futures_util/io/
copy_buf_abortable.rs

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1use crate::abortable::{AbortHandle, AbortInner, Aborted};
2use futures_core::future::Future;
3use futures_core::task::{Context, Poll};
4use futures_io::{AsyncBufRead, AsyncWrite};
5use pin_project_lite::pin_project;
6use std::io;
7use std::pin::Pin;
8use std::sync::atomic::Ordering;
9use std::sync::Arc;
10
11/// Creates a future which copies all the bytes from one object to another, with its `AbortHandle`.
12///
13/// The returned future will copy all the bytes read from this `AsyncBufRead` into the
14/// `writer` specified. This future will only complete once abort has been requested or the `reader` has hit
15/// EOF and all bytes have been written to and flushed from the `writer`
16/// provided.
17///
18/// On success the number of bytes is returned. If aborted, `Aborted` is returned. Otherwise, the underlying error is returned.
19///
20/// # Examples
21///
22/// ```
23/// # futures::executor::block_on(async {
24/// use futures::io::{self, AsyncWriteExt, Cursor};
25/// use futures::future::Aborted;
26///
27/// let reader = Cursor::new([1, 2, 3, 4]);
28/// let mut writer = Cursor::new(vec![0u8; 5]);
29///
30/// let (fut, abort_handle) = io::copy_buf_abortable(reader, &mut writer);
31/// let bytes = fut.await;
32/// abort_handle.abort();
33/// writer.close().await.unwrap();
34/// match bytes {
35///     Ok(Ok(n)) => {
36///         assert_eq!(n, 4);
37///         assert_eq!(writer.into_inner(), [1, 2, 3, 4, 0]);
38///         Ok(n)
39///     },
40///     Ok(Err(a)) => {
41///         Err::<u64, Aborted>(a)
42///     }
43///     Err(e) => panic!("{}", e)
44/// }
45/// #  }).unwrap();
46/// ```
47pub fn copy_buf_abortable<R, W>(
48    reader: R,
49    writer: &mut W,
50) -> (CopyBufAbortable<'_, R, W>, AbortHandle)
51where
52    R: AsyncBufRead,
53    W: AsyncWrite + Unpin + ?Sized,
54{
55    let (handle, reg) = AbortHandle::new_pair();
56    (CopyBufAbortable { reader, writer, amt: 0, inner: reg.inner }, handle)
57}
58
59pin_project! {
60    /// Future for the [`copy_buf_abortable()`] function.
61    #[derive(Debug)]
62    #[must_use = "futures do nothing unless you `.await` or poll them"]
63    pub struct CopyBufAbortable<'a, R, W: ?Sized> {
64        #[pin]
65        reader: R,
66        writer: &'a mut W,
67        amt: u64,
68        inner: Arc<AbortInner>
69    }
70}
71
72macro_rules! ready_or_break {
73    ($e:expr $(,)?) => {
74        match $e {
75            $crate::task::Poll::Ready(t) => t,
76            $crate::task::Poll::Pending => break,
77        }
78    };
79}
80
81impl<R, W> Future for CopyBufAbortable<'_, R, W>
82where
83    R: AsyncBufRead,
84    W: AsyncWrite + Unpin + Sized,
85{
86    type Output = Result<Result<u64, Aborted>, io::Error>;
87
88    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
89        let mut this = self.project();
90        loop {
91            // Check if the task has been aborted
92            if this.inner.aborted.load(Ordering::Relaxed) {
93                return Poll::Ready(Ok(Err(Aborted)));
94            }
95
96            // Read some bytes from the reader, and if we have reached EOF, return total bytes read
97            let buffer = ready_or_break!(this.reader.as_mut().poll_fill_buf(cx))?;
98            if buffer.is_empty() {
99                ready_or_break!(Pin::new(&mut this.writer).poll_flush(cx))?;
100                return Poll::Ready(Ok(Ok(*this.amt)));
101            }
102
103            // Pass the buffer to the writer, and update the amount written
104            let i = ready_or_break!(Pin::new(&mut this.writer).poll_write(cx, buffer))?;
105            if i == 0 {
106                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
107            }
108            *this.amt += i as u64;
109            this.reader.as_mut().consume(i);
110        }
111        // Schedule the task to be woken up again.
112        // Never called unless Poll::Pending is returned from io objects.
113        this.inner.waker.register(cx.waker());
114
115        // Check to see if the task was aborted between the first check and
116        // registration.
117        // Checking with  `Relaxed` is sufficient because
118        // `register` introduces an `AcqRel` barrier.
119        if this.inner.aborted.load(Ordering::Relaxed) {
120            return Poll::Ready(Ok(Err(Aborted)));
121        }
122        Poll::Pending
123    }
124}
futures_util/io/copy_buf_abortable.rs

futures_util/io/
copy_buf_abortable.rs
