Trait futures_util::io::AsyncBufRead

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

Read bytes asynchronously.

This trait is analogous to the std::io::BufRead trait, 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.

Required methods

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

Attempt 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.

Implementation

This function may not return errors of kind WouldBlock or Interrupted. Implementations must convert WouldBlock into Poll::Pending and either internally retry or convert Interrupted into another error kind.

pub 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.

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Implementations on Foreign Types

impl<'_> AsyncBufRead for &'_ [u8]

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

pub fn consume(self: Pin<&mut &'_ [u8]>, amt: usize)

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

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

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

impl<'_, T> AsyncBufRead for &'_ mut T where
    T: AsyncBufRead + Unpin + ?Sized, 

pub fn poll_fill_buf(
    self: Pin<&mut &'_ mut T>,
    cx: &mut Context<'_>
) -> Poll<Result<&[u8], Error>>

pub fn consume(self: Pin<&mut &'_ mut T>, amt: usize)

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

pub fn poll_fill_buf(
    self: Pin<&mut Box<T, Global>>,
    cx: &mut Context<'_>
) -> Poll<Result<&[u8], Error>>

pub fn consume(self: Pin<&mut Box<T, Global>>, amt: usize)

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Implementors

impl AsyncBufRead for Empty

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

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

impl<A, B> AsyncBufRead for Either<A, B> where
    A: AsyncBufRead,
    B: AsyncBufRead, 

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

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

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

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

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

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

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

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

impl<St> AsyncBufRead for IntoAsyncRead<St> where
    St: TryStream<Error = Error> + Unpin,
    St::Ok: AsRef<[u8]>, 

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

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

impl<T> AsyncBufRead for AllowStdIo<T> where
    T: BufRead, 

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

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

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

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

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

impl<T, U> AsyncBufRead for Chain<T, U> where
    T: AsyncBufRead,
    U: AsyncBufRead, 

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

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

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

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

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

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