a problem if ready! returns early because transfer_one_direction for the
        // other direction will keep returning TransferState::Done(count) in future calls to poll
        let a_to_b = ready!(a_to_b);
        let b_to_a = ready!(b_to_a);

        Poll::Ready(Ok((a_to_b, b_to_a)))
    })
    .await
}