1 files changed, 109 insertions, 0 deletions
diff --git a/tokio/src/io/async_buf_read.rs b/tokio/src/io/async_buf_read.rs
new file mode 100644
index 00000000..1499bd4f
--- /dev/null
+++ b/tokio/src/io/async_buf_read.rs
@@ -0,0 +1,109 @@
+use crate::io::AsyncRead;
+
+use std::io;
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Read bytes asynchronously.
+///
+/// This trait inherits from `std::io::BufRead` and indicates that an I/O object is
+/// **non-blocking**. All non-blocking I/O objects must return an error when
+/// bytes are unavailable instead of blocking the current thread.
+pub trait AsyncBufRead: AsyncRead {
+    /// 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.
+    ///
+    /// [`poll_read`]: AsyncRead::poll_read
+    /// [`consume`]: AsyncBufRead::consume
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>;
+
+    /// 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`].
+    ///
+    /// [`poll_read`]: AsyncRead::poll_read
+    /// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
+    fn consume(self: Pin<&mut Self>, amt: usize);
+}
+
+macro_rules! deref_async_buf_read {
+    () => {
+        fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>)
+            -> Poll<io::Result<&[u8]>>
+        {
+            Pin::new(&mut **self.get_mut()).poll_fill_buf(cx)
+        }
+
+        fn consume(mut self: Pin<&mut Self>, amt: usize) {
+            Pin::new(&mut **self).consume(amt)
+        }
+    }
+}
+
+impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for Box<T> {
+    deref_async_buf_read!();
+}
+
+impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T {
+    deref_async_buf_read!();
+}
+
+impl<P> AsyncBufRead for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncBufRead,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        self.get_mut().as_mut().poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        self.get_mut().as_mut().consume(amt)
+    }
+}
+
+impl AsyncBufRead for &[u8] {
+    fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(Ok(*self))
+    }
+
+    fn consume(mut self: Pin<&mut Self>, amt: usize) {
+        *self = &self[amt..];
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncBufRead for io::Cursor<T> {
+    fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(io::BufRead::fill_buf(self.get_mut()))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        io::BufRead::consume(self.get_mut(), amt)
+    }
+}