Revert "util: upgrade tokio-util to bytes 0.6 (#3052)" (#3060)

This reverts commit fe2b997.

We are avoiding adding poll_read_buf to tokio itself for now. The patch is
reverted now in order to not block the v0.3.2 release (#3059).

tokio-util/src/lib.rs

@@ -57,3 +57,37 @@ pub mod either;
 
 #[cfg(feature = "time")]
 pub mod time;
+
+#[cfg(any(feature = "io", feature = "codec"))]
+mod util {
+    use tokio::io::{AsyncRead, ReadBuf};
+
+    use bytes::BufMut;
+    use futures_core::ready;
+    use std::io;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    pub(crate) fn poll_read_buf<T: AsyncRead>(
+        cx: &mut Context<'_>,
+        io: Pin<&mut T>,
+        buf: &mut impl BufMut,
+    ) -> Poll<io::Result<usize>> {
+        if !buf.has_remaining_mut() {
+            return Poll::Ready(Ok(0));
+        }
+
+        let orig = buf.bytes_mut().as_ptr() as *const u8;
+        let mut b = ReadBuf::uninit(buf.bytes_mut());
+
+        ready!(io.poll_read(cx, &mut b))?;
+        let n = b.filled().len();
+
+        // Safety: we can assume `n` bytes were read, since they are in`filled`.
+        assert_eq!(orig, b.filled().as_ptr());
+        unsafe {
+            buf.advance_mut(n);
+        }
+        Poll::Ready(Ok(n))
+    }
+}