Trait virtual_fs::AsyncRead

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pub trait AsyncRead {
    // Required method
    fn poll_read(
        self: Pin<&mut Self>,
        cx: &mut Context<'_>,
        buf: &mut ReadBuf<'_>
    ) -> Poll<Result<(), Error>>;
}
Expand description

Reads bytes from a source.

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

Specifically, this means that the poll_read function will return one of the following:

  • Poll::Ready(Ok(())) means that data was immediately read and placed into the output buffer. The amount of data read can be determined by the increase in the length of the slice returned by ReadBuf::filled. If the difference is 0, EOF has been reached.

  • Poll::Pending means that no data was read into the buffer provided. The I/O object is not currently readable but may become readable in the future. Most importantly, the current future’s task is scheduled to get unparked when the object is readable. This means that like Future::poll you’ll receive a notification when the I/O object is readable again.

  • Poll::Ready(Err(e)) for other errors are standard I/O errors coming from the underlying object.

This trait importantly means that the read method only works in the context of a future’s task. The object may panic if used outside of a task.

Utilities for working with AsyncRead values are provided by AsyncReadExt.

Required Methods§

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fn poll_read( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

Attempts to read from the AsyncRead into buf.

On success, returns Poll::Ready(Ok(())) and places data in the unfilled portion of buf. If no data was read (buf.filled().len() is unchanged), it implies that EOF has been reached.

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

Implementations on Foreign Types§

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impl AsyncRead for &[u8]

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fn poll_read( self: Pin<&mut &[u8]>, _cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

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

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fn poll_read( self: Pin<&mut Pin<P>>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

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impl<T> AsyncRead for &mut T
where T: AsyncRead + Unpin + ?Sized,

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fn poll_read( self: Pin<&mut &mut T>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

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

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fn poll_read( self: Pin<&mut Box<T>>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

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

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fn poll_read( self: Pin<&mut Cursor<T>>, _cx: &mut Context<'_>, buf: &mut ReadBuf<'_> ) -> Poll<Result<(), Error>>

Implementors§

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impl AsyncRead for ArcBoxFile

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impl AsyncRead for BufferFile

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impl AsyncRead for CombineFile

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impl AsyncRead for CopyOnWriteFile

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impl AsyncRead for DualWriteFile

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impl AsyncRead for virtual_fs::host_fs::File

Available on crate feature host-fs only.
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impl AsyncRead for virtual_fs::host_fs::Stderr

Available on crate feature host-fs only.
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impl AsyncRead for virtual_fs::host_fs::Stdin

Available on crate feature host-fs only.
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impl AsyncRead for virtual_fs::host_fs::Stdout

Available on crate feature host-fs only.
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impl AsyncRead for tokio::fs::file::File

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impl AsyncRead for tokio::io::stdin::Stdin

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impl AsyncRead for Empty

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impl AsyncRead for DuplexStream

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impl AsyncRead for Repeat

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impl AsyncRead for virtual_fs::mem_fs::Stderr

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impl AsyncRead for virtual_fs::mem_fs::Stdin

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impl AsyncRead for virtual_fs::mem_fs::Stdout

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impl AsyncRead for NullFile

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impl AsyncRead for Pipe

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impl AsyncRead for PipeRx

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impl AsyncRead for RandomFile

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impl AsyncRead for DeviceFile

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impl AsyncRead for WebCFile

Available on crate feature static-fs only.
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impl AsyncRead for StaticFile

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impl AsyncRead for ZeroFile

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impl<R> AsyncRead for BufReader<R>
where R: AsyncRead,

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impl<R> AsyncRead for Take<R>
where R: AsyncRead,

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impl<R, W> AsyncRead for Join<R, W>
where R: AsyncRead,

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impl<RW> AsyncRead for BufStream<RW>
where RW: AsyncRead + AsyncWrite,

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impl<T> AsyncRead for ArcFile<T>
where T: VirtualFile + Send + Sync + 'static,

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impl<T> AsyncRead for ReadHalf<T>
where T: AsyncRead,

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impl<W> AsyncRead for BufWriter<W>
where W: AsyncWrite + AsyncRead,