pub trait AsyncSeek {
// Required method
fn poll_seek(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64, Error>>;
}Expand description
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>>
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.
Implementations on Foreign Types§
§impl<R> AsyncSeek for BufReader<R>
impl<R> AsyncSeek for BufReader<R>
§fn poll_seek(
self: Pin<&mut BufReader<R>>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64, Error>>
fn poll_seek( 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::seek_relative or
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<R> AsyncSeek for BufReader<R>where
R: AsyncSeek,
impl<R> AsyncSeek for BufReader<R>where
R: AsyncSeek,
§fn poll_seek(
self: Pin<&mut BufReader<R>>,
cx: &mut Context<'_>,
pos: SeekFrom,
) -> Poll<Result<u64, Error>>
fn poll_seek( self: Pin<&mut BufReader<R>>, cx: &mut Context<'_>, pos: SeekFrom, ) -> Poll<Result<u64, Error>>
Seeks 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()][BufReader::into_inner()]
immediately after a seek yields the underlying reader at the same position.
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()][AsyncSeekExt::seek()] with SeekFrom::Current(0).