Trait tokio::io::AsyncRead

pub trait AsyncRead {
    fn poll_read(
        self: Pin<&mut Self>, 
        cx: &mut Context<'_>, 
        buf: &mut ReadBuf<'_>
    ) -> Poll<Result<()>>;
}

Reads bytes from a source.

This trait is analogous to the std::io::Read trait, but integrates with the asynchronous task system. In particular, the poll_read method, unlike Read::read, will automatically queue the current task for wakeup and return if data is not yet available, rather than blocking the calling thread.

Specifically, this means that the poll_read function will return one of the following:

• Poll::Ready(Ok(())) means that data was immediately read and placed into the output buffer. The amount of data read can be determined by the increase in the length of the slice returned by ReadBuf::filled. If the difference is 0, EOF has been reached.

• Poll::Pending means that no data was read into the buffer provided. The I/O object is not currently readable but may become readable in the future. Most importantly, the current future’s task is scheduled to get unparked when the object is readable. This means that like Future::poll you’ll receive a notification when the I/O object is readable again.

• Poll::Ready(Err(e)) for other errors are standard I/O errors coming from the underlying object.

This trait importantly means that the read method only works in the context of a future’s task. The object may panic if used outside of a task.

Utilities for working with AsyncRead values are provided by AsyncReadExt.

Required methods

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

Attempts to read from the AsyncRead into buf.

On success, returns Poll::Ready(Ok(())) and fills buf with data read. If no data was read (buf.filled().is_empty()) it implies that EOF has been reached.

If no data is available for reading, the method returns Poll::Pending and arranges for the current task (via cx.waker()) to receive a notification when the object becomes readable or is closed.

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Implementations on Foreign Types

impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<P> AsyncRead for Pin<P> where
    P: DerefMut + Unpin,
    P::Target: AsyncRead, 

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for &[u8]

fn poll_read(
    self: Pin<&mut Self>,
    _cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<T: AsRef<[u8]> + Unpin> AsyncRead for Cursor<T>

fn poll_read(
    self: Pin<&mut Self>,
    _cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

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Implementors

impl AsyncRead for File

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    dst: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for DuplexStream

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for Empty

fn poll_read(
    self: Pin<&mut Self>,
    _: &mut Context<'_>,
    _: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for Repeat

fn poll_read(
    self: Pin<&mut Self>,
    _: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for Stdin

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for TcpStream

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for UnixStream

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for tokio::net::tcp::OwnedReadHalf

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for tokio::net::tcp::ReadHalf<'_>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for tokio::net::unix::OwnedReadHalf

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for tokio::net::unix::ReadHalf<'_>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for ChildStderr

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl AsyncRead for ChildStdout

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<R: AsyncRead> AsyncRead for BufReader<R>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<R: AsyncRead> AsyncRead for Take<R>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<(), Error>>

impl<RW: AsyncRead + AsyncWrite> AsyncRead for BufStream<RW>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<T: AsyncRead> AsyncRead for tokio::io::ReadHalf<T>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

impl<W: AsyncWrite + AsyncRead> AsyncRead for BufWriter<W>

fn poll_read(
    self: Pin<&mut Self>,
    cx: &mut Context<'_>,
    buf: &mut ReadBuf<'_>
) -> Poll<Result<()>>

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