async_hal/io/
async_read.rs

1use super::Read;
2use core::{
3    pin::Pin,
4    task::{Context, Poll},
5};
6use void::Void;
7
8/// Read bytes asynchronously.
9pub trait AsyncRead {
10    type Error;
11
12    /// Attempt to read from the AsyncRead into buf.
13    /// On success, returns Poll::Ready(Ok(num_bytes_read)).
14    /// If no data is available for reading, this method returns Poll::Pending
15    /// and arranges for the current task to be woken.
16    fn poll_read(
17        self: Pin<&mut Self>,
18        cx: &mut Context,
19        buf: &mut [u8],
20    ) -> Poll<Result<usize, Self::Error>>;
21
22    /// Tries to read some bytes directly into the given `buf` in asynchronous
23    /// manner, returning a future type.
24    ///
25    /// The returned future will resolve to both the I/O stream and the buffer
26    /// as well as the number of bytes read once the read operation is completed.
27    /// ```
28    /// use async_hal::io::AsyncRead;
29    ///
30    /// let mut bytes = [1, 2, 3].as_ref();
31    /// let mut buf = [0; 3];
32    ///
33    /// # let fut = async {
34    /// bytes.read(&mut buf).await?;   
35    /// # Ok::<_, void::Void>(())
36    /// # };
37    /// # futures::pin_mut!(fut);
38    /// # async_hal::block_on(fut, || {}).unwrap();
39    ///
40    /// assert_eq!([1, 2, 3], buf);
41    /// ```
42    fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
43    where
44        Self: Unpin,
45    {
46        Read::new(self, buf)
47    }
48}
49
50macro_rules! deref_async_read {
51    () => {
52        fn poll_read(
53            mut self: Pin<&mut Self>,
54            cx: &mut Context,
55            buf: &mut [u8],
56        ) -> Poll<Result<usize, Self::Error>> {
57            Pin::new(&mut **self).poll_read(cx, buf)
58        }
59    };
60}
61
62#[cfg(feature = "alloc")]
63impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T> {
64    deref_async_read!();
65}
66
67impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T {
68    type Error = T::Error;
69
70    deref_async_read!();
71}
72
73impl AsyncRead for &[u8] {
74    type Error = Void;
75
76    fn poll_read(
77        mut self: Pin<&mut Self>,
78        _cx: &mut Context,
79        buf: &mut [u8],
80    ) -> Poll<Result<usize, Void>> {
81        let amt = core::cmp::min(self.len(), buf.len());
82        let (a, b) = self.split_at(amt);
83        buf[..amt].copy_from_slice(a);
84        *self = b;
85        Poll::Ready(Ok(amt))
86    }
87}
async_hal/io/async_read.rs

async_hal/io/
async_read.rs
