2 files changed, 60 insertions, 25 deletions

diff --git a/tokio/src/io/util/async_read_ext.rs b/tokio/src/io/util/async_read_ext.rs
index 0ab66c28..96a5f70d 100644
--- a/tokio/src/io/util/async_read_ext.rs
+++ b/tokio/src/io/util/async_read_ext.rs
@@ -1,6 +1,6 @@
 use crate::io::util::chain::{chain, Chain};
 use crate::io::util::read::{read, Read};
-use crate::io::util::read_buf::{read_buf, ReadBuf};
+use crate::io::util::read_buf::{poll_read_buf, read_buf, ReadBuf};
 use crate::io::util::read_exact::{read_exact, ReadExact};
 use crate::io::util::read_int::{
     ReadI128, ReadI128Le, ReadI16, ReadI16Le, ReadI32, ReadI32Le, ReadI64, ReadI64Le, ReadI8,
@@ -14,6 +14,8 @@ use crate::io::util::take::{take, Take};
 use crate::io::AsyncRead;
 
 use bytes::BufMut;
+use std::io;
+use std::task::{Context, Poll};
 
 cfg_io_util! {
     /// Defines numeric reader
@@ -185,7 +187,7 @@ cfg_io_util! {
         ///
         /// On a successful read, the number of read bytes is returned. If the
         /// supplied buffer is not empty and the function returns `Ok(0)` then
-        /// the source as reached an "end-of-file" event.
+        /// the source has reached an "end-of-file" event.
         ///
         /// # Errors
         ///
@@ -231,6 +233,28 @@ cfg_io_util! {
             read_buf(self, buf)
         }
 
+        /// Attempts to pull some bytes from this source into the specified buffer,
+        /// advancing the buffer's internal cursor if the underlying reader is ready.
+        ///
+        /// Usually, only a single `read` syscall is issued, even if there is
+        /// more space in the supplied buffer.
+        ///
+        /// # Return
+        ///
+        /// On a successful read, the number of read bytes is returned. If the
+        /// supplied buffer is not empty and the function returns `Ok(0)` then
+        /// the source has reached an "end-of-file" event.
+        ///
+        /// # Errors
+        ///
+        /// If this function encounters any form of I/O or other error, an error
+        /// variant will be returned. If an error is returned then it must be
+        /// guaranteed that no bytes were read.
+        /// ```
+        fn poll_read_buf<'a, B>(&'a mut self, buf: &'a mut B, cx: &mut Context<'_>) -> Poll<io::Result<usize>> where Self: Unpin + Sized, B: BufMut {
+            poll_read_buf(self, buf, cx)
+        }
+
         /// Reads the exact number of bytes required to fill `buf`.
         ///
         /// Equivalent to:
diff --git a/tokio/src/io/util/read_buf.rs b/tokio/src/io/util/read_buf.rs
index 696deefd..7df429d7 100644
--- a/tokio/src/io/util/read_buf.rs
+++ b/tokio/src/io/util/read_buf.rs
@@ -40,33 +40,44 @@ where
     type Output = io::Result<usize>;
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
-        use crate::io::ReadBuf;
-        use std::mem::MaybeUninit;
-
-        let me = self.project();
+        let mut me = self.project();
+        poll_read_buf(&mut me.reader, &mut me.buf, cx)
+    }
+}
 
-        if !me.buf.has_remaining_mut() {
-            return Poll::Ready(Ok(0));
-        }
+pub(crate) fn poll_read_buf<'a, R, B>(
+    reader: &'a mut R,
+    buf: &'a mut B,
+    cx: &mut Context<'_>,
+) -> Poll<io::Result<usize>>
+where
+    R: AsyncRead + Unpin,
+    B: BufMut,
+{
+    use crate::io::ReadBuf;
+    use std::mem::MaybeUninit;
 
-        let n = {
-            let dst = me.buf.bytes_mut();
-            let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
-            let mut buf = ReadBuf::uninit(dst);
-            let ptr = buf.filled().as_ptr();
-            ready!(Pin::new(me.reader).poll_read(cx, &mut buf)?);
+    if !buf.has_remaining_mut() {
+        return Poll::Ready(Ok(0));
+    }
 
-            // Ensure the pointer does not change from under us
-            assert_eq!(ptr, buf.filled().as_ptr());
-            buf.filled().len()
-        };
+    let n = {
+        let dst = buf.bytes_mut();
+        let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
+        let mut buf = ReadBuf::uninit(dst);
+        let ptr = buf.filled().as_ptr();
+        ready!(Pin::new(reader).poll_read(cx, &mut buf)?);
 
-        // Safety: This is guaranteed to be the number of initialized (and read)
-        // bytes due to the invariants provided by `ReadBuf::filled`.
-        unsafe {
-            me.buf.advance_mut(n);
-        }
+        // Ensure the pointer does not change from under us
+        assert_eq!(ptr, buf.filled().as_ptr());
+        buf.filled().len()
+    };
 
-        Poll::Ready(Ok(n))
+    // Safety: This is guaranteed to be the number of initialized (and read)
+    // bytes due to the invariants provided by `ReadBuf::filled`.
+    unsafe {
+        buf.advance_mut(n);
     }
+
+    Poll::Ready(Ok(n))
 }