[−][src]Trait futures::io::AsyncSeek
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>>
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.
Implementations on Foreign Types
impl<'_, T> AsyncSeek for &'_ mut T where
T: AsyncSeek + Unpin + ?Sized,
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T: AsyncSeek + Unpin + ?Sized,
fn poll_seek(
self: Pin<&mut &'_ mut T>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut &'_ mut T>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
impl<T> AsyncSeek for Cursor<T> where
T: Unpin + AsRef<[u8]>,
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T: Unpin + AsRef<[u8]>,
fn poll_seek(
self: Pin<&mut Cursor<T>>,
&mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut Cursor<T>>,
&mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
impl<P> AsyncSeek for Pin<P> where
P: DerefMut + Unpin,
<P as Deref>::Target: AsyncSeek,
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P: DerefMut + Unpin,
<P as Deref>::Target: AsyncSeek,
fn poll_seek(
self: Pin<&mut Pin<P>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut Pin<P>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
impl<T> AsyncSeek for Box<T> where
T: AsyncSeek + Unpin + ?Sized,
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T: AsyncSeek + Unpin + ?Sized,
fn poll_seek(
self: Pin<&mut Box<T>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut Box<T>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
Implementors
impl<A, B> AsyncSeek for Either<A, B> where
A: AsyncSeek,
B: AsyncSeek,
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A: AsyncSeek,
B: AsyncSeek,
fn poll_seek(
self: Pin<&mut Either<A, B>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut Either<A, B>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
impl<R> AsyncSeek for BufReader<R> where
R: AsyncRead + AsyncSeek,
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R: AsyncRead + AsyncSeek,
fn poll_seek(
self: Pin<&mut BufReader<R>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut BufReader<R>>,
cx: &mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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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T: Seek,
fn poll_seek(
self: Pin<&mut AllowStdIo<T>>,
&mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
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self: Pin<&mut AllowStdIo<T>>,
&mut Context,
pos: SeekFrom
) -> Poll<Result<u64, Error>>
impl<W> AsyncSeek for BufWriter<W> where
W: AsyncWrite + AsyncSeek,
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W: AsyncWrite + AsyncSeek,