[][src]Trait futures::prelude::AsyncSeek

pub trait AsyncSeek {
    fn poll_seek(
        self: Pin<&mut Self>,
        cx: &mut Context,
        pos: SeekFrom
    ) -> Poll<Result<u64, Error>>; }

Seek bytes asynchronously.

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

Required methods

fn poll_seek(
    self: Pin<&mut Self>,
    cx: &mut Context,
    pos: SeekFrom
) -> Poll<Result<u64, Error>>

Attempt to seek to an offset, in bytes, in a stream.

A seek beyond the end of a stream is allowed, but behavior is defined by the implementation.

If the seek operation completed successfully, this method returns the new position from the start of the stream. That position can be used later with [SeekFrom::Start].

Errors

Seeking to a negative offset is considered an error.

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.

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Implementations on Foreign Types

impl<T> AsyncSeek for Box<T> where
    T: AsyncSeek + Unpin + ?Sized
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impl<'_, T> AsyncSeek for &'_ mut T where
    T: AsyncSeek + Unpin + ?Sized
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impl<T> AsyncSeek for Cursor<T> where
    T: Unpin + AsRef<[u8]>, 
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impl<P> AsyncSeek for Pin<P> where
    P: DerefMut + Unpin,
    <P as Deref>::Target: AsyncSeek
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Implementors

impl<A, B> AsyncSeek for Either<A, B> where
    A: AsyncSeek,
    B: AsyncSeek
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impl<R> AsyncSeek for BufReader<R> where
    R: AsyncRead + AsyncSeek
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fn poll_seek(
    self: Pin<&mut BufReader<R>>,
    cx: &mut Context,
    pos: SeekFrom
) -> Poll<Result<u64, Error>>
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Seek to an offset, in bytes, in the underlying reader.

The position used for seeking with SeekFrom::Current(_) is the position the underlying reader would be at if the BufReader had no internal buffer.

Seeking always discards the internal buffer, even if the seek position would otherwise fall within it. This guarantees that calling .into_inner() immediately after a seek yields the underlying reader at the same position.

To seek without discarding the internal buffer, use BufReader::poll_seek_relative.

See AsyncSeek for more details.

Note: In the edge case where you're seeking with SeekFrom::Current(n) where n minus the internal buffer length overflows an i64, two seeks will be performed instead of one. If the second seek returns Err, the underlying reader will be left at the same position it would have if you called seek with SeekFrom::Current(0).

impl<T> AsyncSeek for AllowStdIo<T> where
    T: Seek
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impl<W> AsyncSeek for BufWriter<W> where
    W: AsyncWrite + AsyncSeek
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fn poll_seek(
    self: Pin<&mut BufWriter<W>>,
    cx: &mut Context,
    pos: SeekFrom
) -> Poll<Result<u64, Error>>
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Seek to the offset, in bytes, in the underlying writer.

Seeking always writes out the internal buffer before seeking.

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