Trait tokio::io::async_read::AsyncRead
source · pub trait AsyncRead {
// Required method
fn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<Result<()>>;
}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 byReadBuf::filled. If the difference is 0, either EOF has been reached, or the output buffer had zero capacity (i.e.buf.remaining()== 0). -
Poll::Pendingmeans 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 likeFuture::pollyou’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§
sourcefn poll_read(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
buf: &mut ReadBuf<'_>,
) -> Poll<Result<()>>
fn poll_read( self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>, ) -> Poll<Result<()>>
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.