Trait futures_util::io::AsyncBufRead
source · pub trait AsyncBufRead: AsyncRead {
// Required methods
fn poll_fill_buf(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<&[u8], Error>>;
fn consume(self: Pin<&mut Self>, amt: usize);
}Expand description
Read bytes asynchronously.
This trait is analogous to the std::io::BufRead trait, but integrates
with the asynchronous task system. In particular, the poll_fill_buf
method, unlike BufRead::fill_buf, will automatically queue the current task
for wakeup and return if data is not yet available, rather than blocking
the calling thread.
Required Methods§
sourcefn poll_fill_buf(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Result<&[u8], Error>>
fn poll_fill_buf( self: Pin<&mut Self>, cx: &mut Context<'_> ) -> Poll<Result<&[u8], Error>>
Attempt to return the contents of the internal buffer, filling it with more data from the inner reader if it is empty.
On success, returns Poll::Ready(Ok(buf)).
If no data is available for reading, the method returns
Poll::Pending and arranges for the current task (via
cx.waker().wake_by_ref()) to receive a notification when the object becomes
readable or is closed.
This function is a lower-level call. It needs to be paired with the
consume method to function properly. When calling this
method, none of the contents will be “read” in the sense that later
calling poll_read may return the same contents. As such, consume must
be called with the number of bytes that are consumed from this buffer to
ensure that the bytes are never returned twice.
An empty buffer returned indicates that the stream has reached EOF.
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.
sourcefn consume(self: Pin<&mut Self>, amt: usize)
fn consume(self: Pin<&mut Self>, amt: usize)
Tells this buffer that amt bytes have been consumed from the buffer,
so they should no longer be returned in calls to poll_read.
This function is a lower-level call. It needs to be paired with the
poll_fill_buf method to function properly. This function does
not perform any I/O, it simply informs this object that some amount of
its buffer, returned from poll_fill_buf, has been consumed and should
no longer be returned. As such, this function may do odd things if
poll_fill_buf isn’t called before calling it.
The amt must be <= the number of bytes in the buffer returned by
poll_fill_buf.