tokio::io

Trait AsyncRead

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

Expand description

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, either EOF has been reached, or the output buffer had zero capacity (i.e. buf.remaining() == 0).
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§

Source

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 places data in the unfilled portion of buf. If no data was read (buf.filled().len() is unchanged), 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.

Trait AsyncReadCopy item path

Required Methods§

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

Implementations on Foreign Types§

impl AsyncRead for &[u8]

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<T: AsRef<[u8]> + Unpin> AsyncRead for Cursor<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<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T>

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

Implementors§

impl AsyncRead for File

impl AsyncRead for TcpStream

impl AsyncRead for UnixStream

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

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

impl AsyncRead for Receiver

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

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

impl AsyncRead for NamedPipeClient

impl AsyncRead for NamedPipeServer

impl AsyncRead for ChildStderr

impl AsyncRead for ChildStdout

impl AsyncRead for DuplexStream

impl AsyncRead for Empty

impl AsyncRead for Repeat

impl AsyncRead for SimplexStream

impl AsyncRead for Stdin

impl<R, W> AsyncRead for Join<R, W>where R: AsyncRead,

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

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

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

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

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

Trait AsyncRead

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

impl<R, W> AsyncRead for Join<R, W>
where R: AsyncRead,