Trait tokio::io::AsyncBufRead

pub trait AsyncBufRead: AsyncRead {
    // Required methods
    fn poll_fill_buf(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>
    ) -> Poll<Result<&[u8]>>;
    fn consume(self: Pin<&mut Self>, amt: usize);
}

Reads bytes asynchronously.

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

Utilities for working with AsyncBufRead values are provided by AsyncBufReadExt.

Required Methods

fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

Attempts to return the contents of the internal buffer, filling it with more data from the inner reader if it is empty.

On success, returns Poll::Ready(Ok(buf)).

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

This function is a lower-level call. It needs to be paired with the consume method to function properly. When calling this method, none of the contents will be “read” in the sense that later calling poll_read may return the same contents. As such, consume must be called with the number of bytes that are consumed from this buffer to ensure that the bytes are never returned twice.

An empty buffer returned indicates that the stream has reached EOF.

fn consume(self: Pin<&mut Self>, amt: usize)

Tells this buffer that amt bytes have been consumed from the buffer, so they should no longer be returned in calls to poll_read.

This function is a lower-level call. It needs to be paired with the poll_fill_buf method to function properly. This function does not perform any I/O, it simply informs this object that some amount of its buffer, returned from poll_fill_buf, has been consumed and should no longer be returned. As such, this function may do odd things if poll_fill_buf isn’t called before calling it.

The amt must be <= the number of bytes in the buffer returned by poll_fill_buf.

Implementations on Foreign Types

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

fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

fn consume(self: Pin<&mut Self>, amt: usize)

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

fn poll_fill_buf( self: Pin<&mut Self>, _cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

fn consume(self: Pin<&mut Self>, amt: usize)

impl AsyncBufRead for &[u8]

fn poll_fill_buf( self: Pin<&mut Self>, _cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

fn consume(self: Pin<&mut Self>, amt: usize)

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

fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

fn consume(self: Pin<&mut Self>, amt: usize)

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

fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8]>>

fn consume(self: Pin<&mut Self>, amt: usize)

Implementors

impl AsyncBufRead for Empty

Available on crate feature io-util only.

impl<R: AsyncBufRead> AsyncBufRead for Take<R>

Available on crate feature io-util only.

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

Available on crate feature io-util only.

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

Available on crate feature io-util only.

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

Available on crate feature io-util only.